GBA Logo horizontal Facebook LinkedIn Email Pinterest Twitter Instagram YouTube Icon Navigation Search Icon Main Search Icon Video Play Icon Plus Icon Minus Icon Picture icon Hamburger Icon Close Icon Sorted
Musings of an Energy Nerd

Wolfgang Feist Defends Thick Insulation

After giving the keynote address at the 2014 North American Passive House Network conference in Maine, Dr. Feist agreed to be interviewed

Dr. Wolfgang Feist visited Portland, Maine in late September 2014.
Image Credit: Scott Gibson

Dr. Wolfgang Feist is the founder of the Passivhaus Institut in Darmstadt, Germany. On September 22, 2014, after Feist gave an address at a Passive House conference in Portland, Maine, he agreed to be interviewed. (For links to my two previous interviews with Dr. Feist, see the “Related Articles” sidebar below.)

Q. What will it take for a higher percentage of new buildings to be built to the Passivhaus standard?

Feist: In North America, the most important thing now is to involve industry to make better components available on a broader level. Far too much is imported now from countries too far away. What is really needed is to have better windows and ventilation systems. That is getting started now. In many European countries, triple glazing is now standard. That means that it is no longer more expensive. It can happen here too. In Germany, if you insist on a double-pane window, it might be more expensive than a triple-pane window.

In North America at the moment you have a lot of educated architects, but they still do it by combining products that are not really suitable for a Passivhaus. Even without the right products, it is possible to succeed, but that is more expensive.

The other step is education of all involved. At the moment, that means especially the construction workers and the HVAC contractors. The HVAC contractors are the most difficult, in Europe as in America.

Q. Is it correct to say that the European Union will require new buildings in Europe to meet the Passivhaus standard beginning in 2020?

Feist: That is almost correct. The EU has said that from 2020, the national governments in Europe are required to establish new construction standards with energy performance levels that are as low as the Passivhaus standard.

You have to be cautious with…

GBA Prime

This article is only available to GBA Prime Members

Sign up for a free trial and get instant access to this article as well as GBA’s complete library of premium articles and construction details.

Start Free Trial


  1. dankolbert | | #1

    For all the reports on the conference. And thanks for staying on the questions.

  2. DavidAlex | | #2

    Not really a defense
    Dr. Feist doesn't so much defend thick insulation as dismiss cost-effectiveness concerns as "nonsense". Budget constraints are a reality for nearly everyone choosing to build, and so a very simple question needs to be answered: why is an extra dollar spent on insulation better than that same dollar spent on PV panels? And I don't think he's answered that question to my satisfaction. (And if we can't even get an answer to that very simple question, then we can't even get to more complex, nuanced questions like, why is an extra dollar spent on insulation better than using that dollar to buy a plot of land closer to work? Or on an electric vehicle? Or paying a poor country to not cut down their rainforest, a la Norway?)

    It's not enough so say that PV and insulation are complementary strategies. That's obvious. The question is -- what is the solution to this optimax problem? And I don't see Dr. Feist showing his work.

  3. GBA Editor
    Martin Holladay | | #3

    Response to David Hicks
    Q. "Why is an extra dollar spent on insulation better than that same dollar spent on PV panels?"

    A. There are several possible answers to your question:
    - Insulation will last longer than PV modules.
    - Energy saved by insulation is more valuable than energy saved by a PV array, which produces surplus energy in the summer when it isn't really needed (in a cold climate, anyway).

    These answers have some merit. But they don't adequately explain the logic of investing $1,872 for extra foam to save just $10 per year.

  4. Expert Member

    So despite all the "Passive House is just one option,why are you so concerned about it?" comments in discussions when it comes up here, we now see a close cousin being enshrined in European codes. That's why it is so important to deal with the absurdities before they get into our standards.
    Feist's dismissive attitude to Martin's questions sits somewhere between funny and annoying, but doesn't speak well of the movement that none within it challenges him on it.

  5. DavidAlex | | #5

    Reponse to Martin
    Martin -- you're right, and I don't mean to dismiss those aspects you mention. This morning on Twitter, Dr Feist said, "Investing in PV is a good-it's not substituting insulation,by the way.It's a Summer/Winter question-therfore,complementary". My point of contention is when you claim two solutions are complementary, you're admitting that there's an optimum combination of those two solutions. In other words, a way to maximize performance while minimizing cost. In this case, maximizing occupant comfort while minimizing either dollars or CO2 emissions. I assert that the PHI standard does not attempt to find this optimum point.

    Thought experiment: posit a world where PV panels are ubiquitous, and insulation is the newfangled thing. Some scientist from Arizona could look at her environment (sunny, lots of cooling needs, not much heating needs) and design a house that entails putting up lots and lots of PV panels to power her A/C. Eureka! It works. Let's make it a standard, and build houses like that in Vermont. It still works, but you need WAY more PV panels. Along comes Bizarro Martin Holladay and says, "wait a sec. This doesn't make sense. Why don't we take some of the money that goes into buying PV and use it to put fluffy stuff in the walls? " The Arizona scientist's response? "I don’t care too much about this. It is not killing anybody. There is no real danger from these PV panels. PV panels are just a tool. Maybe you might really need 20kw of panels, and if you do, it's not that bad." And she'd be right. Nothing she said here is wrong. But it also obviously misses the point -- why is the Vermonter spending so much money on PV and so little on insulation?

  6. Ken Levenson | | #6

    problem with footnote example
    As is the case with most "cost analysis" of Passive House the footnote is showing just one "toggle/dial" in the optimization, when in actuality, any rigorous optimization requires adjusting many dials. The footnote describes a false choice and is a strawman argument. What about the wall insulation levels? the roof insulation levels? The window sizing and orientations and thermal values? These all may or may not be optimized - but to land on subslab insulation every time as "THE dial" is ridiculous. Certainly adding loose fill attic insulation will cheaply raise the insulation levels - but maybe the design wasn't actually optimized to do this. Key to success of optimization is starting from the first line drawn on the paper - everything else is shoehorning.

  7. GBA Editor
    Martin Holladay | | #7

    Response to Ken Levenson (Comment #5)
    I have a huge collection of cold-climate Passivhaus projects with R-35 subslab foam and R-40 subslab foam and even R-55 subslab foam. Every time I do a calculation to show that this is a waste of money, the Passivhaus adherents have the same response: "Maybe the design wasn't actually optimized."

    Really, Ken? All of them? Why does this keep happening?

    Say what you will, but this house spent $1,872 on extra foam to save $10 per year. If they built the exact same house with only R-20 foam, the energy bills would be only $10 higher. That's my point.

  8. GBA Editor
    Martin Holladay | | #8

    Response to Malcolm Taylor
    Here in the U.S., building scientists are able to mount a cogent, critical analysis of the Passivhaus standard, and are able to determine which aspects make sense (the airtightness target) and (at least in cold climates) which don't (the 15 kWh/m2*year target). This analysis is a strong bulwark that should prevent the adoption of the Passivhaus standard as a code minimum requirement in cold climates.

    It's now time for European building scientists to mount a similar critique for the cold climates of Scandinavia. It will be interesting to see if such an analysis arises before the 2020 deadline.

  9. GBA Editor
    Martin Holladay | | #9

    Response to David Hicks (Comment #6)
    I love your analogy of the PV-heavy Arizona standard being applied in Vermont. You made me smile.

  10. GBA Editor
    Martin Holladay | | #10

    Response to Ken Levenson (Comment #9)
    It's a convenient response.

    Martin: Cold-climate Passivhaus buildings require insulation that isn't cost-effective. Look, this one has 7 inches of sub-slab foam.

    Ken: Don't count that one. It was shoe-horned.

    Martin: OK, how about this one? It has 10 inches of subslab foam.

    Ken: Don't count that one. It was also shoe-horned.

    Martin: I'm noticing that most of these cold-climate Passivhaus buildings have really thick subslab foam. Look, this one has 12 inches of subslab foam.

    Ken: Please don't count that one.

  11. Ken Levenson | | #11

    Response to Martin
    Yes, Martin - they are all shoehorned.

    I should add: most are the first project - with each project the optimization improves. Show us an example of such a building that is by a team with several Passive Houses behind them.

  12. Ken Levenson | | #12

    Please take me out of your fantasy.

  13. user-1081937 | | #13

    The big bad insulation
    Somehow the entire track of these conversations have narrowed to a piss match about who is cheaper. May I suggest that rather than attacking insulation levels we should look at life term impact of our built environment with a systems thinking. This means not excluding super high performance houses. We did this before in the 80s and now we are stuck with decades of near zero progress. Its quite sad to see a respected website tear down the work of pioneers rather than support them.

    I have seen pathetic passive houses that are first generation, and brilliant passive houses that are third generation. I designed two that have zero foam in the foundation and are both very cost effective to build. The problem is not costs, it is design. We are getting OK in the US but in Europe they are nailing the cost side. I know that I can dramatically improve the next one.

    I refuse to build the same old rule-of-thumb junk that we call green building and have no idea how it works in the real world. The great challenge is to make these very low impact and comfortable buildings affordable for the life use of the project. Add some solar, make more energy than you use, great now I can take you seriously.

  14. GBA Editor
    Martin Holladay | | #14

    Response to Andrew Michler
    I am not advocating that we build "the same old rule-of-thumb junk." I am simply challenging designers to do a little math before they thicken up their subslab foam.

    If the foam makes sense, I'm all for it. But do the math.

  15. user-1081937 | | #15

    big bad insulation II
    Just to be clear Martin, your complaint is about the cost of the foam. We are designing to specific r-values (which are optimized properly) so why is not finding an effective way to do that the debate? Just because we see a lot of projects use slab on foam in these first gen PH projects for instance does not make that the optimal solution. What your inquiry is feeding a throw the-baby-out-mentality by less nuanced readers. The whole notion of simple payback is a disservice to the high performance profession and will bite us in the ass. Que the build-to-code folks.

    This continuing narrow inquiry without any context as to the thermal comfort side and cascading effects on energy needs via reduced heat demand from radiantly neutral surfaces and client well being is a disservice to the debate.

  16. Bronwyn Barry | | #16

    Keep on debating - but give the workers real tools.
    Martin - Thanks for the two great posts you've written about our NAPHN14 Maine conference. It was great to have you attend and enjoy the positive energy and atmosphere surrounding what was very much a Pro-Passivhaus event. We've had excellent feedback from our post-event survey so far, particularly regarding the substantial international presence we actively cultivated. It was good to confirm our suspicion that North Americans want to participate as part of a global community. We have much to contribute and learn from a constructive dialog, with the focus on a methodology that is actually working.

    I did want to make an observation about your curious fixation on the sub-slab insulation thickness of Passive House projects. None of your calculations would be possible without the ability of all these building designers to give you highly accurate information and output data from the PHPP. I've yet to see any 'Net Zero' house designer be able to deliver anything close to its accuracy and reliability. It would be good to see you deliver comparable calculations on the sub-slab cost-effectiveness - or any cost-effectiveness numbers - of non-passivhaus projects without access to the PHPP.

    Whether you support using less or more insulation in lieu of more PV or not, none of these decisions would be possible without the incredibly useful tool that is the PHPP. (It is also the tool that was used to develop Wufi Passiv by the other German Institute that is now also promoting PH.) Whichever path you choose to support, the reality is that we have access to an incredibly valuable and useful tool that we can use to help make informed choices for our clients. It's important to recognize that none of this wonderful dialog and debate would be possible without it.

  17. david_white | | #17

    PHPP error
    Martin, I did the PHPP work for the Bolton House. Feel free to show me your work, but if I change the slab insulation thickness in my PHPP file from 8" to 4" (which drops the slab R-value from R-35 to R-19), I get a savings of 529 kWhth/yr. Assuming COP 2.5, this is 211 kWh electrical, or $32/year using your price/kWh figure of $0.15. How did you get $10/year using one of my PHPP files?

  18. GBA Editor
    Martin Holladay | | #18

    Response to David White
    I really appreciate your numbers. My numbers came from Steven Toomey, the homeowner, who said that they were from his PHPP runs. Steven's e-mail says, "The source heating energy numbers are straight from our PHPP, which assumes an air-source heat pump with an annual coefficient of performance of 3.76." So I guess you two will need to decide which COP makes more sense for the climate of Connecticut: a COP of 2.5, as you suggest, or a COP of 3.76, as PHPP (evidently) and Steven suggest.

    Using your numbers (which are different from Steven's obviously, and which assume R-19 instead of R-20 for the thinner foam), along with Steven's COP assumption, would yield 141 kWh savings per year, worth about $21 at 15 cents/kWh.

    That changes the picture, of course. The simple payback period shortens from 180 years to 89 years. Still, the PV array option yields almost 4 times as much energy.

  19. GBA Editor
    Martin Holladay | | #19

    Response to Bronwyn Barry
    You wrote, "None of your calculations would be possible without the ability of all these building designers to give you highly accurate information and output data from the PHPP. I've yet to see any 'Net Zero' house designer be able to deliver anything close to its accuracy and reliability."

    Here are three points:

    1. Like you, I am grateful for the development of PHPP. By all accounts, it's a great tool.

    2. In fact, many designers of net-zero-energy homes use PHPP for modeling; so that it's fair to say that such designers can, in fact, deliver good modeling results.

    3. Finally, the history of energy modeling programs goes back several decades before PHPP. I agree that PHPP is a useful tool, but energy-conscious designers weren't just wearing skins and grunting in the dark before the wizards from Darmstadt brought fire to our caves. We can debate the merits of other programs -- DOE2, Energy-10, Hot2000, and REM/Rate, for instance -- and many will probably agree with you that PHPP is the best of the lot for designers of superinsulated homes. But other energy modeling programs can give designers a pretty good idea about when they have specified subslab insulation that is too thick.

  20. Expert Member
    Dana Dorsett | | #20

    OK, say it saves $32 /year ... (response to #18)
    With $1800 worth of foam, that's an internal rate of return of less than 2% . Try to make that work out to NPV+ on a house-lifecycle basis. Compare that to a more reasonable discount rate, factor in some amount of energy price deflation, and the net present value drops even further into the red.

  21. Expert Member
    Dana Dorsett | | #21

    Didja calculate the net present value of the "extra" R15?
    Dr. Feist's comment was:

    " So this new standard is for all these guys who don’t think in terms of net present value. If the government wanted to do something really good, they would make net present value calculations mandatory.

    Indeed! Run that present-value calculation! Using the example in the footnote...

    If a simple-payback is 180 years, what how can you adjust the terms or period in an NPV calc would be needed to make it work 'reasonably", given a whopping IRR of ~0.5%?

    It doesn't take an NPV calc to come up with "this doesn't make sense", but if Feist begs to differ, let's see how HE calculates net present value!

    According to a recent CitiGroup analysis, by 2020 the cost of PV + batteries in Massachusetts will have a lifecycle cost cheaper than grid energy, and have "payback" in only 16 years (which is within the anticipated lifecycle of the system), and in California it'll be more like 10 years. See figure 28:

    It's the follow-on to last year's "Energy Darwinism" piece, which is well worth absorbing when considering the value of VERY high R:

    Yes, the fossil fuel infrastructure & fracking developments are at real risk of becoming stranded assets for those companies before 2030, but the value of that additional R15 under the slab is as-good-as-stranded the day the pour the slab. The cost of renewable energy will become cheaper than energy costs are today well before the lifecycle of the new house is done. Building the anticipated energy price deflation into the NPV model would probably mean a good fraction of the remaining R20 is NPV negative over the lifecycle of the building too.

