Solar Powered Refrigerators

Solar power, often referred to as photovoltaics, is gaining traction as part of the overall energy efficiency solution. Applications range from powering our homes to charging cell phones and radios; and recent technological developments suggest that widespread production of solar powered automobiles will soon be a reality. Along these same lines, tremendous strides have been taken in applying this technology to refrigerators:

• The most common one being the NASA-licensed SunDanzer, which, but for the photovoltaics, operates similar to a traditional refrigerator, and
• A recent innovation, Eco-Fridge that changes the whole paradigm around harnessing solar energy.

The SunDanzer-An Application of Traditional Solar Power

The SunDanzer was initially developed by NASA scientists for use on the International Space Station (ISS). Given the challenges of providing more traditional electricity to remote locations and developing third world economies and the need for refrigeration of medications, vaccines, and food, efforts were initiated to expand this technology to the world at large.

The actual operation of the SunDanzer refrigerator is similar to a traditional one:

• A refrigerant gas is compressed causing it to heat up.
• As the gas cools down, it condenses into a liquid, which passes through a lower pressure area.
• This liquid then expands and vaporizes, which absorbs heat, rapidly cooling the coils of the refrigerator.

The difference between the SunDanzer and a traditional refrigerator is not the process described above. In fact, in all likelihood, this describes the operation of refrigerators in 90 percent of all homes. The difference is the use of photovoltaic cells instead of the more traditional forms of generation, where:

• The refrigerator’s solar panel requires five hours of sunlight per day to maintain 38 degrees F, and
• It can store enough excess solar energy to stay sufficiently cold without sunlight.

The Eco-Fridge

The eco-fridge represents a total departure from refrigeration as we understand it – it has:

• No moving parts to produce a cooling effect,
• No photovoltaics or electricity, and
• No chemical refrigerant

It uses an evaporated cooling system, depending entirely on the heat provided by the sun and water. It provides an optimal solution to the challenges of developing third world countries where electricity is scarce and there is no funding to support the installation of photovoltaic systems. The genius is in its simplicity:

• It is constructed of 2 cylinders, one inside the other
• The outer cylinder can be made of almost any material (typically wood or plastic) with holes to allow access of sunlight.
• The inner cylinder is made of metal.
• In the space between the 2 cylinders, organic material such as sand or dirt is added.

The item to be refrigerated is placed inside the inner metal cylinder which is then closed up. The organic material in between the 2 cylinders is then saturated by pouring fresh water, and the whole setup is placed in the sun. The sun will heat the outer cylinder, which will, in turn, heat up the wet organic material and evaporate the water. This evaporation will remove the heat from the organic material which will, in turn, making a cold inner cylinder in the range of 43 degrees F. This process will continue until the water is completely evaporated, after which organic material can be continually replenished, allowing for the continuation of cooling.

There is no battery backup, thus relying on a steady supply of sunlight. And though relatively rudimentary, this approach has been used with success in South Africa and Namibia where sunlight is consistently available 10 hours per day.