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Community and Q&A

On-Site Renewable Energy and High-Performance Windows

Peter L | Posted in Energy Efficiency and Durability on

A builder stated that it’s better to invest money into solar/wind/battery storage than it is to invest money into better windows, during a new house build. The reasoning was that since you are on a solar system with battery storage, having efficient windows is not necessary, as you are not losing $$ on energy bills since the solar or wind are making up for it. He said the money is better spent on the renewable energy systems than buying high performance windows?

Does he have a valid point?

I thought it was always better to make the house as energy efficient as possiblRenwae so it uses the least amount of electricity/gas to keep it heated/cooled. Using passive methods & making it efficient makes the house more comfortable to live in. His philosophy is more akin to build it however you want it (energy code minimum wise) and just use the additional funds to buy solar/wind/battery storage, to heat and cool the home.

Last I checked solar, wind and battery storage is not “inexpensive” but compared to dual pane vs triple pane windows.

Any input?

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Replies

  1. DCContrarian | | #1

    There is no easy answer. You have to run the numbers. If it helps, it's actually two separate questions, do energy efficiency improvements pay for themselves, and does energy production capacity pay for itself. Because the fact that you're using one for the other doesn't really affect the payback calculation.

    A major compounding factor is that you're measuring things on different time scales -- the expenditures are today, the savings are over years or decades. You quickly run into a lot of questions about assumptions: what will happen to energy costs in the future? What about interest rates? How long will you live in the house?

    He may be right in one respect, which is that energy efficiency doesn't sell homes, and that an efficient house doesn't command any kind of a premium when it's time to sell. Solar panels on the other hand probably do. So if you're building a house to sell, or if you don't plan to live there long, efficiency improvements don't make financial sense.

    However, if you're building a house for yourself, in addition to the financial concerns there is a real benefit: a tight house is a comfortable house. Efficient houses tend to have more even temperatures and to be quieter and less drafty.

    1. Trevor Lambert | | #2

      There was an article here just a few days ago that says that solar panels do not add anything to resale value.

      If one has real concern about the environment, then any option including a lot of batteries loses big time. I have a hard time believing such a system would win financially either.

      1. John Clark | | #15

        They generally don't add a lot of value due to the fact that a large percentage are leased. The new homeowners assume the lease.

    2. Charlie Sullivan | | #11

      If you opt to directly compare spending $5k on improved windows vs. spending $5k on PV, you can skip the complexities of evaluating time value of money. You can simply find the point at which buying PV gets you more benefit than spending more on the envelope.

      But there are still lots of reasons one might prefer the better envelope--the comfort aspects you mention, but also the resilience in a power outage, and the larger scale benefit that you are contributing less to mismatch in seasonal and daily variations in PV production and load that need to be compensated by other generation sources and storage.

  2. Expert Member
    Zephyr7 | | #3

    Nope, he doesn't have a valid point, with a few minor exceptions.

    First, forget about "battery storage" for a grid tied system. Batteries are a big expense, a big maintenance item, and introduce a lot of risk (safety and fire) to a solar installation. Don't bother with batteries, just go with a grid tied system.

    Remember that insulation saves all energy, including solar. It will also help with comfort. Solar can't make up for comfort.

    Residential wind power isn't really practical. Stick with solar, which is much less hassle and a lot more reliable.

    Bill

  3. Roger Berry | | #4

    No. Windows and walls are 24/7, wind and solar aren't. Maybe if perovskite panels finally become available so cheaply that you can cover your house with them and tie them to some future cheap and safe battery bank your builder will be vindicated. Current probabilities for that occurring are quite low. He also ignores the maintenance aspect of battery banks and the code requirements (at least where I live). Zephyr is quite right to warn you off batteries.

    Your second viewpoint is much more sensible. Good windows will make it much more comfortable to be near them and reduce the nuisance of condensation if you are in a cold climate. Also handy for reducing summer heat loads if the SGHC is selected properly. Good walls and windows will carry you longer through power failures and long snow days if that is what your climate dishes up.

