solar quotes & info feedback
concerned with proper sizing and associated costs of course…
we’ll be building a “pretty good” 100% electric house in the the white mountains of NH, USA and this is a huge question that we need to answer. of course i have the requisite fear of undersizing…
some rough details:
1350 SF conditioned space
will be using mini splits for heating
heat pump water heater
possibly condensing/heat pump dryer
wife may go all electric car in future
quotes from one company all prices USD:
option 1:
28 solar world 300 watt panels 8.4 KW system, $22000, net cost $14300, 8.6 yrs payback period, 11.6% ROI
option 2:
28 LG 335 watt panels 9.38 KW system, $24350, net cost $16000, 8.6 yrs payback period, 11.6% ROI
option 3:
36 solarworld 300 watt panels 10.8 KW system, $25800, net cost $17000, 7.9 yrs payback period, 12.6% ROI
option 4:
36 LG 335 watt panels 12.06 KW system, $29000, net cost $19000, 8.8 yrs payback period, 12.5% ROI
thanks in advance for any feedback and i apologize if i left out any relevant info.
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Replies
The envelope please! What are the specifications for the building? Peak heating load, heating degree days and the like.
Peak heaing & cooling loads isn't as important as the annual energy use projected. Has this house been simulated with BeOpt?
A ~10kw system may be considerably oversized for a 1350' "pretty good house", or not. If using the excess for an EV, the miles/year make a difference too.
What's the net metering deal in NH? In Maine, you lose any power produced that exceeds annual use, so there's little incentive to get a bigger system that you need.
Your smallest quoted system, 8.4 kw, should produce between 10 and 11,000 kwh annually. Assuming you meet Pretty Good House standards for insulation and air sealing, you'll probably use about 5-7,000 kwh per year, without an electric car. I base that estimate on my own PGH power use of about 10,000 kwh per year, with a conventional resistance water heater and a power sucking hot tub.
Even With an electric car, the 8.4 kw system is probably fine.
sorry!
envelope is dbl stud wall w/ cellulose, windows, r5.6, walls r45, ceilings r60+, approx .76 ach50 post air sealing, trying to dig out the other info from stuff builder has sent, heres what ive got so far....
total heat loss btu/hr 22,484
heating degree days (approx) 8382
will dig out whatever else i can-thanks!
stephen:
is this the proper info?
-Residential customers in the Eversource net metering program, for example, have been getting 16.5 cents per kilowatt hour for electricity “exported.”
-• Residential systems will still be credited monthly at 100 percent of retail energy and transmission charges but only 25 percent of distribution charge; and will receive cash credits on their electric bills instead of kwh credits.
dana
to my knowledge it has not. the first quote i rec'd came back quick with no back & forth between the solar co and my GC
John: Our bills come from Central Maine Power. In Maine, transmission and distribution companies, like CMP, can't own generating assets, but handle retail billing. Our power bill is divided into a transmission and distribution portion and an energy portion. Right now, each is about 8¢ per kwh. Starting soon, new pv sysyems will receive a credit for 100% of power use but only 90% of T&D, with that number declining over time. There is a good chance the new system will be repealed, especially once we elect a new governor.
From your post, it looks like Eversource charges separately for distribution, as opposed to lumping T%D together. You'd need to look at a bill, or ask Eversource what the current rates are.
John - Are all your prices for a full retailer/installer system? You are not doing the installation, right? If so, $2.60/kW is really cheap compared to our markets in TX. Ours is at least $1.25/kW more.
John, I would be looking more closely at a scheme where you could deploy incremental phases, if possible. For example, if you have a roof layout potential of X horizontal rows, you deploy X-1 at the start - can always add another row, right? The 16.5 cent per kWh payback for excess production is a pretty good deal - but we've seen how these things are 100.0% political and can evaporate overnight. Again on the political side, the US tax credit is not here indefinitely, so that might argue for bigger. But you are not fully off-grid, right? So under-sizing just means that you have a net take of power from the grid. I suspect when you do the math, that monthly fee becomes chump change. Given that most grid-tied folks do well with a basic 6kW system, perhaps with your added loads 8-9kW might be plenty. I assume you have plenty of roof space, so to the question of a higher versus smaller wattage per panel, it's all about the $/W. Higher watts per panel is great, but usually means higher $ per watt, and really only makes sense when you have a roof space constraint. You'd want to have your installer break out that incremental cost, versus lumping it in with all the labor/racking/inverter/wiring infrastructure. Best of luck, Mark
Without an outside design temp at which the peak heating load hits 22,484 BTU/hr there's no way to use the 8382 HDD65 to estimate the annual heating energy use.
John: If you take MarkM3's suggestion, and leave room for a bigger of array to be added layer, make sure your inverter will be able to handle the additional load.
John, are the "1350 sq f conditioned space" and "total heat loss btu/hr 22,484" correct? I seem to remember you started with a small design and then went bigger? I also ask because our house with very similar specs was rated at closer to 12,000 btu/hr by our Energy Star HERS rater.
As I said, our house on the eastern side of the White Mountains has very similar specs to yours with 1320 sq feet of conditioned space if you don't count the foot thick walls. We have a regular electric tank (30 gallons) water heater, combo LG washer/dryer (condensing), and no dishwasher. We are conservative with our electric use: we dry clothes on a line and stuff like that. We have a 6.72kW solar PV system installed June 2015. In 2016, our first full year with solar, we used 6736 kWh and the solar generated 8497 kWh, making the year net positive by 1761 kWh. This will of course vary year to year, but I think we'll be net positive 1500-2000 kWh each year....well, except that we now have a Nissan Leaf (which we love). I'm glad we oversized our system for the house, because our significant kWh credits are being used by the Leaf. We are lucky to get full kWh credits for exported electric by NHEC.
If you're family doesn't waste energy, I think the house (not counting a car) would easily be net zero and likely be net positive with even the smallest 8.4 kW system...but this depends on your actual use.
I would factor in an electric car(s) with your forecasted use. I believe it's also easier and less expensive to go with a larger system up front versus adding on in the future. To make this decision, you really need to come up with some rough numbers on forecasted annual electric use for the house/car(s) and also factor in how your electric provider treats exported electric from the solar PV.
John,
I have built similar homes in a like climate and with the specifications you describe you will be somewhere between .8 an 1 Btu/sf/hdd. At 1 your total annual heat loss is 11,315,700 Btu at 8382 hdd. I think you are way over on your peak heating load calculation, at -20 design temp. you are at 4,481 Btu per hour.
STEPHEN SHEEHY,
Any idea how much energy your hot tub consumes?
Thanks guys for all the very detailed and thoughtful responses.
I’ll definitely double check the heat loss calculations with my builder. It’s entirely possible I misunderstood his data.
Brian thank you very much for the detailed and first person account especially from not that far away. That’s extremely useful – thank you! While I don’t think I’m going back to the days of handwashing dishes (Spent literally 3 months, cumulatively, washing dishes at our first house over the course of 7 years!), I could see us going with some of your ideas and I definitely like the idea of an electric vehicle especially as used Nissan leafs have become pretty affordable.
ultimately getting to net zero is my goal, or as close as our budget will allow-thanks again guys
Brian, congratulations on the 6736 kWh usage--that's lower than most passive houses I've heard reports on in this region. And thanks for the detailed report.
Calum: my best estimate is the hot tub uses around 1500-2000 kwh annually, but that's a wild guess. It is located in an insulated, but unheated room.