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Batteries Included

The Passive House + Renewable Energy Advantage

Image 1 of 2
Homes that comply with the Passive House standard can help address the “duck curve” problem. (So called “duck curve” graphs show the extent to which the daily peak in photovoltaic production fails to align with peak electricity demand.) The photo shows an all-electric Passive House in Alamo, California. The home was designed by the author in collaboration with the builder, Allen Gilliland of One Sky Homes.
Image Credit: Image #1: One Sky Homes
Homes that comply with the Passive House standard can help address the “duck curve” problem. (So called “duck curve” graphs show the extent to which the daily peak in photovoltaic production fails to align with peak electricity demand.) The photo shows an all-electric Passive House in Alamo, California. The home was designed by the author in collaboration with the builder, Allen Gilliland of One Sky Homes.
Image Credit: Image #1: One Sky Homes
Hourly load profiles of renewable energy (RE) electricity (cumulative) and electricity demand for a Passive House in Seattle. The left represents a week during winter with little RE availability, compared to a week during summer on the right, with much higher RE supply. Lower graphs illustrate the normalized storage capacity for the renewable energy with periods in January where short-term storage is not recharged and is unable to meet demand.
Image Credit: Image #2:
Passive House Institute

Almost everyone has a story about receiving an awesome gift, only to find they couldn’t use it until hours later because the box lacked one essential item — the battery. Remember the frustration, and how easily that manufacturer could have made you happy if they weren’t so cheap?

You may be equally annoyed to learn that well-intentioned codes and green building certifications, with the exception of Passive House, have been doing exactly the same as these manufacturers — omitting an essential operational item from their packaging and short-changing building owners, many of whom intended to be significant contributors to addressing climate change.

How is this possible?

The skewed economics of net metering

In the rush to accelerate and incentivize the installation of PV systems, well-meaning governments and utilities set up net metering1 or feed-in tariff pricing structures whereby building owners are paid for all the energy they supply to the grid (generally at the utility wholesale price and sometimes at full retail price) regardless of when the energy is generated and whether there is a demand for it. This worked well — until it didn’t. When excess summer generation started to wreak havoc on grid pricing structures, the flaw in net metering could no longer be ignored and utilities were still required to supply peak loads when renewable energy generation couldn’t match demand.

Utilities2 started to push back against these newly empowered (pun intended) home energy generators, who now had access to their own means of production (but not distribution.) These new grid contributors failed to recognize that their energy was not being saved for use at a more convenient time — the grid is not a storage system and is not set up to provide banking services. Yet they still felt entitled to be paid, regardless of whether their energy was being used or not.

This issue of electricity demands that are misaligned with solar contributions hit the early adopter regions of Germany first, followed by the states of Hawaii and California, where it has set off the biggest duck-related crisis since California’s 2004 attempt to ban foie gras3. Many a power-point pundit prematurely clanged the death-knell of the utility business model, as they simultaneously scratched their collective heads on how to flatten the “duck curve”4 — the name given to the graph illustrating the exacerbated ramp-up of daily peak demand caused by the incongruous timing of increased solar generation. Clearly, renewables alone were not going to meet our daily energy demand cycles or relieve utilities of the burden of meeting peak loads — which still commonly must be met using fossil fuel sources.

Which peaks matter?

To make matters worse, well-intentioned policymakers, code developers, and building certification entities may have inadvertently exacerbated this misalignment by pushing building programs optimized by net-metering economics, which rest on the flawed assumption that the grid functions as a bank. This assumption increases the difficulty of meeting winter peak loads.

We must first acknowledge that there are actually two peaks in building energy use: daily and seasonal. The duck curve reflects the daily peak cycle, but the more challenging peak happens as we move from cooling to heating loads. Because net-metering economics distribute PV generation over the year, rather than seasonally, this seasonal peak is discounted, as are the benefits of increased efficiency measures. Efficiency improvements become disproportionally skewed by the decreasing costs of generation and are made to look less cost-effective. Insulation levels become determined by annual average building performance, rather than by seasonal requirements. (This is the equivalent of advising someone to wear the same outfit all year round, instead of dressing according to the season.) Building programs — including many aiming at net zero — may have missed the opportunity to optimize performance for worst-case, seasonal loads, which in turn makes a transition to all renewable energy generation that much more difficult.

The arc of efficiency

One of the few building standard frameworks that has not fallen into this net metering trap is that developed by the Passive House Institute (PHI). When PHI overhauled their source energy targets in 2015 to include an equitable accounting for renewable energy, both short- and long-term battery storage were carefully considered. Efficiency measures were kept isolated from solar generation credits, while the need for electrical storage was factored into, planned for and optimized for the future scenario of an all renewable energy. As a confirmation of this methodology, a 2016 study conducted by Delia D’Agostino of the Joint Research Center, European Commission and Danny Parker of the Florida Solar Energy Center modeled a baseline building in various climates across Europe to find the most cost-effective options for reaching the European Union’s nearly Zero Energy Building (nZEB) targets. Both U.S. and European researchers confirmed “that it is possible to reach a very low energy design in new buildings with source energy savings approximately between 90% and 100% or beyond.”5 Their study affirmed the need to include costs for short-term electrical storage as part of a more accurate economic assessment.

We now know that commercial-scale battery storage combined with solar — a combination that helped address peak loads in Kauai6 —can easily “confit” the duck curve of our daily peak loads. Further innovations in short-term battery storage will quickly (and likely economically) solve our daily peak challenge. However, in order to fully wean ourselves off fossil fuels, we will need to shift our building frameworks to mirror those of Passive House standards, which focus specifically on reducing peak demands in order to shave peak seasonal loads. To do so, the cost of storage must be included in all optimization calculations in order to economically transition to an all-renewable-energy future.

Factoring in storage

The new Primary Energy Renewable (PER) factors utilized by the Classic, Plus, and Premium Passive House standards include a localized assessment of requirements for short- and long-term storage. These naturally differ by climate and are a function of renewable energy supply over on-site seasonal demand. As we can see from the graphs shown in Image #2 (below), short-term battery storage is only fully effective in the summer, when these batteries can be regularly recharged. However, the winter month of January shows long periods where these batteries are not replenished and supplemental grid power is required. These periods will require innovation in long-term renewable energy storage technologies in order for our grid to become truly fossil-fuel free.

The race for renewable energy storage currently looks like a competition between two gasses: the conversion of renewable energy into either hydrogen or methane, both of which can be burned cleanly and (hopefully) safely at the power plant. Whichever gas wins, it’s clear that we will need to bend the arc of energy efficiency to drastically reduce peak winter demands in order to transition to an all renewable energy future. This is exactly what Passive House already does.

Passive + Renewables is the focus of the upcoming 2017 North American Passive House Network Conference & Expo, being hosted in Oakland from October 4th to 8th, 2017. The Primary Energy Renewables framework will be more deeply explored at this event in workshops and presentations during the core conference program.

This article was originally written for Passive House Buildings, the magazine of the North American Passive House industry, which is published by Low Carbon Productions.


1. Net metering (or net energy metering, NEM) allows consumers who generate some or all of their own electricity to use that electricity anytime, instead of when it is generated.

2. Nevada Utility Continues Rooftop Solar War, Opposes Net Metering – EcoWatch.

3. The California foie gras law, California S.B. 1520,[1] is a California State statute that prohibits the “force feed[ing of] a bird for the purpose of enlarging the bird’s liver beyond normal size” (California Health and Safety Code § 25981) as well as the sale of products that are a result of this process (§ 25982).

4. In commercial-scale electricity generation, the duck curve is a graph of power production over the course of a day that shows the timing imbalance between peak demand and renewable energy production.

5. Comprehensive Modeling of Optimal Paths to Reach Nearly Zero Energy Buildings (nZEBs) for New Constructions in Europe by Delia D’Agostino and Danny Parker.

6. “Hawaii co-op signs deal for solar+storage project at 11¢/kWh.”

