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Unit 8 Power Engineering 1. Read, translate and give the summary of the text ―Renewable Energy‖. Renewable Energy To put our energy use in context it is interesting to realize that the energy incident on the Earth from the Sun amounts to about 180 thousand million million watts (or 180 00 0 terawatts, 1 TW = 10¹² W). This is about 14
000 times the world‟s average energy use of about 13 million million watts (13 TW). As much energy arrives at the Earth from the Sun in forty minutes as we use in a whole year. So, providing we can harness it satisfactorily and economically, there is plenty of renewable energy coming in from the Sun to provide for all the demands human society can conceivably make. There are many ways in which solar energy is converted into forms that we can use; it is interesting to look at the efficiencies of these conversions. If the solar energy is concentrated, by mirrors for instance, almost all of it can be made available as heat energy. Between one and 63
two percent of solar energy is converted through atmospheric circulation into wind energy, which although concentrated in windy places is still distributed through the whole atmosphere. About twenty per cent of solar energy is used in evaporating water from the Earth‟s surface which eventually falls as precipitation, giving the possibility of hydropower. Living material turns sunlight into energy through photosynthesis with an efficiency of around one per cent for the best crops. Finally, photovoltaic (PV) cells convert sunlight into electricity with an efficiency that for the best modern cells can be over twenty per cent. Around the year 1900, very early in the production of commercial electricity, water power was an obvious source and from the beginning made an important contribution. Hydroelectric schemes now supply about six per cent of the world‟s commercial energy. Other renewable sources of commercial energy, however, have been dependent on recent technology for their implementation. In 1990, only about two percent of the world‟s commercial energy came from renewable sources other than large hydro (these are often collectively known as „new renewables‟). Of this two per cent (Table 11.5), about three- quarters was from „modern‟ biomass (called „modern‟ when it contributes to commercial energy to distinguish it from traditional biomass), the other 0.5% being shared between solar, wind energy, geothermal and small hydro sources. Returning to commercial energy generation, in order to put renewable sources into context, it is useful to inspect the detailed projection of the WE C (Table 11.5) for the contributions from different „new renewable‟ sources which make up the twelve per cent of total energy supply in the year 2020 assumed for the WEC scenario C. The main growth expected is in energy from „modern‟ biomass and from solar and wind energy sources. Table 11.6 provides detailed summary information about the status and cost of different renewable energy sources.
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In the following paragraphs, the main renewable sources are described in turn and their possibilities for growth considered. Most of them are employed for the production of electricity through mechanical means (for hydro and wind power), through heat engines (for biomass and solar thermal) and through direct conversion from sunlight (solar PV). In the case of biomass, liquid or gaseous fuels can also be produced.
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