Do you have a roaring, monstrous sounding boiler firing your home today? Dread the idea of putting such a monster into your new home — as well as a tank full of toxic, climate-damaging fuel? Well, good news! Your solar-powered home of the future needs no oil or gas at all!
This is all possible thanks to modern heat pumps. Modern cold-climate heat pumps work by using a refrigeration process similar to the way your home’s refrigerator works. Warmth is extracted from the ambient outside air (down to temperatures around -15F) and transferred into your home. Since the heat pump is moving, not creating, heat, it is highly efficient. Powered by solar, a heat pump can heat your home for the equivalent of around $1/gallon for oil!
While it’s possible to keep drafty old homes warm with heat pumps, they are far more effective when used in a tight, well-insulated house, hence us recommending that you build one!
If you build a good quality house, then you can heat primarily with heat pumps, and install a small backup system (say a wood or pellet stove or electric baseboard) to supplement the heat pumps during periods of extreme cold weather.
Since heat pumps are powered by electricity, you can use solar power you bank in the summertime as your fuel source in the winter!
Sizing it Up
We love designing a whole-house heat pump system! Here are some of the considerations that go into it:
- What is the approximate square footage (and volume) of the space? How many rooms? What is the layout?
- What is the approximate insulation level of the home? Is it insulated above code?
- Is there full basement, crawl-space or slab on grade?
Once we have some of these specs, we can start running through formulas calculating stuff like:
- Expected heat needs on an hourly basis in the worst of winter.
- Expected heat needs over the entire winter season.
- Heat output per indoor heat pump unit.
And use those combinations of factors to design a viable system!
The next step, once you have a plan for an all-electric heating system, is to figure out how many solar panels you’ll need to power it.
kWhs and BTUs
Kilowatt-hours (kWhs) and British Thermal Units (BTUs) are both units of energy, with the former tending to be used for electricity and the latter for heating. 1kWh = 3,412 BTUs.
Since we can easily convert between units, we can develop an estimate for how much electrical energy will be required to produce enough heat energy to keep a space comfortable.
Firstly, heat pumps generate 2.5 units of BTU for every 1kWh they consume (a concept called “Coefficient of Performance,” or COP).
That means, 1kWh of electricity = 8,530 BTUs of heat energy.
Each 1kilowatt of solar panels = ~1,200 kWhs of solar electricity each year.
It’ll vary, but an above-code insulated house needs around 15,000 BTUs per square foot, per year. So a 2,000 sq. foot house to this standard, needs 30,000,000 BTUs / 8,530 = 3,516 kWhs annually… Or about the equivalent of 3 kws of solar (9’ish panels).