decade (Thresher et al., 2007). And while the turbine tower is not expected to get much taller, advances will likely occur in installing and maintaining these machines in difficult-to-reach locations. One possibility, for example, is self-erecting towers. In the future, turbine rotors will be made of advanced materials such as fiberglass, and they will have improved structural-aerodynamic designs, sophisticated controls, and higher speeds. By reducing the blade-soiling losses (e.g., through dust or insect buildup) and installing damage-tolerant sensors and robust control systems, reductions in energy loss and improvements in turbine availability can occur. In addition, drive trains will be modified to include fewer gear stages, medium- and low-speed generators, distributed gearbox topologies, permanent-magnet generators, and new circuit configurations. As shown in Table 6.1, these improvements will have significant impacts on annual wind energy production and capital costs over the next decade. It should be noted that future capital costs also will be greatly influenced by global supply and demand for wind turbines. Some of these issues are discussed in the section titled “Deployment Potential” later in this chapter, as well as in the report by the Panel on Electricity from Renewable Resources (NAS-NAE-NRC, 2009).

Along with improvements in onshore wind-turbine designs, offshore wind-turbine technologies will soon be actively enhanced to take advantage of the abundant U.S. offshore wind-energy resources. The technologies associated with offshore wind turbines will face fundamentally different challenges, however, attributable to the difficulties of building and operating turbines in the ocean and installing and maintaining transmission lines underwater.

Solar Photovoltaic Power

When sunlight strikes the surface of a PV cell, some of the light’s photons are absorbed. This causes electrons to be released from the cell, which results in a current flow, namely, electricity. The two main PV technologies entail flat plates, which consist of crystalline silicon deposited on substrates, and concentrators, which typically involve lenses or reflectors that, together with tracking systems, focus the sunlight onto smaller and more efficient cells.

Silicon is used to form semiconductors in PV cells by taking advantage of the conductivity imparted when impurities (“doping” elements) are introduced. Because the efficiency of these crystalline PV modules is only 12–18 percent, further development is required—not only to increase efficiency but also to lower production costs (DOE, 2007a).



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