How it Works

You’ve probably seen calculators that have solar cells — calculators that never need batteries, and often don’t even have an off button. As long as there is enough light, they seem to work forever. You may have also seen solar cell arrays on satellites, where they are used to power the electrical systems.

The solar cells that you see on calculators and satellites are solar photovoltaic cells or modules (a group of cells electrically connected and packaged in one frame). As the word suggests (photo = light, voltaic = energy), photovoltaic units convert sunlight directly into solar electricity.

Solar photovoltaic (PV) cells are made of semi-conductor materials such as silicon, which is currently the most commonly used material. When the silicon absorbs light, it releases electrons. PV cells all have one or more electric fields that force these freed electrons to flow in a certain direction. This stream of electrons is a current, and by placing metal contacts on the top and bottom of a PV cell, we can draw that current off for external applications.

Solar cells alone cannot produce usable power. They need to be interconnected with other system components that ultimately conduct a specific electrical demand, or “load.”

Solar photovoltaic systems can either be independent or grid-connected. With grid-connected systems, the PV system produces power in parallel with the electrical utility. It can feed power back into the utility grid if the onsite load does not use all of the PV system’s output, this is called Net Metering.

When the sun is shining, the direct current (DC) electricity from the PV modules is converted to alternating current (AC) through an electronic inverter, and then fed directly into the site power distribution system where it supplies electric power. Any excess solar electricity is exported to the utility power grid and any shortfall is made up with electricity supplied by the grid. When sunlight is unavailable, the site is supplied by utility power alone.