156 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1933 



up its heat by circulating it about a boiler or heat exchanger con- 

 taining some volatile liquid, such as ammonia or sulphur dioxide. 

 The vapor generated by this heat, after operating an engine, was 

 condensed and returned to the boiler to be used again. The water, 

 after giving up its heat to the sulphur dioxide, was sent out through 

 the solar heater to collect again the heat in the sun's rays. Theo- 

 retically, the plan meets all the requirements for the transformation 

 of solar heat into continuous, uniform power (fig. 4) . 



The sulphur dioxide engine used in this experiment was a vertical 

 automatic cut-off, which at times, with a boiler pressure of 215 

 pounds, probably developed 15 horsepower. The two heater sections 

 exposed an area of about 1,000 square feet to the sun, but as the heat 

 was taken from storage and not directly from the heater, it is not 

 fair to assume the above proportion of heater surface to horsepower 

 developed. 



The condenser consisted of 6 stacks of horizontal pipes, 12 pipes 

 to the stack. The cooling water, pumped from a well 43 feet deep, 

 had a temperature of 75° F. Only enough water was allowed to drip 

 over the pipes to keep them wet, and so great was the evaporation 

 in the dry desert breeze that the cooling water left the lower pipes 

 at 64°. By using the cooling water over and over, the condenser 

 gave very satisfactory results. A shade of arrow weed, a straight 

 willowlike shrub abundant along the Colorado River, kept the sun- 

 shine from the condenser pipes and permitted a good air circulation. 



At times the storage valve would be opened after dark, allowing 

 the solar-heated liquid to flow over the exchanger pipes and thus 

 start up the engine. Up to the year 1910 this was probably the first 

 sun-power plant that was ever operated at night with solar heat col- 

 lected during the day, and it came nearer than any other plant to 

 the commercial utilization of solar heat for power purposes; it was 

 also the largest sun-power plant of which there was any record. 



From the foregoing, the cost of installing a sun-power plant may 



be estimated : 



Heater, 24-hour size per horsepower.. $100.00 



Storage, lOO-hour size do 10.00 



Engine, pumps, etc do 20.00 



Vaporizer do 15.00 



Condenser do 15. 00 



Liquid sulpliur dioxide 1.25 



Emergency steam boiler 2. 75 



Total 164.00 



At that time the costs of steam-power plants were said to range 

 from $40 to $90 per horsepower. The cost of a Willsie sun-power 

 plant was accordingly from two to four times that of a steam plant. 



