Solar Engineering

the branch of technology that studies the conversion of solar radiation energy into other forms of energy suitable for practical use.

The sun sends an inexhaustible flux of radiant energy to the earth. The density of this flux at the boundary of the atmosphere runs to 1.4 kilowatts (kW) per sq m, but a substantial portion is absorbed by the earth’s atmosphere. At sea level the intensity of direct solar radiation is rarely more than 1.0 to 1.02 kW per sq m. For solar-engineering calculations an average value of 0.815 kW per sq m is used.

Attempts to utilize solar radiation energy were made even in ancient times but did not achieve really practical application. It was not until 1770 that H. Saussure (Switzerland) built a solar plant of the “hot box” type. Interest in solar engineering increased markedly in the second half of the 19th century: experimental models of air and steam solar engines were developed by A. Mouchot (France) and J. Ericsson (Sweden). In Russia in 1890, V. K. Tseraskii made a series of experiments on melting different metals at the focus of a parabolic mirror. A solar power plant producing about 45 kW, proposed by F. Schumann (Germany) and W. Boyce (Great Britain), was built near Cairo, Egypt, in 1912 and was the largest of its time. During the 1930’s engineering design methods were developed for solar plants, which chiefly came into use in areas with a large number of sunny days per year; they were used as electrical power sources, water de-mineralizers, driers, and the like. Work on the direct conversion of radiant solar energy into electricity has taken on special importance in connection with the conquest of space.

Solar energy is “free,” but utilizing it is not always economically expedient because of the high capital investment in the construction of a solar plant. Different investigators have evaluated the prospects of solar energy in various ways. The French physicist F. Joliot-Curie reckoned that solar energy would be used extensively in the next few decades. Intensive research efforts are being made in many countries. Solar plants for practical applications are made in lot production in the USA, Japan, France, and other countries. In the Soviet Union important work is going on at the G. M. Krzhizhanovskii Power Institute in Moscow, where staff members have worked out many fundamental problems of solar engineering theory and have created a number of experimental plants which have been tested successfully. Research is being conducted on solar engineering in laboratories in Uzbekistan, Turkmenia, and Armenia.

The extensive practical use of solar energy is hampered by its comparatively low intensity and the variability of its inflow. On this account it is essential to have large surfaces for collecting the solar radiation or to set up solar concentrators that increase the flux density and produce a high temperature on the receiving surface of the converter. The variability of solar energy makes it necessary to accumulate energy (by thermal, electrical, chemical, and other accumulators) and finished production (for instance, when distilling mineralized water or lifting water from wells) or to use schemes that permit energy consumption on an unrestricted schedule (for instance, irrigation and land reclamation).

The most promising use of solar engineering is in agriculture for the many low-power and widely dispersed consumers: often, the construction of expensive electric transmission lines is economically inadvisable and fuel must be transported from far away. Such conditions are typical, for example, in a number of the USSR’s southern regions.

Solar engineering is of particular importance for the development of animal husbandry, specifically in the Turkmen SSR, where large pastoral areas are by no means used completely because of a lack of fresh water. In such regions the distillation of mineralized waters by solar energy is as yet the most economical means of obtaining usable water.

Modern achievements in physics and chemistry and the use of cheap materials with excellent technical characteristics (construction plastics, transparent and aluminized synthetic films, selective coatings on the receiving surfaces, and so on) make it possible to increase the productivity of solar plants and to lower their costs, thus substantially extending the limits of practical usefulness for solar energy.