    If you are being rigorous about it, energy price deflation is far more likely than flat pricing or price INflation on the time scale of the lifecycle of a house. It's the financial sector (Bloomberg, Sanford Bernstein, CitiGroup, Kepler Cheuvreux and others) who are saying so. Methinks investment banker-wonks do a better job of calculating the present value and tail end risks than Dr. Feist & the building-science gang in Darmstadt. Before admonishing builders to start thinking in terms of net present value he needs to show his math, so we know that he has in fact done the same. The evidence would seem to indicate a math error.

    Methinks the Darmstadt gang needs to start thinking in terms of net present value in earnest, and not simply treat it as a throwaway line- actually show the math. It may be they actually made an NPV calculation 20 years ago (?), but the terms in the equation haven't stood still, and they were never the same in the US as they were in Europe anyway. Physics works the same everywhere, and so does arithmetic.

  22. GBA Editor
    Martin Holladay | | #22

    Response to Andrew Michler (Comment #15)
    You wrote, "This continuing narrow inquiry without any context as to the thermal comfort side and cascading effects on energy needs via reduced heat demand from radiantly neutral surfaces and client well being is a disservice to the debate."

    In fact, I have often addressed the question you bring up. I challenge any human being in a superinsulated building, heated to room temperature in winter, to tell the difference between a concrete slab with R-20 subslab foam (that's 4 inches of XPS or 5 inches of EPS) and a concrete slab with R-35 foam. I'll let you do the test with bare feet. You won't be able to tell the difference.

    This debate has nothing to do with occupant comfort. That's a red herring.

  23. jackofalltrades777 | | #23

    Don't Drink the Kool-Aid
    Apparently Ken Levenson drank the Kool-Aid. Reading this entire exchange makes it seem like the Passivhaus movement is a religious movement and if you dare question it, the followers will come out and brand you a hater and heretic.

    This sums it up for me:

    Q. PHIUS is developing different standards for different climates. Would the Passivhaus Institut consider a similar approach in Europe?
    Feist: No.

    Q. Do you see any possibility of a reconciliation between the Passivhaus Institut and PHIUS?

    Feist: No. It’s not depending on us. I don’t think it is good to go deeper into the reasons on both sides. We don’t want to deepen this discussion.

    You can read & sense the hostility in Dr. Feist's responses to the questions posed. The questions were reasonable but Dr. Feist's responses were incomplete and hostile. I'm glad the split with PHIUS happened and I will go with the PHIUS since they are more reasonable and adapt to change. Being stubborn and hostile is not the way to survive in the US.

    The answer given for R-80 Walls and R-40 underslab foam was not even an answer. It was basically stated that we are not to question the reasons why but just to accept it as so. The homeowner pays for the R-80 walls and R-40 foam and waits to see a ROI that will take 180 years. The house will not even make it past its effective life expectancy, which is usually 50-75 years for a wood-frame home. At least the foam might be able to be reused :)

  24. user-1058478 | | #24

    Hayfield House -- It's not just economics
    The broader context for any project is that the building needs to satisfy a complex set of client requirements. The role of an architect is to integrate these needs -- shelter, comfort, space, circulation, utility, privacy, daylight, energy, etc. -- into a unified whole. This is what Ken's getting at when he talks about optimization. Passive House certification is just one of many features.

    Our concept was a modern New England farmhouse, and we worked with GO Logic to design the house’s program and facades to look and feel that way. This was a traditional architecture process, no spreadsheets required. We figured out an efficient layout with generous views and light on all 4 sides of the building. Of course, Passive House was always part of the requirements and so the house's massing and facades were developed with this in mind, relying on experience from previous GO Logic projects.

    The program and facades set constraints in terms of the energy modelling and levels of insulation required to be a Passive House. For example, if we reduced our 72 ft^2 of north glazing, we could get away with less foam under the slab. But we really wanted those north windows plus everything else in the design. So this meant fine-tuning the insulation, window, and electricity-related specs until we hit the magic numbers. This is where the process departs from being architect-driven to being spreadsheet-driven.

    Our builder did us a huge favor by hitting 0.2 ACH50, which in the end meant that we could have spent less on insulation and still hit the standard. Overall, we have about $40k of insulation in our 2,100 ft^2 house, between the 8" subslab foam, the 8" Neopor SIPS, and the cellulose in the wall and roof framing.

    At many points during the process we could have opted out, but then we wouldn't have a Passive House and that was ultimately important to us, perhaps in the same way that granite countertops or hot tubs are important to other buyers. Again, Passive House is a feature, not the sole reason for being. Let’s not forget that many of our house-related decisions are driven by emotion versus rational thought.

    The bottom line is that the house works as well as or better than we thought it would, and our energy consumption is generally in line with predictions (PHPP didn't account for the arctic Northeast US winter of 2013-14). Yes, there is a long economic payback period on the last few inches of insulation, but we got everything we wanted in terms of the aesthetics and the living experience. It’s hard to put a price on those intangible qualities.

  25. GBA Editor
    Martin Holladay | | #25

    Response to Steve Toomey
    Your explanation is clear, and your logic is consistent. You ended up with the house you wanted, and that's great.

    Anyone who builds a custom house can pursue their dreams, without having to justify their decision.

  26. user-1081937 | | #26

    Passive House is a comfort standard
    Martin- Comfort is what I see as the fundamental blind spot in how you report on this topic. Yes it is all about comfort, Passive House is a comfort standard. (surprised?) It achieves that by reducing the HVAC to a tiny fraction by making it up via thermally neutral surfaces, using high performance glazing and insulation. I have an r-18 floor in my house and an r-56 floor in my passive house and, ohhhh hell yes! I can tell the difference (notwithstanding other performance differences in the two buildings).

    That is the metrics for every surface not just the floor >61f and no more than 5.4f degrees difference for thermal radiant symmetry. I dont think you can properly address PH without looking at designing for comfort. So rather than a red herring it is a whale.

    At some point we will talk in circles because this is too narrow a discussion to take seriously.

  27. GBA Editor
    Martin Holladay | | #27

    Response to Andrew Michler
    Of course your passive house is more comfortable than your other house. I have been preaching the advantages of superinsulation for many years. You don't want cool interior surfaces in winter. I get that. You want airtight construction. I get that.

    I have no idea how leaky the floor was in your old house, or what type of R-18 insulation you had in your old house, but it certainly doesn't surprise me that you can feel the difference between a passive house with an R-56 floor and an older house with an R-18 floor. But those weren't the two options under discussion for the Toomey house.

  28. Expert Member
    Dana Dorsett | | #28

    The ROI will not be 180 years- try four to five centuries.
    The longer term cost trend on energy will be downward going forward to 2025, as the learning curves of wind, solar, and batteries are all still pretty steep. The cost of grid-tied PV has dropped by 22% every time the installed base has doubled, if one looks at a 40 year price trend. But the trend over the past decade has been a drop in cost of 30-40 every time the worldwide installed base doubles.

    Now that the levelized cost of PV is at "grid-retail parity" for roughly half the developed world (including a good fraction of the US), the doubling of installed capacity has accelerated, now taking less than 2 years. That means the year-on-year reduction in the cost of energy from PV is more than 10%, which means every year an even bigger portion of the population is at grid-retail parity, and even more people have electricity prices well ABOVE what they could get out of PV, making the economics of that investment even more favorable. The rate of doubling (and with it the cost of reductions) is accelerating on a time basis. In something like 10 years (maybe less than 5) PV is expected be cheaper than all other forms of grid power, even at the wholesale level.

    The cost bottom for PV is as-yet unknown, but we're nowhere near the bottom yet. And still...

    That ever cheaper energy going forward will be even more steeply leveraged by the periodic 20-25 year replacement of heat pumps, which are also on a fairly good learning curve. The efficiencies of heat pumps are still pretty far above the theoretical limits imposed by thermodynamics- there is plenty of room to grow. In the past decade the real efficiency of mini-splits has improved by more than 15%, while the inflation adjusted costs have been between flat and falling.

    That pushes out payback term even further.

    By 2050 (~1/3 of the way through a 100 year lifecycle of a house built this year), the per-kwh cost of electricity will likely have a real cost pf something like half what it is today, and the heat pump using it will be delivering 20-30% more output per kwh.

    Electricity price deflation is nothing new. Since 1980 the inflation adjusted price of residential retail rates in the US has dropped by about 20%. (See: select "residential electricity", then use the cursor to adjust the scale to cover 1980-2014) But that's before the precipitous learning curve of PV solar crossed into that territory, still headed way down. Even as barely 1% of the total generating capacity it has had measurable effects on moderating peak power pricing, but it's effects won't really become dead-obvious to everyone until it's crossed over 10%, cutting into the business models of many utility companies.

    This is a huge disruptive force in the power industry, but the net effect over the NEXT 35 years will be to drive electricity prices much lower and far faster than the 1980-2014 period. See:

    None of us have seen anything this disruptive to the energy market fundamentals in our lifetimes. Not even the oil shocks of the 1970s are comparable- those were political, not fundamental to the cost of sourcing energy. It has the financial markets all nervous (and excited), but so far most of us haven't been close enough to it to feel the heat. But you can bet by 2025 just about everyone will understand that the renewable energy transformation is coming at an energy cost savings- it's cost negative compared to any other path.

    Going high-R at 3 cents/R-foot (say, cellulose) has a much higher rational limit than 10 cents/R-foot EPS, but even that is well under R80. If it pencils-out on a 40-50 year NPV assuming ZERO price inflation/deflation on assumptions that electricity costs 15 cents/kwh and heat pumps deliver an average COP of 3, it's real payout may still take 150 years given the tsunami of cheap PV that will be occurring within the first 40-50 years. The IEA (international Energy Agency) this week projected that half of all electricity in 2050 will be coming from solar, but they (like the US D.O.E.'s EIA) have consistently underestimated the rate of rollout of both wind & solar going back to their inception, missing the mark by more than 50%. The IEA says PV power will average 7-13 cents/kwh by 2030. But PV power purchase agreements are already at that price point or lower from large utility scale projects in the US RIGHT NOW!. Figure at most half that by 2030, even lower in 2050.

    The fact that PV is modular and can be scaled to the local loads, there aren't huge economies of scale the way there is with coal plants, or nukes. Yes, it's cheaper to build at utility scale, but it's going to be much cheaper than the grid-rate to produce some or all of your power on-site. This makes it a real competitive marketplace- the prices WILL adjust to the new cheaper reality.

  29. david_white | | #29

    Re: response to David White

    I spoke with Steve. The number Steve gave you was source, not site (see your quote in your response to me). This was the main reason for the error. Also - the COP of 3.76 is based on the rated HSPF - it works for certification because it's "official," but I expect 2.5 to be closer to the truth. So a 60 year MARGINAL payback is more realistic. Note that if the marginal payback is shorter than the life of the component, it's a profitable investment.

    I also think the comparison to PV should be more rigorous. Slab insulation is there for the life of the building with no maintenance cost, but we typically give PV a 30 year life expectancy, and maybe 15 years for the inverter. If we take 60 years as building life, and assume zero maintenance for the PV, these two options are around par.

    There's one other issue. I expect problems with dehumidification in summer in these low-load houses, and in my peak dehumidification calc, the losses to the ground often cause a sensible heat fraction too low for my comfort. In one project that was strongly cost-driven, I went from 4" to 6" of type II EPS for this reason, even though 4" was closer to cost optimum. This doesn't justify the 8", but would call 4" into question (that question didn't come up on this project).

  30. Bronwyn Barry | | #30

    Small Thinking
    Peter - not sure who called you a 'hater or heretic' but I'm pretty sure it wasn't Ken Levenson. You may want to dial it back a touch there? This is just a (usually respectful) on-line forum, not the West Bank or Jonestown. (I'll send you a Kool-Aid mix, if you send me a self-addressed, stamped envelope?!)

    One other point: call me a pragmatist, but can anyone tell me where all this additional PV is being installed that is theoretically being traded for sub-slab insulation? I've yet to see anyone effectively install PV under a slab. In most residential cases the roof is already solidly covered with PV. In larger buildings all sorts of shenanigans have to happen in order to reach 'net zero' (however that is defined.) Anyone recognize this (really wonderful) building? Let's be sure to acknowledge that this PV vs Insulation debate is mostly limited to the detached, single-family home for the lucky few able to afford to build their own home.

  31. LukeInClimateZone7 | | #31

    A little context
    Let us remind ourselves that Passivhaus certification is just that... a certification, a voluntary program that some people choose to use to guide the design and construction of their projects.

    What I have always really enjoyed and appreciated about PH is that it raises the bar and provides a locus of standards, benchmarks, etc. for us to talk around. It's an artificial bright line, to be sure, but at least its a bright line (Ja/.Nein fallacy notwithstanding). Otherwise, I was succumbing to this grey tyranny of the long tail of highly sensitive optimizations for my projects. Having a bright line is helpful for "Anchoring"

    One answer seems fairly obvious-- if PH modeling and optimization takes a project in a direction which conflicts with the clients goals, then maybe its ok to not get certified. Maybe having an almost PH (apparently some call this a Half-assive House) is actually better.

    I find Martin's questions for Dr. Feist very engaging though. In my mind, it's about the longevity of the PH brand. If PHI can't provide good, clear arguments for why each of its requirements is not only sufficient, but truly necessary, then I will be happy to recommend to my projects that they not certify with PH if it may result in assemblies that provide vanishingly small benefits to the client as well as to the broader environment.(e.g. the slab insulation debate).

    But why the debate is important--I really don't want to discourage certification. I, like many, feel that PHI and PHIUS may be doing so because of its Ja/Nein certification system.

    Martin's voice as a sort of megaphone for a lot of folks is very important and I appreciate it because I like to know that PHI and PHIUS are both hearing concrete and specific feedback on how sometimes their programs are the 'perfect' being the enemy of good.

    And when I hear that some more ardent followers of the PH Method (including the Ja/Nein mentality) dismiss the projects I work on as pejoratively Half-Assive, then I bristle and think to suggest that not every shares their sclerotic values. And it's not about my values-- it's actually about the homeowners' values.

    Perhaps the loudest action (albeit least articulate) is the few project registrations under my belt. In a few cases, PH is currently a good fit for my projects. In many cases, I find it to be a bad fit since it might lead to less than optimal outcomes that will leave the homeowner frustrated. And if that means that PHI/PHIUS each fail as a sustainable brand because of this indifference to their market, then so be it, And I will be slightly bitter that the loss could have been avoided, in spite of many's efforts (including Martin's).

  32. Expert Member
    Dana Dorsett | | #32

    Response to David White (#29)
    " Also - the COP of 3.76 is based on the rated HSPF - it works for certification because it's "official," but I expect 2.5 to be closer to the truth. "

    In Connecticut? I can point you to a study of a fleet of 10 1-ton Mitsubishis in Idaho Falls ID monitored in-situ by researchers for the NEEA that averaged 2.96 for a reasonable average, and that was the older -FE12NAs (HSPF= 10.6) not the -FH12NA (HSPF= 12.5) . Given that Idaho Falls has an average winter temp more than 5 F colder than any location in CT it'll do measurably better in CT than in Idaho Falls.

