242 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1958 
If the solar energy could be converted into electricity through a 
heat engine and dynamo, or through a photovoltaic cell with an 
efficiency of 10 percent, one “roof” of radiation would generate about 
7 kilowatts while the sun is shining at the rate of a million calories 
per minute. If this electrical work is produced throughout 8 hours 
of sunshine, but averaged over the whole 24-hour day, the roof would 
produce at the rate of 2.3 kilowatts. A 5-percent efficiency would lead 
to 3.5 kilowatts during sunshine and 1.2 kilowatts for the day’s aver- 
age. The limits of 5 and 10 percent for conversion of heat into useful 
electricity give an optimistic but not an impossible range. 
SOCIAL IMPLICATIONS 
Solar-energy utilization holds out special hope for improving the 
standard of living in areas which have not yet become industrialized. 
In marginal agricultural areas human labor can be conserved and 
work animals with their high food consumption reduced—if some ex- 
pert is able to come up with a sufficiently practical and inexpensive 
solar engine. Pumping of water for agriculture, for household use, 
and for sanitation is the most obvious use of solar energy. ‘There is no 
way to make the sun shine at night and the intermittency of solar 
energy is a powerful deterrent to its use. Water pumping is not 
handicapped by this intermittency. Electric lights for homes and 
villages might come next in importance, but for this purpose some sys- 
tem of power storage must be provided, possibly for only a few hours. 
Village industries, weaving, wood turning, furniture making, and 
machine work might be encouraged with solar engines of 1 to 100 
horsepower. Solar refrigeration could conserve food and make 
possible the use of additional protein materials with a resulting 
improvement in nutrition. 
Solar heating and cooking are definite possibilities if the units are 
cheap enough. 
I have a letter from Mexico telling me that the women of the 
village spend much of their time walking to the hills 6 miles away to 
collect firewood for their cooking and heating. The letter goes on to 
say, “We have plenty of sunshine all around. Can’t you do something 
to help us?” Maybe wecan. Let’stry! The challenge is not only to 
save time and labor for the housewife, but to conserve the soil against 
erosion caused by removing the grass and shrubs for firewood. In 
some areas the cow and camel dung now used for cooking fuel 
might be saved for use as fertilizer. 
Possibly the solar distillation of salt water and the solar heating 
and cooling of houses might open up new land areas to settlement and 
thus tend to relieve some of the world’s population pressures. 
In some undeveloped and uninhabited areas, a premium price could 
undoubtedly be paid for electricity, for pumping of water, and for 