Bronwyn Barry is an architect and the president of the North American Passive House Network (NAPHN.)


  1. vensonata | | #1

    The storage revelation
    A timely article. This storage issue is looming, and the floodgates are just about to open in Australia, Germany, Hawaii and California, with many others to follow. Australia has learned that at 20-25% rooftop PV you can oversupply the community at mid day. And they have already achieved those levels of penetration. The other part of the equation is that as residential PV gets cheaper (and it is 70% cheaper in Australia than America) larger arrays are installed. "Why not put 10kW on your roof if it only costs $15,000" is the new reasoning. So that is when storage comes into the picture. Keep the juice for later. Obvious, put previously expensive. Now, beginning to be affordable, although probably requiring a little subsidy for a few years.
    Next: seasonal issues in cloudy, cold, winter environments. Apparently they have discovered the batteries don't get charged so much in January! Yep. Off gridders know that big time! So...having thought about this for a few decades, I think the answer is somewhat in line with the article. Hydrogen summer production for over generation, for winter use. It is low efficiency but excess electricity is "free". Just like storing pickled zuchinni for the winter. The other way is hot water or heat sink storage. With passive house levels, plus heat pumps, seasonal storage is not outlandish. It used to be, but needs to be revisited. 1000 kWh of hot water storage is quite simple to do.

  2. Bronwyn Barry | | #2

    The race for stored renewables
    Thanks for your comments, Ven. I'm also eager to see which direction the race for stored renewables ends up heading. I've read about a number of experimental attempts using water, or converting the excess summer production into either hydrogen or methane. Bottom line is, that will still cost more money than simply reducing (primarily winter) demand. Therefore the NegaWatt still rules and we need to design for a GOT future, where despite the reality of global warming, 'Winter is Coming!'

  3. Expert Member
    Dana Dorsett | | #3

    Cars are going to flatten the duck faster than home batteries.
    Bloomberg New Energy Finance is predicting electric vehicles (EV) will be cheaper than internal combustion engine cars in the US & Europe by 2025, and they are fairly conservative prognosticators. Several more aggressive predictions are putting it in the 2020 time frame.

    Whatever the time frame, the total amount of energy-sink available in an EV that can go 200+ miles is on the order of 10x the storage size required for managing diurnal self-consumption PV array on a typical Net Zero Energy house, let alone the even smaller size needed for managing it on a Passive House. The total amount of distributed storage capacity made available from the electrification of the transportation sector and smart car-chargers will outpace that of distributed home batteries. (Nissan's latest-greatest bigger battery Leaf even comes with vehicle-to-grid capability built in.)

    Treating each house as a solar-only nano-grid needing seasonal storage in huge error, given that non-PV renewables don't really scale down to pipsqueak size economically. The example graph for foggy-dew Seattle treats it as that sort of problem, while completely ignoring the fact that the very clouds and storms taking the big bite out of the wintertime PV is also re-charging the VERY substantial legacy regional hydroelectric capacity (and storing much of it for summertime use as snowpack), and ignores the very substantial wind power capacity (most of which has yet to be built) within the well connected existing grid infrastructure. . Very few (if any) locations are ideal for year round solar +battery only grid. Hawaii may be close, but Seattle would be toward the other end of that scale. Still the cost of long term storage has to become cheaper than over-building and simply curtailing excess solar (and other renewables) output. Even if long term storage eventually becomes cheap, Seattle is one of the least likely locations ton need summertime sunshine for wintertime use- there are other grid resources that are ready compete with that as a solution.

    Seattle's duck is already guaranteed to be pretty flat for quite awhile due to the flexibility and low cost of curtailing legacy hydro should the PV dominate the mid-day load. Barring a truly spectacular deployment rate for PV in Seattle (not likely, given the low retail cost of electricity there relative to the unsubsidized levelized cost of rooftop PV), the EV tsunami is likely to arrive in plenty of time.

    The solutions for seasonal capacity problems will differ by region, but the existing grid infrastructure in the US is far better equipped to handle it than in Europe, and can be improved when the economic case can be made. In New England and the Mid Atlantic the offshore wind resource is better than in the North Sea and it's output increases in winter. It can probably be deployed more cheaply than long-term storage in combustible gas form. (It's getting cheaper every year!)

  4. STEPHEN SHEEHY | | #4

    Aren't we trying to get away from greenhouse gases? Rather than manufacture methane with excess solar, we can more cheaply take it out of the ground.Using methane, however produced, is still going in the wrong direction, isn't it? Or am I missing something?

  5. Expert Member
    Dana Dorsett | | #5

    Methane infrastracture doesn't need to be built @ stephen sheehy
    The natural gas storage, distribution & generators already exist, which makes conversion of sunshine to methane more compelling than some other approaches. Methane created in a zero-carbon/low-carbon facility using otherwise-curtailed sunshine & wind would be displacing fossil methane being extracted from the ground by various methods, and (presumably) would have less fugitive methane releases & other environmental damage associated with gas exploration & extraction. Burning it still has the same CO2 emissions though, unlike harder-to-handle hydrogen, that has less pre-existing infrastructure for storage.

    The storage density of methane is also quite a bit higher than gaseous hydrogen. Some amount of hydrogen can be injected/mixed into natural gas fuel without harm, but at high concentrations H2 takes a toll on the gas grid infrastructure ( metal embrittlement, etc.) Renewables-produced hydrogen can be stored and shipped as liquified ammonia (NH3) at similar energy density to liquid methane (CH4), a concept that has considerable traction in some quarters. But reconstituting the hydrogen > ammonia > hydrogen for use in a fuel cell has a bigger net energy penalty than hydrogen > methane > combined cycle gas generator. NH3 could be burned directly as a fuel, but it has high NOx emissions to be managed as well as N2O, a powerful greenhouse gas 10x that of methane, 300x that of CO2. There also isn't a pre-existing infrastructure for burning it for power generation.

  6. Bronwyn Barry | | #6

    Dana - Your statement: "Treating each house as a solar-only nano-grid needing seasonal storage (is a) huge error" suggests you may have mis-read my article. The new Primary Energy Renewables (PER) framework absolutely does not suggest that pathway for buildings - but it doesn't disallow it. It simply assesses the dissonance between seasonal demand and supply and recognizes the necessity for storage (which should most economically be installed at grid-scale) in each climate. Wind and hydro are also accounted for, as are limited amounts of bio-fuels and district heating systems. I've presented more extensively on this here: The research source of info on this framework may be found on Passipedia here:

    As for EV's being able to serve as substitutes for either on- or off-site storage, I'm skeptical of that becoming a reality since I've seen from my own client's homes with EV's that they never charge the car at the time of peak solar production - so again, the alignment is off. (The whole point of my article!)

    Stephen - I agree that methane is problematic from a GHG perspective. I'm not advocating for that here, but simply recognizing that it is one option being explored. I expect that if methane storage is further developed, it would only be used at the power plant, and not piped to the end user.

  7. cussnu2 | | #7

    You are going to need a long cord
    to plug you EV into your home in the middle of the day......people do still work in this country..

  8. GBA Editor
    Martin Holladay | | #8

    Response to B.W.
    As the range of the typical electric car increases, many commuters will be able to make a round-trip to work without recharging their car.

  9. Expert Member
    Dana Dorsett | | #9

    Your clients aren't being paid for their car-charging.
    I read the article correctly , but didn't express myself well. Focusing only on the solar duck curve in the graphic then pivoting to seasonal storage implies a solar dominated grid, not off-grid. Treating Seattle as a solar only or mostly-solar grid is almost a silly as the single house nano-grid, which is why I went there.

    Peak grid loads occur as summertime air conditioning load (even in Seattle), and reasonably well correlated with PV output. In a PV-heavy version of Seattle the peak duck curve would be during the shoulder seasons (just as in CA) when heating & cooling loads are low. But EVs are destined to become the all-season grid-responsive load-leveler for all seasons, once the regulatory structures are in place.

