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= Solar Powered Refrigerators = Solar-powered refrigerators which harness solar energy are used in the developing world to help mitigate poverty and climate change. They are used to keep perishable goods, such as meat and dairy cool. Doctors also use them to store important vaccines. An innovative portable solar-powered refrigerator that can be constructed by simple components has recently been produced by a 21-year old British student that is perfect for areas of the developing world where electricity is often not reliable. Other solar-powered refrigerators were already being employed in areas of Africa which vary in size and technology, as well as their impacts on the environment.

Environmental Impacts of Refrigerators
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 refrigerator is inefficient it will also contribute to global warming. The use of solar energy to power refrigeration strives to minimize the negative impacts refrigerators have on the environment. .

History of Solar Refrigeration
“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,”. 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 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. They can also be difficult to adjust which can result in the freezing of medicine. 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.

Battery Supplemented Solar Refrigerator
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. 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. These problems and the resulting higher costs have been an obstacle for the use of solar powered refrigerators in developing areas.

SolarChill Fridge
Recently a product has been developed that does not require the use of toxic lead batteries. It is called the “SolarChill” fridge (Figure 1) which requires no batteries or any other energy inputs to stay cool therefore it also emits no carbon dioxide. In addition it requires little maintenance, is cheap to run, and uses no ozone-damaging refrigerants. There are two designs for the solar powered fridge. One has a fifty liter chest and is intended as a vaccine cooler which holds vaccines between the required 2 ºC and 8 ºC during typical day-night solar cycles. It can provide a secure cold chain for vaccine and medicines which has remained problematic in many regions of the world that are off the electrical grid or the electrical supply is unstable. Weak links in the cold chain result in large quantities of spoiled vaccines each year. The other is a 100 liter upright freezer cabinet modified to be a food refrigerator. This model is useful for hot climates where food preservation is challenging and is also utilized in emergency circumstances, refugee camps, rural blood banks, and small scale commercial applications in developing countries. It also has the potential to be used for off-the-grid recreational cottages in industrialized countries.

How it works
Both models run on the same principles and design. When sufficient light is captured, three 60-Watt solar panels supply energy that runs a direct current (DC) compressor running at 3500 rpm. The DC compressor pushes refrigerant through the cooling system that enables the cooler to form an ice in a separate compartment from the vaccine storage unit that maintains the required temperature in the cabinet ). A fan then circulated the air by convection and temperature is regulated by a thermostat .  Instead of storing energy in lead batteries, power from the sun is stored in an ice battery and kept cold by thick insulation that ensures the fridge stays cold even after the sun goes down and during periods of low sunlight ).

Environmental Benefits
The “SolarChill…bridges health, development and the environment” ). It uses isobutane  and cyclopentane  as the foaming agent, both of which are harmless to the Earth’s ozone layer.  It helps developing countries avoid dependence on CFC’s and kerosene as well as the associated carbon dioxide emissions.  The use of ozone layer depleting and global warming fluorocarbons, such as HCFC’s and HFC’s are bypassed. Solar energy also helps shift from a reliance on fossil fuels as a primary source of energy towards a renewable energy source.

Limitations
In developing countries where the technology is most needed, road access can be limited creating difficulties for transporting the large fridges. Bulky solar panels are also difficult to transport and require careful packaging to ensure their safe arrival. They are also expensive to purchase, however, low maintenance and zero fuel costs do balance some of the original price tag over time.

Portable Solar Powered Fridge
A Portable solar powered fridge has been produced for use in the developing world (Figure 2). The basic design uses the principle of evaporation. 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.

How it works
The refrigerator employs a combination of conduction and convection, requires no electricity and can be made for commonly available material such as cardboard, sand and recycled metal. The device is comprised 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. 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). (Figure 3)

Usage
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 (Figure 4). It is easily transported and reduces negative environmental impacts but is limited by size and requires the availability of water.

Related information

 * Solar energy is energy derived from the sun. Used synonymously with solar power, it is the ability of the sun to convert sunlight into electricity


 * The ozone layer protects the Earth from the ultraviolet rays sent down by the sun


 * Global warming is the increase in the average temperature of the Earth's near-surface air and oceans since the mid-20th century and its projected continuation.


 * CFC’s have been used worldwide as refrigerants and insulation foam blowing agents in refrigerators since 1940’s. Scientists in the 1970-80’s discovered that the large scale emissions of these substances and their eventual molecular breakdown in the atmosphere caused ozone layer depletion and also significantly contributed to global warming (UNEP, 2005).


 * Hydrochlorofluorocarbons, commonly known as HCFCs, are a group of man-made compounds containing hydrogen, chlorine, fluorine and carbon. They are not found anywhere in nature.


 * Solar panel refers to two types of devices that collect energy from the sun: Solar photovoltaic modules use solar cells to convert light from the sun into electricity, and Solar thermal collectors use the sun's energy to heat water or another fluid such as oil or antifreeze.


 * SolarChill aims to deliver environmentally-sustainable vaccine and food refrigeration to regions of the world that lack electricity or have inadequate electrical supply. The Project has evolved into a unique partnership between seven international organizations, which today comprises DTI, German Government Development Agency GTZ ProKlima, Greenpeace International, Programs for Appropriate Technologies in Health (PATH), UNEP, United Nations Children’s Fund (UNICEF) and the World Health Organization (WHO) (Pedersen & Maté, 2006).


 * The term “cold chain” refers to the cooling network that is required to safely deliver vaccines from the manufacturer to the recipient. This network ensures, as much as possible, that vaccines are kept at the proper temperature as they are distributed from the manufacturer to the locations where they are administered.


 * Isobutane, also known as methylpropane or 2-methylpropane, is an alkane, isomeric with butane. Recent concerns with depletion of the ozone layer by freon gases have led to increased use of isobutane as a gas for refrigeration systems.


 * Cyclopentane is used in the manufacture of synthetic resins and rubber adhesives and also as a blowing agent in the manufacture of polyurethane insulating foam, as found in may domestic appliances such as refrigerators and freezers, replacing environmentally damaging alternatives.


 * Renewable energy, any naturally occurring, theoretically inexhaustible source of energy, as biomass, solar, wind, tidal, wave, and hydroelectric power, that is not derived from fossil or nuclear fuel.


 * Conduction is the transfer of heat between two parts of a stationary system, caused by a temperature difference between the parts.


 * Convection is the transfer of heat by the circulation or movement of the heated parts of a liquid or gas