Solar cells are solid-state electronic devices that convert light into electricity. However, they do not respond to all forms of light; solar cells pick up energy from most colors in the visible light spectrum as well as some kinds of infrared light. In addition, solar cells require a certain level of brightness in order to produce useful amounts of electricity.
Anatomy of a Solar Cell
A solar cell is a two-layer sandwich of silicon; one layer contains traces of elements such as arsenic to give the material a negative electric charge, the second layer is laced with other elements that give a positive charge. Electrically, the two sides act like the terminals of a battery; when connected to a circuit, an electric current flows from the positive side, through the circuit components and to the solar cell’s negative side.
Brightness or luminosity is the amount of light that shines on a solar cell. In total darkness, a cell produces no electricity. As the amount of light increases, so does the cell’s current. At a certain level of brightness, however, the cell’s output reaches a maximum; beyond this point, more brightness gives you no additional current. A solar cell’s specifications include a nominal voltage and current rating which is the cell’s output under the light equivalent of direct bright sunshine.
Visible light is part of the electromagnetic spectrum, a form of energy that also includes radio waves, ultraviolet and X-rays. The colors of the rainbow contained in visible light have different wavelengths; the wavelength of the color red, for example, is about 600 nanometers. Solar cells respond to many of the same wavelengths detected by the human eye, although some differences exist. Solar cells can also use some types of infrared light, but not the longer wavelengths of infrared; these simply pass through the cell.
Sunlight or Artificial Light
Solar cells generally work well with natural sunlight, as most uses for solar-powered devices are outdoors or in space. Because artificial sources of light such as incandescent and fluorescent bulbs mimic the Sun’s spectrum, solar cells can also work indoors. Other artificial sources such as lasers and neon lamps have very restricted color spectra; solar cells may not work as effectively with their light.