Environmental Problems, Their Causes, and Sustainability 1

and availability of cheaper ways to produce electricitysuch as combined-cycle natural gas and wind turbines.How Can We Produce Electricity withSolar Cells? Use Your Roof or Windowsas a Power PlantSolar cells that convert sunlight to electricity can beincorporated into roofing materials or windows, andthe high costs of doing this are expected to fall.Solar energy can be converted directly into electricalenergy by photovoltaic (PV) cells, commonly calledsolar cells (Figure 18-20). A typical solar cell is a transparentwafer containing a semiconductor materialwith a thickness ranging from less than that of a humanhair to a sheet of paper. Sunlight energizes andcauses electrons in the semiconductor to flow, creatingan electrical current. These devices have no movingparts, require little maintenance, produce no pollutionduring operation, and last as long as a conventionalfossil fuel or nuclear power plant.The semiconductor material used in solar cells canbe made into lightweight paper-thin rigid or flexiblesheets and incorporated into traditional-looking roofingmaterials (blue in Figure 18-20). Glass walls andwindows of buildings can also have built-in solar cells.In 2004, energy giant British Petroleum (BP) beganbuilding the world’s largest factory to produce windowsand cladding and roofing materials that will incorporateBP’s power-producing solar cells.Easily expandable banks of solar cells can be usedto provide electricity in developing countries for1.7 billion people in rural villages without electricity.Such banks of cells can also produce electricity at asmall power plant (bottom drawing in Figure 18-21),using combined-cycle natural gas turbines to providebackup power when the sun isnot shining. Another possibilityis to use arraysof solar cells to convertwater to hydrogen gasthat can be distributedSingle Solar CellBoron-enriched SunlightsiliconJunctionCellPhosphorusenrichedsiliconDC electricityto energy users by pipeline, as natural gas is. Withfinancing from the World Bank, India (the world’snumber-one market for solar cells) is installing solarcellsystems in 38,000 villages, and Zimbabwe is bringingsolar electricity to 2,500 villages. By 2004, morethan 1 million homes in the world, most of them in villagesin developing countries (and about 200,000 in theUnited States), were getting some or all of their electricityfrom solar cells mostly because they were longdistances from a power grid.Figure 18-21 lists the advantages and disadvantagesof solar cells. Current costs of producing electricityfrom solar cells are high but are expected to dropbecause of savings from mass production and new designs.Solar cells can also be incorporated into carbonbasedpolymers similar to Teflon that can be applied tosurfaces in thin layers. The first generation of such organicsolar cells that can convert 20–35% of the sun’s energyinto electricity could enter the marketplace withina few years. These solar cells could be printed on asheet of paper, stuck onto your house or car windows,painted on your house, or even incorporated into yourclothing—making you a walking tiny power plant.Some envision incorporating tiny rods of semiconductorswith a thickness of several nanometers (a tinyfraction of the thickness of a hair on your head) inplastic materials. Such nano solar cells can be manufacturedin extremely high volumes at a very low cost.Stay tuned.Currently solar cells supply only about 0.05% ofthe world’s electricity. But with increased governmentand private R & D and greater government tax breaksand other subsidies they could provide over a quarterof the world’s electricity by 2040. If such projections arecorrect, the production, sale, and installation of solarcells could become one of the world’s largest and fastestSolar-Cell RoofFigure 18-20 Solutions:photovoltaic (PV) (solar)cells can provide electricityfor a house or buildingusing new solar-cell roofshingles or PV panel roofsystems that look like ablue metal roof. Arrays ofsuch cells can also produceelectricity for a villageor at a small powerplant.Roof OptionsSolar Cells Panels ofSolar Cells394 CHAPTER 18 Energy Efficiency and Renewable Energy