Understanding How Photovoltaics Work

 More and more we’re looking to photovoltaics (PV) and renewable energy to supply our future energy needs. Some science behind PVs is well over a century old—Albert Einstein’s 1905 explanation of the photoelectric effect won the Nobel prize in physics in 1921.

PVs absorb sunlight and convert it into electricity through a nonmechanical process. The PV cell’s materials are able to absorb photons from at least part of the sun’s electromagnetic radiation. Traditionally, PVs have used treated silicon as a semiconductor in both the n-type and p-type layers of PV cell, which allow for the flow of electrons.

Newer technologies like thin-film PV, nanophotovoltaics and organic PV have greatly reduced or in some cases eliminated the use of silicon in PVs. Thin-films use micron-thin layers of copper indium gallium deselenide (CIGS) or cadmium telluride (CdTe) to perform the functions of n-type and p-type layers.

Sunlight emits energy as photons. The photons have varying energy capacities at different wavelengths of sunlight (which include the visible spectrum). The PV cell is designed to absorb photons of certain wavelengths, while others are rejected or pass through the panel. Atoms in the PV cell’s n-type layer absorb photons emitted by the sun, and in the process, the atoms shed excess electrons. The PV cell itself is designed specifically to allow for the free movement of these electrons.

As the dislodged electrons move from their former position, subatomic holes in the p-type layer attract the free-roaming electrons. The electrons from the bottom of the cell move toward its surface to fill the holes. The movement of these electrons creates the potential for a small voltage or electricity discharge. When the bottom and top layer of the PV cell are connected to negative and positive electrodes, the voltage becomes an electrical current and can be collected for use in homes and appliances.

Since each PV cell is small—most are no more than 8 inches wide. They produce small amounts of electricity, usually about 1 to 3 watts. PV modules band together numerous cells to increase the wattage of each panel. The modules are connected together into a PV array, sized to meet the needs of the end-user. The array produces a stream of direct-current (DC) electricity that is converted into AC electricity for transmission or direct use.

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