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Sun, wind, waves, rivers, tides and the heat from radioactive decay in the earth's core as well as biomass are all abundant and ongoing, hence the term "renewables". Only one, the power of falling water in rivers, has been significantly tapped for electricity so far. Solar energy's main human application has been in agriculture and forestry, via photosynthesis, and increasingly it is harnessed for heat. Biomass (eg sugar cane residue) is burned where it can be utilised. The others are little used today. Turning to the use of renewable energy sources for electricity, there are immediate challenges in actually harnessing them. Apart from photovoltaic (PV) systems, the question is how to make them turn dynamos to generate the electricity. If it is heat which is harnessed, this is via a steam generating system. |
