944 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1958 
heat. The light half, of course, can be used as heat also. Thus all the 
energy is available as heat. We can start at once developing heat uses. 
The principles are well known. The difficulty is in economics. Some 
say just wait for new technological developments and new materials. 
The technological ceiling will certainly rise. Yes, but it rises only be- 
cause a few pioneers like to bump their heads against the ceiling. Let’s 
start now on large-scale experimentation and pilot plants using the 
heat of the sun for heating, cooling, distillation, and for solar-heat 
engines. Let’s accelerate our fundamental research in trying to use the 
light of the sun. We are a long way behind in competing with agri- 
culture, but agriculture in turn utilizes only a small fraction of the 
solar energy which it could theoretically utilize. The greatest long- 
range hope lies in photochemistry and photoelectricity. 
Intensive research and development should be directed toward uti- 
lizing solar heat to help the nonindustrialized countries now and 
toward utilizing the solar light at some later time. 
SOLAR ENGINES 
Solar engines require a higher temperature than is ordinarily needed 
for house heating, absorption refrigeration, or for distillation of salt 
water. This higher temperature can be achieved through concentra- 
tion of the light onto a small area with the help of parabolic or para- 
bolic-cylindrical mirrors; or by heat traps with multiple glass plates 
which allow sunlight to pass through, but which minimize the loss of 
heat in the form of long infrared radiation from the heated receiver. 
The focusing type of engine has the advantage of reducing the area 
of the boiler and this, in turn, reduces the heat losses and the cost of 
equipment. It is, however, nearly useless except in direct sunshine. 
The flat plate collectors will continue some operation on cloudy days. 
The focusing type may well be more suitable for sunny climates and 
the flat plate collectors more suitable for regions in which the direct 
sunlight is frequently cut off by clouds. In either case, the important 
problem is to keep the capital cost low. Large areas of reflectors or 
glass plates are expensive. 
STORAGE OF POWER 
Intermittency is one of the handicaps of solar energy. There is no 
way by which the sun can be made to shine at night. There are 
many ways in which mechanical or electrical power can be stored. 
The question is the economic cost. An engine can pump water up to 
an elevated reservoir, and as the water falls back to ground level it 
can do work in a water turbine. The difficulty with this method is 
the high cost of a reservoir which has appreciable capacity. One 
kilowatt-hour of heat is equivalent to 4,100 cubic feet of water or 
