of Winnipeg and Edmonton evacuated tube collectors Solar energy has been which consist of a number touted by misguided en- --are very good. The solar system is generof concentric glass tubes thusiasts as the answer to ally designed to provide with a central black-painted mankind’s energy probcollection surgace. lems. While the amount of less than 100% of the heatHighly effective insulaenergy falling onthe earth is ing needs because a law of diminishing returns sets in tion is achieved by evacuatenormous (enough solar percening the space between two energy falls on the planet in at high solar-energy of the concentric tubes. tages. In general, each solar one hour to meet current heating system has a means In the case of water-based demands for three years), of collecting the heat, a storsystems, heat is there are numerous Bractiage device, and a control usually accomplished by cal difficulties encountered system which decides when keeping the heated water in in tapping this source. tank. In The energy can be con- to collect heat, when to de-, a large insulated and air-based systems, the heat verted into useful forms in a liver it from storage, is stored in a rock bed made the auxnumber of ways. The most when to activate common method is to con- iliary heating- s@ern. up of thousands of stones a Colle&ors are Usually of couple of in&es in dimevert the sunlight directly the flat-plate variety conter. into heat through the use.of sisting of a collection plate The heated air is blown a dark-painted collector, or some other over the rocks, which and then to use the heat di- of copper _-_- then rectly for space or water heating. This is known as a A new solar energy collector patented by the Franklin low-temperature applicaResearch Centre boasts several advantages over existing tion. panels. Made of three coextruded polycarbonate layers, In high-temperature apits cost of about $23 per square meter is one quarter of the plications, the light is concosts of other units, and its weight of-4 kilograms per centrated, often using resquare meter compares well with conventional weights flectors, onto a smaller colof 25. lector area. In some cases, a Westinghouse’s new photovoltic cell has achieved a series of collectors is used to remarkable efficiency of 15.5%. Their process produces boil water which is then a high quality single crystal ribbon of silicon by drawing used to turn turbines to genthe metal from a liquid film, using two silicon filament erate electricity. edge supports. Westinghouse expects to meet their goal In a variation on this conof 50 cents per watt in 1979. cept, a “power tower” could An advanced Rankine-cycle engine developed by be constructed in a desert Solar Energy Systems, if used to drive generators, may location, consisting of a well provide an efficient means of generating electricity boiler mounted on a tall from solar energy heat. Although the projected cost of tower, surrounded by $1.20 per watt is rather high, the adaptability of the thousan’ds of mirrors, all resystem to waste heat from industrial flues gives it a flecting and concentrating decided advantage over competing systems. the solar rays on the boiler. An electrochemical method of storing energy from However, enormous areas of solar cells (or windmills), developed by RCA, employs a land would be required. stream of oil bubbles at the cathode of an aqueous electroSolar energy can be used lyte to produce formic acid. This product could then be’ to generate electricity diused to produce electricity (& a fuel cell), to produce rectly through the use \of hydrogen, or as a carbon source for the petrochemical photovoltaic cells. These industry. cells make use of semiconStephen w. Coates t ductor technology to generate electricity with an effibecome heared. The storag metal that has been painted ciency as high as 11 percent. systems L3r& usually d flat black to absorb the sun’s However, the cost of these rays. signed to hold enough heat cells is very high. One Thih collection plate for two to three cloudy days, scheme proposed in the Unheats up and transferes the although annual-capacity ited States involved putting storage systems have been heat to a working fluid, a huge array of photovoltaic built. The capital cost of anwhich may be water, air or cells into orbit around the anti-freeze, which is runnual systems is very much earth, where the sun always ning in tubes or ducts at- higher. shines and there is no at- tached By properly channeling to the collection mosphere to interfere, and plate. the heated air flow, a tempbeaming the energy to earth To prevent heat loss to the erature gradient (say, 35 devia microwaves. surrounding air, the collecgrees at the inlet, 25 degrees Paradoxical as it may tor is insulated at the back at the outlet) can be mainseem, solar energy can even and the front is covered tained. This allows air to be be USed for cooling. Conwiti one or more glass covheated to temperatures ventihal flat-plate solar ers. Less cOmmOn are the higher than the average -1 1 collectors can be used as a heat source to drive absorptive-cycle air conditioning units. The most natural way to use solar energy is through of the process ‘Rooms are available for the photosynthesis-that is, of course, using the sun to Winter Term. Male and female. grow plants which can be burned for fuel. Wood is the most obvious fuel produced by photosynthesis, although recent work has studied algae and other plants. The &st and most widespread use of solar energy in Canada will be for space and water heating. There are numerous solar homes in Canada already; the industry is becoming well established and is growing rapidly. The key economic factor is not the outside temperature, but the amount of sunlight that a location reNEW LOCATION ceives. It is for this reason that the balmy-weather city LOW OVERHEAD-LOW PRICES I of Vancouver is a relatively poor location for solar heat46 KING ST. SOUTH WATERLOO ing, while the colder cities 666-1360 lOAM-9PM SAT. 6PM
heaters not so hot storage
temperature of the rock be& Another form of heat storage is the use of a phasechange material. A phasechange material is a solid which has a melting point a . few degrees above the ambient temper$ure. (20 degrees .) The fact that much more energy is needed to melt a solid than heat it a few degrees allows such materials tq store far more energy for a given volume than rock bed systems. The energy is, of course, released whFn the solid is melted.
be seen from the road between St. Agatha and Petersburg that has coils of black hose mounted in a wood frame on the roof. In the summer, water is pumped through the hose, and enough energy is gained to heat the small pool in the back yard.
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However, despite the many research programs going on around the world, an adequate phase-change material has yet to be found. Nevertheless, a significant breakthrough, could render all rock storage systems obsolete. Passive solar systems do not require the pumps, fans and equipment associated with active solar systems. Passive solar buildings rely on building orientation, south-facing windows, and the thermal mass of the building structure itself to collect heat.
The University of Waterloo is particularly active in solar energy research in Canada. Studies are being done on collector and storage design, solar-assisted heat pumps, and the computer simulation of solar systems. John W. Chinneck
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In this age of limited energy reserves, passive solar heating principles should be applied to all buildings during the design stage. Although the solar systems described above may sound complex, it is important to realize that the principles of solar heating can be applied in even the crudest devices. There is a house that can
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