    If the thing tests at an HSPF of 12.5-13 it'll hit around 3.5 in CT (and WAY above 2.5), but probably not 3.76.

    "I also think the comparison to PV should be more rigorous. Slab insulation is there for the life of the building with no maintenance cost, but we typically give PV a 30 year life expectancy, and maybe 15 years for the inverter."

    That's why one uses the levelized cost of energy for those comparisons, and not the marginal costs. The levelized cost of energy is a fairly well scrutinized topic, amongst energy policy wonks and financial analysts, but if you want to also throw in the 20 year replacement cost of the heat pump to the energy cost equations while you're at it, go ahead, it doesn't change the larger picture. The all-in levelized cost of PV power 6 years ago was about 50-60 cents kwh, but it's about 1/3 of that today, and will be about 1/10 of that by 2030. The levelized cost of PV with the current subsidy is well under the retail cost, and the net delta using levelized cost will be well over $32. (Though clearly not the full marginal cost difference.)

    So WHAT if you have to replace the PV in 20 years? The levelized cost of power out of the replacement system will be less than half what it is for the initial system, and a fraction of current retail electricity ates. (The replacement mini-split will also be more efficient, and probably cheaper, but not by as much as the solar.)

    More nuanced levelized cost estimates:

    See the PV cost "learning curves" on page 48 for where it's really headed:

    The nightmare stuff for the electric utilities:

    Bottom line, the LCOE of PV with the current subsidies in CT are cheaper than retail grid rates in CT now. and in 20 years it will be WAY cheaper. So that $32 cost savings base on the grid-retail price today is actually less of savings than that if it's offsetting PV derived power at today's PV prices. Over subsequent PV replacement cycles it will be even less.

  33. Expert Member
    MALCOLM TAYLOR | | #33

    Question for Andrew Michler
    "I designed two that have zero foam in the foundation and are both very cost effective to build."

    Can you flesh out how you did this? I'd like some viable high R alternatives to sub-slab foam.
    Thanks, Malcolm

  34. Ken Levenson | | #34

    quick thoughts
    Peter L - Kool-Aide? Religious movement? Haters? Heretic? Sense the hostility?.....please take a deep breath...all anyone is trying to do is build better low-energy buildings.

    Steve, I love the image of substituting the meaning of a high-performance buildings standard for granite countertops - we should all be guilty of it. It's a great project.

    As Lucas Morton notes - sometimes the client's desires will work against achieving Passive House certification - that's okay too. I/most agree, for what it's worth.

    But tastes change and client priorities change and the professionals can help drive the change. I predict a decade from now, with a bit of luck and a lot of work the debates we endlessly have about gas cooktops and gas dryers and insulation levels and the high cost of components will all seem very quaint. Regardless of the endless bickering about this particular aspect or that particular aspect of Passive House, it seems that Passive House is driving a big change for the better and itself is getting better by the change it is making.

    And while the term "shoe-horning" is a strong one, it is still fair - and that's okay, I think. It was clear from the NAPHN14 conference and the multitude of experiences that we are all learning, details are getting better, calculations are getting better - it is still early, it is still formative, but the progress is real and accelerating.

    Passive House costs more now, but with the investments we make today, the payoff will be in the market transformation that pays off for all of society in a big way. Every inch is worth that.

  35. user-1072251 | | #35

    The point is that it helps us
    The point is that it helps us all to have a standard to aim at, even if we choose not to reach for it. You're saying there are better ways to spend our money; thats true for cars, jewelry and pretty much everything else we buy, including houses. So what? There will always be people buying the best and others buying the most cost efficient.

    I was impressed that a large number of the building discussed at the Portland conference were either not-quite-Passive or uncertified Passive; proving us thrifty Yankees who know how to save a dime. Some will want the Passive House label just for the "plaque on the wall", some for the feature that the thermal benefits are part of the building structure; either way it gets people talking and paying attention, and maybe they'll build a "pretty good house"instead of the other Standard - "as cheap as the law allows", aka "code". Our overall goal is to improve the built environment - Passive House is one way, Pretty Good and Net Zero are other ways. Time to stop arguing among ourselves and get to work.

  36. AntonioO | | #36

    Question for Dana Dorsett
    These are interesting numbers that you have put up with regard to energy cost projections. I'm left wondering who will own the PV systems. My suspicion is that my local power company will not just take this big cut in revenue passively--pun intended. I once subscribed to satellite service and saw that I could purchase a set top box for the cost of a couple years of box rental. Later in another home I was told by the same satellite service provider that set top box rental was required. Similarly, my current internet service provider only does router rental. The last router I purchased (many years and two internet service providers ago) could be had for one years router rent from my current ISP. Now, I don't think power companies will ever be able to capture the PV market. But will they own a substantial percentage of PV generation and thereby be able to artificially set the price? And why wouldn't they if it is cheaper than generation by fossil fuels? Moreover, the upfront costs would be much easier for them to overcome than for the average consumer. Or could the grid itself become the utility that individual PV owners pay a substantial fee to use? Will there be a movement for grid neutrality? Anyway, what are your thoughts? Thanks.

  37. jinmtvt | | #37

    Antonio :
    The thing is that you cannot just buy part in a large hydro central and they can't restrict you to buy and install your own PV system. Within a few decades, we shall have a suitable "battery" storage of a certain type for residential use with a "decent" price and capacity, and grid connected power will be history.

    Energy systems will probably be something to purchase just as a central climate unit was some decades ago.

    The only thing "wise" energy companies can do now is invest in PV manufacturing and research .

    As for mr Feist,
    i am a bit deceived by the answers given to Martin to such important questions.

    Some of us might view all of this merely as economical pov,
    some others are really trying to push for carbon and the planet.

    The truth is that it has to be both,

    because there will never be a wide acceptance here where energy prices are cheap compared to europe, if there is not incentives for regular folks that are usually as egocentric as the sun system is.

    And we are all still discussing about so few projects realized that it does not even dent a sand grain off the scale of the problem.

    I will not accept anything else than the true path, or at least as close as we can "detect" to it,
    and rigid PH for all different climates,energy sources and economical situations is just unacceptable.

    The only thing PHI is achieving here in NA, is to push us to discuss and realize the possibilities of more efficient buildings, but it would've come from elsewhere even if PHI would not be there.
    It propelled everything, now if they can't understand logic i am sorry but i am not interested.

    The reason why we are still discussing this very topic today must be because we are many to not agree with such rigid "foam" foundations ( pun intended ...first time i use this term! hope its not wrong :p )

    Now let's hope PHIUS can do MUCH better, because the only achievement in the next few years might be still more discussion and a few hundreds of isolated projects,

    and we'd all prefer a few thousands of insulated projects instead :p

    Dana: as much as i agree with you on the PV POV,
    insulation is still maintenance free, and if used in a high quality resilient building, will continue
    to perform for 100+ years.
    The ROI is not the only thing we need to consider here and i am sure we all agree
    to choose a compromise that suits everybody in building systems.

    What we really need now is cheaper insulation and cheaper way to install it.

  38. GBA Editor
    Martin Holladay | | #38

    Response to David White (Comment #29)
    You wrote, "The number Steve gave you was source, not site (see your quote in your response to me). This was the main reason for the error. Also - the COP of 3.76 is based on the rated HSPF - it works for certification because it's "official," but I expect 2.5 to be closer to the truth."

    You're right that Steve gave me source energy, but he also gave me the site/source conversion factor, and I did the calculations based on site energy, not source energy. Here is what he wrote: "TFA 176.5m or 2100 ft^2 usable. Baseline 8" EPS (R-35) = 2471 kWh/a; R-20 = 2647; R-50 = 2118. I quoted source kWh, not site. Divide by 2.6."

    So, using his source numbers, here is the math for going from R-20 (2,647 kWh/year source energy) to R-35 (2,471 kWh/year source energy):
    2647 - 2471 = 176 kWh/year savings (source energy)

    Converting source energy to site energy, we get:
    176 / 2.6 = 67.7 kWh/year site energy savings

    I'm happy to make corrections to my analysis if we can pinpoint the math error -- but so far I'm not sure if you and Steven know which number is correct. It doesn't appear that there was an error based on a confusion between site energy and source energy -- at least on my part.

    [P.S.: Although there is still no clear explanation of why Steve Toomey's numbers differ from David White's numbers, I have edited my footnote to reflect the information David provided.]

  39. GBA Editor
    Martin Holladay | | #39

    Response to Bronwyn Barry (Comment #30)
    You wrote, "In larger buildings all sorts of shenanigans have to happen in order to reach 'net zero' (however that is defined.) ... Let's be sure to acknowledge that this PV vs Insulation debate is mostly limited to the detached, single-family home for the lucky few able to afford to build their own home."

    Whether the client wants a net-zero building or a Passivhaus building, "all sorts of shenanigans" are necessary. (Passivhaus buildings have shenanigans like very thick subslab foam, miles of European tape, and $8,000 Zehnder HRVs. They might be good shenanigans, but they are definitely shenanigans -- not business as usual.)

    And you are right -- the privilege of owning a net-zero house is definitely limited to "the lucky few able to afford to build their own home." The same can be said for the privilege of owning a Passivhaus.

  40. GBA Editor
    Martin Holladay | | #40

    Response to Lucas Morton (Comment #31)
    Thanks for your comments.

    One of your sentences provides a thoughtful summary of where many of us now stand: "If PHI can't provide good, clear arguments for why each of its requirements is not only sufficient, but truly necessary, then I will be happy to recommend to my projects that they not certify with PH if it may result in assemblies that provide vanishingly small benefits to the client as well as to the broader environment."

  41. GBA Editor
    Martin Holladay | | #41

    Response to Antonio Oliver (Comment #36)
    You wrote, "I'm left wondering who will own the PV systems. My suspicion is that my local power company will not just take this big cut in revenue passively."

    You're quite right that the details of the net-metering agreement offered by one's local utility will (for the foreseeable future) determine whether any particular proposed PV system is cost-effective.

    But here is why architects and designers need to pay attention to the dropping price of PV: the current cost of PV-generated power should be seen as an upper limit to the likely future price of electricity -- even for customers who aren't able to own their own PV system. So if you are designing your wall assemblies and floor assemblies based on the assumption that electricity will, in the future, cost more than PV does now, you are probably designing for a future that will never come. And that's why some examples of very thick insulation are a waste of the planet's resources.

  42. GBA Editor
    Martin Holladay | | #42

    If some readers are wondering what Lucas Morton (in Comment #31) meant by the "Ja/Nein Fallacy," he was referring to a mode of thinking that I defined in one of my 2012 blogs. Here is what I wrote:

    "At the Building Energy 12 conference in Boston, Matthew O’Malia, an architect at GO Logic in Belfast, Maine, explained how Passivhaus designers approach their work. “PHPP is a massive spreadsheet,” said O’Malia. “It’s the mother of all spreadsheets. Here’s what I like about the Passivhaus approach: You either achieve the standard or you don’t. At the end of the spreadsheet, your answer appears in this box. The answer is either ‘Ja’ or ‘Nein.’ There is no ‘maybe’ in German.”

    "Some Passivhaus designers go further than O’Malia, implying that a building that falls short of the magic 15 kWh per square meter is at risk of failure. To these designers, the Passivhaus standard represents an important threshold for performance and moisture control. The implication is that designers who aren’t conversant with WUFI or THERM can end up designing buildings that encourage condensation and mold.

    "I propose a name for this mistake — the “Ja/Nein Fallacy.”

    "In fact, there is no evidence that superinsulated buildings that fall on the “Nein” side of the Passivhaus divide are experiencing moisture or performance problems. Moreover, as Blasnik pointed out, once the homeowners move into their new Passivhaus abode, variations in plug loads can overwhelm the small envelope issues that Passivhaus designers lose hours of sleep over."

  43. Brian Knight | | #43

    Materials improvement
    Love the coverage of PH and all the issues raised. Would like to see more good benefits of the PH movement mentioned like improving domestic windows. Why are we so far behind in window performance? Why arent we looking more into code improvements in Ufactor and having equitable air infiltration labeling of standard window units? Does this have to be entirely market driven or is this fruit low enough?

  44. girwin | | #44

    Long Term Thinking?
    I'm not an expert on energy policy and economics, but it seems to me that "net zero" is a doomed idea. I'd welcome informed feedback on the following.

    From what I understand, the only reason utilities are tolerant of/able to afford "net zero" is that the energy they barter (winter baseline) is less valuable than what they receive (summer peak) in exchange. Summer electricity is certainly much more valuable/expensive where I am. On that level, it seems a very bad deal for the PV owner, who is, in theory, providing a very valuable commodity at a much lower price than it's worth. The approach adopted in Germany, a "feed-in tariff" (FiT), where owners of renewable energy systems are empowered (pun intended) to sell their commodity on the market, seems to be more just, more successful and even more cost-effective than our current tax credits and subsidies, according to NREL (

    Solar energy has this funny aspect to it - the more sun there is, the more energy you get. As such, it is rather problematic as a power source for heating-dominated buildings because it poops out precisely when you need it most! This is not a coincidence, this is causal. Using solar energy to heat buildings that need heat because there's no sun is like trying to use a disease as its cure.

    What happens when we get a lot more PV on the grid? We may see, as Germany has, a negative wholesale price at times of peak solar output ( Likely, this won't persist, and the market will find ways to address this, with seasonal industries, chemical storage, trans-hemispheric power transmission, etc. Regardless, it will NEVER be easier to generate solar electricity in winter than summer, and it is extremely unlikely that any functional utility system will agree to trade valuable winter energy for cheap summer energy at par.

    What happens to the economics of your "pretty good" house in the Maine woods then, with its relatively poor PV output ( and a market not much interested in what you have to sell?

  45. GBA Editor
    Martin Holladay | | #45

    Response to Graham Irwin
    Like "Passivhaus," the phrase "net-zero house" has a definition. (Several definitions, actually -- just like "passive house" will when PHIUS finishes its new standards.) Once a builder decides on a definition (for example, an all-electric house that produces as much energy on site on an annual basis as the occupants use), then building and occupying such a house becomes possible.

    So I'm not sure what you mean when you write that "net zero is a doomed idea." It's not doomed; people are doing it right now. You don't have to build such a house if you don't want to, but you can.

    Time will tell whether an investment in the features of a net-zero house make economic sense -- just as time will tell whether investing in the features of a Passivhaus make economic sense.

    If you want to discuss whether the features of a net-zero energy house make environmental (rather than economic) sense, I believe they do. Right now in the U.S., PV systems are used to generate 0.23% of the nation's electricity -- a very tiny fraction. Coal is used to generate 39% of the nation's electricity. It other words, the electricity that powers a U.S. home is 169 times more likely to be coal-generated electricity than PV-generated electricity.

    So when a homeowner's PV array feeds electricity to the grid, that electricity displaces electricity generated by other means -- most of which are more environmentally damaging than PV-generated electricity. That's good for the planet.

    Although PV represents a very tiny fraction of U.S. electricity production, PV installations are growing rapidly. On the island of Oahu, some neighborhoods generate so much PV electricity that the local transmission lines have a hard time handling it. So that can happen (although the problem is years away in most U.S. locations). There are technical solutions to these problems when they arise -- and these technical solutions will eventually be implemented. The electric utilities may resist these coming changes, but that doesn't mean that "net-zero is a doomed idea."

