Solar-powered refrigerator is a cooling appliance that works completely with energy provided by the sun. They are mostly used in hot climates to keep food so it would not perish and to keep vaccines at their appropriate temperature. Some solar-powered refrigerators use combination of solar panels and lead batteries to store energy when there is no sun (on the cloudy days and at night), while other use heat of the sun to make refrigerator work.
The first to have an idea for a solar-powered refrigerator was an engineer Otto Mohr in 1935. He designed all of the correct components needed to build the solar refrigerator and with them it would work. Since then many engineers, scientists, and researchers improved his ideas and built their working variants of a solar-powered refrigerator. In 1950’s USA installed a flat plate collector system. At the same time USSR made a parabolic mirror which could produce 250kg of ice per day. An absorption machine with a cylinder-parabolic mirror was made in France and it could made 100kg of ice per day. There were also built systems that charged during the day and cooled during the night. Today, solar refrigerators are mostly used for camping and in developing countries where electricity is scarce.
Refrigerators generally keep food cool through the process of evaporation. Compressor, which is a part of a refrigerator, turns the refrigerant gas into a liquid. Pressure is then removed; the refrigerant turns back into a gas and absorbs heat because it has to take energy from somewhere. That cools its surroundings. Solar-powered refrigerator works similarly but the refrigerant is replaced with ammonia or lithium bromide mixed with water. Instead of compressor, the heat of the sun is used to increase the pressure of the gas. From here solar refrigerator works as a common refrigerator: gas again turns into a liquid, heat is removed, the liquid evaporates and lowers the temperature.
Solar-powered refrigerator is useful for many reasons. First it is used in regions that have no electricity but have greater number of sunny days a year. Secondly, such regions often use kerosene or gas-powered absorption refrigerated coolers which require constant supply of fuel and generate large amounts of carbon dioxide. They are also very difficult to adjust which can result in the freezing of medicine which is kept in those coolers. Fuel is also costly and there is risk of causing fires. Solar-powered refrigerator can replace these kinds of coolers and make cooling safer.
Solar-powered refrigerator that have batteries work on electricity but it is supplied from solar panels. These refrigerators are expensive and have heavy lead-acid batteries which deteriorate quickly in hot weather. Batteries also must be replaced approximately every three years which makes them more costly and there is also disposing of these batteries because, if not disposed properly, they can result in lead pollution. Solar-powered refrigerators don’t have these problems but they are very dependent on the sun and on the cloudy days they don’t work and have to have reserve systems that will maintain low temperatures on such occasions.