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SG-W:/ Solar Mirrors



                                     Solar Facility
 
           I have been thinking for a long time how solar energy could be used across the country. If we reduce our consumption by 50% there is a possibility that we could supply 10 to 20% of our needs from solar. The first large desert installations should be designed for the manufacturing of essential things like fertilizers, liquid fuels, and metals. It should be noted that the first things that suffered in the western power shortages were fertilizer and aluminum plants. I believe that mirrors will be more important to electric generation than solar voltaic cells simply because their cost per square foot is much lower.
            Here in Michigan it has been overcast for several days now. In spite of that fact I believe that solar could help take the place of other energy and should be ubiquitously used. My design model would be a solar facility for an apartment house- general purpose building which I call an Ecomindium. This would be a part of a Sustainable Community.My favored approach would be large parabolic mirrors that would focus on a central tower boiler or manufacturing target. It would be better if the target were on top of the building but that would entail a fairly high tower and great care in limiting beam travel. Such a beam would be very dangerous.
         .Things that I think could be done would include the generation of electricity using a steam engine, lighting the building using light pipes, heating the building with heat from the steam condenser or through window illumination, purification of water, and pyrolization of biomass to make liquid or gaseous fuel. In winter there might not be enough heat to make electricity but there still might be some for building heat. Liquid fuel for tractors will be highest priority for an energy starved country and might well be manufactured on a local basis. The easiest thing to accomplish would be to generate electrical capacity to satisfy the summer air conditioning peak.
           The solar tower type of installation would require long focus parabolic mirrors, perhaps with 200 to 300 foot focal length. The reflector would be mounted on a low set turntable for azimuth and would be hinged in order to adjust elevation and to deploy in high winds. It is my belief that some of the parts could be made from wood. Rather than steel. (The mirrors used in commercial solar tower systems are usually called heliostats and were made in very large diameters by stretching metal membranes over large steel dishes. Evacuating air behind the membranes and adjusting the air pressure is used to focus the heliostat.)
             Building this type system by the public is limited by the availability of commercially available parts. One of the things I would like to see the government do would be to mass produce solar mirrors in units perhaps 4 feet square. These could then be ganged on a frame and used in various ways. A thought for mechanic builders would be to build mirrors using 1 ft square mirror tiles. These could be arranged on a flat surface to form a large Fresnel mirror. Each tile would of course have to be tipped in just the correct way. I believe it would be easy to build a boiler from tubing and an efficient steam engine from gasoline engines. In full sunlight each mirror tile would catch about 100 watts of energy and the efficiency of conversion to electricity could be as high as 20%, so you could strive for 20 watts per sq ft. An 8 by 8 array then would yield about 20,000 Btus/hr raw heat or 1200 watts/hr electricity. For an apartment building one might want a mirror as big as 32 by 32 or 1000 sq ft.
          I am interested in comments from people who have more experience than I do on the possibility of using ordinary 1 sq ft mirror tile to make a composite reflector, the possibility of urging the Government to put a 4 ft by 4 ft mirror module into production, comments on what is available, problems in making and steering the long focal length mirrors needed for solar tower installations, the possibility of using light pipes to send solar light and heat into a building, and the possibility of making liquid and concentrated fuels from biomass by using solar energy. 
           The process of using desert areas for solar manufacturing of such indispensables as fertilizer, processed metals, liquid fuel from biomass, glass, and concrete would reduce the problems of shipping electricity or hydrogen for long distances. It might be possible to use solar to make a concentrated fuel from shale.  
 
                                                Kermit Schlansker    PE