    At the present penetration of EVs the battery capacities are small enough to promote range anxiety, and not a big enough load to the grid to become a severe grid-capacity constraint & scheduling problem. EV owners (with rare exceptions) are not being compensated for allowing the grid operator or utility to schedule their charging, and are for the time being choosing to plug in whenever it's convenient, or to take advantage of crude time of use rates, etc.

    That all changes when EVs start to become ubiquitous. Smart chargers responsive to utility or grid operator signals have already been invented, and opens the opportunity for EV owners to be paid for providing critical grid services (such as soaking up the belly of the duck to limit overvoltage on the feeders on light-load sunny days) or even fast response frequency & voltage control. For transportation to become significantly electrified that sort of technology will HAVE to be employed to avoid the high cost of huge capacity upgrades on the distribution grids. Ten EVs on a typical residential block transformer charging at the same time would melt it down, but all could be still charged on a rotating schedule under utility control with "be fully charged by time- xx:xx" &/or "charge only when the wholesale price is below $yy/Mwh" options selected by the EV owner, without capacity upgrades to the distribution grid.

    Different approaches to remuneration for grid services can be taken, such as being paid when the wholesale price goes negative, or being paid for using the load for frequency control and other ancillary services (something that is already happening with electric water heaters in the PJM region) can be taken. But at least some variation on the theme will be necessary by the time even 10% of the cars on the road are electric. The technology exists, but the utility regulatory structures aren't all there yet. The regulations will have to be ready by 2025- if they don't EV charging will become an even bigger problem than the duck. It's cheaper and better to make EVs the solution to the duck problem rather than just another problem. The range anxiety issue goes away for most people at some level of kwh capacity, but to be useful as a grid solution it's useful to incentivize keeping it plugged in even when there is plenty of range left. Being able to accept an unspecified amount of charging for free would be incentive enough to keep it plugged in for many people, but being PAID for accepting the mid-day excess energy and for ancillary grid services would make staying plugged in even more attractive.

  10. Expert Member
    Dana Dorsett | | #10

    The geography must be severely constrained for Figure 2
    Examining the January vs. July load & renewables curves in figure 2 make me believe the size of the PV and wind resources have been cherry picked or contrived for effect, and/or that the geography is severely constrained. Is that supposed to be the available renewables resources within Seattle City Light's service area, the city limits, King County, or what?

    The high correlation of summertime solar & wind output peaks simply isn't true across the well connected BPA grid (though it might be for Seattle-proper) , and the regional hydro output is not some down scaled constant baseload generator. Regionally those hydro resources are quite large, and reasonably well suited for diurnal load tracking. Unlike inflexible nukes & thermal coal, there is no reason to run the hydro AT ALL during the hours depicted as excess solar + wind, yet it still appears, a steady thin blue stripe, dwarfed by the towering excess solar. The hydro capacity may still be there during PV excess, but there's no advantage to running during negative-price hours, and no rational operator would. It doesn't add up. Even in the constraint geography scenario, as of 2014 about 90% of Seattle City Light's power was sourced from hydro:

    The net grid load profiles in winter vs summer seems similarly contrived and seems to assume all space heating is via the grid(?). Is that load profile supposed to be the total load, or only what the grid operators can track?

    Regarding the necessity or financial rationale for long term storage: At the current 6 cent/kwh levelized cost of utility scale solar (and even cheaper wind) any long term storage would have to be shown to be cheaper than simply building out more solar & wind and curtailing the output during times of energy glut. At the rate the levelized cost of solar is still continuing to fall, it seems unlikely that long term storage will be financially rational against over-built solar. The Sun Shot Initiative is currently targeting a 3 cent levelized cost for utility scale PV by 2030, and if history is any guide (not always the case with manufacturing technology learning curves, but usually) it'll probably be there in the 2025 time frame. At 3 cents you can spill half of it on the floor (for an average 6 cents for the electricity that's used) and still look pretty competitive against most long term storage options being bandied about. Converting the spilled half to methane and burning it to create electricity later is still going to be substantially more expensive than 3 cents.

    In 2016 utility scale onshore wind had a levelized cost between 3-6 cents, and that too is still getting cheaper year on year (just not as quickly as large scale solar.) Within a few months we'll likely see Lazard's LCOE analysis version 11.0, and be able to compare it to v. 10.0 ( ) as well as comparing their updated levelized cost of storage analysis, which as of v. 2.0 was only looking at short to medium term, not long-term technologies.

  11. Expert Member
    Dana Dorsett | | #11

    Response to But Why? ( #7)
    "You are going to need a long cord to plug you EV into your home in the middle of the day......people do still work in this country"

    Why does it have to be at home? What's so special about it?

    Why plug in at home when you can plug in at work or while shopping, especially if/when there's a financial incentive to doing so?

    The confluence of ubiquitous PV and ubiquitous EV happens to be a match made in heaven. If managed reasonably they will solve each others' potential grid problems at low or negative cost to non participating ratepayers. But that doesn't work if you're only plugging it at home rather than during the sunny hours.

    For about three years the Los Angeles Air Force Base has had a fleet of EVs & smart charger (2-way power flows, in this case) earning money on the grid-services they provide by being plugged in when parked. This approach can be applied elsewhere for duck-taming and other grid services, whether it's 2 way or charging only. See:

    To tame the duck there has to be incentives for folks to plug-in in the middle of the day, and those incentives will appear as the duck gets fatter. At the moment the CA duck's belly isn't very fat, and there aren't enough EVs to make a huge difference, which is why ratepayers are stuck paying for building out a lot of dedicated grid storage. By 2025 when EVs start to become ubiquitous it'll be a lot cheaper to pay people to plug into utility or CAISO controlled chargers and let them charge at a discount, or even pay them than it will be for ratepayer to capitalize ever more utility-owned grid storage simply to manage the duck.

    Dispatchable loads are as good as dispatchable generators from the grid operator's point of view, and in the 20 months or so since FERC Order 745 was blessed by the Supremes the mechanisms for being able to reward distributed dispatchable loads for those services have begun to emerge. Fleets of electric water heater controllers are pretty good, but have nowhere near the energy dump capacity that EVs are destined to become.

  12. Bronwyn Barry | | #12

    EV's as the storage option
    Dana - we have a presentation that will cover this exact topic at NAPHN17. (See Friday, 1.45pm.) EV's may well be the best way to tame the duck in some places. However, the point of this whole article is that winter renewable generation (including hydro, wind and solar) will not be sufficient to fully cover winter demand - even in sunny places like California. EV's are short-term storage and if you need to buy two cars to cover your winter storage demand, you may as well install better windows. They'll be cheaper than building another garage...

  13. exeric | | #13

    The difference between extrapolation and intuition
    Dana, I understand what you're getting at but think you are simplifying something that isn't as obvious as you are implying. There are still deep limitations to any existing electrolytic battery technology. For instance, they wear out and then have to be replaced at great expense to the owner generally in about 7 years. This limitation exists if the owner is a homeowner or if it is a utility. I haven't seen anyone completely solve this problem even though batteries have been developed continuously for the last 200 years or so. Also, electrolytic battery processes don't have the stability of many chemical processes where elements combine or separate through the addition or subtraction of energy. If electrolytic battery technology has been worked on for 200+ years and this long term stability problem hasn't yet been licked do you think it's going to be in our lifetimes?

    It seems to me this is an invitation to begin thinking differently about this. If you don't put the money into research there won't be good opportunities to lower costs on gaseous chemical conversion of energy and its storage. Think about all the money that has been put into research and development on solar cells and how it has lowered cost dramatically.

