Encyclopedia of Environmental Science and Engineering, Volume I and II

318 ENERGY SOURCES—ALTERNATIVES

Solar Power Plants In-Orbit and Terrestrial-Based

Systems

Several concepts for utilizing solar energy in a centralized

power plant have been proposed. Glaser^52 outlined a concep-

tual system that uses a satellite with a large array of solar

cells placed in a synchronous orbit. The solar cells would

convert the solar energy to electricity and this energy would

be beamed by microwave to a receiving station on earth. To

supply the annual electrical energy demand of the northeast

region of the US in 1980, estimated at 1.7 
 10 15 Btu, a

105 square mile array of silicon cells would be required on

the satellite and the receiving antenna on earth would be of

the order of 20 square miles. Another scheme proposed by

Meinel^53 involves a terrestrial-based plant that would capture

thermal energy from the sun by means of specially coated

surfaces to provide a “greenhouse” effect. A working fluid

would be heated to a temperature of about 1000°F for use in a

power cycle to produce electricity. A terrestrial-based system

of 1000 MW electric capacity would require a land area of

about 5.5 square miles. The satellite concept, like the utiliza-

tion of fossil and nuclear resources, does add to the thermal

burden that must be dissipated to the environment, while the

terrestrial-based solar plant merely implies a redistribution of

energy that impinges on the earth in any event.

Single and Dual Purpose Power Plants: Advantages

and Problems

The more simple service of electricity generating units is

the operation of single purpose power plants, on the other

hand a second purpose can help to increase the efficiency

of the plant, using for instance, the waste heat for district

heating systems or desalination of sea water. Naturally the

structure of the regional or national energy economy must

allow the technical and economical interconnection of two

aims. The increasing cost of fuel oil and natural gas may

promote the use of fossil-fueled and nuclear power plants

for the district heating in high populated towns and regions.

When fully used for the two purposes the efficiency of a

coal-fired power plant can increase up to 75 to 80%. But

the high investment costs of big district heating systems and

the take out of heat in the power plant brings the advantage

of higher efficiency only during the winter period, in the

summer time there will be needed in parallel the normal wet

cooling tower. This is only one argument, the other is, that

the coal, fired in the plant boiler, substitutes fuel oil unbur-

dening the national balance of payment from the import cost

for petroleum. If suitable a dual purpose power plant may

be taken into consideration in the prefeasibility study period

of new projects and here, in particular, also under the aspect

that district heating systems could result in a dramatic reduc-

tion of air pollution in towns.

Decentralized Stationary Power Plants

Energy conversion systems currently utilized in this cat-

egory involve mainly combustion devices for space heat and

industrial process heat applications. For economic reasons

they are generally not as amenable to as high a level of emis-

sion control as larger centralized systems, save for conver-

sion to cleaner fuels such as natural gas and perhaps methane

or hydrogen produced from coal. These applications are also

candidates for conversion to electrical energy thereby shift-

ing the emission problem from decentralized plants to cen-

tralized power generating facility.

Decentralized electric power generating facilities of up

to 5 MW output are sometimes installed in shopping centers

and housing complexes. These now use diesel generators

or gas turbines but could also use fuel cells when these are

developed. Waste heat from these power plants is used for

space heating and air-conditioning, and it is claimed^54 that up

to 85% of the energy in the fuel may be effectively utilized

in these systems as compared with only about 40% in central

station power plants.

The use of solar energy for individual home space con-

ditioning and water heating will further on increase but

involves a substantial capital investment in these applica-

tions. The payback time for the investment costs, however,

will become shorter, because the natural gas, fuel oil, and

electric costs will rise in future overportional to the cost of

primary energy.

Nuclear reactors are not competitive in small decentral-

ized applications for economic and technical reasons par-

tially attributable to the requirement for shielding and other

auxiliary systems. They are used, like other new devices such

as fuel cells, in special military and space applications and

may have potential in very large aircraft. Certain isotopes,

produced by neutron irradiation in a nuclear reactor, have

also been used as energy sources for small power systems in

space and remote terrestrial applications.

Mobile Power Plants

Energy conversion devices used in motor vehicle, rail, and

aircraft applications must provide acceptable performance

characteristics in terms of horsepower–weight ratio and

specific fuel consumption. The gasoline-fueled, internal-

combustion (I-C) engine has dominated the motor vehicle

field and the gas turbine has achieved the same level of

preeminence in aircraft. An appraisal of automotive trans-

portation in relation to the problem of air pollutant was per-

formed by a Department of Commerce panel.^55 Alternate

systems were reviewed and a five-year development pro-

gram was recommended to support innovative develop-

ments on energy sources, propulsion systems, and emission

control devices. Alternative energy sources were considered

further in system studies performed on electric vehicles by

A.D. Little^56 and on the whole spectrum of unconventional

low pollution- potential power sources by Battelle Memorial

Institute.^57 It also is possible to use alternate fuels such as

propane, methanol, natural gas, and hydrogen in I-C engines

to reduce the level of emissions. Propulsion devices that

may have some future potential include gas turbines, exter-

nal combustion systems operating with a steam of organic

Rankine cycle or with a Stirling cycle, fuel cells, and bat-

tery driven electric motors. The characteristics of some

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