    Dr. Feist has predicted that excess PV power will be converted to hydrogen or methane during the summer, so that the hydrogen or methane can meet winter heating demands. That may happen, although I think other solutions are more likely (including development of sources of energy that are available in winter, such as wind power, tidal power, deep geothermal power, and biomass).

    If we want to address climate change, we need to fundamentally change the way we generate electricity. These changes are coming, whether we want them or not, because wind power and PV power are getting dramatically cheaper. That's good for the planet. Eventually we will figure out how to use these sources of electricity to meet our needs year 'round.

  46. GBA Editor
    Martin Holladay | | #46

    Response to Brian Knight (Comment #43)
    Q. "Why are we so far behind in window performance?"

    A. The U.S. window industry could definitely do better. Like you, I have long been frustrated by the specifications of windows sold here. The U.S. window industry has been slow to offer triple glazing. Moreover, most window suppliers offer only low-SHGC glazing -- a type of glazing that isn't suited for south-facing windows in cold climates.

    Mysteriously, when U.S. window manufacturers offer triple glazing, they often choose low-SHGC glazing instead of high-SHGC glazing. This is very odd, since no one in Florida is buying triple glazing. The only customers for triple glazing are builders in places like Minnesota and Maine, where high-SHGC makes more sense than low-SHGC glazing. But the window manufacturers don't get that basic point.

    Hopefully, U.S. window manufacturers will do a better job addressing these issues in the future.

    However, there is a limit to likely improvements in window technology -- namely, the fact that an investment in better windows usually doesn't make economic sense. For a thorough discussion of that fact, see Study Shows That Expensive Windows Yield Meager Energy Returns.

  47. Peter Hastings | | #47

    Net Zero Doom
    As Martin points out 'it all depends on what you mean by net-zero'. If we use Martin's definition (on average generate as many kJ as you use) then you have to buy expensive winter energy and sell cheaper summer energy. You're still net-zero but you also have utility bills - although these should be small if your house isn't an energy hog. If you want net-zero bills then you'll need to generate the same value, not quantity, of summer energy as winter energy. Both seem possible technically so it's a simple economic choice.

  48. iLikeDirt | | #48

    Windows may be worse
    If anything, I think expensive windows (especially expensive vinyl windows) are a better example than extreme sub-slab foam. Does anyone really think vinyl windows are gonna last 50 years--especially ones in a sunny climate? If you factor in the likely replacement costs, I suspect that these things are never ever gonna even reach the simple payback point.

  49. Expert Member
    MALCOLM TAYLOR | | #49

    Reply to Nathaniel
    I've taken to dividing my buildings up into components expected to last for the duration of the structure and those needing to be replaced. Once you do this you can then detail them appropriately. Windows are a perfect example. While it is annoying and expensive to have to replace them, it is infinitely more so if they have been detailed to that the siding has to be removed and the flashing and WRB are difficult to reinstall correctly.

  50. jinmtvt | | #50

    Malcolm and Nathaniel ...
    and that is exactly why window framings should be made out of long term durable materials
    such as aluminium .

    Replacing failing glazings in 25-30 years is a piece of cake if the window frames are built to last 100years + .

    All materials that are outside , exposed to weather and UV should be chosen with respect.

    Martin : while we all agreed on that last dicussion that heavy investment in windows do not pay off
    ( even more when considering the JWen -HDepot offerings @ ~ 1.7U for ~200$ )

    Tooling and design for efficient frames has a 1 time cost, which is probably very close to the same manufacturer design expenses as going for an inefficient window product.

    The reason why we are lagging Euro products is the same as discussed prior on this thread...
    There was and is still not much point to improve window performance because of our low current and future energy cost, economically-wise.
    Try and sell windows to regular folks of builders for double prices by telling them that they are going to make up the price different of a few thousands within 100 years or so ...
    Market demand dictates products.

    ( i intend not to follow this rule on any of what i will be doing in the future :)

    If you dig a bit, you guys will see that in most Euro countries, with high prices of energy,
    most window upgrades from good to PH performance usually pays for themselves within the 20-40 years of expected life, and they tend to design buildings for 100 years spawn or more.

    As for Net Zero , half of the projects i've seen that are quite close of meet NZ are nothing more than regular buildings built a bit hgher than code with very large PV array slammed onto them.
    I tend to disqualify any buildings that do not even feature shadings for summer sun angles,
    and most of them do not. ( cheapest ever energy feature you can build in a house )

    for now, NZ is as serious as the owner/designer is, nothing more.

  51. Expert Member
    MALCOLM TAYLOR | | #51

    We are back to discussing longevity in isolation, as though it were largely dependant on the the quality of the building components and not social factors. Look at Europe. The factors that lead to the demolition or abandonment of millions of houses in the last century wasn't envelope failures it was war and population shifts. In Britain it was the de-industrialization of the north.
    The recent large scale abandonment of housing in North American was due to economic hardship and demographic changes. Who in Detroit cares about the ROI of their windows? I keep hearing posters here present the choice owners should make between granite counter tops and more insulation. Well my clients don't get either. Too many of the arguments around highly efficient houses are still couched in terms that only make sense in the context of boutique projects and ignore the world we live in around us.

  52. jinmtvt | | #52

    you summed up the reason why building performance must be a rule and not a choice.
    I don't see many abandoned houses in my corner of the world.
    ( actually i can't recall seeing any in my hole life .. )
    Not that it will not happen in the future, it might ... but the % will be very low with current "crazy" prices of housings ....everybody is looking for a "deal" for a house.

    We need more houses built in larger projects, to higher standards , with higher building efficiency which leads to lower costs of additional performance items.

    If you let regular folks decide , of course they are going for the countertop
    ( i do not see a reasonable granite counter top as a stupid is natural and very long lasting )

    Just try and "sell" to a future homeowner why they should use smaller windows and most of them should be placed in south.
    You'll get a " small windows are so out " look for sure.

    You can't teach the mass anything, so you need to impose.
    Their head is already full trying to remember all of those expensive wearable brands and Hollywood
    actors names etc ...

    ok enough rant ..
    cheers :)

  53. GBA Editor
    Martin Holladay | | #53

    Response to Jin Kazama
    You wrote, "I don't see many abandoned houses in my corner of the world."

    I live south of you, and I definitely see abandoned houses where I live. When I moved to this corner of Vermont in 1975, there were still houses standing in a nearby village named Piperville. The last residents abandoned Piperville in the 1920s; it was said that the young Vemonters who were drafted to fight World War I were reluctant to return to their hardscrabble lives scratching out a meager living in the hills of Vermont.

    Malcolm Taylor cites the disruptions that have hit cities like Detroit and Cleveland, as well as the wrenching disruptions that tore Europe apart from 1939 to 1945. Can we predict a future without similar disruptions? I doubt it. If anything, our changing climate is likely to make these types of disruptions more rather than less common.

    Will the suburbs around Phoenix, Arizona be thriving in 40 years? Or will the region be littered with abandoned homes? Stay tuned.

  54. GBA Editor
    Martin Holladay | | #54

    A blog by Bronwyn Barry
    Bronwyn Barry recently posted a blog called NAPHN14 in Maine, Martin and a Few Inches of Sub-Slab Insulation. Barry's blog may be of interest to GBA readers who are following this debate.

    Barry wrote, "Here’s the main reason why calculating your insulation investment based on the current price of solar PV is highly problematic: it doesn’t scale and does not apply universally to all projects." Barry assumes that my use of the current price of PV-generated electricity as a reality check means that I advocate installing a PV array on every project. I don't. I'm just saying that it's hard to imagine a future in which the cost of electricity exceeds the current price of PV-generated electricity. That's why the price of PV energy is a useful benchmark and reality check.

    Barry wrote, "If we’re going to attempt to address the possibility of maintaining some form of life here on earth, we have to look at emissions from transportation." No argument there. I've been saying that for years, as have several other regular GBA bloggers. For example, see these GBA articles:

    Houses Versus Cars

    Green Buildings Aren’t Truly Green Without Location Efficiency

    Location Efficiency Trumps Home Energy Efficiency

    Where You Build May Matter More Than What You Build

    Barry ends her blog this way: "I’m hoping that the few hundred extra dollars you’ll pay for a couple more inches of sub-slab insulation will start to look like a bargain." I'm sorry, but they still don't -- and Barry hasn't provided any argument to explain why she thinks that they do.

  55. Peter Hastings | | #55

    Net Zero Doom II

    As for Net Zero , half of the projects i've seen that are quite close or meet NZ are nothing more than regular buildings built a bit hgher than code with a very large PV array slammed onto them.

    And this is heinous why ?

  56. AntonioO | | #56

    Question for Martin
    I read the Houses Versus Cars article. Question: How much would that comparison change if energy loses in production and transmission were considered? It seems to me that the car is at a disadvantage because the energy to work loss occurs with the end user whereas with electricity, for example, the electricity generation loss occurs before the user gets it. Or maybe I'm confused. My local natural gas company keeps telling me that my electricity company has lost 60-70% of the energy content before the electricity reaches my house. The gas company claims they only lose a few percent in production and transmission. Natural gas is "greener" they say, though that is slightly away from the cars versus houses issue.

  57. GBA Editor
    Martin Holladay | | #57

    Response to Antonio Oliver
    Your question boils down to this: what if this comparison between house energy and vehicle energy is made for source energy instead of site energy?

    If you want some conversion factors for site energy to source energy, you can find them near the bottom of this article: Understanding Energy Units, under the heading "What’s the difference between “site energy” and “source energy”?"

    If you want to convert all of your site energy figures for your home's energy budget to source energy figures, you can use these factors:
    Grid electricity, x 3.365
    Natural gas, x 1.092
    Fuel oil, x 1.158
    Propane, x 1.151

    I imagine that the factor for gasoline is similar to the factor for fuel oil (x 1.158).

  58. Expert Member
    Dana Dorsett | | #58

    Answer for Antonio Oliver (#36)
    "These are interesting numbers that you have put up with regard to energy cost projections. I'm left wondering who will own the PV systems. My suspicion is that my local power company will not just take this big cut in revenue passively--pun intended. I once subscribed to satellite service and saw that I could purchase a set top box for the cost of a couple years of box rental."

    Ownership of YOUR rooftop PV can have various forms, but it's up to the state & local regulators as to how much that can be restricted. Third party ownership of rooftop PV is allowed in 43 states of the US, including California, where something like half of the home PV systems installed last year are owned & maintained by third party solar companies, and leased back to (or sold on long term loan) to the home owner. Since these deals are often $0 up front, but results in a lower utility bill (typically a 20 or 25 year power purchase contract, with limitations on rate increases.) That model is expressly disallowed in a handful of states, and allowable in others only if the local utility agrees to it.

    More on third-party ownership issues:

    In Arizona the statewide utility company has petitioned to be allowed to compete directly by the third-party solar companies, and own some residential rooftop systems, but the solar companies are pushing back, since as a regulated monopoly the utility has an unfair competitve advantage, in that they are allowed to rate-base all of their capital spending, charging all customers for the cost of the solar systems, a factor which also gives utilities access to capital at a lower cost. (I don't know if the AZ case has been fully resolved yet.)

    Several large utilities have sought to impose monthly fees on grid tied PV, but few have succeeded in demonstrating that there was an actual cost associated with the PV that needed to be recouped. Indeed, a recent analysis published by the Lawrence Berkeley National Laboratories indicates that even at penetration levels of 10% there is little to no cost shift of grid costs onto non-PV ratepayers, and that in fact the presence PV was putting a damper on the wholesale cost of electricity (particularly the more profitable peak-hours), which ends up reducing profits for the competing generation sources. For an investor owned utility the shareholders take a hit. See:

    Basically, if the regulators are doing their job, privately owned PV on the grid will reduce electricity cost for the rest of the customers. But they're not always on the ball.

    In Australia grid tied PV is only paid the spot-wholesale price for power exported to the grid, which reduces the size of the PV array that makes financial sense. (Use it while it's being produced or get paid next to nothing for it: ) But that doesn't mean it's not cost-effective to put PV up there- it's only a matter of how much, based on your mid-day power use patterns (which can be adjusted, to some degree.) But that sort of approach to compensating PV invites grid defection, if batteries or co-generation can fill in the gap. Case in point: The town of Feldheim Germany installed some municipal wind turbines, and a bunch of PV, as well as a biogas heat & power cogenerator. The deal with the regional utility was rigid- sell all your power at wholesale, and we charge the standard rates for what you use. The town did the math, and built their own micro-grid running completely parallel with, but not connected to the utility, and are paying half what they used to:

    "But will they own a substantial percentage of PV generation and thereby be able to artificially set the price? And why wouldn't they if it is cheaper than generation by fossil fuels? Moreover, the upfront costs would be much easier for them to overcome than for the average consumer. Or could the grid itself become the utility that individual PV owners pay a substantial fee to use? Will there be a movement for grid neutrality? Anyway, what are your thoughts?"

    As in Feldheim, there are limits to how far they can go on fees and surcharges before it becomes financially rational to un-plug. CitiGroup estimates that the cost of solar + battery in 2020 will be cheaper than grid-retail in much of the northeast over the lifecycle of the systems. And Morgan Stanley's estimates are similar:

    If large numbers of people start unplugging from the grid, that DOES become a true cost to the other ratepayers, since the grid stablization and rate stabilization of having those PV & storage assets on the grid go away, and all of the grid maintenance & stabilization costs get shared by a shrinking pool of ratepayers. As the utilities get regulatory relief with rate hikes, it then enhances the attractiveness of further grid defection. This has been termed the "utility death spiral" by industry analysts, a scenario becoming painfully real in Germany, Hawaii, and Australia today. This movie will showing soon at a utility near you within the next decade- but you get to see the trailers first- hopefully your version won't be as painful as Hawaii's. To better manage the disruptive force of cheap PV and other distributed generation the state of New York is being proactive, and completely rewriting the regulatory rule book, actively under revision right now. The first rough-draft lives here:

    The $64 trillion is who will pay for the stranded assets of those utilities who keep building expensive large centralized power generation under a regulatory guarantee of making a profit on the expenditure? If they try to stick the ratepayers with the whole bill, the death spiral is all but guaranteed, and it won't be pretty. With investor owned utilities the shareholders may have to take the write down, but the publicly owned utilities may have to seek tax payer (not ratepayer) relief to keep the lights on if they own too much of that really cool junk that just won't be needed, and is to expensive to run. The vertically integrated statewide monopoly in Georgia seems particularly at risk, having huge sunk-costs in brand new nuclear plants. (Those nukes will be cheaper to decommission if they never load the fuel and throw the switch, but that doesn't seem too likely.) Georgia Power (sorta) sees it coming, and have tried (and failed) to limit privately owned PV on their grid, but have drawn the ire of everybody from the Green Party left to the Tea Party right in the process.

    The transition is very disruptive to the business models of the utilities, but it's still the right thing to do. Turning protected monopolies into successful energy price competitors won't happen overnight, but distributed power generation with PV does not have large economies of scale. A 50 megawatt array costs about as much per-watt as a 500 kilowatt array, and only slightly less than a 5-10kw array that a homeowner can afford to install on the roof and go net-zero with. What the utilities won't be able to do is make it too expensive for you once rooftop PV is really THAT cheap (meaning, even cheaper than it is in Germany today, which clearly WILL happen, and soon.)

