Energy in Transition, 1985-2010 Final Report of the Committee on Nuclear and Alternative Energy Systems (1980) / Chapter Skim
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6 Solar Energy
6 Solar Energy
Pages 345-384
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From page 345... ...
or indirectly (as in wind power, ocean thermal energy conversion, wood burning, or those prospective technologies designed to turn plant matter, or "biomass," into liquid and gaseous fuels)
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From page 346... ...
. This approach is referred to as solar thermal central station energy conversion.
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From page 347... ...
Nonetheless, if national energy policy mandates it for social and environmental reasons, the more nearly economic solar applications can be rendered competitive with conventional alternatives by some form of subsidy. For example, California has adopted a 55 percent tax credit on solar heating systems intended to promote significant market acceptance at the current prices of competing fossil fuels.
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From page 348... ...
More detailed information on how these scenarios were developed is given in the report of the Supply and Delivery Panel's Solar Resource Group.' LOW-SOLAR-ENERGY SCENARIO This scenario is based on the assumption that no policy other than the current federal tax credits is implemented to assist the entry of solar energy into the energy market, that the costs of other energy sources increase only slowly, and that the costs of solar energy technologies remain high (i.e., follow the estimates of the Solar Resource Group without breakthroughs in the costs of advanced solar technologies)
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From page 349... ...
The high-solar scenario is based on mandated deployment of three technologies—solar thermal central station energy conversion, solar thermal total energy systems, and dispersed wind energy systems—without implying that these would necessarily be the specific 'See statement 6-2, by H Brooks, Appendix A
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From page 350... ...
This is a 15 percent annual growth rate. The estimates for solar thermal total energy systems are based on the estimates given above for solar heat delivered for space heating, air conditioning, and industrial process heat.
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From page 351... ...
The total cost of implementing such a scenario, at today's costs for solar technologies, might be around 3 trillion dollars, perhaps 2-3 times the cost of obtaining equivalent energy from conventional nonrenewable sources. The increment, if provided as a subsidy by government, would be much larger than the total amount provided to date by government to stimulate energy production by conventional means (including nuclear)
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From page 352... ...
The government's present concentration of funds on demonstrations of solar thermal central station power plants may turn out to be an example of such premature demonstration programs. DIRECT USE OF SOLAR HEAT Heating buildings and domestic water and providing industrial and agricultural process heat and low-pressure steam are by far the simplest and most economical applications of solar energy.
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From page 353... ...
(Solar hot water or process heat systems, for example, operate all year long and thus yield fairly constant returns on the initial investments. Solar space heating systems normally do not, and this lowers their value.)
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From page 354... ...
However, if public policy so dictates, because of the social and environmental benefits from solar heating, it is possible to bring decisions on new heating systems more into line with minimum life cycle cost and thus to render consumers more likely to select solar systems on a Btu-forBtu comparison with conventional alternatives. This can be done by means of additional solar tax credits, low-interest or interest-free loans, thermal performance standards for buildings or additional taxes on nonrenewable fuels.
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In such buildings active solar space heating systems are in direct competition with conventional systems. To make economic comparisons of solar space heating systems with conventional systems, it is obviously necessary to know the costs of installed solar systems.
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Further, the owner of a solar heating system now receives a federal income tax credit (and in many states, a state income tax credit or rebate)
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Some may choose to compare the cost of solar heat with that of using electricity rather than natural gas, even though gas is now cheaper, because they expect gas to be unavailable or extremely expensive in 20 years. Some may assume that the pace of alternatives will rise fast enough over the 20 years to make solar heating economic.
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From page 358... ...
The Electric Power Research institute investigated this question from the perspective of minimizing the total cost of the system including the building and the utility and concluded that solar heating and cooling systems are not inherently less efficient in their use of electrical generating capacity than conventional all-electric homes 16 INDUSTRIAL PROCESS HEAT Another potentially important direct use of solar energy is to provide industrial process heat for use in small- and medium-size applications, as in laundries, food processing operations, and crop drying. At present about half of industrial process heat in the United States is supplied by natural gas, which is increasing in pace and becoming less readily available.
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From page 359... ...
Of particular interest are the possibilities of using the sunshine falling on the surfaces of the building to provide some of the functions of space conditioning, by so-called passive solar design. In a passive solar energy system the transfer of solar heat takes place by natural convection, radiation, or conduction without the use of special mechanical pumps or blowers.
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From page 360... ...
Active and passive solar energy systems are not mutually exclusive; that is, a building can be designed with passive solar concepts to minimize its energy demands for space conditioning and can use an active solar system to satisfy part of the remaining demand. Further, some systems that use air for collection and transfer of solar heat cannot be clearly categorized as either active or passive but represent a hybrid.
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From page 361... ...
:S How expensive is the energy provided by passive solar systems? Although a passive system provides energy in a way that cannot be directly compared with the workings of a normal heating and cooling system, the energy cost of a passive system can in principle be estimated by comparing the total initial cost of the building and its total energy requirements for all purposes with those of an otherwise similar building without passive solar design.
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From page 362... ...
This might be true even though a smaller collector surface area would be required, since the cost of the noncollector parts of active solar heating systems do not decrease in proportion to collection area as size is reduced. This intimate technical and economic relationship among active and passive solar systems and energy-conserving building design makes it important that government-sponsored research and development and demonstration programs in these areas be integrated.
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From page 363... ...
The result is a passive solar heating system that may not be as effective as it would be if the entire building had been designed initially for this, but it does provide significant energy savings. This approach is being rapidly adopted in northern New Mexico, where the clear, cold winters allow this
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SOLAR ELECTRICITY GENERATION Four concepts for generating electric power from solar radiation are under active development. Today the one that is receiving the most attention in government research programs is solar thermal conversion, which involves concentrating sunshine to achieve high-temperature heat.
