Power from Sunshine

A Pioneer Solar Power Plant

THE direct utilization of the natural forces in the development of power suitable for human activities has been for centuries a matter of continued scientific research. To a limited extent these forces have been used from the dawn of civilization in the common forms of the. windmill and various types of water-driven motors. It has not, however, been hitherto possible to practically utilize the central dominating forces of nature-the suns heat-in any direct manner, though obviously all power generators are dependent upon this great source for their existence. For many years engineers and physicists have been occupied with this problem; notably Ferry, Millochan, Mouchat and Tellier in France; Giintner and Althaus in Germany; and Langley, John Ericsson, and ,illsie in America. These experimenters based their efforts ither upon the use of lenses or mirrors to concentrate the sun's rays upon a small surface, or l1pon the heating of fluids of a low-boiling point, with subsequent power generation from the vapor under pressure. It has always been attempted to create vapor at high pressure, and then utilize this in the ordinary engine, but with the high temperatures involved, the losses by conduction and convection are so great that the power produced was of no commercial value. Where lenses or mirrors are used, the primary cost of the lenses, .and the apparatus necessary to continuously present them toward the sun, have rendered them impracticable. Where fluids of low boiling point, such as ether, sulphurous acid, and liquid ammonia were used, the results were of little value by reason of the inherent inadequateness of these fluids as power generators. A sun-power plant, in order to be ]racticable, must possess, first, high efficiency; low cost of installation and maintenance; well"marked length of service; and should not require specially trained mechanics for its operation. In order to be efficient, it is not necessary that the plant generate continuously, inasmuch as the great value of such a plant lies in its use as an irrigation apparatus; it is only necessary that the plant run about eight hours daily. It must, however, consist of units which may be assembled to produce a power plant of any required size, the larger the plant the greater the efficiency. It is entirely practicable to produce a sun-power plant in this manner up to 10,000 horse-power and over. An ideal plant must be subject to 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 absorber 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 oTdinary steam-power plant of the same size. This price is sufficiently 10w, lowever, so that even if the extra interest is taken into consideration, the faet that after installation no fuel Is required, is such an enormoqs advantage as to entirely offset the increased cost, and In addition cause great prOfts. Some ten years ago the writer became Interested in the problem of obtaining power by absorbing the sun's rays. It was found, by experiment, that if a vessel were so arranged that the sun's rays could impinge upon it, and if all heat losses by conduction, convection and radiation were prevented by a theoretically perfect method of insulation, the temperature within , the vessel would rise certainly to a thousand degrees Fahrenheit without any attempt being made to concentrate the rays of the sun. For commercial purposes it is impossible to secure any form of insulation which would even approach 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 go up to 350 deg. F. in latitude 40 north, possibly easily to 450 deg. F. near the equator. The production of steam at atmospheric pressure, however, keeps the temperature in the vessels down to 212 degrees; and whatever excess of heat is produced by the sun's rays over and above that lost, is converted into steam, and may therefore be utilized. The experience of additional years will, no doubt. lead to designs considerably better than this first attempt on a commercial scale. Sun power must go through the same long and gradual ('ourse of development that has brought other forms of mechanical power to the present high plane of efficiency, but the principle will remain fundamentally correct. With this idea in mind the first Shuman -generator was built. It 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 16 feet long, insulated at the bottom, and inclosed in a box covered by a double layer of glass. Here again ether was disti1led, 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 18 x 60 feet, and the motor being an ether engine. With this apparatus 3% horse-power was obtained. With the knowledge so gained, the present generator, to be described below, was gradually evolved. The sun-power plant in its present development consists of the absorber, a low-pressure steam engine, condenser, and auxiliaries. The absorber, in a general way, is composed of a series of units, each containing a flat metal honeycomb water vessel rectangular in shape, and resembling closely” a large waffle. This vessel is inclosed in a flat wooden box covered with two layers of glass having a i-inch air space between them, and having the under surface of the box insulated against heat loss downward by a 2-inch layer of regranulated cork and two layers of water-proof cardboard. The boxes are mounted on supports which elevate them some 30 inches above the ground, and which permit