USE OF SOLAR ENERGY FOR HEATING WATER 



By F. A. Brooks 

 Agricultural Engineer, California Agricultural Experiment Station 



[With 3 plates] 



Direct use of solar energy as heat is now being made by several 

 thousand solar water heaters in Florida, California, and the South. 

 Successful use depends, of course, on the number and regularity of 

 sunshine days and on the proper design of the heating system. There 

 are two common types of solar water heaters and several methods of 

 combining the solar heater with other water-heating systems. 



Recommendations for installations and construction of solar water 

 heaters are to be found on pages 174 to 181. Investigations and experi- 

 ments in California - concerning water temperatures and the rates of 

 heating water in different solar-heater systems are described on 

 pages 161 to 174. Methods of steam generation, distilling, and cooking 

 by solar energy in which Dr. Abbot uses aluminum reflectors to ob- 

 tain high temperatures have been described in a previous publication 

 of the Institution.^ 



AVAILABILITY OP SOLAR ENERGY 



The amount of radiant energy coming from the sun is almost con- 

 stant — 7.15 B. t. u.* per square foot each minute — on a surface per- 

 pendicular to the sun's rays outside the earth's atmosphere.^ Re- 

 flection and scattering of the sun's rays occurs in the outer atmosphere 

 by dust and water and gas molecules. Absorption there is mainly by 

 ozone. In the lower atmosphere reflection by clouds and absorption 

 by the water vapor and carbon dioxide gases and by smoke and dust 

 further diminishes the solar radiation reaching the earth's surface. 



Atmospheric depletion of solar energy. — The large variation in 

 energy received on the earth's surface on clear days at the same time 



1 Material selected from University of California College of Agriculture Bull. 602, 1936. 



- Brooks, F. A., Solar energy and its use for heating water in California. Univ. Cali- 

 fornia, Coll. Agr. Bull. 602, 64 pp., 1936. 



s Abbot, C. G., Utilizing heat from the sun. Smithsonian Misc. Coll., vol. 98, No. 6. 

 publ. 3530, pp. 1-11, 1939. 



* B. t. u., or British thermal unit, which is the quantity of heat required to raise the 

 temperature of 1 pound of water 1° F. 



"Abbot, Charles G.. The Sun. 2 ed., 433 pp. (see specifically p. 296). D. Appleton & 

 Co., New York, 1929. 



157 