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From page 365... ...
Because of the intermittent nature of sunshine and the lack of a practical energy storage technique, however, it would be unable to displace much generating capacity. Solar thermal conversion systems for smaller-scale on-site generation would be roughly similar, but smaller.
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An alternative to storage is the use of oil and gas for backup generating capacity, as in repowenug. One promising extension of solar thermal electric conversion designs is the so-called solar total energy system, in which the waste heat from the generator is used near the power plant.
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From page 367... ...
A 100-MWe solar electric plant would use, for the arrays of heliostats alone, 30,000 40,000 tons of steel, 5000 tons of glass, and 200,000 tons of concrete, as compared with about 5000 tons of steel and 50,000 tons of concrete for the construction of equivalent capacity with nuclear power. Equivalent capacity in a coal plant would require considerably less steel and concrete 28 Many of the air pollutants produced in mining and manufacturing the steel, glass, and cement for such a solar thermal plant—notably sulfur and nitrogen oxides, carbon monoxide, and particulates—would be comparable in kind and amount with I year's effluents of an equivalent coal-fired plant using current control technology, except for the particulates, which would be an order of magnitude greater for the solar plant.
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The social impacts of building central receiver plants in large numbers in the Southwest could be substantial. There might be significant population shifts to that region.
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From page 369... ...
Wind energy is more limited in choice of sites than other solar technologies, because available wind energy density varies greatly with average wind speed. To accommodate variable wind energy to the regular cyclic needs of a utility system, large amounts of electrical storage capacity are needed unless the delivered energy can be economically used when the wind happens to be blowing or if the wind energy is used in a supplemental mode.
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From page 370... ...
These must be spread over a large area so that the individual devices do not interfere with one another, and the land area required would be several times that of a solar thermal power plant of equivalent output. The land required for 1000 MWe of installed wind electric capacity has been estimated to be between 200 and 500 square miles.33 (This land could still be used for other purposes, such as agriculture, so it need not be considered lost.)
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From page 371... ...
This is the only earth-based solar electric technology that is naturally suited for base-load generation of electricity; all others require special storage devices or other backup systems. A small ocean thermal conversion experiment was operated briefly in 1929.
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From page 372... ...
In the distant future such a system might become the most suitable energy source for large electricity grids if energy sources like breeder reactors, nuclear fusion, and earthbound solar electric technologies should prove to be unattractive. The attraction derives from a longer solar day, freedom from weather, and a solar flux about twice that of the southwestern desert on a clear day.
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From page 373... ...
Other solar technologies can produce fuels over the long term. At present the federal solar research and development program places too little emphasis on these technologies; only 6 percent of the program's funds go to support biomass technologies.34 Some research on generating fluid fuels from organic municipal and agricultural wastes is supported, but this is given a rather low priority.
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From page 374... ...
Furthermore, such wastes are increasingly being sorted to recover various nonfuel materials, and this operation would at least partially offset the expense of energy conversion. The economics of recovering energy from municipal wastes thus depend strongly on the value of the nonenergy materials recovered and on the credit given to the operator for disposal of the wastes, which would otherwise be a cost to the municipality.
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The Solar Resource Group estimates that the gross annual availability of these wastes is about 8 quads and that their real availability is about half that value. The energy available as fuel from agricultural wastes depends on the conversion process.
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Growth of Biomass for Energy Existing farming methods could be used in "energy farms" to produce significant amounts of biomass. Since in an energy fann the goal is to produce the maximum amount of biomass, crops such as eucalyptus trees, rubber plants, or sunflowers might be used because of their rapid growth and high energy content.
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This means a gaseous fuel (methane) from biomass production could cost as much as $5.50 per million Btu, or as little as $1.20 per million Btu (less than the present wellhead price of natural gas)
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Commercialization is not likely in this century. Photochemical Conversion One attractive long-term alternative to the growth and conversion of biomass is direct solar fuel production by photochemical conversion.
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There are some promising ideas about the form such chemical systems might take, and some electrochemical systems have been demonstrated in the laboratory, but this must be considered a long-term research problem. The achievement of a practical technology Or photochemical conversion to produce fuels will depend on significant advances in our fundamental understanding of primary photochemical processes and the subsequent processes involved in the transfer of the energy of electronic excitation to stable chemical products.
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The design of a practical process will be a challenging task. Electrolync Conversion An alternative to thermochemical production of hydrogen is to use any solar electric technology to generate electricity initially and then use the electricity to produce hydrogen by electrolysis of water.
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From page 381... ...
In particular, the government should stimulate the integration of solar heating into energy-conserving architectural design in both residential and commercial construction through support and incentives for passive solar design. Since all solar energy technologies are capital intensive, uses that are distributed throughout the year, such as domestic water heating and low-temperature industrial process heating, are likely to be economically competitive earlier than uses for which there are large seasonal variations in demand.
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From page 382... ...
For example, cheap energy storage systems would benefit the economics of all systems containing capital-intensive generating technologies. Large-scale government demonstrations of long-term solar technologies, such as the planned demonstration of a solar thermal central station power plant, could be counterproductive if undertaken prematurely.
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From page 383... ...
12 D S Ward, Solar Heating and Cooling Systems Operational Results Conference Summary (Golden, Colo.: Solar Energy Research institute (SERI UP 49 209)
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From page 384... ...
33. National Research Council, Selected Issues of the Ocean Thermal Energy Conversion Program, Assembly of Engineenng, Manne Board, Panel on Ocean Thermal Energy Conversion (Washington, D C.: National Academy of Sciences, 1977)
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