Heating With a Solar-Powered Electric Boiler
I’m seriously considering buying a solar panel system. I was thinking of not only using it to cover the electric bill, but to also use it to heat my home if I bought an electric boiler. I’m finding it difficult to see how much energy would be needed. I tried to calculate BTUs to kWh and came up with a number of 158,555 (for a 150000 cubic ft home) kW/year (using 31 degrees as the temperature difference between inside and outside). But this is kW, not kWh
Then I saw this site
https://energyusecalculator.com/electricity_furnace.htm?
and used 4 hours as the amount of time per day that the boiler would be in use (recommended from the site) for an 18 kW boiler, and the number comes out to 72 kWh/day or 26,280 kWh/year.
A solar panel company quoted me a production of 7000+ kWh/yr. So, in either case, it doesn’t seem possible. I’m located in the Northeast, in the mid Hudson Valley.
Any help would be greatly appreciated!
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Replies
Watts is a measurement of instantaneous power. As such, the amount of "158,555kW/yr" is non-sensical. It's like reporting your car's mileage as 100mph per year.
It looks like you've got a lot of assumptions and rules of thumb built into your number, which will never result in a very accurate estimate. If this is an existing home, your best bet is to extrapolate heating data from your bills. Once you have that, it's a pretty simple matter of converting between BTU and kWh.
https://www.convertunits.com/from/Btu/to/kWh
If it's a new build, or your billing details include other loads besides heating, your next best bet is to model the energy requirement using a Manual J type calculation and climate data.
If you're looking to just supplement your heating with solar, that might be a reasonable goal. Given your location, supplying all the heat by solar is almost certainly going to be impossible.
I should also have mentioned that any scheme of EV solar panels feeding an electric boiler is going to lose versus any kind of heat pump setup. You could do a hybrid of those two, but my gut tells me that the payoff is not going to be worth the extra cost and complexity.
You're going to get a LOT more production from your solar panels in the summer than you will in the winter. Overcast, short, winter days are going to result in FAR less energy output from the solar panels. You can't just average out the production over the year and assume a constant number of kwh/day. In terms of heating, solar panel production tends to be least (winter days, and especially winternights) when you need it most.
You would need to know more about the system sizing to see if the numbers you were quoted in terms of production would work out. I doubt very much that they will in this case. As Trevor mentioned, a heat pump is going to win out every time in terms of overall energy efficiency, which in your case means heating your home with the smallest possible solar system. The reason for this is that heat pumps don't make heat, they move it, so they have a "coefficient of efficiency". That's essentially a fancy way of saying that a heat pump can provide (slightly different from "produce) more heat per unit input energy than if you used the energy to heat directly. If you use an electric resistance boiler, you get EXACTLY the same output thermal energy per unit input electrical energy. This is why a heat pump is always a better option in terms of energy efficiency when compared to electric resistance heating, especially when you're in an area that doesn't get super cold in the winters.
The only advantage electric resistance has is that it's cheap to buy. You can use it as a place to 'dump' excess solar production, but I don't think the economics will work out where oversizing the solar system to save on the heating system beats out a smaller solar system with a more expensive, but much more efficient, heat pump heating system.
Bill
I think it would be helpful to define exactly what you're trying to do. With solar electric, you can be either grid-tied, where you are connected to regular electric service, or off-grid, where you aren't. Most electric companies allow grid-tied customers to do what's called "net metering," where your monthly bill is the difference between the electricity you produced and the electricity you consumed that month.
If you have net metering, a common goal is to be "net zero," where over the course of the year you produce as much as you consume. At your latitude solar production in June is going to be about 6-7 times what it is in December so being able to bank electricity in the summer for use in the winter is very handy. Net Zero is a well-established building practice, I know there are whole subdivisions of them going up not far from you in Massachusetts. (See https://www.eastbranchhomes.com/ for example) You should Google "net zero" to get a flavor for what it entails.
If you decide net zero is for you there are two sides to it, designing your solar collectors and designing your mechanical systems. Each of them is probably worth a book on its own. That said, designing a heating and cooling system for a net zero house isn't fundamentally any different from designing it for a regular house, other than it's going to be all-electric. In your area I suspect that an all-electric heating and cooling system normally involves an air-source heat pump.
Keep asking questions, we'll walk you through the process.