Photovoltaic roofing shingles
manufactured by United Solar
look like conventional roofing
but provide electricity at the
rate of 17 watts each. Photo by
Stellar Sun Shop, courtesy of
National Renewable Energy
Laboratory

Solar Electricity Generation

The process of converting light to electricity is called the photovoltaic effect. It's like a tree leaf absorbing solar energy for photosynthesis. Here's how it works:

Sunlight is absorbed by a cell that allows electrons to separate from their atoms and flow to produce electricity. Solar cells are grouped together in flat plates called modules, and several modules connected together are called an array. Several such arrays produce enough electricity for a household. Thin-film solar panels are even made to look like shingles so they blend in with traditional roofing.

Some states have net metering, which simply means you get a credit back from your utility for the power you produce that exceeds what you use. This applies to a home system that produces more power than it needs during the day and sends it back to the electric grid. At night, the house draws power from the grid.

Turning sunlight directly into electricity with photovoltaic cells is becoming more efficient, which means fewer cells are needed to produce the same amount of power. This improvement in efficiency is bringing down the cost. According to the DOE's National Renewable Energy Laboratory, the installed cost of a 2-kilowattt system that will offset the needs of a very energy-efficient house will be from $16,000 to $20,000. If electricity for such a home costs $100 per month, the system would pay for itself in about 15 years (or fewer if your utility offers net metering).

Green Building and Remodeling Materials