    I just think you are not applying the same standard of thought to chemical storage of gas from solar output as you are to electrolytic batteries technology. There is an amazing amount of progress in that area that can be envisioned. You are not giving it a chance and are just extrapolating what's happening currently. I really think chemical storage after gas separation from solar and other renewable resources is the future. It's even foreseeable that once that is accomplished it could be transported long distance through pipelines just like NG is today so. Only a fraction of the national and transnational research money has been put into this as has been put into electrolytic batteries and solar cell technology. That gas would be just as green as renewable resources as long as CO2 is not produced in burning.

  14. Jon_R | | #14

    Thermal storage, electric
    Thermal storage, electric vehicle storage, etc are quite doable. But until the retail cost charged for electricity tracks the cost (or environmental damage) of production, there will be little motivation to adopt them.

  15. Expert Member
    Dana Dorsett | | #15

    EVs as power dumps @ Eric Habegger
    The 7 year lifecycle of an EV battery is only is only for it's application as an EV battery, and it's cost-effective at that lifecycle for that application. Choosing to use it as a power dump for taming the grid or for voltage & frequency control doesn't change it's lifecycle as an EV battery- it's the same number of charging cycles. The only than that changes is the timing of when that charging occurs in order to optimize it's value to the grid. Remuneration for the grid services provide it offsets the "...great expense to the owner..." when it comes time to replace it.

    The 7 year limitation for lithium ion EV batteries does NOT apply to the utility or grid operator. At end of life as an EV battery it still has 5+ years of available service life as a home storage or grid battery, or as a storage device to power fast DC charging of EVs (to level out the peak draws from the grid for fast DC charging.) There are other battery technologies out there that are more suitable for dedicated grid batteries (flow batteries, etc) but the battery type depends on what it's being used for. There are already companies in the business of testing & repackaging used EV batteries for both fast DC chargers and behind-the-meter storage systems targeted at the commercial ratepayers seeking ti minimize demand charges. But at the rate that EV battery prices are falling the value of a used EV battery is even lower, and may not always be worth the re-testing. This is a busniess in a rapid state of flux, but at the bottom line, a lithium ion grid battery or self-consumption PV system battery has a lifecycle MUCH longer than 7 years- it's at least 2x that, probably closer to 20 years.

    If using the battery still in the EV to power the grid during the duck's neck ramp there is potential for some amount of battery degradation, but again, if the EV owner is remunerated properly for that high-value grid service it's not a problem. It's still cheaper than building and maintaining low capacity factor fast ramping gas peakers to manage a grid event lasting a couple of hours (and not every day.)

    There is plenty of money going into battery research, driven by the coming EV tsunami, the booming portable electronics business, and now grid storage.

    The seasonal long term storage issue is completely different, but it's also not clear that it's necessary. A shortcoming of the approach for the Passivehouse analysis in picture 2 ( ) is that it seems to be constraining all power & energy to be sourced and stored locally. It's a mini-grid, unlike the nano-grid single house analogy that I botched, but it's the same problem. The Seattle example is an apt one: To use ONLY very local resources Seattle would need long term storage to go 100% renewables. But the pre-existing reality is that the sole electric utility for the city (Seattle City Light) is already nearly 100% renewables, but using hydroelectric and wind resources located in some cases hundreds of miles from the city. A huge amount of "seasonal storage" already exists in the form of snowpack in the mountains, and the water behind the dams. The Passivhouse analysis mis-driects pointing toward doing something different than what's already working and affordable.

    The picture they use for Stuttgart suffers the same problem See figure 3 on this page:

    The high correlation of solar and wind output can only be a very local phenomenon. But wind power in much of the world has a very different characteristics, particularly off-shore and near-shore wind power. The ERCOT analysis of wind power for Galveston/Houston a year or so ago showed that the availability of near-shore wind power was much higher in the early evening than any other period, ramping up as the sun was going away (presumably a function of shore breezes driven by daily temperature swings over the land relative to the water temperature), making it an ideal resource for offsetting the duck-curve ramp. In New England the offshore winds are steadier, but deliver ~2x more in winter (when the grid energy use average will be higher, and PV output lower). Being selective in the resource mix for the local climates & loads, AND pretending the pre-existing grid resources really do exist (not hard to imagine), the amount of seasonal storage or even diurnal storage drops off dramatically. We're not going to power the grid seaonally from EVs (never meant to suggest that) but a study of the PJM region a handful of years ago showed that the amount of storage needed for 100% renewables at minimal curtailment was pretty small - smaller at 100% than at 80% renewables.

    And curtailment of renewables is only a "problem" if/when it's more expensive than seasonal storage. The efficiency of grid-to-methane to gas-generator-to grid is really pretty lousy (absolutely pathic, in fact.) Even if the power is "free", the economics aren't going to work out compared to curtailing 2 or 3 cent (levelzed) renewables, even at a 3-4x overbuild factor on the renewables. In Germany they can make a financial case for (almost) free-renewables methane for injection into the gas grid, but only because gas is many times more expensive than it is in the US.

  16. Bronwyn Barry | | #16

    Dana, you're missing the point...
    Respectfully, Dana, you've totally missed the point here and I'm afraid you may be digging a rabbit hole of your own making...

    It appears you're overthinking the graphs showing estimated consumption overlaid with renewable energy production? Not sure how you conclude from these graphs that Passivhaus "seems to be constraining all power & energy to be sourced and stored locally." It doesn't. All that the PER framework does is to provide an indication how "valuable" or "expensive" energy is at different times of the year. The lower level graphs simply illustrate that local storage - in whatever form: batteries, EV's or other - is insufficient for some period during the winter months. This is exactly why stored renewable energy will need to be developed. I'm guessing this will most likely and cost-effectively be delivered by utilities via the grid.

    No doubt, the cost-effectiveness of storing renewable energy will become a fascinating debate for the future. (Your crystal ball is as reliable as anyone else's in predicting that future.) In the meanwhile, the point clearly being made here is that we need to design buildings to reduce seasonal peak loads as much as possible or we'll all be flooded out of our favorite rabbit holes soon enough.

  17. DEnd2000 | | #17

    Great Article...
    One of my issues with the Net Zero Energy house approach is that it only marginally (ok somewhat more than marginally) addresses the seasonal demand difference. I used to follow a thread on the Tesla Owners Club forums about a guy who re-pourposed a couple of Model S batteries to try and go no holds barred off-grid. Granted he didn't do any efficiency upgrades to his house that I can recall but even with roof array and a large ground mount solar array and well over 100kWh of storage he still is connected to the grid and on some days drawing a substantial amount of electricity from the grid (mostly to charge his two Teslas). That scaled across society leads to more expensive electricity and little to no net generation (from non- solar, wind, hydro, etc... sources) capacity reduction. Power plants are expensive and plants that can only recoup their cost a few days or weeks of the year are much more expensive for the customer.

  18. GBA Editor
    Martin Holladay | | #18

    Response to Donald Endsley
    No one is advocating the off-grid approach -- certainly no one at GBA. The off-grid approach is nuts.

    We all need the grid.

  19. ethant | | #19

    We all need the grid...
    ... But I don't think this validates Donald's claim that a whole community of net zero homes would make electricity more expensive for the consumer. We should assume, or demand, that most net zero homes are also practicing demand reduction. Sure, maybe you can assert that 'off-grid' is nuts. But so is installing 100kw of solar without making any upgrade to home performance. (And, for that matter, so is owning two Teslas).

  20. exeric | | #20

    I agree with Bronwyn
    I agree with Bronwyn that no one holds the key to the future. That's why it can be dangerous to predict what will happen. But certainly it is also dangerous to keep one's head in the sand about the known problems with all conventional electric batteries. There are economic vested interests in presenting electric batteries as the key to the future and to minimize those problems that we all experience with them. I think people have a tendency to paint with a broad brush and not hold simultaneous ideas in their head at the same time. Conventional electric batteries WILL help solve the problem of global warming and are (presently) much more efficient at conversion of energy to useable form than electrolysis of water into in hydrogen or methane and then storage of those respective gases. Electric batteries are also mobile whereas comparable stationary electrolysis processes that separate gases and store them are not.

