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An enormous amount of solar energy is available and it has been used for centuries.76 Because of the history and great availability, harvesting solar energy has again attracted much attention. 77 The contiguous 48 states have a total area of 8,018,880 square kilometers (8.019xl016 cm2). As described earlier, the sun provides 8.38 Joules/cm2/min. There are 525,600 minutes per year. On the average, the sun shines V2 the time. Thus, the 48 states receive 1.766x 1023 Joules per year. From the Table 2.1 the 1999 United States energy use is 1.019 x 1020 Joules per year; thus, the sun provides 1,733 times more energy than we use in the United States.

Calculations indicate that if we can harvest solar energy at 5% efficiency then 1.12% of the area of United States could provide all the energy we need. At first glance, 1.12% does not sound like a large area. Expressing this area in other ways provides a feel for the immense scale of the collectors needed if we are to supply all our energy needs from sunlight. This 1.12% of the United States is 89,811 square kilometers, or nearly the area of the state of Indiana, at 92,902 square kilometers. Of course, sun does not shine all the time in Indiana; it is cloudy some of the time. The 89,000 square kilometers must be located where the sun shines a good portion of the time. This means the collection sites must be located in New Mexico, Arizona and southern California.

Dedicating 89,000 square kilometers to the production of energy might be a good investment if practical solar energy conversion techniques can be developed. However, even with practical systems to harvest the solar energy, remember solar energy is already in full use by the ecosystem. It drives the weather, heats the oceans and grows the plants. For example, if a large part of the solar energy falling on Arizona is converted to electric energy and moved out of state, Arizona will become cooler. Significant cooling of Arizona will result in changes in the weather in Arizona and in all the contiguous states. The weather change will likely bring more clouds that will reduce the efficiency of the solar energy collectors.

World wide the change will be the opposite of that change in Arizona. Large scale solar energy collectors will change the albedo of the earth, which is the amount of radiant energy the earth adsorbs or reflects. As with artic ice, the change in the albedo will affect the heat balance of the earth. When solar collectors adsorb light they reduce the albedo. This will have the same effect as carbon dioxide; it will warm the earth. So Arizona will become cooler and the rest of the country will become warmer. This will augment the changes in weather patterns.

Little will grow in the shade of a solar collector. Lack of plant cover under the solar collectors will affect the stability of the soil and the absorption and movement of water. These environmental effects are likely to prevent large-scale collection of solar energy in one place for use in other places. 78

Brown, Kathryn S., "Bright Future-or Brief Flare-for Renewable Energy?", Science, Vol. 285, No. 5428, July 30,1999. Page 678

Buti, Ken, Perlin, John, "The Golden Thread", Van Nostrand Reinhold New York 1980

McVeigh, J. C-, "Sun Power", Pergamon Press London, New York, 1977

Wholesale transfer of solar energy from one place to another may cause a level of environmental damage similar to that caused by the combustion of fossil fuels.

In addition to the potential for environmental harm from large-scale collection of solar energy, grave doubts exist concerning our ability to collect the energy. Solar energy researchers have been working hard since the oil price crisis of the mid-seventies. Thus far, they have not found an economically viable method of harvesting solar energy on an extensive basis.

"Point-of-Use" collection of solar energy is feasible in many circumstances. Small scale dispersed solar heating of homes has been demonstrated as technologically feasible.79 A few such systems are in use. The initial capital cost of solar energy collection equipment, adequate to provide year around solar heating, is 3 to 5 times higher that a simple fossil fuel heat source. Because of its intermittent nature, a method of heat storage is essential for a solar heated home. A large portion of the cost of construction of full time solar heated houses is in the heat storage facility. This facility also takes a large space. Much effort must be expended to keep the solar collectors clean, as modest amounts of dirt dramatically reduce the collector's capability to efficiently collect energy. A reliable windshield wiper, similar to those used on automobiles, is possible. Such wipers will add another increment to the cost of the system and another mechanical system that must be maintained.

If the solar system is less ambitious and designed to provide only part of the heat, the cost of the solar collecting system is less. In this case, the cost of the solar harvesting system must be added to the cost a second heating plant to heat the house when solar heat is inadequate. With the combined costs of solar and conventional heating systems, the dual system requires 15 to 20 years for the savings in conventional fuel costs to equal the cost of the solar collectors. Because of the complexity, maintenance problems and costs there is little incentive to install solar heating in homes.80

In the deep south of the United States, swimming pools are often solar heated. Plastic pipe collectors are in common use. Rows of black plastic pipes are laid on the south-facing roof of the house. The pipes are plumbed so that the pool pump can circulate some of the pool water through the pipes. The black pipes adsorb the solar heat and warm the water. In Florida a well-engineered system allows the use of pool a month or so earlier in the spring and a similar time later in the fall. Few solar systems are capable of heating the pool to a satisfactory temperature all year round. People who like to swim all year round use gas, oil or electric heat pump heaters in addition to their solar heaters.

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