By now, photovoltaic (PV) panels are familiar to most Americans. You’ve seen them on your hand-held calculator, on top of illuminated highway signs, and maybe even on your neighbors’ roofs. With PV systems becoming more common, perhaps you’ve been dreaming of making some homemade electricity. The dream is achievable, as long as you own a sunny patch of lawn or an unshaded south-facing rooftop, and as long as you have a bank balance of several thousand dollars.
A PV array is made up of rectangular modules (or panels) that measure between 2 and 5 feet on a side. The most common type of PV module has an aluminum frame and a glass cover protecting a collection polycrystalline PV cells. When exposed to light, each PV cell produces 0.5 volt DC — so if you add up the number of cells and divide by 2, you know the voltage of the module. The best performing commercially available PV cells are roughly 20% efficient at converting solar energy into electricity.
Unlike polycrystalline PV cells, thin-film (amorphous) PV products are manufactured on a flexible sheet. These thin-film PV products have many applications; for example, they are used to make PV roof shingles and peel-and-stick membranes designed for use on metal roofing. Thin-film PV products have relatively low efficiencies — usually in the range of 10% to 12% — so they require almost twice the area required for a polycrystalline PV array with the same electrical output.
Both polycrystalline and thin-film PV arrays produce DC power. This DC electricity can be used directly to charge a battery; in most homes, however, the solar electricity is sent to an inverter that converts the DC power to AC. The inverter’s AC output can then be used directly by the homeowners or fed into the power grid.
Most grid-connected PV systems won’t provide any…