How do solar cells generate electricity?

Friday, March 28, 2014

Q. I've read about people using solar cells to generate electricity from sunlight. How do they work?

A. Solar, or "photovoltaic" cells are basically silicon diodes with a transparent electrode. As in an ordinary diode, they have a barrier potential of about 0.6V across the PN junction.

The barrier potential produces an electric field in the region where the P and N materials meet. Light is made of wave-particles of electromagnetic energy called "photons". When photons collide with the electrons in the outer orbits of the doped silicon atoms, they  dislodge electrons. This produces two charges carriers: the electron and the "hole" it leaves behind.

Due to the electric field across the junction, the electron is pulled one way and the hole the other way. The electrons and holes accumulate in the P and N material of teh diode. This creates a voltage between them, and when a load is connected, current will flow through it, driven by the energy of the sunlight.

At the surface around the equator, the earth receives about 1250 watts of energy per square meter in the form of sunlight. Since they are made of silicon, photovoltaic cells are sensitive to only a part of the spectrum around the infrared region.

Theoretically, the maximum possible efficiency of a photovoltaic cell is about 25 to 28 percent. Typically, one cell produces a maximum current of 100mA at about 0.4V. Like chemical cells, they can be connected in series for more voltage and in parallel for more current.

Learn more about Photovoltaic technology through our Photovoltaic Certificate Program.

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