Page 145 - Geosystems An Introduction to Physical Geography 4th Canadian Edition

Chapter 4 atmosphere and Surface Energy Balances 109
(a) Kramer Junction solar-electric generating system in southern California.
▲Figure 4.1.2 Solar thermal and photovoltaic energy production. [(a) and (b) Bobbé Christopherson. (c) Daniel J. Bellyk.]
watts. long troughs of computer-guided curved mirrors concentrate sunlight to create temperatures of 390°C in vacuum- sealed tubes filled with synthetic oil. The heated oil heats water; the heated water produces steam that rotates turbines to generate cost-effective electricity. The facility converts 23% of the sunlight it receives into electricity during peak hours (Figure 4.1.2a), and operation and mainte- nance costs continue to decrease.
Electricity Directly from Sunlight
Photovoltaic (PV) cells were first used to produce electricity in spacecraft in 1958. Today, they are the solar cells in pocket calculators and are also used in rooftop solar panels that provide electricity. When light shines upon a semiconductor mate- rial in these cells, it stimulates a flow of electrons (an electrical current) in the cell.
The efficiency of these cells, often as- sembled in large arrays, has improved to the level that they are cost competitive, and would be more so if government support and subsidies were balanced evenly among all energy sources. The residential installa- tion in Figure 4.1.2b features 46 panels, pro- ducing 9680 W total, at a 21.5% conversion efficiency. This solar array generates enough surplus energy to run the residential electric metres in reverse and supply electricity to the power grid. The Sarnia Solar Project (Figure 4.1.2c), the largest in Canada, pro- duces enough power for 12 000 homes.
(b) A residence with a 9680-W rooftop solar photovoltaic array of 46 panels. Excess electricity is fed to the grid for credits that offset 100% of the home’s electric bill, plus producing surplus electricity for charging an electric vehicle.
in the United
States, the na-
tional Renewable
Energy laboratory
(nREl; www.nrel
.gov/solar_
radiation/facilities
.html) and the national Center for Pho- tovoltaics were established in 1974 to coordinate solar energy research, devel- opment, and testing in partnership with private industry. Testing is ongoing at nREl’s Outdoor Test Facility in Golden, Colorado, where solar cells have been de- veloped that broke the 40%-conversion- efficiency barrier!
Rooftop photovoltaic electrical generation is now cheaper than power line construction to rural sites. PV roof systems provide power to hundreds of thousands of homes in Mexico, indone- sia, Philippines, South africa, india, and norway. (See the “Photovoltaic Home Page” at www.eere.energy.gov/solar/ sunshot/pv.html.)
Obvious drawbacks of both solar heating and solar electric systems are periods of cloudiness and night, which inhibit operations. Research is under way to enhance energy storage and to improve battery technology.
The Promise of Solar Energy
Solar energy is a wise choice for the future. it is economically preferable to further
(c) Sarnia Solar Project in southwestern Ontario.
development of our decreasing fossil-fuel reserves, or further increases in oil imports and tanker and offshore oil-drilling spills, investment in foreign military incursions, or development of nuclear power, espe- cially in a world with security issues.
Whether to pursue the develop- ment of solar energy is more a matter of political choice than a question of technological possibilities. Much of the technology is ready for installation and is cost-effective when all the direct and indirect costs of other energy resources are considered.
On the MasteringGeography website for Chapter 4, you can find several list- ings of URls relating to solar energy ap- plications. Take some time to learn more about these necessary technologies (solar-thermal, solar-electric photovoltaic cells, solar-box cookers, and the like). as we near the climatic limitations of the fossil-fuel era and the depletion of fossil- fuel resources, renewable energy tech- nologies are essential to the fabric of our lives. What kinds of solar technology are available and in use in your area?
glass, building geometry, pollution, and human activity such as industry and transportation. For example, an average car uses 10 litres per 100 km and produces enough heat to melt 4.5 kg of ice per km driven. The removal of vegetation and the increase in human-made materials that retain heat are two of the most significant UHI causes. Urban surfaces (metal, glass, concrete, asphalt) conduct up to three times more energy than wet, sandy soil.
Most major cities also produce a dust dome of air- borne pollution trapped by certain characteristics of air circulation in UHIs: The pollutants collect with a de- crease in wind speed in urban centres; they then rise as the surface heats and remain in the air above the city, af- fecting urban energy budgets. Table 4.1 lists some of the factors that cause UHIs and compares selected climatic elements of rural and urban environments.