    So the two processes, conventional electric batteries and separation of gases from water through electrolysis, are complimentary. It's tempting to read into this that one form will replace the other but that's not the obvious thing that will happen. It will probably be a mix of the two where each is used in the form that it's energy storage capacity is used to it's best advantage.

    There is one thing to look out for in this whole discussion. Vested economic interests like the oil and gas lobby will lobby tooth and nail to stop any wholesale change at the utility level to electrolysis of water from the current plants burning NG to produce electricity. Their sunk costs will no longer be profitable. The same thing will probably threaten to a lesser extent Elon Musk's emerging battery based empire. He is counting on the fact that he expects to supply utilities with large amounts of electric batteries every 7 years to stabilize the grid. If he can only count on supplying electric batteries for more mobile applications like his cars that will create a diminishment of his profits. Remember, part of the reason his lithium battery production facilities have been such a good bet is because he is envisioning an extremely wide use of his batteries AND the fact that all those batteries have to be replaced about every 7 years. That is something that won't happen, at least in the elimination of sales to utilities that might instead use the splitting of water and gaseous storage. Expect a big resistance to change here from these vested economic interests.

  21. DEnd2000 | | #21

    Response to Martin
    Sorry Martin, I Probably wasn't entirely clear. What I was trying to say is that even with renewables plus storage, even on the utility scale don't really change peak demands. I know Dana will argue that renewables can meet those demands, and he may be right but I've yet to be convinced partially because of the Tesla guy.

  22. GBA Editor
    Martin Holladay | | #22

    Response to Donald Endsley
    There are many ways to address peak loads; battery storage is one of them. Another is to invest in high-voltage transmission lines that deliver wind energy from areas of the country with excess wind production. It's not the only answer, and it has disadvantages -- but it's probably part of the solution to our puzzle.

    For more information on this topic, see The Cheapest Way to Scale Up Renewable Energy?

  23. Expert Member
    Dana Dorsett | | #23

    Demand response markets and storage fix peak grid demands @ #21
    "...renewables plus storage, even on the utility scale don't really change peak demands"

    Huh? They sure as hell DO change peak demands (in several ways!) If your statement were true, it means the folks managing & regulating the California grid didn't do their homework or can't do math (despite ample evidence of competence with both.)

    The duck curve of just the PV fraction of renewables has without question lowered the absolute peak, and moved the daily peak to a point later in the day. It's the ramp between the mid-day excess and the now later peak that CAISO (and others) have identified as a potential problem, and the regulators in California have implemented a grid storage MANDATE to guarantee that it doesn't become a problem. Peak hourly demand is pretty easily managed by utility scale storage, and is already cost-competitive with fast-ramping gas fired peakers, which are soon to go the way of the dodo bird for new generating capacity.

    Batteries can ramp much faster than gas peakers, and can at scale manage the "duck's neck" ramp. And for the time being existing gas peaker operators are finding it economic to buy battery packs to provide the "apparent" spinning reserve rather than actually burning gas spinning at idle, and only firing up the gas-burner when the projected peak durations will exceed the storage capacity of the batteries:

    Former CEO of NRG (a large merchant power generating company) David Crane went on record a couple of years ago that the last gas-fired peaker built in the US will happen prior to 2020, and that was even before FERC Order 745 was blessed by the Supremes. But it's fairly short years before batteries are cheap enough that even existing gas peakers will no longer be economic, as demand response markets develop, and more batteries go onto the grid. We're really at the thin edge of the wedge on both, and both are already more economic than the status quo, with much bigger impacts on both the timing and magnitude of the peak grid loads than has been seen to date.

    Renewables can be considered reliable energy supply, even as baseload over sufficient geographic area, and the grid infrastructure for doing that is pretty good, and getting better. Flexible loads & batteries are the go-to low cost solution to managing peak demands. Traditionally grids have been managed with a bunch of inflexible "baseload" generation, with flexible (but sometimes lower efficiency) "peaker" generation to manage the changes in load over a few hours or even days, and utility regulations supported spending capital on those assets. But it's been decades since that approach made economic sense as the sole way to manage the grid.

    Even though regulations have been slow to change, the lights would have long since gone out in the PJM region without employing demand response, where loads that can be displaced in time can be moved away from less flexible loads. These methods have been in use for about 40-50 years by some local utilities as a means of avoiding the high cost of importing peak power or firing up low-capacity-factor peakers, but have become an essential tool for grid reliability in the PJM region, and it has worked well. There has been a great deal of legal dispute as to how demand response programs by third party aggregators of demand response, but FERC Order 745 stipulates that demand response be paid for the NEGAwatt- hours and capacity market payment at the same capacity rates and spot-market energy rates as active generators are paid for megawatt-hours. This was argued all the way to the US Supreme Court, which upheld Order 745.

    But that was less than 2 years ago, and the market mechanisms have not been fully developed in all areas (in fact, most areas don't yet have it under control), but it's coming, and it's will have a HUGE effect on wholesale energy markets, and peak grid demand. A problem most regulators crafting these markets are struggling with now is how to accurately measure the nega-watts, or un-metered uploads from batteries, etc. See:

    Just because it hasn't been fully implemented and the details still need to be ironed out doesn't mean predictions of it's imminent arrival is in the realm of crystal-ball gazing. Markets work, and aggregated demand response is cheap. The AMOUNT of aggregated demand response capacity will grow quite a bit with the arrival of the EV tsunami which also isn't crystal ball stuff. Larg-ish nations with growing car markets or existing large car markets are already establishing dates-certain for when new internal combustion cars will be contraband. (The UK is one, India is another, China- the largest car market in the world seems to be headed that way but hasn't announced a date yet.) With increasing manufacturing volumes come lower costs, and even if Team USA is a laggard on the regulatory front, the economics will be compelling in the new car market in less than a decade, even using very conservative learning curve assumptions on battery costs.

    As EVs become ubiquitous smart chargers will become mandatory to avoid melting down the grid from the very high local peak loads each car represents. But an EV is a ready-made demand response load, perfect for stabilizing the grid. That's true in both a high-renewables highly variable generation environment or a slow inflexible generation environment. In the US most cars are parked more than 90% of the time, and on the road less than 10% of the time. That allows great flexibility in the timing of when the cars are actually being charged, or how much they are charge in any hour interval. Once the driving ranges are well north of 200 miles, charging during peak grid-load (or low variable renewables output periods) can be defered in most case, often for days. In the aggregate the EV fleet will eventually be a load big enough to crash the entire grid if charged all at once, but since the charging can be spread out it's a load that can be shaped to track the available power hour by hour, minute by minute if need be. There has to be incentives and it has to be made easy to keep them plugged in to the smart chargers in order for them to be available for that purpose, but that's where demand response markets, smart charger developers, and demand response aggregators are putting their creative energies (today!). EVs will not be (indeed are not now) the whole demand response pie, but it'll be big enough slice to really matter for dealing with day-to-day or even week-to-week variations in average grid load and average variable renewables output.

  24. exeric | | #24

    Jeez, Dana!
    I give you an inch and you take a mile. You cannot even mention the desirability of long term storage of electricity from summer to winter in this sales rant. Half of the abbreviations you are using are indecipherable to the average human without prior knowledge. I can't speak for others but to me the overwhelming repetition of these slick buzzwords gives the impression that you are not at all a neutral voice that is sizing up all sides fairly.

