Solar cell is a small unit of material that can produce photovoltaic effect, in which process energy of light (energy of photons) converts into electrical current. This is called Solar Power. Today most solar cells are in fact large area semiconductor diodes. In the future, other materials, such as ceramics and organic compounds, may be engineered into solar cells.
At p-n junction, an electric field is built up which leads to the separation of the charge carriers (electrons and holes). At incidence of photon stream onto semiconductor material the electrons are released, if the energy of photons is sufficient. Contact to a solar cell is realised due to metal contacts. If the circuit is closed, meaning an electrical load is connected, then direct current flows. The energy of photons comes in "packages" which are called quants. The energy of each quantum depends on the wavelength of the visible light or electromagnetic waves. The electrons are released, however, the electric current flows only if the energy of each quantum is greater than WL - WV (boundaries of valence and conductive bands). The relation between frequency and incident photon energy is as follows:
W = h * v
Where h is Planck constant (6.626ยท10-34 Ws2), v is the frequency (Hz).
Major types of solar cell
| Solar cell type
| Efficiency
| Lifetime
| Price
| Power/Area
|
| Monocrystalline | 10 - 13% | 25 years, 90% rated power; 30 years, 80% rated power; typical | high | high
|
| Polycrystalline | 9 - 13% | 10 years, 90% rated power; 25 years, 80% rated power; typical | moderate | moderate
|
| Amorphous | 6 - 8% | 10 years | low | low
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Solar efficiency
Lab solar cells have the efficiency of up to 20 %, and classically produced solar cells up to 15 %.
Photovoltaic modules
A photovoltaic module is the basic element of each photovoltaic array. It consists of many jointly connected solar cells.
