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Unit 10: Energy Challenges // Section 11: Direct Solar Energy

Direct solar power systems typically generate electricity in one of two ways. Photovoltaic (PV) cells, the type commonly seen on homes and commercial buildings, use semiconducting materials such as silicon to produce electricity from sunlight: when light hits the cells, the material produces free electrons that migrate across the cell, creating an electric current. Alternatively, large-scale solar concentrating systems focus sunlight with mirrors to heat a liquid that boils water, creating steam to turn a turbine. Solar energy can also be used for residential water heating (replacing fossil fuels or electricity) by circulating household water or a heat-carrying fluid through roof-mounted solar collection systems.

Concentrating solar power is best suited for power plants in areas with strong sunlight and clear skies, like the southwestern United States, while PV and solar hot water systems can be used in a wide range of climates and latitudes. PV cells are used widely as power supplies in electronic consumer goods such as hand-held calculators. However, because PV technologies for consumer applications have a maximum efficiency of about 15 percent, large expanses of PV cells are required to generate significant amounts of electricity. It would take more than 25 square kilometers of standard photovoltaic cells to generate the same amount of electric power as a large coal-fired power plant.

Residential PV systems are now available at major home-supply stores in several states that offer financial incentives to promote home solar power, including California and New Jersey. Some developers are integrating them into energy-saving home designs (Fig. 19). Making solar energy cost-competitive on a large scale will require further gains in efficiency and reductions in the cost of manufacturing PV cells.

Solar-powered housing complex, Watsonville, California

Figure 19. Solar-powered housing complex, Watsonville, California
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Source: © Dan Coyro.

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