  25. DEnd2000 | | #25

    Response to Martin, Dana, and Eric
    Appologies again Martin I was in a rush, and I tend to have trouble with writing (I don't English so good). I completely get what you are saying. But at best storage really just shifts when demand happens, granted that can be a really good thing as peak demand can be lowered, resulting in longer more efficient power plant runs than what a peaker would run. Yes wind and eventually wave power helps reduce those run times, but eventually the wind won't blow and someone will be too far from shore to benefit from wave power. At this time, and into the foreseeable future (yes Dana I know you totally disagree with me here) we're still going to have to burn stuff to generate electricity, and burning stuff even if it is Hydrogen or Methane produced by excess renewables still pollutes, though arguably fuel cells almost eliminate that. Regardless of pollution there will still be a cost that will be paid for by customers. The only way to reduce the need to eventually burn stuff is to reduce demand, regardless on if the peak amount of that demand is shifted to even out the peaks and troughs. That is my argument for needing better than just Net Zero Energy. Unfortunately I don't know how to even start making that argument work economically.

    And Dana, My apologies to you too I did not mean to set you off on a tangent. I do appreciate your argument, Though I honestly hope it doesn't take you as long to write a response as I take. You're arguments tend to be very well researched and I do appreciate them as I read each link. However I was more referring to seasonal peaks instead of the hourly peaks we normally refer to as peaks. That was the reason I talked about the Tesla Guy, even with his massive solar arrays and huge battery he still had days of massive draws from the grid. Since he is near me I know that on those days he imported power from the grid almost 60% of that power was generated by burning stuff. Yes he could draw at off peak times making reducing the amount of stuff burned by better utilization of the generation capacity. A few days of the year he still needs a certain amount of kWh produced, and that needed capacity is really no different than it was if he had no renewable power generation and a much smaller battery.

    Eric, I don't think anyone really confuses Dana with being neutral. He's an Advocate for renewable energy (as is Martin). That's a good thing, especially since they both want renewables to be the economic choice (as I do).

  26. exeric | | #26

    I'm afraid my point was lost
    I'm afraid my point was lost but I won't add to the extreme tedium of this discussion by trying to re-clarify. it's hopeless.

  27. Expert Member
    Dana Dorsett | | #27

    Not neutral, especially when it comes to cost @ Eric Habegger
    It's hardly a "...sales rant...", these are large and rapid changes happening right now, on a grid near you!

    If long term grid storage was financially viable, with a learning curve history that indicated it was even close I'd be all over it. But it's none of that. Wind and solar still delivers in winter, and if it's currently cheaper to over-build the renewables so that it puts out ENOUGH in winter than it is to use long term hydrogen / methane / ammonia storage.

    The numbers on all this stuff are pretty rough, but at the current state of the art on round-trip efficiency for long term storage as hydrogen, methane, or ammonia in the mostly-renewables scenario, the over-build of renewables needed to store up enough methane for even 1/4 the winter load would be enough capacity to supply the energy in winter directly (via grids) with no long term storage. When the dollars and cents are factored in for the US case at least the capital is better spent on overbuilding the renewables, even if it means more curtailment of the output. It's only slightly different in Germany with it's crummier and more expensive wind and crummier PV, and more expensive gas, and fleet of inflexible coal/nuke plants that can't economically be used for load following the way combined cycle gas works in the US.

    For a solution to be effective, it has to be cost-effective, and for now long term storage as doesn't seem like it'll work well enough soon enough to be relevant in the US, and maybe not even in Germany. The net carbon return on investment of that approach is even lower than the net cash return on investment.

    Donald: Sounds like "Tesla guy" was trying to build his own private one house nano-grid or something?

    The wind is always blowing somewhere within any of the major grid regions of North America, and the sun shines every day in at least some portion of each grid region. ( ) The amount of storage required to manage it all within any of the large grid regions is proportionally very tiny compared to what it takes for a single house or a single city / county / state.

    Within these grid regions the transmission capacity is pretty good, and being improved. Interconnections between grid regions are also pretty good between some regions (though ERCOT is pretty isolate) and being improved. In the western interconnect when it's cold in the northwest it's usually sunny with low air conditioning loads in the southwest. Presently under current state regulators that grid capacity is underutilized. The reluctance of California to widen their markets to offload excess solar and limited import from other generators in the region is actually BAD thing for the region as a whole, but the hurdles are regulatory/legislative, not technical. Right now regulators & legislators in Missouri are holding up a transmission line that would insert a large interconnect between the midwest (which has large and growing amounts of cheap wind) and southeastern states (which have a lot of coal & gas fired capacity.)

    The amount of stuff the US has to burn for electricity I(or for transportation) can go down pretty quickly and VERY cost-effectively when the regulatory environment catches up (and I'm fairly confident that it will.)

  28. Expert Member
    Dana Dorsett | | #28

    A fun primer on managing the duck curve.
    This came out in 2014, when the cost of Li-ion battery storage was 2.5-3x what it is now, and before it was obvious to everyone in the auto industry that EVs are likely to dominate the market by the mid 2020s:

    EVs & smart car chargers will magnify the effects of strategy #4 & #9, giving the system operator a pretty big hammer to wield whenever necessary.

    That was also before it was clear that FERC Order 745 was going to become the law of the land, which also gives strategy #9 a lot more heft even without EVs.

    Their pet project strategy #5, storing thermal energy as ice, works and is cost-effective at the commercial scale, but requires a sharper pencil (or very high electricity prices) to pencil out at the residential scale. The only product I'm aware of targeting the residential market with thermal cooling storage as ice (with or without grid operator control) is Ice Energy's Ice Cub:

    They began installing Ice Bears and Ice Cubs over this past summer on the island of Nantucket (MA), subsidised by the state and local utility to avoid the high cost of increasing the peak capacity under-sea transmission line to the mainland.

    It's not clear how cost effective that will be in lower energy cost locations that already have sufficient grid capacity, but it'll be a reasonable demonstration of how letting the utility manage residential storage (thermal or chemical) can work for everyone's benefit.

  29. Jon_Lawrence | | #29

    I think batteries are the
    I think batteries are the solution to flattening out the curve, but the EV battery, not a stationary battery. Build out charging stations in parking lots and let people charge their cars between the hours of 8am and 4pm while they are at work. Frankly if that does not happen, then the grid is going to get overwhelmed at night as more and more people charge their cars during off-peak hours.

    Then all we need is for the EV manufacturers to allow people to back-feed their homes at night with their cars' batteries that were charged during the day and we can make a real dent in our carbon footprint.

    Btw, I think this 7-year life-cycle of an EV battery is hogwash. My current Tesla that I have owned for 3.5 years and has 60k miles on it has lost maybe 5% of its storage capacity. From what I have read, the largest decrement is storage capacity occurs in the early years and then it levels off. Would I scrap my car in 7-years if the battery was only 90% or even 75% of its originally capacity. No. Even at 25% of its original capacity I would be able to cover 99% of my daily driving.

  30. exeric | | #30

    Per Bronwyn's apt thesis
    "...the point of this whole article is that winter renewable generation (including hydro, wind and solar) will not be sufficient to fully cover winter demand - even in sunny places like California. EV's are short-term storage and if you need to buy two cars to cover your winter storage demand, you may as well install better windows"

    Dana, you seem to not get this. From the very start you have concentrated on batteries and EV storage treating the Duck curve. No one has disputed that can work and will help time shift energy to hours when it is more needed. That is never what her article was about. We are very far from an overbuilt renewable energy society in this country. I have only ever lived in the USA and my only affinity for Bronwyn's argument is because it makes sense, not because she is originally from Germany.

    In the current environment it makes sense to not throw away renewable energy. Curtailing of renewable energy on an annual basis isn't even an option now. I think you may be confusing excess renewable peaks that happen daily during a few times a year (at least here in California) with annual surplus of renewable energy. The annual excess isn't happening and won't happen for many decades. The daily excesses can be cured by batteries in whatever form they are. Not so the huge annual renewable deficit. I'm not buying your argument that somewhere the wind is blowing or the sun is shining. That is a completely specious argument if the whole country is only harnessing 10% of the current annual energy needs with renewable resources. What do you not get about that?

    Remember what I said about most people not being able to hold two different ideas in their head at the same time. Even smart people. People often come to conclusions because it "feels" good to think a certain way. Your creating answers to topics that were never disputed in Ms. Berry's original posting. Do you have stock in Tesla or something?

