Solar-powered refrigerator

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This article is about electric refrigerators which use solar power. For evaporative devices which use the sun's heat, see pot-in-pot refrigerator.

A solar-powered refrigerator is a refrigerator which runs on electricity provided by solar energy.

Solar-powered 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.

Solar-powered refrigerators may be most commonly used in the developing world to help mitigate poverty and climate change.

Rationale[edit]

There is 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 (CFCs), in their insulation foam or their refrigerant cycle, are the most harmful. After CFCs were banned in the 1980s, 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 used 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.[1][2] Since 1992, Fishermen in the village of Maruata, which is located on the Mexican Pacific coast 18 degrees north of the equator, have no electricity. But for the past 16 years[when?] they have been able to store their fish on ice: Seven ice makers, powered by nothing but the scorching sun, churn out a half ton of ice every day.[3]

There's a global scramble to drive down emissions of carbon dioxide: the electricity to power just refrigerators in the U.S. contributes 102 million tons annually. Solar refrigeration can also be inexpensive and it would give the electric grid much-needed relief. Electricity demand peaks on hot summer days—150 gigawatts more in summer than winter in the U.S. (A gigawatt equals one billion watts.) That's almost 1.5 times the generating capacity of all the coal-fired power plants west of the Mississippi River. Further, solar is plentiful. The solar energy hitting 54 square feet (five square meters) of land each year is the equivalent of all the electricity used by one American household, according to data from the National Renewable Energy Laboratory and Energy Information Administration, both part of the U.S. Department of Energy.

Making cold out of hot is easier than one might think.[according to whom?] In 2008, a group of students at San Jose State University built a solar-powered ice maker with $100 worth of plumbing and a four-by-eight-foot (1.2-by-2.4-meter) sheet of reflecting steel. No moving parts, no electricity, but give it a couple hours of sunshine and it can make a large bag of ice.[4]

The key is the energy exchanged when liquids turn to vapor and vice versa—the process that cools you[who?] when you sweat. By far the most common approach, the one used by the refrigerator in your house, uses an electric motor to compress a refrigerant—say, Freon—turning it into liquid. When the pressure created by the compressor is released, the liquid evaporates, absorbing heat and lowering the temperature.

Absorptive chillers like solar refrigerators use a heat source rather than a compressor to change the refrigerant from vapor to liquid. The two most common combinations are water mixed with either lithium bromide or ammonia. In each case, the refrigerating gas is absorbed until heat is applied, which raises the temperature and pressure. At higher pressure, the refrigerant condenses into liquid. Turning off the heat lowers the pressure, causing that liquid to evaporate back into a gas, thereby creating the cooling effect.

As with most technologies, the efficiency of such absorptive refrigeration depends on the degree of engineering (and expense) brought to bear. Single-effect devices have a coefficient of performance of 0.6 to 0.7—that is, they create 60 to 70 Btus (British thermal units) of cooling for every 100 Btus of input heat. That low level of efficiency can be achieved with something as crude as some pipe, a bucket of water, some calcium chloride (as absorbent), ammonia (as refrigerant), and a sheet of shiny metal (the solar collector).

On the topic of solar powered refrigerators, Tom Mancini, program manager for solar power at the Sandia National Laboratories in Albuquerque, remarked "That approach ought to be comparable to photovoltaics, or a little better,"[5]

It would take a fair-size collector—86 square feet (eight square meters), assuming 40 percent panel efficiency—just to deliver the cooling of a small (6,000 Btu per hour or half-ton) window air conditioner. And central air-conditioning units are often 30,000 Btu or more; few homeowners could spare the space for that.

History[edit]

"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".[6] 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.[2][7] 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.[6] They can also be difficult to adjust which can result in the freezing of medicine. The use of Kerosene as a fuel is now widely discouraged for three reasons: Recurrent cost of fuel, difficulty of maintaining accurate temperature and risk of causing fires.[7]

Technology[edit]

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.[6][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.[6] These problems and the resulting higher costs have been an obstacle for the use of solar powered refrigerators in developing areas.[2][7]

In the mid-1990s NASA JSC began work on a solar powered refrigerator that used phase change material rather than battery to store "thermal energy" rather than "chemical energy." The resulting technology has been commercialized and is being used for storing food products and vaccines.

See also[edit]

References[edit]