them to be inclined perpendicular to the sun at the meridian. These adjustments of the inclination need only be made about once In three weeks. Plane mirrors of cheap construction are mounted on two sid e s of th e boxes In order that more rays of the !un may be absorbed and reflected upon the lurfaee of the water vessel, This latter Is connected at one end to a feed pipe from the water supply, and at 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 is 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 10ES is from accidental leakage, which is carefully guarded against. The power of this first plant is used for pumping water by means of a reciprocating steam pump of the ordinary type, and whenever the sun has shone during the past six weeks, this plant has pumped water successfully and practically. The capacity of the present plant, in this latitude, is 3,000 gallons of water per minute, lifted to a height of 33 feet. From actual tests made in Philadelphia in August, 1911, it was found that from the absorber of 26 banks of units, each containing 22 single units and having a Ught 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 normal to the- plant, as it was built for tropical use and was entirely unfitted for commercial work in northern latitudes. It is found by observation that the steam generated in a sun-power plant is reduced largely by humidity and the presence in the air of smoke, haze, etc. It follows, then, that the efficiency will be greatly increased when the apparatus is tested in a dry climate free from atmosphe.ic impurities attendant upon proximity to a large city. The plant was set up at Philadelphia, not because it was considered to be a commercial thing there, but because the necessary experimenting with a new plant thousands of miles from home would have been exceedingly expensive. Within . a month or two this plant will be taken down and erected in Egypt. This can be conveniently done, as the entire heat absorber is practically portable. Again. the loss of heat by conduction and convection in northern latitudes is enormous. If the present apparatus is placed in an average air temperature of 100 deg. F., such as obtains throughout all equatorial regions, it is safe to assume that the power will be multiplied three-fold. Having described the mechanism of the sun-power plant, it remains to discuss the opportunities for its use. The immediate opportunities for sun power are in those regions in the tropics where the sun practically shines throughout the year, and fuel is very expensive, coal costing in some localities $30 per ton. There is room now for at least half a million horsepower in such tropical fields as the nitrate district of Chile, the borax industry in Death Valley, and for general purposes in places where the outside temperature runs from 110 to 140 degs. F. As an irrigation engine there is no limit to the amount of ,power that can be practically utilized; and for this purpose the conditions need not be so very favorable as those mentioned above. Throughout most of the tropical regions Sln power will prove very profitable in irrigatIon. One advantage of the sun power, or, In fact, of any condensing plant for Irrigating purposes, Is that the water used for the condenser costs nothing, as the main output of the engine can be passed through the condenser first be· 292 SCIENTIFIC AMERICAN Septem bel' BO, 19 J fore entering the irrigating canals for distribution. ; The interior of Australia was, at on time, a fertile country, as is videnced by the fossilized trees. Here is an area of som 600 miles in each direction which is entirely valnless. During a drought there have been times when one-third of the sheep raised on the margins of this desert died from thirst, causing great fnaneial loss. In this locality the sun shines with an intensity sufficient to produce an average daily temperature of .100 to 140. degs. F. The occasional rains nourish the sparse vegetation necessarv for sheep, which are watered from wells drivn in the ground and pumpe,d, generally by horse power, very oftn by hand, and sometims by means of fuel oil, which, by the time it reaches its destination, brings the coal equivalnt up to some $20 per ton. By building sun engines in this region, and pnmping from the always present underground water which in this r-gion lies at a depth of from 15 to 40 feet, this country can b m[e productive and valuable. Throughout Eastern India and Ceylon many thousands of square miles of farm land can be improved three-fold hy mechanical. irrigation. Hand pumping is mainly the present form of irrigation used. In Egypt agriculture depends entirely upon irrigation furnished by the River Nile through its periodic overflow. The English governmnt built the Assuan Dam at an enormous xpense, and widened the irrigable area about half a mile on each side of the Nile, {hus adding greatly to the tillable portion of Egypt. Of course, when the Nile is in flood infinitely more water than necessary is furnished; but the demand is for a supply which can be dependd on from day to day, especially at seasons of low water. This supply at present is furnished by the hand labor of some 100,000 fellaheen who pump by means of th shadoof method. One sun engine, such as is now erected in Tacony, will do the work of about a thousand of these laborers. Throughout Arizona, Nevada, New Mexico and Southern California there is roon for any amount