  31. Expert Member
    MALCOLM TAYLOR | | #31

    Can you try and be civil to people who disagree with you?

  32. exeric | | #32

    I generally try, not always successfully. This was one of those times. My problem here was that Dana is mostly right about things and generally pretty knowledgeable. Because of that there is a predisposition for people to take his word as gospel because he is generally so (justifiably) confident. This was a case where his confidence was not at all warranted. But individuals that follow this forum didn't know that.

    Bad advice, in my opinion, is worse than no advice. We should all strive to not make situations worse by contributing bad info. Hubris is something we are all subject to. In this case I assessed that he was attacking the very valid points brought up in this article because of his previous extensive knowledge on many other topics. I felt I needed to take him down a notch with much more energy than I would ever do to someone who did not have such a good reputation. Sorry if it came off as arrogance.

  33. GBA Editor
    Martin Holladay | | #33

    Malcolm and Eric
    It looks like things are settling down rather than getting more heated, and that's good.

    A general rule for forum discussions: marshal evidence to support your position and convince readers, without introducing any attacks on the motives of other people posting comments.

    Looks like we are back on track.

  34. Bronwyn Barry | | #34

    Eric - I appreciate your efforts to keep the focus on the topic of my blog post. We all periodically need some redirecting and we both thought Dana missed the mark on this rare occasion.

    BTW, I'm actually South African by birth (fourth generation) and now American by choice, so I'm not quite sure where you got that I was German? I'm also an EU passport holder since part of my gene pool is partly Irish and they're pretty generous with their passport issuing policies (!) I do travel to Germany frequently for various international energy-efficiency-related conferences and meetings, so perhaps that is why you assumed I was of German origin? No big deal either way. I admire many of the energy-related policies that modern Germany has implemented. (Their building and energy issues are are more similar to our own than they are different.) We all share the same atmosphere, so finding the fastest, smartest path to the largest carbon emissions reduction is what keeps my curiosity most stimulated.

    For those of you also intrigued by this topic, here's another interesting article on the need for improvements in battery storage:

  35. exeric | | #35

    "BTW, I'm actually South
    "BTW, I'm actually South African by birth (fourth generation) and now American by choice, so I'm not quite sure where you got that I was German? I'm also an EU passport holder since part of my gene pool is partly Irish and they're pretty generous with their passport issuing policies (!) I do travel to Germany frequently for various international energy-efficiency-related conferences and meetings, so perhaps that is why you assumed I was of German origin?"

    Who knows where I got that. Probably all of the above mixed with the fact that "Bronwyn" is an unusual name and assumed it was German. My bad. I'm glad it's sorted though.

  36. Expert Member
    Dana Dorsett | | #36

    You're right, I DON'T get it! @ Eric et al
    "....the point of this whole article is that winter renewable generation (including hydro, wind and solar) will not be sufficient to fully cover winter demand - even in sunny places like California. "

    The reason I don't get it it because it's mostly not true, given the capacity and geographical range of the US transmission grids. It only becomes a serious seasonal-total-energy problem when constraining the geography to something the size of California (or Germany, which the Passive House people use as their paradigm case.)

    I would contest the whole notion that "...Dana is mostly right about things and generally pretty knowledgeable...". That's mostly not true either- just ask my wife! :-)

    But I probably know more about the wholesale electricity markets and how these markets are designed and are rapidly being re-designed to address potential (and real) problems than most. It's a really hot topic in places like Australia and Germany that have large inflexible generating fleets facing operational and financial difficulties in the face of increasingly large amounts of variable-output renewables. Parts of the US are seeing related issues, but the cheap natural gas has already replaced a large amount of the inflexible fossil generators with far more flexible plants, and the grid infrastructure in the US has better import & export capacity than the European grid, and better able to manage the huge development of midwestern wind, which is cheap enough to make increasing wind-export transmission capacity financially viable. (The German grid capacity between the windy north sea (offshore & on) and the not-so-windy south is pathetic by comparison. Excess German north sea wind has been causing problems for Poland's transmission grid where a large fraction of that power sometimes ends up. It's a work in progress.)

    The "...even in sunny places like California..." comment misses the mark regarding seasonal load issues, unless there is requirment that all power on the CA grid be sourced in CA, and it comes with implication that it also needs to be a mostly-solar powered solution. The recent drought has underscored the limitations of CA's hydro capacity too. Counting on sunshine alone or wind alone is problematic even at a larger geographic scale. But with wind & solar combined there are compelling studies out there showing that even the PJM region (geograhically not much bigger than CA or Germany, but with massive grid infrastructure interconnects to neighboring regions) could hit 100% wind + solar + hydro with only a modest amount of grid-storage and no seasonal storage. California's relative grid-isolationism creates an apparent seasonal shortfall artifact, but that can be changed with legislation and better grid control/market coordination & regulation. The legislature in California just balked (again), but the arguments for playing a greater role in the broader western interconnect electricity market may eventually become too economically compelling to stay the course while still moving toward the 100% renewables goal. This is largely a legislative & regulatory problem, not a technical problem or a total seasonal resource problem.

    I'm not suggesting for a minute that EV batteries are useful for dealing with season average load shifts, but it's absolutely enough capacity to address a large fraction of the duck curve problem at very low cost. Combining the duck curve issue and the seasonal energy load/storage issue in the same blog confuses the discussion a bit, since they are orthogonal issues, completely unrelated, and should not be conflated.

    Fixes for the duck curve MAY intersect if there is no option other than expensive seasonal storage to deal with longer term average-load issues, but it's not automatically the case, and would have to be designed that way. The duck curve is completely a very short-term PV induced problem, with lots of ways to fix it. Transmission grid solutions to the seasonal energy issue don't affect the duck curve, but COULD if designed to be part of the solution. But there doesn't need to be any overlap unless there is a compelling economic case to that makes it so.

    Well ahead of the EV tsunami, the California independent system operator (CAISO) looks like they're moving to develop a new electricity market designed to optimize short term storage use as part of the duck curve fix, without incentivizing wasteful use of power during power glut hours:

    Regionally, California is something of an outlier when it comes to wind power. Most regions of the US have much higher average wind speeds in winter than in summer, whereas California it's inverted, sharply peaking in summer, with little to cover the wintertime load. While most parts of the heating-dominated US can do a lot of seasonal average load balancing by developing more wind, that doesn't work for California, since both wind an PV output fall off for the winter season. See:

    But that's not to say California couldn't IMPORT a lot of wind from nearby (or even fairly remote) regions. There is currently a very large wind farm project being hammered out in Wyoming, with an associated dedicated transmission line to California to be able to take the cheapest possible wind to the higher priced markets of southern California:

    Wyoming's total wind resource is world-class, and dwarfs the total power needs for that large but low-population density state. As the coal mining business there is waning, employment prospects in the wind industry are poised to eclipse the all-time record high numbers for employment in Wyoming's oil, gas, & coal industry. The fact that Wyoming wind peaks in winter when CA wind & solar is at it's nadir doesn't hurt it's prospects either- it's good kind of customer to have!

  37. Bronwyn Barry | | #37

    No efficiency credits for reducing winter peaks?
    So Dana, if I'm to understand your argument, you don't think there's much benefit to designing buildings to reduce winter peak loads since we - in California, at least - can import wind energy from Wyoming?

  38. Expert Member
    Dana Dorsett | | #38

    I support the concept in general @ Bronwyn
    There are good reasons to reduce the peak daily weekly loads of buildings, but once the domestic hot water is dominating the average energy load (which it is in most Net Zero houses) the rewards of further improvements on the thermal performance of the building envelope diminish rapidly. The peak hourly draw of each will be related to when hot water is heated & used, or when and at what rate the EV is being charged, so the impact taking it to PHI levels on the duck curve isn't really very much. The duck curve is primarily a shoulder season problem, when the air conditioning loads are low for all houses, not just PHI or Net Zero houses.

