Monday, July 21, 2008

Solar heating in the home

Wendy Bounds has a story in the Journal about her efforts to heat her home through solar power (free WSJ Digg link). The story isn't about using photovoltaics to generate electricity for heating, but rather using a solar-thermal system.

Nationally, an average-size, 4.5 kilowatt residential photovoltaic system costs $40,000 to $50,000, before any tax credits or rebates, according to the Solar Energy Industries Association. The lowest estimate I got was about $17,500 after rebates and credits, with an estimated payback period of 15 years. (A kilowatt-hour equals the energy needed to run a 100-watt bulb for 10 hours.)

But for a smaller investment, sun can be used to heat water for showers, laundry and dishwashing. At $2,000 to $8,000, these solar-thermal systems typically pay for themselves in under a decade. With extra equipment, they also can help heat homes.
The story is full of good links to find local installers and information on tax breaks the feds and states give for solar.

I did a search and found a science fair project that refers to the most efficient photovoltaic cells having 15% efficiency, and the most efficient Stirling engines having 30% efficiency. I found another site that states solar-thermal is 5 times more efficient than photovoltaics at heating water. Solar-thermal is a cheaper, more efficient option for heating water and a home, but won't necessarily provide electric power (unless you want to set up your own solar-thermal electric plant in your backyard.