  4. Walter Ahlgrim | | #5

    Maybe yes if the builder wants to build to a modern code and you want to build to passive house numbers.

    Maybe no if the builder wants to build R11 wall and R19 ceiling in zone 6 or if you are on a tropic climate.

    When I look a BEopt models of homes the cost to build and operate the code min house and the passive home are often very similar numbers in the monthly cost

    Seems to me you want the Opium House The only way to get there is to run your numbers in your BEopt model.

    https://www.nrel.gov/buildings/beopt.html

    Walta

    1. DCContrarian | | #6

      The Opium House? Sounds expensive.

      1. Walter Ahlgrim | | #8

        Passive = expensive!

        Opium house has the best return on investment. Given all the variable for your house like your fuel cost, your weather, your guess at inflation, your interest rate window selection and a dozen more choices.

        In the graph I copied from the net it cost $900 a year less to own than the passive house and $500 less than the code min house.

        Walta

  5. Paul Wiedefeld | | #7

    Like most things, I consider this a “it depends.” There are certainly diminishing efficiency and comfort returns to some levels of insulation, at which point adding another panel or two probably makes more sense (solar probably makes sense regardless, so it’s often a question of size). That insulation amount will vary by situation so definitive statements aren’t helpful.

  6. Tom May | | #9

    I always say, efficiency is in the user. Even a tight house can be inefficient if one keeps the thermostat at 80 in the winter and 60 in the summer. Just like anything else, one can do some things now and other things later if needed. So your builder has some sound points.
    If you don't mind opening the blinds to let the sun in and putting on a sweater occasionally, or just get up and do something, the cold may not be a problem in the winter, just as closing the blinds and venting out the hot air can keep you cool in the summer. Maintaining a constant temperature is much better to lower heat loss/gain minimizing your delta T.
    Investing in a small off grid set up, to offset electrical usage, can be grown over time. The thing with off grid is, if you move you can take it with you. The same can't be said for windows and insulation. It also gives you peace of mind in case of power outages and can be used to run a boiler and lights if necessary.

    1. Expert Member
      Zephyr7 | | #10

      A constant temperature is good with heat pumps, but with conventional systems, running cooler at night (for heating season) will save you a bit. Constant temperature operation is NOT optimal for a conventional heating system.

      A grid tied system is better than an off grid setup, and you can still take it with you. If you install your solar panels on a ground-mounted rack, it's much easier to remove them to take them with you, and you have no risk of damaging the house when you do. I wouldn't count on the solar system as a backup power source. People underestimate the issues with the batteries here.

      Bill

    2. Expert Member
      Malcolm Taylor | | #12

      "The thing with off grid is, if you move you can take it with you."

      Does anyone really do that? Strip the solar array and wiring off their roof and install it in their new house?

      1. Charlie Sullivan | | #13

        Now that module costs are the minority of the cost of a residential system, that wouldn't make much sense unless you had an emotional attachment to those particular modules. (Perhaps Martin feels that way about the modules he bought back in 1980.)

        Another option available to some people is to buy into a community solar system, and get net metering from an off-site installation. As long as you are in the same utility region, you can take that virtual connection with you when you move.

        1. Joe Norm | | #17

          I think there is a bit of confusion between off-grid and grid tied systems in relation to modern all-electric homes.

  7. John Clark | | #14

    Depends on where you live. For example California updated their building code a couple of years ago and builders have been meeting the new requirements with solar. However the climate in California is vastly different from other states.

  8. Peter L | | #16

    Also, solar panels and especially battery storage, requires maintenance $$ and eventually replacement on the batteries $$. Windows are basically "lifetime" and require no maintenance.

    The LG lithium batteries for solar storage had a recall as they would catch on fire. Over 10,000 batteries had to be recalled. Tesla had a few cars catch on fire during recharge. So the lithium battery is not without issues and dose pose a fire risk.

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