Harnessing the power of the wind is one of the most promising alternative methods of electricity generation as it has the potential to generate substantial amounts of energy without pollution. Wind can also be used to drive water pumps in order to store energy, to charge batteries in remote regions, or as off-grid power sources. The potential for wind power has been recognized and wind farms have been installed in at least 15 countries including Brazil, China, Denmark, Spain, USA, India and the UK (Herbert et al., 2007).

Geothermal

The centre of the Earth is very hot at about 4000°C, and most of the heat which reaches the surface cannot be utilized, but in areas of volcanic activity high-grade heat is retained in molten or hot rocks at a depth of 2-10 km. The heat from these hot or molten rocks can be extracted from hot springs and used to run steam turbines directly for the generation of electricity. If the water is below 150°C, it can be used as a supply of hot water for industrial or domestic heating.

Solar energy

Sunlight can be used either directly or indirectly for solar panels for hot water gener­ation, solar collectors for steam generation, solar architecture for heating buildings, solar thermal-electric, and steam linked to electricity generation, photovoltaic, direct generation of electricity and solar hydrogen generation. A recent review of photo — voltaics was published in 2007 (Jager-Waldau, 2007).