    The bigger differences will be the seasonal energy-use, but that's also a pretty small difference, and soluble by redefining what constitutes a "region" that's more relevant to the existing and future infrastructure in the US, which has substantially more throughput capacity and interconnectivity than what's available in Europe.

    My problem with the Passive House PER approach is that the "regions" aren't well defined in the discussion, but seem to be pretty clear that it's a Germany (or European country X) sized region, and doesn't reflect the interconnectivity and much wider climate variations found in the US.

    In the PHI discussion ( ) they state:

    "The methodology to derive PER factors, as described in this article, to begin with are only valid for the specific climate data set used. Calculations for the very same location but a different climate data set (e.g. different time period, different source) will lead to slightly different results. Furthermore, these calculations are purely local, meaning that the influences of RE generation in the nearby surroundings is not at all taken into account. In reality, electricity production and electricity consumption cannot be viewed as strictly local but must be seen in a regional context. Electrical grids are in many ways influenced by politics and developments, locally and worldwide, cannot be reliably foreseen. However, it is clear that a purely local energy supply, though technically possible, is needlessly complex and therefore an assumption that is too pessimistic."

    But their stated solution to that is a bit opaque, nearly content-free:

    "The PER factors to be used in the PHPP are thus not based on individual local calculations but rather on a combination via a global Fourier approximation of the results calculated for over 700 locations worldwide. In addition, the minimum value used in the PHPP is 1 (supply = demand). Figure 6 shows the average value and variation of the PER factor for space heating of all locations currently integrated into the PHPP."

    I don't blame PHI for their generally Germany-sized region perspective on things, but as much as they try it's not particularly pertinent to the US case. Germany's entire land area is substantially smaller than the ERCOT controlled grid region of Texas, and similarly weakly connected to the rest of the European grid. It's also similarly sized (but smaller) than California's CAISO grid, which is already BETTER connected than Germany's grid and getting better. The PJM region (this is an integrated power market region mind you) is nearly twice the size of a Germany, has far better wind & PV resources (mostly undeveloped) over a broader range of climate & weather, and better grid connectivity to neighboring larger-region-than-Germany grids for import/export of power. And that's just the existing grid, not including the transmission projects under development, let alone other still being proposed.

    The total throughput capacity of the existing western interconnect (WECC) is more than sufficient capacity to manage seasonal differences for California, given the right renewables resource mix across that broader region. But the current regulatory structures within states can limit access to those remote resources, which is clearly an issue for CAISO. The truly massive existing energy throughput capacity potential of the WECC is currently very under-utilized. Locale weekly storage might be needed for a renewables-resource optimized WECC to go 100% renewables in a drought year, but seasonal storage? Not so much.

    California's comparative grid-isolationism notwithstanding, the political hurdles for transmission systems between states and regions in the US are nowhere near as high as those between countries of Europe, or even states within India. California's grid is already better connected to neighboring regions than any country in Europe, and the raw economics more readily drive transmission projects here much more readily here than in Europe. The prospect of a Euro-style Brexit and the ensuing financial complexities happening in the US are extremely remote. There's a far better rationale for better use of the existing and future transmission grid resources in the US than there is for the high cost of seasonal storage. (The fact that even if the energy is free methane produced and stored for seasonally is at least 3-5x as expensive as fracked US gas doesn't make the economic case any easier. It's an easier case in Europe at European gas prices.)

    The giga-wind farm in Wyoming and the associated transmission line is driven purely by the economics. It is almost certainly a more cost effective seasonal energy vs. local energy source storage fix than making all new houses in California as of 2020 PHI rather than Net Zero Energy. But more wind farms + transmission line are almost certainly NOT going to be more cost effective than upgrading existing building stock to something much better than they are today. I haven't read up on how Title 24 2020 is addressing building efficiency upgrades yet, but it's probably pretty substantial, given the 100% renewables by 2045 target.

  39. Bronwyn Barry | | #39

    Hold that thought, Dana...
    I have much to say in response, Dana, but am slammed today with a deadline, plus a few logistics issues to deal with in preparation for the NAPHN17 conference next week... I'll respond as soon as I can.

  40. Bronwyn Barry | | #40

    Response to Dana
    Hi Dana,

    Here's the response I promised earlier...

    While it's clear you're skeptical of the need for long-term renewable energy storage (and have conveniently dismissed the idea as a 'German-specific' viewpoint) it's looking like you may be in the minority. In just the past two weeks I've stumbled upon numerous articles where this idea is being explored or tested right here in the good ol' USA:

    Yesterday SoCal Gas and NREL announced their installation of a test facility to convert renewables into methane: I'd say this is a pretty strong indicator that they must not be too sure they can rely on the wind capacity in Wyoming for their winter and peak loads.

    In another study, the cost of storage to accurately assess grid power parity is confirmed: (This one doesn't appear to differentiate between short- and long-term storage costs, but essentially finds that the grid is still needed in most parts of the world, essentially for seasonal load delivery.)

    This list of articles touches on various storage combinations and permutations being implemented in various parts of the US. Most articles reference the need for building designs to optimize peak load reduction to maximize the cost-effectiveness of storage:

    While we essentially agree that upgrading our building stock to better than current code will be much more cost effective than storage, it appears we disagree on the degree of peak load reductions required to eliminate the need for new peaker plants (or power lines from Wyoming.) Given that in most of California, the increase in building envelope requirements to meet PHI's Passive House standards is not such a big leap, perhaps we're splitting hairs? What I do see we’ll all need to keep a close eye on in the coming years is what is being referred to as ‘the performance gap’ – the difference between predicted and monitored energy targets. This is where I’ve seen PHI’s program provide phenomenal results that I’m not seeing consistently delivered elsewhere. Time will tell… Let’s hope we have that luxury?

  41. Expert Member
    Dana Dorsett | | #41

    Picking up on a slow conversation... @ Bronwyn Barry
    The fact that NREL et al are looking at bio-enhanced electricity-to-methane isn't surprising- they're charged with reasarching all sorts of renewable options, but that doesn't instantly translate into a perceived need for seasonal storage, even though it makes seasonal storage of renewable energy possible.

    There is also a large gap between demonstrating that a technology can work, and making it more financially viable than over-producing renewable energy and simply curtailing the excess. Carbon capture and sequestration is also technically feasable, but not even remotely economically rational. At US energy prices (present & future) I expect that to be the case for grid-to-methane, barring a truly major technology breakthrough. It's good for NREL to keep funding process innovations, but that's not necessarily an indicator that the technology will ever succeed in the marketplace. They're still studying cellulosic ethanol too, but it needs to get a lot cheaper very quickly to be competitive/relevant as the transportation sector passes the electrification tipping point that now appears inevitable.

    In the meantime Denmark is already paying EV owners about $1500/year to provide rapid response grid stability as both power sink & power source, as well as supplying peak energy to the grid with 2-way smart chargers. California can (and probably will) do that too, a major mallet for mashing the PV curve mallard. This is still more of utility & grid operator regulation problem than a energy & hardware technical problem.

    And California is getting closer to opting to take advantage of the existing WECC regional grid, which can perform a very large amount of seasonal and daily peak load shifting without buying massive storage (of any type):

    FERC Order 745 (mandating the creation of demand response markets) has yet to be fully implemented, but that's another major mallet coming soon to a grid near you, destined to grow in size , simply because demand response so CHEAP compared to the alternative methods of providing peak capacity and stabilizing the grid. During the extreme grid peak loads induced by the Polar Vortex of 2014 it was wind power and PJM's already reasonably well developed demand response market that kept the grid from crashing due to gas pipeline capacity constraints limiting gas-fired generation, and frozen coal piles & frozen coal handling equipment taking several large coal fired generators off line. More renewables and more demand response will only make that task easier, whereas no quantity of stored grid-to-methane gas will increase pipeline capacity.

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