UTILIZING HEAT FROM THE SUN 



By C. G. ABBOT, 



Secretary, Smithsonian Institution 



(With Four Plates) 



In large regions lying in the low latitudes desert conditions prevail. 

 Day after day the sun glares down, occasionally dimmed a little by 

 cirrus clouds, or perhaps by a few heaping cumuli. In such regions 

 80 percent or even more of the hours of daylight would be useful 

 for furnishing solar heating. 



QUANTITY OF SOLAR ENERGY 



The quantity of energy available from solar radiation under such 

 conditions as I have pictured is immense. As I shall show in what 

 follows, we may count on the possibility of converting 15 percent of 

 the energy of such solar rays as are intercepted by our devices into 

 mechanical work. Assuming that to avoid appreciable losses through 

 shading one unit by another, and to allow plenty of room for other 

 purposes, only one-tenth of the area available is actually covered by 

 heat collectors, and further allowing for night and cloudy weather, 

 still the State of New Mexico could supply from solar radiation over 

 ten trillion horsepower-hours per year of mechanical power, which 

 compares with the power possibilities of all coal, oil, and water at 

 present used annually for heat, light, and power combined in the 

 United States. 



INTERMITTENCE AND STORAGE OF SOLAR POWER 



Like hydroelectric power, solar power demands no continuing 

 expense other than for care and interest on the investment. Unfor- 

 tunately, however, solar power is subject to the drawback that it 

 ceases during night hours, and when the beam is intercepted by clouds. 

 There are certain uses, such as pumping water for irrigation for 

 instance, where this intermittence is no serious objection. But for 

 most purposes power must be available at all times. Hence to become 

 a great industrial factor solar power demands the association of 

 storage of energy, either as heat, or in chemical, electrical, or 



Smithsonian Miscellaneous Collections, Vol. 98. No. 5. 



