Solar Energy

What is Solar Energy ?

Solar energy is produced in the sun. This radiant energy is transmitted through photons to the earth. About 10^18 KWh of this energy hits the earth every year. This is more energy in one hour than all people in the world use in one year. The photons include small packages of solar energy. This energy can be used in several ways. The first way is to produce heat and transform it to electricity (called solar thermal power stations). The second way is to convert the sunlight into electricity. This technology is called photovoltaics. Our report only describes the possibility to produce electricity through photovoltaic cells called solar cells.

About photoelectric effects and photovoltaics

The word photovoltaics comes from the Greek "Photos" meaning light and the last name of Allesandro Volta who was an early researcher in electricity. Experiments in 1890 showed that the photoelectric effect couldn't be explained by the physical theories of that century. These old theories were based on the idea that all electromagnetic radiation and light have the same behaviour as waves. In 1905 after Albert Einstein developed the quantum theory these experiments could be explained. Albert Einstein suggested that light could be considered to behave like particles in some instances, and that the energy of each light particle, or photon, depends only on the wavelength of the light. To explain the external photoelectric effect, he envisiged light as a collection of projectiles hitting the metal. A free electron in the metal that is struck by a photon absorbs the photon's energy. If the photon is sufficiently energetic, the electron is dislodged from the material. Einstein's theory explained many features of the external photoelectric effect, including why the maximum energy of electrons ejected from a metal is independent of the intensity of the incident light. According to this theory, the maximum energy of a dislodged electron depends only on the energy with which a photon strikes the electron; the photon's energy, however, has nothing to do with the light intensity, because intensity only measures the number of photons striking the metal. The photon's energy, and thus the maximum possible energy of a dislodged electron, depends only on the light's frequency. Einstein's theory was later verified through further experimentation. His explanation of the photoelectric effect, with its demonstration that electromagnetic radiation can behave like a collection of particles in some situations, contributed to the development ofquantum theory. [1]

Photovoltaics is one process of the photoelectric effect; it's the possibility to transfer the radiation energy in electricity. (Other processes of the photoelectric effect are photoionization (the ionization of gas) and photoconduction (electrons conduct electricity).

next page: the history of solar energy