Is Solar Viable For Our New House?

Q: We are in the process of designing a new house in Mendocino county (CA). I am trying to get an idea of how far I can (and should) go with alternative power. We currently live in the Bay Area and our electric bill last month showed 1000 kwh. This included an electrically heated hot tub (new), 2 refrigerators (one pretty old), but no electric heat. If I subtract the hot tub and extra refrigerator I would guess it would bring our electric usage down to 600 kwh / month(?). What is a reasonable usage for a fully solar electric house? I an trying to get an idea of how much our lifestyle would change vs. how much we would have to spend on a solar system. Any guidelines? Most of the stuff I have read is way too detailed and starts with having to go around and measure the usage of every appliance.

A: I'm in a similar situation but a little farther ahead. Our new house is nearly completed. I have engineered this PV system to death and am ready to start procurement. I decided to make the house all-electric and size the PV array to handle the entire load (7.5 kw array). Some might criticize this but at my age I can be idealistic. Your 600 kwh per month usage would need nearly 400 square feet of PV panels, provided you have an unobstructed view to the south. Would you be limited to roof space, or have you room for an array on the ground? Here's a suggestion: Consider using a ground-source (geothermal) heat pump for both heating and air conditioning. They are a slightly different form-factor than the usual split gas-electric units, but you can easily design to accommodate either. With the price escalation of natural gas and propane, it's to the point where you will save money with this form of electric heat. In our case, with propane the only available fuel, I was motivated to expand the PV array to accommodate the heat pump. For example: If you install a 90+% efficient condensing natural gas or propane furnace, and if your fuel cost is $2.10 per gallon for propane or $2.33 per 100 cubic feet for natural gas, even a mediocre geothermal heat pump will produce equal heat at equal cost with electricity at 26 cents per kwh. At the moment, with the electric rate cap in effect, the heat pump will really save you money. And if, I mean when, electric rates get higher, the payback using PV power for the heat pump becomes comfortable. I'm sure you must be aware of the California Energy Commission's Buydown program. It really makes PV power a viable thing to consider. If you wrap the cost of the PV system into your mortgage and consider you get a small additional tax deduction for it's share of the interest, you can probably show that the increment in your monthly mortgage payment is less than your avoided cost for PG&E power. Oh, one more suggestion: Consider using solar heat collectors for your domestic hot water. The best collectors available at the moment are the Nippon Electric Glass evacuated tube models. You can also get DHW heat from the geothermal heat pump, but not quite for free. I hope this helps get you started. Feel free to contact me if I can be of more help.

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