Solar energy: photovoltaic electricity generation

The Sun, the largest obiect in the Solar System, is positioned some 150 million kilometres from the Earth's surface and generates its electricity through fusion reactions, converting its hydrogen into both helium and emitted energy. The solar radiation is emitted at a temperature of about 6,000K and a power density of 63.1MW per metre squared from its surface. This is attenuated and dispersed significantly, until it is received by the Earth's atmosphere at approximately 1,300W per metre squared. The amount of energy received from the Sun in just one hour is actually more than the world consumes in an entire year. Figure 4.1 shows the global solar radiation distribution. The light received is an entire spec-trum of wavelengths, ranging from 300 nanometres (ultraviolet region) to about 2 micrometres (infrared region). The peak of the spectrum is in
the visible region (McDaniels, 1979).Nature has derived energy from the Sun for millions of years, mainly through the process of photosynthesis. Other forms of renewable energy are also dependent on the Sun - for example, hydroelectricity and wind and wave power. The generation of electricity from solar energy has come into fruition only since the 1950s. Today there are a multitude of applications, broadly categorised into two types: in remote areas (off-grid), or in supplying grid electricity (on-grid). To convert solar energy into electricity, a solar cell is required. A solar cell can be simply under-stood as a battery whereby the charge at the two electrodes is maintained by the absorption of light, rather than through chemical reactions in the electrolyte of the battery.