Sunlight falling on the solar shingles produces direct-current electricity. Under the best conditions of temperature and humidity, each shingle produces 17 watts on a clear afternoon.

Photovoltaic panels have been used on satellites and space stations over the past decades. The roof shingles are their new brothers, manufactured flexible film, rather than hard plates, and made into shingles. Engineers call it "thin-film technology."

The Duvall's run their house's attic fan with energy supplied from a solar panel. Photo by Pam Owen.

In building the garage, the contractor coordinated with a solar engineer, Bryan Walsh of Solar Connexion in Blacksburg, Virginia. The contractor installed the regular shingles to precise measurements, leaving room for the solar section. Later, the engineer fastened the photovoltaic shingles in place atop the black felt that is the successor to the tarpaper of days gone by.

Walsh then ran the electric wires through the roof. Such shingles are manufactured by several companies. The ones he used on roof are Unisolar products and are guaranteed for 20 years.

The small wires are connected along the garage ceiling, and run to an inverter, which turns direct current into alternating current for household use. The wire from the inverter goes to the ordinary circuit-breaker box (at right) before going on to our house.
Using photovoltaic panels to generate some of the electricity the house consumes reduces the need for power delivered from the grid of the local power company—in this case, the Rappahannock Electric Cooperative. Homeowners can install a bank of batteries to store electricity during the day for use at night. However, in this project, we chose to, in effect, use the power grid as our batteries.

"A recent survey conducted by the Davis Energy Group found that 67 percent of recent homebuyers likely would have paid $8,000 more for their new house if it generated 40 percent of its own electricity. Another 26 percent said they would have considered it." —Solar Today www.solartoday.com

The fifty shingles on our garage are rated at 850 watts. That is, with the right temperature and humidity, the garage roof produces that many watts. With greater humidity, production can drop to 60 percent. On a cool, crisp day, the production figure might rise to 130 percent.

What does this cost? Roughly, about $15 per watt for an installation of this (small) size. Ouch! That’s nearly $13,000! Well, yes. But in 17 to 30 years that money will have come back to us. Such large numbers startle and frighten people until one figures the long-term savings in dollars for electric power. Further, as fuel costs rise, electricity prices will rise with them. As those increases bite, the payback time will be reduced considerably.

Photovoltaic power also has many agricultural applications: Drying crops. Heating space and water in livestock barns. Heating greenhouses. Remote applications, such as electric fencing, lighting, and water pumping, where such systems may be much cheaper than installing power lines and step-down transformers.

What will this installation do? At our house, we expect it to reduce the monthly electric bill somewhat. Since we are using the air conditioning a great deal at the same time that the solar shingles are being connected, the change in the bill might not be terribly obvious—but it is there. Were this group of shingles and the expensive inverter installed in a remote cabin, with no grid connection available, it could pump water out of a well, run a few lights, and keep a television and VCR running.

Finally, there is another gain: from the moment these shingles were connected, the air was a little bit cleaner. Not a change you would notice. But there is a tiny bit less pollution around because of this installation. We put up the shingles for the same reason someone drives a Prius: the mileage is good, but making the air cleaner is paramount.