Characteristics of Solar Energy and its Chemical Conversion

Solar spectrum on the earth ranges from 250 to 2400 nm, having its maximum at 500 nm. The energy abundant ultraviolet region below 400 nm contributes only 5 % the visible region between 400 and 800 nm occupies about half the spectrum. The conversion of this visible irradiation is therefore important. 

The total energy reaching the earth amounts to 3 x 1024 J/year, which is about ten thousand times as much as the energy consumption of the mankind. For a conversion system of 10% efficiency, 1/50 area of the desert is enough to satisfy all the energy requirements. 

The conversion of the solar irradiation into electricity by solar cells seems to be the nearest goal in the present stage of research. However, considering that storage is 

For a fuel, an electron source is needed. Water is the ultimate electron source from an economical point of view. Water photolysis is the simplest among the chemical conversion systems of solar energy. Photochemical reduction of nitrogen or carbon dioxide to produce ammonia or hydrocarbons with the electrons from water is also an attractive system of conversion. 

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