of power for irrigating purposes alone. These States show an average of 90 per cent sun light, and the” (ost of fuel is practically prohibitive in most of this rfgion. To summarize all of the above statemnts. it may be assumed that 10 per cent of the earth's land surface will eventually depend upon sun power for all mechanical operations. Given inexhaustible power, whieh is, of course, always obtainable from the sun. and utilizing the nitrogen in the air for fertilizer in the form of nitrates and such compounds as calcium cyanamide, th human race will be enabled to draw directly on th source of all life for power and sustenance. A question of paramount importance in the possibilities of a general use of sun power is the cost of the apparatus. In the Shuman type of sun-power plant, the engine, condenser and auxiliaries are similar to those in daily use by steam plants, and may therefore be eliminated from comparison; leaving the absorber and the ordinary steam boiler alone to be compared. It is found that at this time the initial cost of the sun-heat ah- sorber in qustion is about double that of a first-class boiler plant of qual power. The great eonomy occurs in th item of fuel. In districts espcially suitable for sun power the cost of coal, or its equivalent, is usually very high, th price ranging generally from $10 to $30 per ton. To offset this, no fuel at all is rquird by the sun heater. In the matter of maintenance and repairs also the advantage lies with the sun power. It is estimated that the repairs should not be in excfSS of 5 per cent per year on the initial cost, inasmuch as the apparatus works at low temperature, while the ordinary boiler requires flue gass up to 2,500 degrees. This wear of the parts must manifestly be much greater in the latter form of power plant. Many parts of the sun-power plant, such as the metal heaters, piping, foundation and insulation, are practically everlasting, barring accidental breakage, the only item of repair being the wooden frames and glass covers; and it is found that after an installation of glass has once been tested out by the heat, and the badly annealed sheets replaced, the remainder will last for years. This was evidenced by the small 18 x 60 feet heater in operation for three years in Philadlphia. There was a replacement of about 10 per cent necessary during the first three weeks; thereafter the heater ran three seasons and only two or three sheets of glass needed replacement, thse being accidentally broken. There is now being tested out a celluloid-like material having all the necessary proprties of glass and being flexible and capable of manufacture in large sheets. The nse of this substance will not only greatly rduce the cost of installation of sun-power plants, but will make repairs a factor of but slight importanee. It may also be said that the large area covered by the sun-power plant would add greatly to the expense, but inasmuch as these plants ar intendd for use where the cost of land is very low, such criticism is not valid. The future development of solar power has no limit. Where great natural water powers exist, sun powr cannot compete; but sun-power generators will, in the near future, displace all other forms of mechanical power over at least 10 pr cent of the earth's land surface; and in the far distant future, natural fuels having been exhausted, it will remain as the only means of existence of the human race. The Current Supplement THE rumor of the birth of synthetic rubber makes us look with renewed interest at those industrifS in which India rubber is worked up into various articles. A review of the Present Status of the Rubber Industry forms one of the principal topics in the current SUPPLEMEXT, No. 1865.-The fifth instalment of Prof. Turner's articl on The Great Star Map continues his discussion of the subject of star positions.-The length and charactr of wood fibers is a subied of interest both to the botanist and to those who carry on industries using wood as a raw material. The subject is discussed in a brief illustrated article. -Every now and again a seemingly new disase becomes fashionable. A case of this kind is appendicitis, which for some years past has sprung into remarkable prominence. The question naturally arises, is it really a new disease, or if not, how came it to eseape our notice until recently? The discussion of this qUestion, by a French physician has appeared in Cosmos, and- is reproduced in this paper.- striking new development, along the lines of Lodge's classieal experimnts on Fog Dissipation, comes to us from California, . whre Prof. Cottrell has succssfully applied electricity for the precipitation of fumes occurring in manufacturing processes. The report of his work, abridged from the Journal of Ind1strial Chemistry, is incorporated in the currnt issue.^-The economies rsuiting from the use of lifting magnets in foundries are expounded by H. F. Stratton.-A simple electroplating apparatus is described.-A. Emerson tells of a newly discovered portrait of Con-stan tine the Great.-Two short articles are devoted to phases in the plant industry, the one on the recovery of useful products from willow bark, the other on a device for testing cereals for their resistance to disease.-The second instalment of F. P. Valntine's valuable paper on Problems in Telephone Traffic Engineering appears in this issue.

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