152 



THE IRRIGATION AGE. 



power and over. An ideal plant must be subject 

 tc a little accident, hence it must lie near the ground 

 in order not to be affected by storms and winds. 



Each unit must be repairable without stopping 

 the operation ; construction must be simple and 

 easily understood by the ordinary steam engineer ; 

 and wear and tear must be reduced to a minimum. 

 The first cost of a sun-power plant to be practical 

 and of commercial value, must be sufficiently low 

 so that the interest on the investment does not 

 make it unprofitable. This is the rock, on which, 

 thus far, all sun-power propositions were wrecked. 

 It is not necessary that the cost of the sun heat ab- 

 sorber shall be as low as that of a steam boiler and 

 fitting of the same power. The cost of the plant 

 described herein is twice that of the ordinary steam 

 power plant of the same size. 



This price is sufficiently low, however, so that 

 even if the extra interest is taken into consideration, 

 the fact that after installation no fuel is required, is 

 such an enormous advantage as to -entirely offset 

 the increased cost, and in addition cause great 

 profits. A decade ago Mr. Shuman became inter- 

 ested in the problem of obtaining power by absorb- 

 ing the sun's rays. It was found, by experiment, 

 that if a vessel were so arranged that the run's rays 

 could impinge upon it, and if all heat losses by con- 

 duction, convection and radiation were prevented by 

 a theoretically perfect method of insulation, the tem- 

 perature within the vessel would rise certainly to a 

 thousand degrees Fahr. without any attempt being 

 made to concentrate the rays of the sun. 



For commercial purposes it is impossible to se- 

 cure any form of insulation which would even ap- 

 proach the theoretical; Commercially, the main 

 object is to produce practical power at a minimum 

 cost, and this has been done by the use of well- 

 known and cheap forms of heat insulation. 



Were no steam made in these vessels as they 

 are arranged in the present plant, the temperature 

 therein would be up to 350 Fahr. in the latitude 

 north, possible easily to 450 hard near the equator. 

 The production of steam at atmospheric pressure, 

 however, keeps the temperature in the vessels down 

 tc. 212 and whatever excess of heat is produced by 

 the sun's rays over and above that lost, is con- 

 verted into steam, and many therefore be utilized. 



No doubt sun power must go through the same 

 long and gradual course of development that has 

 brought other forms of mechanical power to the 

 present high plane of efficiency, but the principle 

 will remain fundamentally correct. 



The first Shuman generator consisted of a 

 wooden box covered by two layers of glass, 'between 

 which was a small air space, and in the box was 

 placed a miniature ether boiler. This apparatus was 

 exposed to the sun's rays, the ether distilled, and 

 the amount of heat which might be absorbed was 

 determined. As an experiment, a small toy engine 

 was successfully run with this original apparatus. 



A second generator consisted of a 2-inch steam 

 pipe 17 feet long, insulated at the bottom, enclosed 

 in a box covered by a double layer of glass. Here 

 again ether was distilled, and the number of heat 

 units absorbed were determined. A third type of 

 power plant was composed of a bed of water pipes 

 properly insulated against heat loss, the unit being 



18x60 feet, and the motor being another engine. 

 With this apparatus 3 l /2 horsepower was obtained. 

 With the knowledge so gained, the next generator 

 to be described below was gradually evolved. The 

 sun-power plant consists of the absorber, a low 

 pressure steam engine, condenser and auxiliaries. 



In this sun-power plant the absorber was com- 

 posed of a series of units each containing a flat metal 

 honeycomb water vessel, rectangular in shape, and 

 resembling closely a large waffle. This vessel was 

 enclosed in a flat wooden box covered with two 

 layers of glass having a one-inch air space between 

 them, and having the under surface of the box in- 

 sulated against heat loss downward by a 2-inch layer 

 of regranulated cork and two layers of waterproofed 

 cardboard. The boxes were mounted on supports 

 which elevated them some 30 inches above the 

 ground, and which permitted them to be inclined 

 perpendicular to the sun at the meridian. 



Plane mirrors of cheap construction were 

 mounted on two sides of the boxes in order that 

 more rays of the sun might be absorbed and reflected 

 upon the surface of the water vessel. This latter 

 is connected at one end to a feed pipe from the 

 water supply, and the other end to a steam pipe. The 

 steam pipes from the various units are connected 

 together and empty into a main 8 inches in diameter 

 in the present plant, which conveys the steam to the 

 engine. The engine used was a new type, low 

 pressure, reciprocating steam engine of great steam 

 economy. 



Connected with it is a condenser of ordinary 

 type, and auxiliaries such as may be found in any 

 condensing plant. The water from the condenser 

 is pumped back into the absorber, thus insuring a 

 continuous closed circuit, whose only water loss is 

 from accidental leakage, which is carefully guarded 

 against. The power of this first plant was used for 

 pumping water by means of a reciprocating steam 

 pump of the ordinary type, and whenever the sun 

 shone this plant pumped water successfully and 

 practically. 



The capacity of the plant was 3,000 gallons of 

 water per minute, lifted to a height of 33 feet. From 

 actual tests made in Philadelphia it was found that 

 from the absorber of 26 banks of units each contain- 

 ing 22 single units and having a light absorptive 

 area of 10,296 square feet and an actual area of 5,148 

 square feet, there could be developed during eight 

 hours 4,825 pounds of steam. 



The power produced was much lower than nor- 

 mal to the plant, as it was built for tropical use and 

 was entirely unfitted for commercial work in north- 

 ern latitudes. The loss of heat by conduction and 

 convection in northern latitude is enormous. When 

 the present apparatus is placed in an average air 

 temperature of 100 Fahr., such as obtained through- 

 out all equatorial regions, power is multiplied three- 

 fold. 



The immediate opportunities for sun-power are 

 in those regions in the tropics where the sun 'prac- 

 tically shines throughout the year, and fuel is very 

 expensive, coal costing in some localities $30 per 

 ton. Mr. Shuman has stated that there is room now 

 for at least half a million horsepower in such tropi- 

 cal fields as the nitrate district of Chile, the borax 

 industry in Death Valley, and for general purposes 



