LITMIR.BIZ

       1

       HISTORY

      THE SUN IS THE CENTER of our solar system. The energy it releases warms our planet and powers all life on earth. Through photosynthesis, solar energy is transformed into organic matter — the food that makes our life possible. The fossil fuels we use are actually stored solar energy. Solar energy is also incredibly abundant. Half a day’s sunlight falling on the US provides enough energy to run our country for one year.

      We often think that modern societies were the first to use solar energy. Not true. Early cave dwellers preferred caves that had openings facing southeast. This allowed the morning sun to warm them up without overheating in the warm months. Native Americans in the Southwest oriented their pueblo dwellings so the low winter sun would heat the buildings by direct solar radiation. Cliffs and overhangs blocked the sun during the summer months, helping to keep the dwellings cooler when the sun was high in the sky.

      The ancient Greeks, with a climate that was sunny almost year round, built their houses to take advantage of the sun’s rays during the moderately cool winters and to avoid the sun’s heat during the summer. Modern excavations of many classic Greek cities show that individual homes were oriented toward the south and entire cities were planned to allow equal access to the winter sun. It is interesting to note that by 500 bc, when the Greeks had almost completely deforested their whole country and needed to find a reliable alternative fuel source, they chose solar energy.

      The Roman Empire advanced solar technology by adapting home-building design to various climates, using clear window coverings, such as glass, to enhance the effectiveness of solar heating and expanding solar architecture to include greenhouses and huge public bath houses. Solar architecture became so much a part of Roman life that sunrights guarantees were eventually enacted into Roman law. This society depleted its forest resource as well.

      After the fall of the Roman Empire, the use of glass to enhance solar gain in buildings was mostly forgotten. Interest in passive solar architecture and greenhouses was rekindled during the Renaissance. As technologies advanced, glass manufacturing was revived, resulting in an increased use of glass windows. This also made large greenhouses possible for agricultural purposes as well as for recreation.

      In the 1700s, a leading naturalist named Horace de Saussure began to experiment with solar hot boxes. These precursors to today’s active solar collectors were simple insulated boxes painted black on the inside and with one side made of glass. They were very similar to today’s solar cookers and, in fact, many early experimenters used their hot boxes for cooking. Many of the solar principles we use today were identified during those early experiments. Unfortunately, these experiments resulted in few successful applications.

      During the late 1800s, domestic water piped directly into homes became more common. Like today, this water supply was cold. People soon wanted hot running water. At first, all water heaters were either coal or wood fired. In 1891 Clarence M. Kemp patented the world’s first commercial solar water heater, called the “Climax.” It was a black-painted water tank mounted in an insulated box with one side made of glass.

      The Climax was instantly popular in California, where it could be used year round. Thousands of Climaxes and similar systems were installed in a short time. They all fall into what we now call “batch-type” solar water heaters: the sun heats the water directly in the tank(s) and the hot water is stored right in the collector tank(s).

      In 1909 a California engineer named William J. Bailey began selling a new system he called the “Day and Night” solar water heater. It consisted of a solar collector and a separate storage tank mounted above the collector. His tanks were among the first to be insulated for better heat retention, and his collectors consisted of a pipe grid attached to a flat plate and enclosed in a compact, glazed and insulated enclosure. Cold water dropped into the collector, where it was heated by the sun. As the water was heated, it rose into the insulated storage tank for later use. Today, we call these heaters “flat plate” collectors.

      In 1913 a freak cold snap hit southern California and many Day and Night collectors froze and burst. To eliminate future freezing problems, Bailey installed a coil of pipe within the storage tank to act as a heat exchanger. Then he used an alcohol and water mixture as the antifreeze solution for his heat exchange medium. As the sun warmed the solar fluid (or heat transfer fluid), it rose to the storage tank heat exchanger. As the heat from the solar fluid was transferred to the water in the storage tank, the solar fluid cooled and dropped back to the collectors for further heating. This system is described today as a “closed-loop” solar water heating system.

      Between 1920 and 1930, huge deposits of natural gas were found in the Los Angeles area. To capitalize on this new, cheap fuel source, Bailey began to manufacture a thermostatically controlled

Скачать книгу