THE problem of the commercial utilization for the production of power of the energy of solar radiation, the wind, and other intermittent natural sources, is • a double one. The energy of the sources must first be changed so as to be available in form; it must next be stored, so as to be available in time. As regards the second of these two' points, one of the expedients which perhaps naturally suggests itself, namely, the use of storage batteries, is commercially quite out of the question owing to its high cost. The method actually employed is storage by gravity. Two reservoirs are constructed, one at a considerably higher level than the other, and the water is first pumped up, and then allowed to fall as desired, and to actuate a turbine. A cubic yard of water falling through one thousand feet is capable of giving out energy equivalent to one horse-power hour. If we consider the possible plans for carrying out this project, the arrangement which perhaps first occurs to us is that of building a tank at the top of a tower. But this is impracticable, for either the volume of water required is excessive, or else the height of the tower becomes prohibitive. The problem assumes more promising form if the upper tank is built on the level of the ground, and the lower tank at the bottom of a deep shaft. Estimates were obtained from three different firms of mining engineers in Philadelphia, which showed that a shaft one thousand feet deep could be dug, properly timbered, and the necessary chambers hollowed out at the bottom, and ferro-con-creted, so as to withstand the water pressure, at a cost not to exceed two dollars per cubic yard. Assuming two weeks' storage and an efficiency of 75 per cent, the capital cost per horse-power will be $37.50. Assuming interest at four per cent, and depreciation at two per cent, the annual cost of water storage facilities, exclusive of the pumps and turbines, will therefore be approximately $2.25 per horse-power. Tenders for the pumps and Pelton turbine wheels for a 3,000-horse-power plant show that the cost of these is approximately $12.50 per horse-power. Allowing four per cent interest and four per cent depreciation, this makes a total annual cost for pumps and turbines of one dollar per horse-power. The total annual cost of storing one horse-power by the negative gravitational method is, therefore, $1.00 + $2.25 = $3.25. As regards efficiency, water storage has the advantage over the electric- accumulator. The energy efficiency of a storage battery is generally given as about 65 per cent, i. e., approximately 80 per cent on charge and 80 per cent on discharge. With water storage it is safe to assume an energy efficiency of 89 per cent,- both at charge and discharge, giving a net efficiency of 80 per cent. We have next to consider the method of obtaining the energy from the sources. There are two main sources available, solar radiation and- the wind. To obtain an idea of the amount of power which solar radiation represents under normal working conditions, a long-continued. series of measurements were * Abridged from a paper read before the British Association for the Advancement of Science. made by Prof. Very, who found that the amount of solar energy received per annum at the earth's surface on an area one hundred meters square in the places indicated is on an average as follows: Kilowatt hours. Central Europe .............. 4,000,000 to 6,000,000 Northern United States ...... 5,000,000 to 7,500,000 Southwestern United States.. 10,000,000 to 15,000,000 As regards the amount of power to be derived from the wind, tests made during a period of one year on a steel tower 420 feet high at Brant Rock, Mass., showed an average of 800 horse-power at the shaft uf a windmill of 300 feet equivalent diameter: These figures are about 30 per cent higher than those ob. tained by Danish experimenters; the difference is probably to be attributed to the fact that the Danish experiments were made near the surface of the ground. To utilize solar radiation, it is proposed to use a solar tank containing water heated to about 100 deg. C.*. The steam so generated at atmospheric pressure is to drive a low-pressure steam turbine, which operates the pump. Low-pressure working is resorted to, because with this arrangement the transparent top of the chamber containing the working fluid can be made very thin, and has to withstand practically no pressure. The transparent roof is designed of double thickness, and contains wire netting imbedded in the glass as a protection against hail. The working fiuid fiows in a thin stream across the bottom of the solar tank, and the thickness of the stream is varied automatically with the amount of radiation received. The working fluid contains a small amount of potassium dichromate. The glass forming the transparent covering contains a small amount of sulphate of iron, - sufficient to give it a pronounced greenish tinge. It has been found that by this means the glass can be made totally refiecting for wave lengths corresponding approximately to those. emitted by the heat of water, while remaining fairly transparent to the radiation from the sun. The thermodynamic efficiency of the system is approximately fifteen per cent, and it is anticipated that about ten per cent would be obtainable on the shaft of the steam turbine. From tenders made, the costs per horse-power have been found approximately as follows: Solar tank .................................$10 Low-pressure steam turbine and condenser.. $25 Dynamo .................................... $15 Adding to this the cost of the pumps and the water turbine, we obtain a total of $62.50 for the first cost .per horse-power for the machinery, exclusive of the reservoirs. Allowing interest at four per cent, and depreciation at four per cent, and two per cent for labor, we obtain a value of $6.25 per annum per horsepower as the cost, exclusive of the reservoirs. Adding in the cost of the reservoirs, we find $8.50 as the actual cost per horse-power. It will be seen that these figures compare favorably with the present cost of producing power from coal. Moreover, these estimates are excessive, for the reason that it is proposed to operate a windmill plant in conjunction with each solar radiation plant. The load will thus be greatly evened, and a much better all-day and all-year efficiency obtained, because the wind is, as a rule, more effective during cloudy weather and at night time, i. e., at the time when solar radiation is diminished or absent. The storage reservoirs employed in connection with this solar plant are, of course, available without additional cost for the wind-power installation. Assuming a solar tank .200 meters square, we may expect