The Science Behind Solar Panels, Part 1

A photoelectric (or photovoltaic) solar cell works as follows: Photons strike the solar cell and are converted into electricity. The material inside a solar cell is silicon or some other semiconductor material. When the light strikes the surface of the solar cell, the photons in the light excite electrons in the silicon. (A ray of light contains countless photons, tiny quanta of light that have no mass.) When the photons excite the electrons in the silicon, an electric current is produced, and this current can be used for household uses or stored.

The silicon in the solar cell is produced in a manner that maximizes its conductive capacity. Two silicon wafers are placed next to each other, separated by a junction. One of the silicon layers or wafers is "doped" with negative material; the other layer is doped with positive material. Such a design facilitates the creation of current.

Moore's Law means that the size of semiconductors will continue to decrease in coming years.

Hobbyists on the World Wide Web have built solar cells at home, and these are useful for understanding the basic physics at play. A basic solar cell is simple: It uses a thin sheet of copper, a bottle of water, salt, and a heat source to cook the copper. After the copper is cooked, it is scrubbed and halved. The top of the water bottle is cut off, salt mixed into the water, and the two pieces of copper are placed on opposite sides of the bottle. A multimeter can be attached by alligator clips to each of the halves of copper to observe the electrical current.

In this simple solar cell, light strikes the modified copper. Some of the photons that strike the first piece of copper excite electrons, and the electrons jump through the salted water to the other side, reaching the second piece of copper. The multimeter shows the electrical current that is flowing from one piece of copper to the other.

Generally, a digital multimeter is better than an analog multimeter because the former is electronic and has fewer moving parts. Analog meters have a moving needle like a speedometer, and therefore they tend not to last as long as a digital multimeter.

Recent breakthroughs that promise to improve the output of solar cells will be explained in the next of this series.