Solar resource

FIGURE 1.2 Geographic distribution of U.S. sustainable energy resources Solar, wind, biomass, and geothermal. SOURCE Presented by John Turner, National Renewable Energy Laboratory. 

Finally, the use of renewable energy resources (solar, wind, and geothermal), in place of fossil fuels, as the energy supply to further minimize energy consumption and greenhouse gas emissions, is an additional option under investigation for membrane-based desalination [26]. 

The use of solar cells is rapidly expanding because they provide a sustainable energy resource. Solar cells can t5rpically be categorized into two types based on the light absorbing material used, i.e., bulk or wafer-based solar cells and thin film solar cells. 

Other sources of energy worth noting are the extensive wind farms, solar projects, and related emerging unconventional technologies. These renewable resources provide only small quantities of energy to the U.S. economy as of this writing. 

G. M. Reistad, paper presented at the Proceedings of the 2nd UN Symposium on the Development and Use of Geothermal Resources, Vol. 1, Lawrence Berkeley Laboratory, San Erancisco, 1975, pp. 2155—2164 "Analysis of the Economic Potential of Solar Thermal Energy to Provide Industrial Process Heat," U.S. ERDN Contract, EY-No-C-02-2829, Intertechnology Corp., 1977. 

The discovery of chemical N2 fixation under ambient conditions is more compatible with a simple, complementary, low temperature and low pressure system, possibly operated electrochemically and driven by a renewable energy resource (qv), such as solar, wind, or water power, or other off-peak electrical power, located near or in irrigation streams. Such systems might produce and apply ammonia continuously, eg, directly in the rice paddy, or store it as an increasingly concentrated ammoniacal solution for later appHcation. In fact, the Birkeland-Eyde process of N2 oxidation in an electric arc has been... 

On the positive side, the three-dimensional nature of the resource provides it with a distinct advantage compared to other solar technologies. Specifically, because siting usually involves placing the individual turbines as high as possible, typically spacing turbines about 2 to 3 blade diameters apart crosswind and 10 diameters apart downwind, only a small fraction of a wind farm area is actually occupied. The rest of the land remains available for other appHcations, such as crop production or Hvestock grazing. 

Much attention is also being given to solar energy. It does not appear that direct solar heat is economically feasible as a large power plant energy source however, this resource has great potential for a number of process and heating applications. 

Resource pessimists counter that this process cannot proceed forever because the eternal persistence of demand for any given commodity that is destroyed by use must inevitably lead to its depletion. I lowever, the eternal persistence assumption is not necessarily correct. The life of a solar system apparently is long but finite. Energy sources such as nuclear fusion and solar energy in time could replace more limited resources such as oil and natural gas. Already, oil, gas, nuclear power, and coal from better sources have displaced traditional sources of coal in, for example, Britain, Germany, Japan, and France. 

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