NO. 5 UTILIZING HEAT FROM THE SUN ABBOT 9 



EFFICIENCY OF SOLAR FLASH BOILER 



Regarding the efficiency of conversion of solar energy into mechani- 

 cal power by the flash boiler, the following computations are pertinent : 



Efficiency of Solar Flash Boiler 



A. Efficiency of the boiler, assumed temperature ioo° C. : 



Mirror reflection 82 percent 



Transmission by vacuum jacket 85 



Absorption by boiler tube 95 



Loss of heat through the jacket 10 



Boiler efficiency 0.82 X 0.85 X 0.95 X 0.90 = 60 



B. Thermodynamic factor for perfect engine : 



Assumed temperature of condenser 30° C. 



Efficiency factor- I9 ° , — ^-^- 34-5 percent 



190 +273 



C. Mechanical efficiency of engine is assumed to be 75 percent. 



D. Final result. Efficiency of conversion of solar to mechanical 



energy : 

 Factor = 0.60 X 0.345 X 0.75 = 15.5 percent 



COMPETITION OF SOLAR POWER AGAINST COAL, OIL, AND WATER POWER 



In the experiments of most earlier inventors, the protection of the 

 boiler tube by a vacuum jacket was not practicable, the cheap but 

 accurate construction of the mirror to give high reflection with per- 

 manency was not feasible, and the simplest arrangement to follow 

 the sun was not generally made use of. Consequently, the cost was 

 up and the efficiency was down. Hence these earlier devices were 

 quite unable to compete with power from coal or water under most 

 conditions. With the high efficiency and great simplicity of the present 

 flash boiler scheme, I compute that power can be had from the sun 

 at not exceeding 0.5 cent per horsepower-hour, and still give a good 

 return on the investment. 



WILLSIE AND BOYLE EXPERIMENTS 



I wish, however, to refer to one of the earlier inventions in which 

 efficiency was sacrificed for cheapness. It was that of Willsie and 

 Boyle who installed a solar power plant at Needles, Ariz., about 1910. 

 Their scheme comprised a large, shallow black-bottomed pond wherein 

 the water attained temperatures considerably below the boiling point. 

 This heat they used to drive a sulphur dioxide engine, cooled by the 

 evaporation of water. They claimed that their device was able to 

 compete with coal in that locality, although both its boiler efficiency 

 and its thermodynamic efficiency were low. It appears not to have 

 come into much commercial use, however. 



