Solar-powered refrigerators may be most commonly used in the developing world to help mitigate poverty and climate change. By harnessing solar energy, these refrigerators are able to keep perishable goods such as meat and dairy cool in hot climates, and are used to keep much needed vaccines at their appropriate temperature to avoid spoilage. The portable devices can be constructed with simple components and are beneficial for areas of the developing world where electricity is unreliable or non-existent. [1]
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There is major environmental concern regarding conventional refrigeration technologies including contribution to ozone layer depletion and global warming. Refrigerators which contain ozone depleting and global warming substances such as chlorofluorocarbons (CFC’s), in their insulation foam or their refrigerant cycle are the most harmful. After CFC’s were banned in the 1980’s they were replaced with substances such as hydrochlorofluorocarbons (HCFCs), which are ozone depleting substances and hydrofluorocarbons (HFCs). Both are environmentally destructive as potential global warming chemicals. If a conventional refrigerator is inefficient or use inefficiently, it will also contribute more to global warming than a highly efficient refrigerator. The use of solar energy to power refrigeration strives to minimize the negative impacts refrigerators have on the environment.[2]
"In developed countries, plug-in refrigerators with backup generators store vaccines safely, but in developing countries, where electricity supplies can be unreliable, alternative refrigeration technologies are required”.[3] Solar fridges were introduced in the developing world to cut down on the use of kerosene or gas-powered absorption refrigerated coolers which are the most common alternatives. They are used for both vaccine storage and household applications in areas without reliable electrical supply because they have poor or no grid electricity at all.[4] They burn a liter of kerosene per day therefore requiring a constant supply of fuel which is costly and smelly, and are responsible for the production of large amounts of carbon dioxide.[5] They can also be difficult to adjust which can result in the freezing of medicine.[6] There are two main types of solar fridges that have been and are currently being used, one that uses a battery and more recently, one that does not. Most battery-free solar refrigerators will simply use ice or another phase change material to store the energy required for cooling. This can practically provide limited cooling for a day or so but with no control over the temperature or the cooling rate this is not suitable for delicate payloads like vaccine. In order to solve this problem new technology such as Sure Chill developed in the UK and the SunDanzer Direct Drive technology are available. Vaccine refrigerators using Sure Chill and Direct Drive technology have demonstrated outstanding performance by keeping vaccines at stable temperatures for two weeks with no power even at an ambient temperature of 32C.
Traditionally solar-powered refrigerators and vaccine coolers use a combination of solar panels and lead batteries to store energy for cloudy days and at night in the absence of sunlight to keep their contents cool. These fridges are expensive and require heavy lead-acid batteries which tend to deteriorate, especially in hot climates, or are misused for other purposes.[7] In addition, the batteries require maintenance, must be replaced approximately every three years, and must be disposed of as hazardous wastes possibly resulting in lead pollution.[8] These problems and the resulting higher costs have been an obstacle for the use of solar powered refrigerators in developing areas.[9]
A Portable solar powered fridge has been produced for use in the developing world. The basic design uses the principle of evaporation.[10] The fridge is solar powered, but does not require solar panels, and can be made from basic household material lowering the cost and making access to the developing world easier. Without using any power the fridge can keep perishable at a temperature of 6 degrees Celsius for days.[11] Also see zeer.
The refrigerator employs a combination of heat conduction and convection, requires no electricity and can be made for commonly available material such as cardboard, sand and recycled metal.[12] The device is composed of two cylinders. The inner metal cylinder is fitted inside the outer cylinder which can be made from what ever the person has access to including wood or plastic.[13] Space is left between the inner and outer chamber to be filled with organic material which can include sand, wool or soil that is then saturated with water. As heat from the sun evaporates the water, the inner chamber cools reducing and maintaining the temperature at 43 °F (6 °C).[14]
The portable solar fridge is used in areas of Africa such as Zambia, Namibia, and South Africa in areas where electricity is often not readily accessible to help preserve perishable foods such as meat and dairy, however, is not yet being used for vaccines.[15] It is easily transported and reduces negative environmental impacts but is limited by size and requires the availability of water.