There are several kinds of solar collection technologies on the market today, but the primary one that catches homeowners’ attention is photovoltaic (PV). Most industrial or commercial solar energy power plants use reflective mirrors to focus the rays of the sun to super-heat fluids that in turn heat water to make steam for traditional steam-powered turbines. PV cells are different because they directly convert energy from the sun into electricity without needing a generator or any moving mechanical parts.
The process of capturing solar energy through photovoltaic cells was discovered in the 1950s. By the late 1960s, the technology was being used in the U.S. space program to power electronic equipment on satellites in orbit. Although there are many new styles of PV cells being developed, two distinct kinds are appropriate for home use:
Crystalline Silicon Solar Cells
Silicon is the second most common material on Earth and is abundantly found in sand. Manufactured silicon crystals are sliced to about 300 micrometers (a micrometer is 1/1,000,000 meter) thick and coated to work as a semiconductor to capture the sun’s energy. Solar radiation (sunshine) lands on a PV cell, and, as the energy is absorbed, electrons are freed and channeled off. The flow of electrons is basic electricity. Silicon PV cells remain the dominant style of PV cell on the market but require more materials and labor to produce than polycrystalline PV cells.
“Thin-film” (Polycrystalline) PV Cells
Thin-film PV cells use either an alternative to silicon as a semiconductor or amorphous silicon. Thin-film PV cells have the advantage that the modules can be relatively flexible or bendable, mass produced, and engineered to directly cover building materials such as shingles and siding. Though thin-film PV cells generate less electricity than the standard crystalline silicon cells, they can operate more efficiently in low light and cloudy conditions.
PV Cell Output
Regardless of the type of PV cell, the amount of electrical output is measured in watts. Each PV cell may be as small as 3 inches square and generate only a few watts of electricity. In order to gather a useful amount of power, cells are linked together to create modules that are the recognizable “solar panels.” A series of modules linked together is called an “array.” An array could have two or a thousand modules, depending on how much electricity is trying to be created.
The PV cells create direct current (DC) electricity, which needs to be converted to alternating current (AC) for use within the home. Conversion occurs when the current is drawn through an inverter. Think of the inverter as the alternator in your car, which takes energy from the generator and converts it into usable electricity.
Solar Panel Electricity Storage
Storing the electricity generated by a PV array is done by running the current into a bank of batteries. Except in the most extreme and remote areas, though, this approach is neither practical nor cost effective for the average homeowner. The size of the array required is often larger than the home can accommodate, so back-up generators are almost always required to maintain an even flow of electricity during dark winter months.