  59. Expert Member
    Dana Dorsett | | #59

    Ja / nein fallacy (answer to Martin)

    Maybe it's just a Darmstadt dialect thing. Most Germans would probably be happy with "kann sein" (literally "can be", meaning "could be" ) or "veileicht" as a pretty good approximation of "maybe". :-)

    But arithmetic is deterministic- I suppose a number either is or is not less than 15kwh/year per square-whatever, and not "kann sein" less than. The problem isn't the answer, but rather the framing of the question. The real question is the rationality of the single number.

  60. GBA Editor
    Martin Holladay | | #60

    Response to Dana Dorsett
    (Trying to tread lightly here, to avoid national stereotypes.)

    Suffice it to say (as I think you understand) that Matthew O'Malia was making a joke when he told the audience that "There is no ‘maybe’ in German.”

    Perhaps he was referring to the possibility of rigidity? Or rigid modes of thinking? Or something like that...

  61. Expert Member
    MALCOLM TAYLOR | | #61

    I have a lot of sympathy for your call for mandated higher building standards, but it does lead us to some interesting ground philosophically.

    The energy efficient housing movement has a strange mixture of libertarian and coercive tendencies which lead to a selective range of things it appears to want too impose on people who build houses.

    We start from the premiss that an individual should be allowed to build whatever they want wherever they want as long as they can afford it, without imposing restrictions based on the size of environmental footprint that the project's scope and location might entail.

    At this point things flip and we feel free to say that the house must meet certain stringent energy consumption standards.

    So what might turn out to be the most meaningful decisions, like building in the suburbs, building in the desert, building a detached single family house, or even whether to build at all, appear to be beyond the remit of the wider community to dictate, but once these are taken we feel free to say how the building envelope must be constructed.

    I struggle to see how are this one area of our decision making should somehow be subject to the aims of the wider community when the rest are exempt, or conversely why I don't hear any of the voices asking for more stringent standards asking for restrictions on the other areas that influence the energy consumption of a home's inhabitants.

  62. GBA Editor
    Martin Holladay | | #62

    Response to Malcolm Taylor
    I'm not sure that it's possible to pigeon-hole the politics of people who believe in green construction principles. I'm sure that you can find no-regulation libertarians as well as planned-economy socialists among the wide range of greenies.

    Moreover, I don't think that a majority of those who believe in energy codes would agree that "an individual should be allowed to build whatever they want wherever they want." Most U.S. towns have zoning regulations that separate commercial zones from residential zones, and dictate minimum lot sizes, setbacks, and so on. There are many restrictions on where people can build homes. These regulations may be illogical or even counterproductive, but they exist.

  63. Expert Member
    Dana Dorsett | | #63

    Response to Martin (post #60)
    Of COURSE it was a joke, as is my comment about "Darmstadt dialect"

    I suspect the "ja / nein" aspect of the PHPP is intended to be absolutely clear, as opposed to some weasely-waffely "kann-sein" approach to whether it is or isn't certifiable under the program. Even those more accustomed to dealing with the nuances it comes off as rigidity, there is something to be said for clarity.

    The fact that occupant behavior has a bigger effect on the actual energy use of a house than the last R20 of wall-R in an PassiveHouse is well understood by those who actually measure stuff. I s'pose there isn't a Darmstadt-dialect idiom for "it doesn't much matter " either. :-) (It's a joke- see the smiley? ) The Beaton PassiveHouse is located near me ( ) with ~R65 walls, but with the multiple game machines & big TVs used by their kids blow the energy budget big-time. They often have cooling loads even in February, even at night ( ). If the plug-load energy use assumptions built into the PH tool diverge from real world use by more that 2x of how people in the US ACTUALLY live, the value of the clarity in a "ja / nein" approach isn't very much.

  64. Marylowcarbon | | #64

    Passive House fine-tuning
    Martin, I've been covering high-performance buildings for decades, as have you, and when I wrote and edited my first article about some Passive House retrofits in 2007, there weren't any retrofits being done in the U.S. that even came close to achieving comparable energy savings to those achieved by PH retrofits in Germany—80% savings of conditioning energy. Then, a 30% savings was considered exemplary, and still is today by some. Passive House has raised the bar high enough in the U.S. to even make this conversation possible--quibbling over the cost effectiveness of several inches of foam. While I am excited about architects, engineers, and researchers figuring out how to cost-effectively make really high-performance buildings that are better adapted to local climates, the tone of this conversation bothers me. Cost-effectiveness calculations are made with all sorts of underlying assumptions about future costs, so it is very difficult, if not impossible, to say that one investment will be guaranteed to be more cost effective than another in 30 years. Every Passive House project, as far as I am concerned, is an ambitious undertaking that will greatly reduce carbon emissions compared to a conventionally constructed building. Debating the finer points of PH implementation is how we all will learn, but the bigger picture of how PH has revolutionized the approach to constructing high-performance buildings shouldn't be lost in these conversations, and neither should the immense value of PHPP as a tool. From all that I have read, other building energy models are not as useful nor as accurate, even though the PHPP consistently underpredicts miscellaneous electric loads in U.S. households. My main complaint is that the PH approach, especially to retrofits, isn't spreading quickly enough. There was a great talk at the international PH conference last April about 153 social housing units being retrofitted to PH with each one taking 7-10 days. Let's figure out how to imitate that pace of energy and carbon reductions from the building sector--and then quibble over the fine points. Finally, I am not very interested in the PHIUS/PHI split, as I am more interested in building science than organizational politics. I would have answered 'No" to your questions on this topic also, but please don't impute all sorts of emotions to this response other than boredom with this topic. Both PHIUS-certified and PHI-certified projects can be great buildings. The PHIUS/BSC research into developing climate-specific standards is certainly interesting, but whether new standards will be helpful for further market transformation is as yet undetermined, and in my mind unlikely, but we will see. I thought the talk by Sam Rashkin that immediately preceded the unveiling of the climate-specific standards was interesting timing. He discussed how important simple, clear messaging was to get customers interested in high-performance buildings.

  65. GBA Editor
    Martin Holladay | | #65

    Response to Mary James
    I'm sorry to hear that GBA's coverage of these issues has disappointed you.

    I agree with most of your points. I agree that Passivhaus retrofits in Europe are achieving substantial energy reductions, and I agree that PHPP is a wonderful and useful tool.

    As a journalist, I believe that it is worth discussing the cost of the deep-energy retrofit jobs you cite, as well as the cost of new Passivhaus projects in the U.S. This discussion necessarily entails a discussion of cost-effectiveness -- even though, as you wrote, it is "very difficult, if not impossible, to say that one investment will be guaranteed to be more cost effective than another in 30 years." (To read what I have written on this topic -- my views are similar to yours -- see Payback Calculations for Energy-Efficiency Improvements.)

    Fortunately, comparisons between the energy benefits of (for example) an extra 6 inches of rigid foam under a slab that already has 6 inches of rigid foam and the energy benefits of a PV system do not depend in any way on future energy costs. The cost of the energy that will be produced by a PV system over the next 30 years is known on the day that the system is purchased and installed. Moreover, the "extra foam vs. PV" comparison can be make on a kWh vs. kWh basis, which is independent of cost.

    You wrote, "My main complaint is that the PH approach, especially to retrofits, isn't spreading quickly enough." One possible reason that the Passivhaus approach is spreading so slowly in North America is that the Passivhaus standard requires builders to include insulation that is unjustifiably thick. We need to discuss this issue if we want more existing buildings to get needed retrofit work.

    You wrote, "I am not very interested in the PHIUS/PHI split, as I am more interested in building science than organizational politics. I would have answered 'No' to your questions on this topic also, but please don't impute all sorts of emotions to this response other than boredom with this topic." In fact, I haven't imputed any emotions to Dr. Feist's response, nor have I made any comment whatsoever about it.

  66. Expert Member
    Dana Dorsett | | #66

    Carbon reductions? (response to Mary James #64)
    " Every Passive House project, as far as I am concerned, is an ambitious undertaking that will greatly reduce carbon emissions compared to a conventionally constructed building."


    An ambitions undertaking, surely , but the carbon content varies dramatically by energy source. (Yet the PH energy use spec is the same everywhere.)

    Take the example of a house in Quebec heated with heat pumps: There is effectively NO CARBON REDUCTION by going from a code min house to a PassiveHouse certified house, since the grid power in Quebec is over 95% hydro. A "great reduction" from nearly-nothing to even less isn't exactly the best bang/buck on carbon mitigation.

    In other locations with other energy sources, there may indeed be a carbon content per kwh in 2014. But those sources too both by location, and over the lifecycle of a house. Estimating on the carbon content of energy in a house between now and 2050 isn't possible to do with any accuracy, even if the carbon content of the first five years might be reasonably known.

    By contrast, building to Net Zero Energy, using only electricity or direct biomass energy sources one can predict the carbon content of the energy use with pretty good precision. The imported power fraction during the heating season may (or may not) have a high carbon content, but on high-carb grids that carbon is largely (sometimes more than completely) offset by the exported power during the sunnier summer season that reduces the net grid-load. As PV has gotten ever cheaper, the economics of offsetting carbon emissions directly with site-sourced low-carb energy have become more favorable and more certain than super-performance building envelopes. This will be even more true over the lifecycle of a building, as the replacement PV is much cheaper than the original.

    The "learning rate" on grid tied PV has averaged about 22% over the last 40 years, meaning that the cost drops 22% every time the installed base doubles. That doubling period is now less than 2 years. In recent years the learning rate has been in the 30-40% range, but even if it drops to 10%, the lifecycle cost of that energy is going down over time. Since the all-in lifecycle cost of PV (including financing) is below grid-retail at current rates, it has a more certain return than very high performance building envelopes. The energy costs will go down with successive PV system upgrades/replacements, and the grid-drawn power will be lower carb too.

    Bottom line: Building near zero-carbon power generation on site sufficient to cover the energy needs of the house is a sure bet on carbon reduction. Building a super-performance building envelope is highly speculative on carbon reduction over the lifecycle of the building, and even in the near term the amount of carbon reduction varies by several orders of magnitude depending on the local energy sources.

    And these grids, they are a changin'... Opting to become a green energy producer makes 'em change even sooner/faster. Rooftop PV in Quebec won't change the atmospheric carbon equation by very much, but it would in most places, and that's right NOW.

  67. Expert Member
    MALCOLM TAYLOR | | #67

    Isn't another variable in the probability of carbon reduction the embodied energy of the components necessary to achieve a certain level of energy efficiency? That's why I don't see how we can just dismiss the debate over high levels of foam used in Passive Houses as being "quibbles about cost effectiveness".

  68. wjrobinson | | #68

    Mary James
    If you were passionately support the Pretty Good House idea then you would be making good sense kid.

    Building PH with no regard to anything but 15KW and leaving PV out of the equation or costs or enviroment is nuts.

    And loving the giant spreadsheet is nuts. I can build a PGH without any spreadsheet and do it tomorrow for less $$ and more green environmentally friendly. And without LEED another nutty program with way way too much overhead.

    Recently there is an ongoing blog where the PHD homeowner paid $50,000 to basically redesign an existing set of PH plans. If I was the law I would have someone arrested for theft of undelivered services.

    One problem with the freedom to speak in the USA is that you and I are miles apart in our logic trains... lucky us.

  69. AntonioO | | #69

    Compelling but...
    Your assertions are compelling and seemingly well thought out. You provide great sources as well. Yet I'm still not so sure the uptake to solar power by consumers should worry the power companies as much as some reporters, think tanks, financial institutions think--at least not in some regions of the country. I think PV power may be great for my house. With no thought of solar positioning in mind at the time of purchase, it seems that my house's position on a clear lot (no trees blocking the sun from the south) is a great candidate for a solar array. My house is an anomaly in the neighborhood. I can say the same about a clear lot for probably little more than a third of single family homes in my zip code. The house also has a major piece of uninterrupted roof real estate which faces very close to solar south. I would say less than half of the houses have a good southward facing roof plane without architectural details like dormers that would allow for a good solar array placement. So I'd estimate that less than one in five houses in this area are good candidates for an array. The big saviour of the electric companies may be trees in the Northeast and Mid-Antlantic. Of course, every area is different. With all the flat roof houses with parapet walls, and the the lack of trees and abundance of sun, well over half the houses in my former neighborhood in New Mexico will be good solar array candidates. But with this and other issues in mind, I'm not anticipating a "utility death spiral" very soon where I live now.

    It would be great to see the conversion efficiency of technology marketed to homeowners take a significant step up. That would at least reduce the amount of roof real estate required to meet a homeowners energy needs or could possibly make the direction the array (or portions of it) more of an option.

  70. jinmtvt | | #70

    Dana :
    The only current way to reduce personal carbon emissions in central Quebec is to use very low MPG/Co2 and or electrical vehicles. Not much more one can do here.

    But, since our winters are still pretty cold, even with our low electricity rates,
    which will be going up in the near future with the recent "liberal government thieving " ,
    the energy cost for a non wood burner is still pretty high and will still be economically favorable for PV installation as soon as the prices drop a notch more.

    And with the same heating cost comes economical interest in at least reducing our energy consumption .

    Still, i wish to push again to think about how a "logical quantity " of insulation on a very long lived building , have a life long effect without any additional costs.
    There are much recycled insulation boards for sale nowadays, which reduces expenses and materials related carbon.

    Since no one knows the future, a sturdier building more insulated is something to consider.
    We must include design labor on durability of the buildings and its envelope in our calculations.

    Martin about Mary James comments :

    As far as i can tell, you are getting wiser by the day ! ( not to say that you weren't , but comparing this interview with then 2 before ... very professional , on a subject that we all know, motivates you )

    AJ: 50K$ for replans?? euh ok
    more than the total budget of insulation for 2-3 regular sized PGH :p

  71. GBA Editor
    Martin Holladay | | #71

    Response to Antonio Oliver
    I'm glad to hear that you have the good fortune of owning a house with an unshaded south-facing roof. That's good.

    You wrote, "So I'd estimate that less than one in five houses in this area are good candidates for an array." I have also seen neighborhoods similar to the one you describe, and you are right. However, the changes to the electric grid that Dana Dorsett and I are describing are coming down the pike, regardless of whether any particular neighborhood has a high proportion of unshaded south-facing roofs.

    As the cost of PV equipment continues to drop, PV arrays will crop up like mushrooms -- covering shade structures on parking lots, WalMart roofs, and abandoned landfills, as well as old brownfield sites that no one wants to develop. In some countries, PV arrays already line the sides of east-west highways, mile after mile.

    You predict that these coming changes won't panic utility executives. I hope you're right. After all, if utility executives get with the program and adopt solar-friendly policies, the coming transition will be smoother for all of us.

  72. RZR | | #72

    Antonio is correct…….
    Utility bills here in the Midwest are very low for most homes insulated to R-13 walls, R-20 roofs, ACH 5-7. $200 on average for 1500 sf, gas and electric. My home in San-Diego double and SDGE is now imposing more fees to the ones on the grid. I think a lot of these folks that live on the east and west coast are out of touch with mid-west reality. We have no energy code here due to fear of breaking the builders bank and it’s been that way for decades. Our code and city officials are looking at 2012 Ch 11 in fear. That has taken decades, just to look. They never heard of Passive house, 3-5 ACH scares them, forget .6. I don’t see PHPP being adopted in most of the Midwest anytime soon, over a decade.

