Hydropower, Geothermal, and Ocean Energy
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dropower, Geothermal, Title Title and Ocean Energy Ralph E.H. Author’s Name Sims(Affiliation) (Massey University, New Zealand, and and Author’s Name International (Affiliation) Energy Agency, France) Abstract Some forms of renewable energy have long contributed to electricity generation, whereas others Abcd... are just emerging. For example, large-scale hydropower is a mature technology generating about 16% of global electricity, and many smaller scale systems are also being installed worldwide. Future opportunities to improve the technology are limited but include upgrading of existing plants to gain greater performance efficiencies and reduced maintenance. Geothermal energy, widely used for power generation and direct heat applications, is also mature, but new technologies could improve plant designs, extend their lifetimes, and improve reliability. By contrast, ocean energy is an emerging renewable energy technology. Design, development, and testing of a myriad of devices remain mainly in the research and development stage, with many opportunities for materials science to improve design and performance, reduce costly maintenance procedures, and extend plant operating lifetimes under the harsh marine environment.
Scope
Renewable energy accounted for over 15% of the world’s primary energy supply in 2004 (Table I1), although about half of this amount came from traditional biomass used for cooking and heating for over two billion people in developing countries. Large hydropower generated 16% of total global electricity, similar to the percentage generated from nuclear power. (Proportions of electricity production were calculated from the energy content of the electricity generated rather than from the installed capacity of the power stations.) Other “new” renewables, mainly wind, geothermal, and biomass, produced just 2.5%.2 Together with solar thermal systems, biomass and geothermal also provided a significant proportion of the total heat demand, although statistical data are difficult to access and therefore uncertain. The business-as-usual scenario of continued growing energy demand from the World Energy Outlook 2006 of the International Energy Agency (IEA) predicted that renewable energy technologies (RETs) will have declined to a 13.7% share of global primary energy by 2030 because of a greater proportion of demand growth projected to be met by fossil fuels.2 Even under the Alternative Policy scenario of the IEA report, RETs will not increase their market share greatly during the coming decades without continued and sustained policy intervention. Other articles in this issue have discussed in detail renewable resources including solar (see the works by Ginley, Green, and Collins; Mehos; Tritt, Böttner, and Chen; Soboyejo and Taylor; and Palucka), wind (Hayman, Wedel-Heinen, and Brøndsted), and biomass (Farrell and Gopal; Wyman; and Gust, Moore, Moore, Vermaas, and Kramer). This article concentrates on several others, including large-scale hydropower and geothermal first-generation mature technologies; second-ge
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