Photovoltaics (PV) convert sunlight directly into electricity, which then can be used to run your daily life. Let's take a look at how this process works exactly. Photons in sunlight interact with the outermost electrons of an atom. Photons striking the atoms of a semiconducting solar cell free it's electrons, creating an electric current. This electric current will have a strength depending on the amount of energy from the sun that is collected. This energy is then used to run everyday things like the hairdryer.

Solar energy used to take the place of utilities is fairly new but the idea of solar energy has been around for a while. The Photovoltaic effect was first discovered in the 19th century, and was used by Bell Labs in 1954 to develop the first PV solar cell. PV was first used in space, providing electricity to satellites. These early PV cells were produced in small quantities from exotic materials. Early PV cells were inefficient, converting less than 1% of the sunlight into electricity. The cells were then quickly increased to 6% when researchers experimented with crystalline silicon, the principal component of sand. Current conversion efficiencies have surpassed 30% in the laboratory, and 15% in large-scale production. So, now that the PV cells are more efficient, they are also more widely used, including home use for solar utilities.

So, how do these cells work, and how do you know what cell you need to meet your utility needs? Well, PV is measured in units of "peak watts"(Wp). A peak watt figure refers to the power output of the module under "peak sun" conditions, considered to be 1000 Watts per square meter. "Sun hours," or "insolation," refers to how many hours of peak sun, on average, exist in different countries. North America averages 3 to 4 peak sun hours per day in summer while eqatorial regions can reach above 6 peak sunlight hours. So, you want a cell that can best utilize the number of peak sun hours your area has.

With the number of peak sunlight hours that U.S. generally has in a day, a standard small SHS can operate several lights, a black-and-white television, a radio or cassette player, and a small fan. A 35 Wp SHS provides enough power for four hours of lighting from four 7W lamps each evening, as well as several hours of television. "System Size" (20, 35, or 50Wp) determines the number of "light-hours" or "TV-hours" available. So, look at the number of hours of electric use a day and then get the right number of cells to meet that need and then some so that you never run out. The initial cost of solar utilities will be high, but the pay off is worth it.