Photovoltaic Energy Systems
“Solar electricity” is another name for photovoltaic energy. The word combines the Greek word for light, “photo,” with “voltaic” from the name of the physicist Allesandro Volta, from whose name we also get the word “voltage.” So photovoltaic means electricity from light.
A photovoltaic (PV) module, or solar panel, is a device that produces electrical energy when exposed to sunlight. Most PV modules are made up of crystalline silicon cells that are linked together in a series, like a string of Christmas tree lights. When sunlight strikes a photovoltaic module, ‘free electrons’ in each silicon cell become excited, creating a flow of electrons through the conductors linking each cell. This flow of energy is electricity; to be specific, direct current (DC) electricity.
A photovoltaic module is solid state: there are no moving parts (excluding electrons). The life expectancy of a PV is predicted to be over 30 years, and it could be much longer. There is nothing exhausted in the silicon cells, and theoretically, if they stay well packaged and protected from moisture they could go on producing electricity indefinitely.
PV modules are used in two basic ways:
- they can directly power appliances like water pumps, fans directly or invertered to alternating current and backfed into the grid.
- they can charge storage batteries, which then keep the energy stored for use as needed.