Giải Sách bài tập Tiếng Anh 7 trang 54 Unit 8 - Reading

Alternative energy sources

A. Alternative energy sources are usually less polluting because they are not the result of burning of fossil fuels. Some popular alternative energy sources are hydroelectric power, solar power and wind power. Other sources are biomass energy, geothermal energy and energy sources from oceans.

B. Biomass is from organic matter. Biomass fuels include wood, forest, animal waste, grains, agricultural crops and aquatic plants. With more use of biomass at lower production costs and better technology, the United States could generate as much as four-and-a-half times more biopower by 2020.

C. Geothermal energy uses heat from within the earth. They drill wells into geothermal reservoirs to bring the hot water or steam to the surface. The steam then drives a turbine-generator to generate electricity in geothermal plants. In some places, this heat directly heats homes and greenhouses or to provide process heat for businesses or industries. Reykjavik, the capital of Iceland, has the heating system using geothermal energy.

D. Oceans cover more than 70% of the earth. They contain both thermal energy from the sun's heat and mechanical energy from the tides and waves. Ocean thermal energy conversion (OTEC) converts solar radiation to electric power. The power of tides can also produce electricity. Wave energy conversion extracts energy from surface waves, From pressure fluctuations below the water surface, or rom the full-wave.