r>iG 



Popular Science Muiil/ili/ 



succeeded in developing about one horse- 

 power for every one hundred scjuare feet 

 of reflecting surface he abandoned his 

 jilan in disgust. "The scheme is im- 

 practicable on account of the great cost 

 of the needed apjiaraius," he declared. 

 "The fact is that although the heat is 

 obtained for nothing, so extensi\c, costK' 

 and complc.v is the concentration ap- 

 paratus that solar steam is many times 

 more costly than steam produced l)y 

 burning coal." 



Even if much water could be boiled 

 by mirrors, enough, let us suppose, to 

 dex'elop a thousantl horse-power, it 

 docs not necessarih' follow that the sun 

 nK)tor will sujjplant the steam engine, 

 l-actory machinery must sometimes be 

 driven at night. How can the solar 

 motor do that? In the desert of Sahara 

 the sun does not shine at midnight. 



Evidently the inventor of a solar 

 power plant must design a storage sys- 

 tem — a piece of apparatus that can be 

 charged with excess power and tapped 

 at will in sunless periods. Ericsson 

 slaved on this phase of the problem as 

 much as he did on the invention of the 

 engine itself. Yet his results were un- 

 satisfactory. Some of his successors 

 ha\e designed machinery to compress 

 air in strong, steel tanks; some ha\e 



planned systems in which a dynamo is 

 made to charge a storage-batter\-; and 

 some ha\'e thought of pum[)ing water 

 into a reservoir from which it could sub- 

 sequently be drawn to turn a water- 

 wheel, ("ompressed air machinery, stor- 

 age-batteries, and pumps cost much 

 me)ne>-, even though the sun's heat may 

 be had for nothing — so much money in 

 fact that a boiler and a steam engine 

 may prove cheaper in the end. 



Askance though he might look at a 

 colleague who really believed in substi- 

 tuting sun's heat for coal, an engineer 

 could not den>- that Ericsson had none 

 too \i\idly [lictured the possibilities 

 that await the successful in\'entor in 

 desert lands. After making due allow- 

 ance for the absorption of the atmos- 

 phere, the total energy received b>- the 

 earth in one day from the sun amounts 

 to about 341,600 million million horse- 

 power — eciuivalent to about two hun- 

 dred anil thirt\' million horse-power for 

 e\ery inhabitant. 



To obtain these figures some instru- 

 ment for measuring the sun's heat was 

 obviously employed. Ordinarily solar 

 heat is mercifully radiated and carried 

 away as fast as it is received; otherwise 

 the sea would have boiled away long 

 ago, and e\ery li\ing thing on the earth 



The parabolic reflectors which serve to concentrate the sun's hciit upon a trouph of water 

 at their focus move automatically with the sun. This solar plant is capable of RivinR an 

 average of fifty horse power. Were it located farther south, it would yield energy amounting 

 to otx)ut sixty five horse power, making due allowance for the absorption of the atmospheie 