    The same ones designing energy efficient homes have lost sight of structure, setting homes on foam makes no sense from a structural point of few, for one. Unless SIPs in continuous or monolithic it makes no sense. Bolting PV arrays on roof makes no sense in 90+ mph wind gust and hail zones that recently is only getting worse. Nor does venting by 2x2 furring to resist these loads. How well will those bolts/nails do in tension cyclic fatigue from 90+ winds in old rafters that bridge and thermally cycle coupled with wind? You don’t need a permit here if the concentrated load(distributed static weight) is 40-lbs or less, and the panel is no greater than 18” high above the roof surface. That fails to considers dynamic and cyclic loads.

    Our roofing company hardly ever runs into PV, if we did there would be an up-charge of 30-50% depending on quantity, to R$R clading. Has that been factored into the price per watt? MANY roofs get replaced every year, a booming business in the midwest, by profitable insurance funds, I wonder how the insurance companies will react to the increase cost of PV R&R?

    When we do R&R we add more holes to the structure degrading it, you should not go back in the same holes in high wind zones. The area of attachment will need reinforcement to handle the dynamic loads and fatigue, more cost in the price er watt? At some point the structure will require replacing. Same holds true for ground pods. Further, that’s all we need in tornado and hurricane alley’s more sharp flying debri that kills, as if 100 mph 2x4s and corrugated metal are not enough? I don’t think most folks idea is to save energy while at the same time putting their live at risk. Not when I get done educating them. Does the price per watt capture the cost of lives? The good thing about all this is it will keep us making lots of $ well into the future as we deal with the structural issues from energy efficient designs from people that do not understand structure and loads. Does Germany allow any yahoo to design homes or do they restrict that to only qualified engineers that understand structural impacts too? We don't need another check list, what we do need are more qualified degree and experienced engineers over seeing the designs, and better codes.

    Been working on our website, all this confusion around here puts us in a great marketing position, here’s a couple of captions and our position we are running by all local age groups as a pre-market analysis. Most around here are more concerned about their health and safety, not energy bills. Since our structure captures that and resist 250+ mph winds and large hail, flood, fire, it will sell itself. No PHPP or mounds of other certs needed nor the R&D cost. While other builders are dealing with the overhead we will be putting the cost into value added designs.

    “Green” building Designs - Building-envelope air-sealing methods gaining popularity (or imposed by future building codes) these days potentially trap indoors toxins that can cause health issues, especially in young children with immature immune systems. Green due to a lack of structural analysis to save energy can also result in structurals issues. The word “green”, therefore, has become a misnomer so, be wary.

    Energy Rating’s and Certifications – RESNET, Energystar, HERs, LEED, Greenguard, and the new one just in from Germany-- “Passivehaus” (most builders, not to mention homebuyers, have never heard of)--and the list goes on and on. There are many ways to manipulate data and methods devised to obtain these certifications and ratings. Upon closer scrutiny, many which have been proven to be inaccurate, producing low performance certified homes and products with misleading high ratings across the country. They are using marketing tools, driven by a money-making bureaucracy, that escalate the builders’, manufacturers’, and clients’ costs, while those very costs should be put into the performance of the buildings directly, rather than satisfying a “checklist” that is lacking critical criteria and that cannot guarantee results. These bureaucracy-controlled programs provide no “guaranteed or your money back” and their administrators won’t be there to cut the owner, or builder, a check for losses when the building fails to perform to their program standards as followed per their specific guidelines. We believe there are only a few metrics, or quantifiable outcomes to prove to our clients: safety and health is number one, measurable indoor air quality, beyond that dramatically reduced utility bills by means that do not compromise structure, and the clients’ own subjective experience of enhanced comfort. It’s truly just that simple. We have the specifications, and we provide the education and data for our clients to review. It’s not ‘rocket’ or ‘building science’ that confuses most consumers and, the scientists themselves debate. We let the client be the rater and judge of performance. The bottom line is, if we did not care that our clients were completely satisfied, we be out of business. To deliver what we promise is key to success and growth. Our product sells itself.

  73. GBA Editor
    Martin Holladay | | #73

    Response to Terry Lee
    Your ideas are all over the map. Most are uncontroversial.

    It is well known that most American homeowners don't care much about energy efficiency, that energy prices are low in the U.S. Midwest, that Passivhaus is a marginal program that most Americans have never heard of, and that large swaths of the U.S. either have no energy code, or an energy code that is unenforced. These are well-known truisms.

    I disagree with your idea that PV systems are deadly, however. "I don’t think most folks idea is to save energy while at the same time putting their lives at risk. Not when I get done educating them. Does the price per watt capture the cost of lives?" In fact, coal-burning power plants are responsible for far more U.S. deaths per year (mostly due to pollution-related lung problems) than PV systems.

  74. AntonioO | | #74

    Response to Martin (71)
    My point was not just to say my particular zip code would not produce much uptake. Every place will have it's own unique issues. I've also lived in Mississippi, a place you'd think at first glance would be ripe for solar. There's lots of sun and high summer electric bills. On the other hand, winters are so mild and natural gas so cheap that your dirt cheap winter gas bills greatly offset your summer cooling costs. Terry Lee points out the issues of high winds in tornado alley.

    On another point commented on by Terry Lee, I hope someone is checking these installs for not only good electrical connections but good structural connections as well. The last thing the industry needs is solar panels flying off roofs because of a rush to get as many panels up and running with little regard for structural integrity.

    Lastly, Martin, your idea about PV panels over brown sites, along highways, etc. gets me back to my initial question of who will own them. Your response about the importance of what kind of rate contracts would be offered seems particularly relevant for these none residential rooftop arrays. Do sell back laws apply equally to what would really be small power generation plants? By the way, your PV future vision seems to be a little different from that of Dana.

  75. GBA Editor
    Martin Holladay | | #75

    Response to Antonio Oliver
    You wrote, "I hope someone is checking these installs for not only good electrical connections but good structural connections as well."

    It's amazing how many mounting and racking options have been developed for roof-mounted PV systems in the last few years. These systems use heavy-duty aluminum and stainless steel hardware, and they have all been engineered. All of these companies offer engineering reports; here is one:

    I just stopped by SolarTech in Sutton, Vermont last week to buy some PV rack components, and Rich Nicol showed me a wide range of options, all impressively well designed.

    You wrote, "Your idea about PV panels over brown sites, along highways, etc. gets me back to my initial question of who will own them and your response of what kind of contracts would be offered by a power company for these." This is a big unknown, of course, and it's a political question more than an energy question. If you foresee a future in which your local utility, Darth Vader Electric, owns all of the PV systems near your home, and forbids homeowners to install PV, the situation will be ripe for the development of mini-grids or off-grid solutions.

    You wrote, "Your PV future vision seems to be a little different from that of Dana." I never claimed that Dana and I were clones.

  76. AntonioO | | #76

    Funny, Martin
    It is true to say that I think that a significant portion of solar generated power will be produced by electric companies. But for the record, I have no problem with Darth Vader Electric owning a portion of PV systems. I'd love to see them offset some coal plants with solar power. I'm just skeptical of this translating into big energy savings for consumers unless they own the PVs themselves.

  77. GBA Editor
    Martin Holladay | | #77

    Response to Antonio Oliver
    Even if electricity prices don't fall over the coming decades -- and many analysts predict that they will -- a greener grid affects the assumptions made by Passivhaus proponents who argue that heroic investments in very thick insulation makes sense because the insulation will result in carbon reductions. The greener the grid, the weaker that argument becomes.

  78. Expert Member
    Dana Dorsett | | #78

    Response to several
    Antonio Oliver: Power companies that don't factor in the distributed privately owned generation into their business models WILL have a very rough time during the transition, as has happened in Germany already. There is a strong argument that the Germans have overpaid for their high (and still climbing) solar fraction with excessively generous tariff structures, and they are having to re-structure those deals after the fact (to much opposition.) There are but a handful of states in the US where the regulators are making at least SOME reasonable attempt to stay ahead of the curve, but even some of those states may have an uncomfortable ride during the write-down of stranded assets held by utility companies. NY seems to be the most proactive, HI has started to deal with it late- only after it became an existential problem for the utility companies, CA seems to be doing OK so far with their CAISO top-down approach, MA is in a state of flux but evolving rapidly, MN has established a statewide agreement on how the value of solar will be compensated, updated annually. But most of the rest of the country is for the most part stuck in a 20th-century grid mindset. VT is evolving rapidly, and is small enough to become something of a test-bed, but it's not clear the 10% cap on net-metering currently established is a realistic or optimal limit.

    Solar City (the largest vertically integrated solar company in the US) just announced a loan plan available in some states where if your FICO score is 680 or higher they will give a 30 year loan at 4.5% (with a 30 year warranty on the system!), to paid for monthly at 16 cents/kwh. After you take the Federal tax credit that becomes something like 12 cents/kwh on a lifecycle basis. On a deal like that the cost of that energy is known for 30 years, and it is less than or equal to the current retail cost of electricity in most of the states where that deal is available. There will be competitors, and as the cost of the goods fall, it will rapidly become a no-brainer for most of the country:


    The question will then become where or if the regulators set the limits on total distributed PV (currently it's 10% of the absolute peak in VT, 4% in MA, but that will be changing to "unlimited" under draft agreements currently circulating itn the MA legislature), and whether local storage will be allowed (or REQUIRED!) at some penetration level to manage the mid-day excess. Solar City offers local storage for their systems in CA, where local storage on grid-tied systems is expressly allowed. In most states it is currently disallowed by regulators under a potential theory of backfeeding into downed power lines posing a potential threat to repair workers, but standards for protecting against that exist.

    NREL estimates that only about 25% of existing homes in the US are currently suitable for PV, but when building a new home those odds can clearly be tweaked to optimize solar by the site orientation and building design. Since we are talking about PassiveHouse, we are expressly talking about new builds, which raises the relevance of the solar issue.

    But that's not to say the 25% of existing homes with pretty-good solar exposure won't be developed as PV generation sources, and that too will will have a moderating effect on the spot-market price for power. In parts of Australia that have a 25% PV penetration (with arrays averaging half the size typically found in the US installations) the mid-day wholesale spot price of electricity goes to near-zero, and the afternoon/evening peak price (where all the profit is for the fossil burners) has been cut by more than half.

    The fact that grid defection will soon be (or already is) financially rational in many locations doesn't mean it will happen. But the mere fact that it could happen will spur regulators to force utilities to take the write-down on the stranded assets ( peaking generation assets will come first), rather than sticking the ratepayers with the bill. That is going to be VERY tough to do in Georgia, but most of the US should be able to manage it without succumbing the utility death spiral. But there will likely be many utilities in need of chapter-11 bankruptcy protection as they sort it all out. What they WON'T be able to do is simply raise the price of electricity. See: and

    Terry Lee: The reality of low cost energy in the midwest is no protection against a technology with a 40 year learning curve of 22% that has already crashed through the cost barriers for higher-priced energy markets running 2x-3x the cost of midwestern energy. The doubling rate on PV is less than 2 years, so at the 40 year trend line what is 2x the cost today will only be about 1.56x the cost in 2 years, 1.22x the cost in 4 years, and 0.95x the cost in 6 years, 0.74x in 8 years, and 0.58x in 10 years. By 2025 net-metered PV will be cheaper than midwestern retail energy rates, and it may come much sooner than that. The learning rate has been increasing over the 40 year trend in the past decade, and the doubling rate has been shrinking.

    As the cost attractiveness increases, the installation rates will likely increase- the doubling rate of the installed PV base isn't fixed at the recent- history ~2 years- it can both shrink or expand. But as the cost drops below retail power rates everywhere my bet is on the doubling period shrinking, not expanding, with or without tax policy support. Utilities attaching fees such as in your San Diego utility are fighting a holding pattern stalling for time, but that will eventually be crushed. That will before 2030 for sure, but probably before 2025, even sooner if the fees become onerous, since it pulls in the date when grid defection becomes rational.

    The more proper way to distribute the costs of the grid isn't to stick it to PV owners with net-zero use, but rather to get rid of the simple fixed block rate structures based on monthly kwh, and instead apply "demand charges" based on the peak draws over incremental periods of time to residential customers as is currently done with commercial customers. Your peak period draw over a half-hour or hour is what drives the cost of higher grid capacity, not your net or average energy use. Currently houses with 8 ton air conditioners that runs 1 hour/day pay the same rate as houses with 2 ton AC that runs 4 hours/day using the same total kwh. But the cost of the infrastructure required to support the 8-ton power-gulper is more than 4x of the power sipper. The current rate structures are a cross subsidy toward installations with oversized systems, and those same systems drive peak-power rates higher, whereas PV drives the air conditioning peaks lower. Sticking the PV owner with the infrastructure bill is a cross subsidy of the PV owners to those that are true driver of the grid cost. A PV operator may also be a peak-power-pig, but assigning the grid cost to the power-pig nature is the more equitable rate solution.

    Jin: Yes, even though there is no carbon offset argument to speak of for PV in Quebec, there will certainly be an economic argument going forward. Even the large scale wind-industry is (rightly) viewing PV as a serious future competitive threat, despite a lifecycle cost currently half that (or less) of PV. The fact that PV is scalable and can live on the ratepayers side of the meter makes PV far more compelling to the homeowner, since they can't buy a share of a wind-farm and net-meter it at retail. Intermediate scale wind is currently pretty compelling for some large industries though, even at a 20% capacity factor (a fairly crummy wind resource profile) if it can be net-metered, since that also reduces demand charges.

    Martin: " I never claimed that Dana and I were clones."

    Clowns, maybe- clones, not so much! :-)

  79. jinmtvt | | #79

    This debate is superbly interesting but ..
    All this info will change much as soon as someone invents and delivers a storage medium that could be used residentially .

    Dana : tell me why aren't we using something as simple as water with heat pumps or something similar to store electricity over production???
    aren't there devices that generate electricty from heat difference yet ??

  80. anderslewendal | | #80

    Thick insulation
    I really like the way David Hicks thinks. The PV analogy was great.

    Diminishing returns on insulation are real. We just need to decide the future cost of heating and we'll know the sweet spot for each climate zone. At least we are talking about it. R-80? Really.

  81. Expert Member
    Dana Dorsett | | #81

    The present day cost of heating for the first 30 years... whatever you can leverage out of 16 cents/kwh PV with a heat pump, if you take up the loan on offer from Solar City:

    That's already comparable to (near record low) current costs of natural gas in much of the country, without the price volatility risk through 2045.

    It's extremely unlikely that at the end of 30 years when it's all paid off, but only performing at 80% of spec or whatever that the cost of new PV will have gone up. It's possible that even with resistance heating new PV would be cost competitive with natural gas in 2045.

    If you build the house to the financial sweet spot assuming the cost of energy is a leveraged 16 cents/kwh it will be somewhat overbuilt on a house-lifecycle basis, but who cares?

    Jin: it takes a lot of water and extremely well insulated tanks to store heat efficiently over long periods with heat pumps. The storage temps can never be high enough to make new electricity out of it, but it can useful to use heat pumps. (IIRC a Net Zero house in Calgary was built with a heat-pump operated thermal storage.) At some price point it's just cheaper to buy more PV than build & insulate more tanks. Battery storage to manage the non-daylight power use has a pretty steep learning curve too, and should be under $100/kwh by 2030, and is fairly scalable.

