Page 144 - Geosystems An Introduction to Physical Geography 4th Canadian Edition

108 part I The Energy–atmosphere System
F cus Study 4.1 Sustainable resources
Solar Energy Applications
Consider the following:
• Earth receives 100 000 terawatts (TW) of solar energy per hour, enough to meet world power needs for a year.*
• an average commercial building re- ceives 6 to 10 times more energy from the Sun hitting its exterior than is re- quired to heat the inside.
• Photographs from the early 1900s show solar (flat-plate) water heaters used on rooftops. Today, installed solar water heating is making a come- back, serving 50 million households worldwide.
• Photovoltaic capacity is more than doubling every 2 years. Solar-electric power passed 89 500 megawatts in- stalled in 2012.
not only does insolation warm Earth’s surface, but it also provides an inexhaust- ible supply of energy for humanity. Sunlight is directly and widely available, and solar power installations are decentralized, labour intensive, and renewable. although collected for centuries using various tech- nologies, sunlight remains underutilized.
Rural villages in developing countries could benefit greatly from the simplest, most cost-effective solar application— the solar cooker (Figure 4.1.1). With ac- cess to solar cookers, people in rural latin america and africa are able to cook meals and sanitize their drinking water without walking long distances collect- ing wood for cooking fires. These solar devices are simple yet efficient, reach- ing temperatures between 107°C and 127°C. See solarcookers.org/ for more information.
in developing countries, the pressing need is for decentralized energy sources, appropriate in scale to everyday needs,
*Terawatt (1012 watts) = 1 trillion W; gigawatt (109 watts) = 1 billion W; megawatt (106 watts) = 1 million W; kilowatt (103 watts) = 1000 W.
(a) Women in East Africa carry home solar- box cookers that they made at a workshop. Construction is easy, using cardboard components.
(b) Kenyan women in training to use solar- panel cookers.
▲Figure 4.1.1 The solar cooking solution. [Bobbé Christopherson.]
such as cooking, heat- ing and boiling water, and pasteurizing other liquids and food. net per capita (per person) cost for solar cook-
ers is far less than for centralized electrical production, regardless of fuel source.
(c) These simple cookers collect insolation through transparent glass or plastic and trap longwave radiation in an enclosing box or cooking bag.
Collecting Solar Energy
any surface that receives light from the Sun is a solar collector. But the diffuse nature
of solar energy received at the surface requires that it be collected, concentrated, transformed, and stored to be most useful. Space heating (heating of building interiors) is a simple application of solar energy. it can be accomplished by careful design and placement of windows so that sunlight will shine into a building and be absorbed and converted into sensible heat—an everyday application of the greenhouse effect.
a passive solar system captures heat energy and stores it in a “thermal mass,” such as a water-filled tank, adobe, tile, or concrete. an active solar system heats
water or air in a collector and then pumps it through a plumbing system to a tank, where it can provide hot water for direct use or for space heating.
Solar energy systems can generate heat energy on an appropriate scale for approximately half the present domestic applications in the United States, includ- ing space heating and water heating. in marginal climates, solar-assisted water and space heating is feasible as a backup; even in new England and the northern Plains states, solar collection systems prove effective.
kramer Junction, California, in the Mojave Desert near Barstow, California, has the world’s largest operating solar- electric generating system, with a capacity of 150 MW (megawatts), or 150 million
move moisture into the air. In New York City, daytime temperatures average 5–10 C° cooler in Central Park than in the greater metropolitan area.
Ongoing studies show that UHI effects are greater in bigger cities than smaller ones. The difference between urban and rural heating is more pronounced in cities sur- rounded by forest rather than by dry, sparsely vegetated
environments. UHI effects also tend to be highest in cit- ies with dense population, and slightly lower in cities with more urban sprawl. Go to www.nasa.gov/topics/earth/ features/heat-island-sprawl.html for an interesting study on UHIs in the U.S. Northeast.
In the average city in North America, heating is increased by modified urban surfaces such as asphalt and