1. Solar energy
Solar radiant intensity we can receive on the ground is usually less than 1 kW/m2, although it varies depending on the latitude, season, angle, and the weather conditions at the given site. The solar constant is defined as the total radiant energy density received vertically from the sun per unit area and unit time, just outside the earth’s atmosphere, when the earth is at its average distance from the sun. Its value is approximately 1,368W/m2, within an accuracy of about 0.2%.
2 Photovoltaic system
A photovoltaic cell can generate electricity based upon the phenomenon that occurs when photons strike electrons. The electrons free themselves from the valence band, leave holes behind them and jump up into the conduction band over the forbidden band. When an incident light is combined with this property in a junction diode, the electrons and holes tend to flow in opposite directions along the potential gradient across the junction, setting up a voltage. With the addition of circuitry, current flows and then electric power become available.
A photovoltaic system is a complete set for photovoltaic power generation, including the array and the balance of system constituents. An array is an interconnected system of photovoltaic modules that consist of plural photovoltaic cells or solar cells. These cells are made of various semiconductor materials including silicon, cadmium sulfide, cadmium telluride, gallium arsenide, Cu(In⋅Ga)Se2 and so on, in single crystalline, polycrystalline, or amorphous forms. A polycrystalline silicon is composed of many multi-oriented individual crystals, and widely used for solar cells, because its fabrication can be easier than that of a single-crystalline type. An amorphous silicon is an alloy of silica and hydrogen with a disordered, non-crystalline internal atomic arrangement. It can be deposited in thin-film layers using a number of deposition methods to produce photovoltaic cells on glass, metal, or plastic substrates.
A Solar Power Satellite system(SPS) is a grand system to supply power from space for use on the earth. A proposed SPS system would have a huge array of solar cells that would generate electric power to be beamed and sent to a central receiver on the earth in the form of microwave energy.
3. Solar thermal energy conversion