    Lithium ion may be the current price/performance leader this year, but for stationary batteries (as opposed to car batteries) I would expect simple, dumb but heavy liquid metal batteries to be cheaper by 2025. Ambri is the current leader on that technology, but I expect competing chemstries to emerge:

    SolarCity is already pre-packaging Tesla (the electric car company) lithium ion batteries with solar installations in California for peak-shifting and short-term islanding capability. The current cost Panasonic is charging Tesla for the batteries is closer to $180-200/kwh (and Panasonic probably losing money at it, for now), but when the new battery factory they are co-building in Nevada ramps up the speculation is that their cost (but not price charged to others) will hit the $100/kwh range. That would be a real paradigm changer in the car biz, which would also affect how the PV-tsunami rolls out (or over) on the utility companies.

    They just broke ground on the battery factory this year- it is a HUGE building, about a mile long (!), and it will eventually become the largest off-grid building on earth, powered by a sea of SolarCity PV on the roof, backed up by their own battery technology. SolarCity's CEO is Lyndon Rive who is a first cousin to Elon Musk, the founder of Tesla, who is also the chairman of the board at SolarCity. They both have a stake in making battery technology cheaper. They will probably stay hooked up to the grid even when Net Zero, unless the utility makes it too expensive for them:

  82. peteramerongen | | #82

    The effectiveness of large
    The effectiveness of large amounts of sub-slab insulation is an interesting and important subject. Screw it up and you are wasting money and misallocating (high carbon) resources that could be better used elsewhere. There are two components to the problem.

    One is proper use of the modeling tool. If you have done a good job on optimizing the envelope, the payback of the last inch of insulation added under the slab should be the same as the payback for the last inch of insulation in the walls or the roof. It works like this. You run the energy model with your best guess envelope. Add an inch (or what ever the practical increment is) of insulation under the slab. Divide the cost of that increment by the energy savings to get the cost per kilowatt hour per year saved. (Eg. If it costs $1200 to add 2” under the slab and it is going to save 300kWh per year then that extra 2 “ of insulation costs $4.00 for every KWH it saves every year. Do the same for the roof and walls. When you’re done, the last inch of insulation you add to the walls and roof should also save $4.00 per kWh per year. If you’re not doing that you haven’t optimized and are probably wasting money by putting too much insulation in one place and not enough in another. You can do the same analysis on air tightness and windows and thermal bridging although the results are a bit lumpier.

    The other problem is the tools themselves. The analysis is only as good as the tools. It has been observed before (by John Straub and others) that PHPP tends to reward larger amounts of subslab insulation than other modeling methods. Besides PHPP, I use a program called HOT2000 which was developed and refined over the last 30 years by National Resources Canada to support energy efficiency programs in Canada. HOT2000 uses finite element analysis rather than the simpler formula embedded in PHPP. With HOT2000, I could never justify more than 4” of sub-slab insulation even with our 40 degree F ground temperature here in Edmonton.

    No shame in getting this wrong. Heat loss to the ground is way more complicated to compute than heat loss to the air. This needs more work and should be addressed by PHIUS’s tech committee when the can get to it.

    If you are in doubt, there are other tools you can use to check your results when it looks like the model is suggesting crazy amounts of insulation: IES, Solidworks, Therm, or the formula’s that Marc Rosenbaum talked about in his excellent recent presentation on Heat Spring.

  83. GBA Editor
    Martin Holladay | | #83

    Response to Jin Kazama (Comment #79)
    Q. "Aren't there devices that generate electricty from heat difference yet?"

    A. Thermoelectric generators exist, but most of these technologies operate within narrow temperature ranges, and are neither long-lived nor cost-effective. Research and development efforts in this field continue, however; for example, see: Finally, a heat-to-electricity device powerful enough for the old-school energy giants.

  84. GBA Editor
    Martin Holladay | | #84

    Response to Peter Amerongen (Comment #82)
    Thanks for your insightful comments.

    After Dr. Feist said, "I don't care too much about this," and Ken Levenson wrote that I was making a "strawman argument," and Andrew Michler dismissed this discussion as "a piss match about who is cheaper," and Bronwyn Barry labeled my questions "a curious fixation," and Mary James dismissed this discussion as "quibbling over the cost effectiveness of several inches of foam," it's gratifying to read your analysis, especially since you are an energy expert.

    I agree with your opening sentences: "The effectiveness of large amounts of sub-slab insulation is an interesting and important subject. Screw it up and you are wasting money and misallocating (high carbon) resources that could be better used elsewhere."

  85. GBA Editor
    Martin Holladay | | #85

    Response to Terry Lee
    It is of course true that during a tornado, a person can be killed by flying debris, including things like flying cars, loose 2x4s, or solar panels that are flying like projectiles. Even a child's toy can kill you when a tornado is hurling it towards you at 100 miles per hour.

    Coal-burning power plants cause 13,000 deaths per year in the U.S., but I have not heard of a single case of a person being killed by a flying solar panel -- although it could certainly happen.

  86. RZR | | #86

    Martin Wrote; I disagree with your idea that PV systems are deadly, however. "I don’t think most folks idea is to save energy while at the same time putting their lives at risk. Not when I get done educating them. Does the price per watt capture the cost of lives?" In fact, coal-burning power plants are responsible for far more U.S. deaths per year (mostly due to pollution-related lung problems) than PV systems.

    It's amazing how many mounting and racking options have been developed for roof-mounted PV systems in the last few years. These systems use heavy-duty aluminum and stainless steel hardware, and they have all been engineered. All of these companies offer engineering reports; here is one:

    I just stopped by SolarTech in Sutton, Vermont last week to buy some PV rack components, and Rich Nicol showed me a wide range of options, all impressively well designed.

    You can’t justify the structural damage PV panels will cause with coal-burning power plant causalities. In 2011 Joplin EF 5 killed 158, injured 377, destroyed 7000 home, and damaged 900. A local powerplant per a “controversial study” of “small particle pollution” are on average 30 deaths per year. Establishing a direct link is controversial. Death from tornado’s is “non-controversial” the flying debri kills and destroys period!

    Have a look for yourself, last one I visited was Piger, NE, few months ago to study the debri and damage, and I have been in discussion with Moore, OK and Greensburg, KS since. One thing they ALL have in common is wood and light construction, metal roofs, have no place in tornado-hurricane alley’s. The concrete walls are the only wall still standing and do not add to the flying debri. But yet, stupid people rebuild with wood expecting to get different results from insanity.

    "We have reviewed the Quick Rack V1.1 photovoltaic (PV) array mounting system (base mount) and
    determined that, for the configurations and criteria described below, it complies with the structural
    requirements of the 2012 International Building Code, the 2013 California Building Code, and both
    ASCE 7-05 and ASCE 7-10."

    2012 code min or 90 mile winds is not going to cut it, not even close. Joplin and Moore, OK have since gone to 150 mile hour code for all building’s, which in my opinion is low. My guess is the low number is so that the wood industry does not lose a ton of money, politics. If they want to be safe they rebuild with what is proven, mass walls and roof designs to take the uplift forces and debri impact.

    The link you provided says “base mount” can withstand code min, 90 mph winds. Structures 101 states “structure is only as good as its weakest link”

    Steel tensile or pull-out strength: 100,000 PSI, stainless: 300,000 PSI.
    Wood: 580 PSI lower with high moisture content and heat.

    Need I write more? They also say on their site to inspect the wood? How the only way is to pull off all the sheathing, clading, at look for rot at the mounting locations, center of rafters, or lets hope noone attaches to perlins.

    Steel fasteners and attaching metal to wood creates hard points that fail the roof structure. Stuctures 102.

    Anyone with average intelligence should know that a high density metal such as stainless added to 200+ mph wind will fly right through light structure like a bullet. It has no place in these regions, it’s deadly!

    In the high wind regions code should mandate 250 mph winds design loads of the sub-structure, PV base structure (meaning the same material allowables) on the ground, sheltered from cyclic winds. Code would establish the same load compliance for the mounts-piers-foundation.

    Foam under foundations and footing’s: The first “model” check should be what is called a “Finite Element” (FEM) that checks combined loads to include but no limited to, compression, tension, bending, creep, deflection. After all what is critical in a foundation in structural integrity and life cycle since R&R is not easy or next to impossible from a cost perspective, energy conservation is second to that. PHPUS or whatever method you want to call it, should check structures first. The thickness of the foam will be determined by the FEM to take the loads, also included should be a cyclic fatigue analysis to see how the foam performs in heat, moisture, in conjunction with the load types over time. My guess is it will take more foam and cost than most use by guessing by far.

    Dana - I'll leave the future outlook of it all to you, I image as we here in the midwest start adopting energy codes soon that take the coal burning of local plants down, it will change the game. I have had discussion with our plants chemist and I know they are being pressured by the EPA to take out the fine particles. In the meantime, I prefer to deal with the here and now rather than speculate, I have better things to do than read all the speculation and opinions out there, from people that are out of tough with the grass roots of many areas. When I drive from the midwest to CA I see no PV until I hit NM, AZ, CA. ..I have been along many highways and lived in many US states, recently MI, and I am not seeing this "solar boom" other than the SW. There I see ground pods serving communities and roof mounts, I guess some pay the developer special taxes since they can make a profit. I seen the new solar farm along I-40 incredible! Not here. Fixed axis suffers a high loss from direct beam, here single axis(e-w tracking) might make sense if the installation could take the wind speeds. I'm going to our developers code meeting next week to see how this would work, a community level PV installation like they have in CA. Homes would need to be very efficient if the special taxes went to the developer rather than the cities. We do have net metering. I hope to work with a developer and become the exclusive builder. Just finding people that are on the same page is a challenge.

  87. RZR | | #87

    Impact Debri
    Yeah, I read that 13000 number too, has to do with "small particle" size under debate, the same could be said about people that smoke and those that don't but get lung cancer. While the PPs and EPA particles sizes and air borne pollutants are going down, mother nature is getting worse, tornado's and flying debri is on the rise, some say from global warming. That's all besides the point, we don't add poison to poison that makes matters worse. You won't find a direct link of PV to deaths since they are very few PVs here. You'll find the basic fact that flying debri causes the most damage. Lets apply some common sense to it, the stronger, the sharper, the worse. If a plastic toy hits a lite wall @ 100 MPH vs stainless steel, the steel penetrates, the toy shatters. The steel is on a deadly path, the toy is not. Physics 101 :)

    Texas Tech as done alot of impact testing. 2x4 are the biggest threat due to quantity. PV not there yet, if high in quantity due the density and sharpness it would replace wood as the biggest killer!

  88. GBA Editor
    Martin Holladay | | #88

    Response to Terry Lee
    I'm glad we agree that PV arrays are "not there yet" when it comes to accounting for deaths caused by electricity generation.

    The bottom line is that you have identified a simple engineering problem that PV rack manufacturers are well aware of and have already addressed.

    This is the type of engineering that was well understood by 19th-century engineers. There is nothing particularly complicated about engineering PV arrays to withstand wind forces.

  89. Expert Member
    Dana Dorsett | | #89

    Here and now is already here (reponse to Terry Lee #85)
    "In the meantime, I prefer to deal with the here and now rather than speculate, I have better things to do than read all the speculation and opinions out there, from people that are out of tough with the grass roots of many areas. When I drive from the midwest to CA I see no PV until I hit NM, AZ, CA. .."

    Three years ago I would have said that about Massachusetts, 5 years ago it would have been true in NJ. The dearth of midwestern PV is not a function of economics, but of policy and scale. The all-in retail cost to buyers of small scale rooftop PV in Germany right now, today, is under $2/watt, which would be cost competitive with residential retail electricity in Kansas, today. Germans aren't any smarter or lower paid than folks in the US. It's only a matter of time, and it's sooner than you think.

    Even in the solar-boom states the same systems in the US are still retailing for north of $3/watt, down from over $5/watt just 2 years ago. The difference in US & German costs are all in the "soft costs", which can easily be pared by revised regulation (there is no need to spec & inspect a 10kw rooftop as if it were a gigawatt nuke), and higher public awareness. There are full-page ads in my local fishwrapper from solar companies shouting how the recently approved rate hike from the large utility can be avoided. It's not wild speculation that when the price of PV in the US hits today's price in Germany (a clear existence proof of the possible) that similar things can happen in your neighborhood.

    SolarCity believes they can get their all-in cost for installing systems down to less than a buck-a-watt before 2020, and have a credible road map on how to get there. Sure, they'll charge YOU a buck-fifty, but they'll finance and warranty it over a 30 year period and beat your utility's residential retail rates. The PV you see in the southwest in 2014 is the thin edge of the wedge, the leading edge of the tsunami. If the investment bankers believe that (and there is good evidence that they do), it becomes almost a self-fulfilling prophesy, since what was once considered risky and thus expensive to finance now becomes bankable at favorable rates. The Yieldco arms of the third party solar companies using a lease model have been returning 10-15% after tax returns to their investors, which in turn has open the financial floodgates to allow low-cost long term financing on PV sales, as is just now beginning to occur. The 30 years @ 4.5% with a 30 year warranty from Solar City works out to 12 cents/kwh after slurping up the federal tax credit.

    In 2-3 years when the cost of the PV is less than half what it is today, it'll be substantially less than 12 cents even without the federal tax credit. The current cost of power in Kansas is 9 cents, and may have to up as new power generation gets built, or old power generation gets cleaned up. At the utility scale wind power makes excellent economic sense for replacing aging power plants, just as it has worked out in Texas. But that doesn't mean the steep glide path of solar costs won't eat into those economics a bit too.

  90. RZR | | #90

    Solar City
    KS is @ .9, last year it was @ .10 cost is going down probably in fear of SC. Other thing you'll find from being around the country is lots of poor folks, MI, Detroit sad, Desert regions, poverty....I just don't see these people qualifying for 4.5% unless SC is stupid! Busy right now, I call them and see what they are offering for this area, if anyone can sell it we can, we have the youth full sales team this year 1 mil so far and growing. Once SC corners the market they'll get creedy like they all do. Consumers Energy, SDG&E, KG&E, HUGH money the solar industry is after.

    Mine are going on the ground into steel structure to keep up with my tornado resistant business model.
    It's not hard to the math for 250 mph wind speeds. Code requires no engineering analysis, and solar companies that I doubt have engineers looking at every home lack the data to do a proper loads analysis. .

  91. Expert Member
    Dana Dorsett | | #91

    SolarCity's new purchase deal...
    ...requires a FICO score of 680 or higher, not surprisingly. Nobody is going to sell you 15-30 grand worth of hardware without some credit.

    The lease terms from most of these large solar outfits aren't as stringent, but I've never picked one of those apart in any detail.

    They are currently only offering the 4.5%/30 year deal in the solar-policy friendly higher-electricity cost states of Arizona, California, Colorado, Connecticut, Hawaii, Massachusetts, New York & New Jersey. But at their anticipated reduction in cost basis that will be expanding.

    Since SolarCity (like the other large solar players) aren't currently doing much business in the low-cost power locations, it's unlikely that they have any affect at all on the markets in Kansas yet. The market is too small, and it's a bit harder to sell, and Kansas doesn't have a state-wide policy on third-party ownership/lease deals, making it an even less attractive market. ( )

    Third party ownership leasing has been up to now a very large fraction of their business, and they have been able to sell off those revenue streams to investors via a separate but related "yieldco" company. The 30 year/4.5% deal is known to work for them based on their experience & success with leased PV, and is more attractive than a lease deal for those with the credit to qualify.

