How Do Solar Cells Work?

To understand the operation of a PV cell, we need to consider both the nature of the material and the nature of sunlight. Solar cells consist of two types of material, often the p-type and n-type silicon. Light of certain wavelengths are able to ionise the atoms in the silicon (causing atoms to either gain or lose electrons) and the internal field produced by the junction separates some of the positive charges ("holes") from the negative charges (electrons) within the photovoltaic device. The holes are swept into the positive or p-layer and the electrons are swept into the negative or n-layer. Although these opposite charges are attracted to each other, most of them can only recombine by passing through an external circuit outside the material because of the internal potential energy barrier. Therefore if a circuit is made (see Figure 4), power can be produced from the cells under light because the free electrons pass through the load to recombine with the positive holes.
 

The Photovoltaic Effect in a Solar Cell.

 

The amount of power available from a PV device is determined by;
• the type and area of the material;
• the intensity of the sunlight; and
• the wavelength of the sunlight.

Reliability:

Solar electric systems have been used by the space program since 1954, and the technology itself (the photoelectric effect) was discovered in the 1800's -- consider that:

• Solar electric systems contain no moving parts -- the entire system is solid state electronics in action
• Solar electric systems need very little maintenance -- keep the modules free from dirt by letting the rain (or a hose) keep them clean, and that's about it
• Solar electric modules (the panels that sit exposed to the elements) come with 25 year warranties (try getting that from a car manufacturer!)
• Solar electricity is used:
  
  • In outer space to power satellites
  • In the Arctic to power expeditions
  • On snowy and windy mountain tops to power telecommunications equipment
  • Along roadsides to power emergency phones
  • In jungles and deserts to power water pumps and refrigeration units
  • By power companies themselves to produce electric power that you are using to read this with your computer