to receive a total radiation of approximately twenty million kilowatt hours per annum. Assuming an efficiency of ten per cent, we should get two million kilowatt hours at the steam turbine shaft. On the basis of a seven-hour day, the solar radiation plant would yield an average of 800 horse-power. Adding to this the energy derived from the windmill, we obtain a total of about 1,500 horse-power. The figures given above are for average conditions. The location of the first plant is, on the whole, much more favorable. It is situated at a copper mine, where the vertical shaft is already available, and where worked-out lateral chambers are used for the lower reservoir. A portion of the pumping machinery also is provided at the mine, thus further reducing the cost of installation. The following is a comparative estimate of the costs of producing one horse-power for one year by steam, gas engine, water power at Niagara Falls, and the present method. The estimates are based on a plant having a capacity of 100,000 horse-power, operating under average conditions : Cost per horse-power Method of generating power. per year. Steam ... .................................... $15.00 Gas engine.................................. 10.00 Water power at Niagara Falls................ 3.75 From intermittent natural sources............ 4.50 Water power under exceptionally favorable conditions .................................. 2.50 It will be seen that while this method of producing power is much cheaper than a steam or 'gas engine, it is approximately on a par with water power under fairly favorable conditions, such as prevail at Niagara Falls. This is because in the present method and with water power the capital first cost is the determin ing factor. The capital first cost per horse-power by the present method using a solar tank is approximately .$62.50; and using windmills in conjunction. with the solar tank, approximately $45. The capital first cost at Niagara Falls is approximately $40. The new method gains chiefiy from the higher fall and from the cheaper and more efficient water motor, also from the fact that only one-seventh as much water has to be handled, and that there are no dams to build or large buildings to erect. It loses from the fact that a pump has to be supplied, also a steam turbine and solar tank or windmill. The method, therefore, may not be of so much value in places favorably situated for obtaining water power. Localities 'so favored are, however, comparatively few in number. The Argon Process In a paper presented to the Academie des Sciences, M. Georges Claude shows that it is easy to obtain argon in the laboratory by using oxygen furnished by the liquefaction of air to begin with. In practice such oxygen is above 95 per cent pure, and the principal impurity, at least with the oxygen which the Claude process procures, is argon, whose volatility is intermediate between those of oxygen and nitrogen. Only a lack of tightness in the oxygen compression apparatus would give a predominance of nitrogen. Oxygen at 96 per cent, for. instance, contains normally more than 3 per cent of argon, and hence it is a raw material which is three times as rich as air for the argon process. Besides, the oxygen is much more easily absorbed than nitrogen. In the method used by the author, he absorbs the oxygen by means of copper and the nitrogen by that of magnesium. We can regain the copper in the metallic state, and the expense for magnesium is small owing to the low percentage of nitrogen. The oxygen is taken from the steel bottle by means of a suitable expansion valve. It is sent into a copper tube filled with reduced copper and heated to a low redness. The residue traverses a smaller iron tube full of powdered magnesium heated to redness, and then an oxide of copper tube designed to absorb the hydrogen 4utl to any initial dampness of the copper or oxygen. The absorption of the oxygen by copper takes place very rapidly and would cause the fusion of the oxide if the delivery of gas were too high, but we should avoid such fusion in order to keep up - the porosity of the mass, this allowing of an easy recuperation of the metal by a hydrogen treatment, so that in practice we use continually the same tube. For instance, ' he uses a copper tube 60 centimeters (23.6 inches) long and 6 centimeters (2.36 inches) diameter, heated over the whole length from the start of the operation by the flame of four Bunsen burners of the butterfiy type. The tube,is charged with 2.5 kilogrammes (5.5 pounds) reduced copper mixed with some fine turnings so as to increase the permeability of. the mass. An iron tube is charged with magnesium, the tube being 40 centimeters (15.7 inches) long and. 3 centimeters (1.18 inches) in - diameter, heated to redness on a grating. The copper oxide is placed in a silica tube 30 by 2 centimeters (11.8 by 0.78 inches) kept at low redness. This apparatus allows of treating 3 liters (85 cubic feet) of oxygen per minute and thus we obtain. 4 to 6 liters (113.2 to 170 cubic feet) of argon per hour during 2 hours, or 8 to 12 liters (226 to 339.7 cubic feet) before exhausting the copper. The best method of following the operation Is to take at the start the densities of the gases collected until we obtain the density due to argon.- No new observations need be made before the last half hour, for the operation is very regular and the absorption quite complete. The recuperation of the copper by hydrogen in the same conditions of heating as above can be completed in less than 1% hours. The Pennsylvania Railway Company announces that it has instituted a new plan of training men to maintain and operate. signals.. It has appointed four signal apprentices who are college graduates. The different divisions of the lines east of Pittsburg have started signal schools, where experienced men give instruction to the division signal employees. The importance of this step is indicated by the fact that whereas in 1902 there were but 7.891 interlocking functions in operation on the lines east of Pittsburg, in 1908 this number ,was 20,725. These functions are operated by 8,792 levers. A total of 12,408 signals is in service, covering 3,385 miles of road, or over 70 per cent of the mileage. Signal apprentices will serve a three years' course, and will then be eligible for the position of assistant signal inspector in the signal engineer's office. After ' attaining this they will be considered for appointment to the following positions: Assistant supervisor of signals, supervisor of signals, inspector, assistant signal engineer, and signal engineer.
This article was originally published with the title "Power Production from Solar Radiation" in s , , 39 (August 2013)