    They're doing good business in both Texas and Colorado though, both of which are on-board at the state regulatory level with third party ownership of residential rooftop PV:

    There is literally no way for SolarCity to corner the market any time soon, but they are likely to remain in the top five. SolarCity is currently leading the pack with over 30% of the total US residential market, as of Q1 this year, but Vivint has a much bigger share than they do in Massachusetts, and Verengo, REC Solar, & Real Goods Solar aren't exactly standing-by. The top five still only account for about 45% of all residential rooftop solar.

    Any player that gets greedy at the point will go out of business- only the ones who can innovate on the financing structures to get the end cost way down have a shot. By shooting for the stars and building their own PV factory SolarCity is taking on some risk, but if it reduces the installed cost they will remain one of the top dogs. They'll never be the only dog though. The US isn't even close to being the largest world market for this stuff. (China is #1, Japan #2). Under under Narendra Modi, the new government policy in India is trying to install as much PV in India by 2025 than has been installed world-wide to date. (We'll see how well that works out- I'm betting they might get somewhere between a quarter or a half that amount installed by then, but I've lost those sorts of bets before.)

    It's sort of like the disruption of the telecom biz by the cellular folks. There are some big players in that market, and they sure took all the profit out of the baby-bell wired-services biz, but none o' them monkeys is going to become the 800lb gorilla that owns it all.

    Tornados are local events. Insurance distributes the risk. Losing a solar array that cost $20K to install can be replaced at less than half the cost, if it made it to year 3 or beyond. I'm sure the actuaries can do the math on it.

  92. RZR | | #92

    Insurance and Trackers
    Tornados are local events, life insurance pays for death if you have a policy. Losing a solar array to flying debri increases the chance of death, the mounting provisions can not take the wind loads which are 250 MPH on average. 500 PSI tensile wood fastened by 100,000 steel bolts, some old wood with a knock down factor to 250 PSI due to age, rot, temp and heat cycles or fatigue. If attached to steel c-channels that distributes load to several large diameter bolts at the side of rafters better. That puts the wood in stronger cross sectional bearing, not tension. You'd need doublers at the faster locations at least the size in volume of the holes removed to replace cross-sectional area. There is no Engineer on the planet that can show attaching directly to wood good at these wind speeds. Might want an umbrella if you do, if the panels fly off and kills someone your liable if you diy. An electrical break away shut off switch may be a good idea too.

    Homes that are built to withstand natural disasters qualify for a reduction in home owner insurance cost. The insured pays an addition amount for PV endorsements. I'm sure a homeowner that paid more for an all steel installation would be in a better negotiating position to quality for a reduction in insurance premiums, just as the ones that build mass homes in these areas vs light are. Insurance is not the answer, safe structure is, and just as putting money into a home to save energy cost, a simple design change that may or may not cost more up front depending on the engineer or architect, as Feist said, can save insurance cost. Given a choice I would hope most people choose safety over energy cost but, you never know. Our design will provide both, win-win, same or less as light construction cost.

    The peel and stick panels look safer if the metal roof is attached well, but my experience with glue that thermally cycles, especially room temp cures, says it won't last. A high temp and pressure cure 200-300 F with vacuum pressure do better, but that's not possible.

    Dana, you or anyone else studied these tracking devices. This article explains a significant loss for fixed mounts. A single axis (e-w) would have a gain of 30% on average. It describes the wind loads I have been btw. The "floating ground mount" sounds sketchy for high winds. The floating mirror may be a hail loss, I don't know if this makes matters worse...I suppose a ground mount that is shielded from wind and hail may work, I can design that. Whats the take these days, pay back period per efficiency? Or do they only make sense for the solar farms with deep pockets and high output for now?

    Were are we at on DC appliances? And inverter cost?

  93. Expert Member
    Dana Dorsett | | #93

    PV system cost issues.
    Inverter costs are quite small compared to the panel costs, and panel costs are well under a buck a watt. It's time to stop thinking of PV panels as expensive- they are commodities that all but guaranteed to be hitting 25 cents/watt before 2020. Ten kilowatts of panel will have a wholesale cost less than $3000, and yes, they can and will be damaged in severe midwestern hail storms, but it's an insurable/repairable sort of thing. ( A 10mph fender-bender with an F-150 may cost more to fix.)

    For small arrays & large, the much higher cost of even single axis tracking is more than adding 30% more panel w / fixed racking to hit the same output numbers. That was not true back when panel costs were $5-10/watt. The up-charge for higher efficiency panels vs. commodity panels (~20% vs. ~15% conversion efficiency) is less than single axis tracking too, but not as cheap as adding 30-35% more panel with fixed racking. But it's a moving target, innovations in cost reducing rack systems of all types is an ongoing & competitive process, competing head-to-head with falling panel pricing. Tracking mounts or high-efficiency panels can be worth it when the real-estate area is expensive (or limited), but typically not.

    FWIW: SolarCity bought a high-efficiency panel company/process (Silevo) this summer, and is building a large manufacturing plant near Buffalo NY as a means to both guarantee access to panels in a competitive world market (where expanding supply isn't always well synchronized to expanding demand), and to better control quality. This was viewed as a risky move by industry insiders, but we'll see how it works out. Their financial backers aren't backing down- they are still in high growth/no-profit mode, but they are a leader on that end of the PV market. The initial production runs of Silvevo's process before the buy-out were running 20-21% efficiency, but SolarCity believes they will be able to make ~24% efficiency panels the standard offering with normal incremental process improvements. That would be a larger advantage over commodity Chinese panels, reducing both racking costs and installation labor.

    They had also bought a rack company about a year ago ( Zep Solar ), leading some to speculate that they may be planning to build pre-racked-pre-wired kilowatt chunks in the Buffalo factory as well, trading $50/hr rooftop labor for $15/hr factory labor (with better quality control) as a means of hitting both their installed $/watt system cost & installation volume targets, and maybe even turn a profit on more than just the financing end.

    The versatility and simplicity of AC voltage conversions across the grid make widespread manufacturing of DC appliances an unlikely proposition in the near or intermediate term. Inverters are pretty cheap and pretty efficient, with year on year improvements in both price and performance. The AC grid is going to continue to be useful for a very long time.

  94. jinmtvt | | #94

    since you are "our expert" on the PV discussion ( i believe you deserve the title ! :P )

    What do you think of the per panel inverter aka Enphase vs larger centralized inverters isntallation ?

    At the rate the panels price is dropping, i would tend to push toward upgradable array sizes with the use of micro inverter from Enphase ( any other manuf have similar inverters? )
    but their are probably disadvantages i do not understand/know of ??

    Current panel prices makes for interesting material to produce fixed sunshades
    even at non perfect south angles , which ends up paying themselves to add up to their basic shading saves, i can only imagine how it will make even more sense in a few years with again dropped prices.

  95. RZR | | #95

    Dana, I set up a meeting next week with our local Builders Association President to discuss all this at a developer energy efficient sub division level . I’ll take your pipe dreams and make them happen here in the Midwest, I guess that’s the difference between you and I. I'd try it in Cali but forget that state, not challenging enough. I’m so tickled pink about it I can’t wait for Oktoberfest so I can do a chicken dance ;) I’m beginning to wonder if you’re not a PV panel yourself as much time as you spend on a computer researching this stuff. HAHA! Thanks for the updates.

    Been building mass test walls for weeks now, tired, I’ll have a different perspective on all this next, I do as you may of noticed like to think outside the box. Stay tuned….

  96. jinmtvt | | #96

    I am unsure if it is my lack of english skills, but you often sound "aggressive" in your wording if i might use the term.
    Even though you seem to have substantial knowledge and experience ( from a very diff POV ) to share
    with us here , i sometimes end up after your posts trying to understand if you were trying to convince yourself, or trying to push something .. i might be wrong, but it is the feeling i get.

    Dana has been nothing but helpful and patient to everybody here, and even though he is probably more than enough able to stand up by himself, i'll stand to his side and i do not think that trying to bang head with him is respectful and productive from your part.

    If i got your intentions wrong, then forgive my intrusion ...if else please open up your discussion
    and level down with other mortal beings.

    May the efficiency be with you !

  97. RZR | | #97

    Anyway back to the discussion. It was mentioned up the thread that cost is insulation vs PV balancing. IMO, the biggest player in heating and cooling cost is the sun, it's free. Some of these guys have taken money out of insulation and PV and designed some very crafty reflector decks to take advantage of the suns direct beam, store that energy in mass (not low density insulation or materials), and release in a designed time lag. Now if we can just figure a way to take those funds to direct beam PV. Seems to me a shaft, couple of plain bearings, motor, programmable timer...a simple design that moves the panels 10 deg starting at sun rise and ending at sunset. Or, ground reflector dects reducing the angle of incidence to the panels. For reasons stated, in this region anyway, less is more when it comes to # of panels, I'd rather shift the cost to a single axis or reflectors made of low cost light colors, steel plates, domes that act as wind and/or hail screens too. Looks like a 3d model is needed here, harbor freight catalog, recycled metal, & a lumber yard.

    The other thing I noticed, correct me if I am wrong, the German architect incorporates alot of clerestory windows when combined with ventilation and some solar reflector decks makes a robust design and use of mother nature. We in the USA have adopted "restrictive covenants" in many sub divisions, most in the middle to upper class neighborhoods. Some for example will restrict radial or dome roofs, PV on roofs, reflector decks, etc...It's starts as a developer needing to approve your plans and architecture that fits into the cookie cutter planning, then it ends up in the hands of a "Association" or "Design Committee" that is composed of anyone from a hair dresser to attorney that more than likely has no architectural design experience. They are legal corporations out of control at that point imo. They do good and bad. Even if energy codes and PV are adopted, trying to get energy efficient architecture in these privately owned areas takes enormous efforts. The declarations and bi-laws are clear, many of which state specific roof types, square feet, etc...If you want to alter them you submit your plans to the Architectural Control Committee (ACC), and if you do not do it properly, they can make you tear down at any time at your legal fee expense. We have tried this, and rather than battle the covenants we decided to seek out a developer that thinks like us, help him/her write the book. I'm amazed how some of these covenants ( I believe they get standards online) restricts well founded innovations.

  98. RZR | | #98

    Text Communication
    Jin, did you know most communication between "mortal beings" is accomplished by body language and eye contact? I know what your mean, many times I think I am under attack by the way people write but I give them the benefit of the doubt and brush it off, most are men out here we don't need to get all emotional. If you don't have tough skin you should not post on any forum. Most of my post are technical and my writing skills are terrible, I'll be the first to admit. I've even seen Dana taken wrong and have to explain himself, and many others. It would help if we had emocions. I look forward to the day when these communications are done by video. IMO. text communication is the worse, it opens the door to misunderstanding's.

    In my last post, I was just playing with Dana, an attempt to add some fun and laughter to the conversation, after all they say is soothes the soul. When I wrote "HAHA" that means I am kidding!

    "Thanks for the updates" ..that means I appreciate your research.

    " I’m so tickled pink about it I can’t wait for Oktoberfest so I can do a chicken dance ;) "

    I'm not sure if you are familiar with German tradition but the chicken dance is hilarious to watch, us mortals been doing it around the world since the 1950's after a few brews, it will crack you up!! Due to the partying nature (which many people need little reason for) it was adopted way faster than their passivhaus will ever be. I recommend you loosen up a little, go find one tonight and try it.... take some pics and post them.

    :) <= That's a poor excuse for a emocion meaning I AM JUST KIDDING! LOL <= That means laugh out laugh (I am laughing), LMAO <= That means my arse is gone I laughed so hard. HAHA!

  99. Expert Member
    Dana Dorsett | | #99

    Inverters, etc.
    Jin- inverters are also a moving target, both in terms of efficiency and functionality. Having built-in hardware hooks for supporting local battery storage or even islanding might be useful in some locations if it seems likely that local storage will be allowed sometime soon.

    Micro-inverters at the panel level buy you a bit of efficiency, and when a panel goes bad from taking a direct hit from one of those fist-sized hail stones in Terry Lee's neighborhood you don't lose the whole string. The micro inverter approach is usually more expensive, but the up-charge is often worth it for large utility scale arrays, since the statistical probability of having a panel going off-spec is that much higher, and it simplifies the repair scheduling issue, and the array as a whole takes less of a performance hit than with string inverters.

    Terry Lee: Good on ya to take it to the subdivision planning stage! In Austin TX the building codes now require new houses to be "net zero ready", meaning, they have to have sufficiently efficient building envelopes and sufficient roof orientation & size to support a typical home's energy use with the mechanical systems installed. They don't prescribe how net-zero is to be achieved, only that there is some credible analysis that it COULD be achieved, leaving it up to the designer to decide where the break points are on insulation vs. passive solar vs. active thermal solar vs. PV, etc. (CA under Title 24 will be requiring ACTUAL net-zero on new builds.) The Austin approach applied to subdivision development in KS could work with a few standardized house designs, taking care to manage site orientation & shading factors. The building's thermal performance requirements would be substantially higher than in Austin, but not nearly as high as it would be in Quebec, or even New England. If the house is up to snuff, the PV could be either a future option (maybe even pre-wired to some degree). If you can get local PV developers on board, their costs go WAY down if they have 50-100 similar houses with similar sized arrays going into one small geographical area. That's how PV gets down to the-$2/watt (sometimes lower, if scuttlebutt can be trusted) in TX, and there's no reason it can't work in KS.

    Another thing to consider with a PV-ready (or PV-installed) subdivision is pre-wiring the houses for car-chargers, as is currently required in a few cities in CA. The cost of electric cars will be falling in the next decade, and the marginal & lifecycle cost of driving on electricity at the lifecycle cost of PV (whether higher or lower than your local utility rates) is already cost effective against gas/diesel. Having the electric car loads available to soak up the excess PV output once the grid penetration of PV hit's the 20-25% range is good for stabilizing the grid, and good for the cost of driving.

  100. bnewell_2000 | | #100

    Numbers Don't Lie
    Ignoring economics, which are the biggest driver to moving efficient building standards to the general marketplace, and using substandard modeling tools will be the death of passive standards. People are catching on that misplaced guidelines and faulty tools are costing them a lot of money when designing and constructing a house. "Near passive" is a quickly growing term.

    I co-authored 12 ASHRAE Journal articles that try to simplify and explain the engineering and economic analysis that need to be done to properly design a house. The components and systems that make up a house are each examined individually, but keeping in mind their interaction with the house as a whole. Martin's points are very much supported in the articles, especially in the Ground Heat Transfer article pertaining to the sub-slab insulation debate.

    In addition, I would invite you to try our FREE, very powerful energy modeling program, which provided the computational analysis for our articles: Simple to use, but has the power to model ground heat transfer, thermal (sensible AND latent), electrical, simple economic, and indoor air quality.

  101. GBA Editor
    Martin Holladay | | #101

    Response to Ben Newell
    I appreciate your words of support.

    It will be interesting to see if your prediction -- that the death of the Passivhaus movement will be due to "ignoring economics... and using substandard modeling tools" -- will come true.

Log in or become a member to post a comment.



Recent Questions and Replies

  • |
  • |
  • |
  • |