Earth Equity News

Solar Refrigeration: a Hot Idea for Cooling. By Duane Schrag, SciAmer, October 20, 2008. "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 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... Making cold out of hot is easier than one might think... The key is the energy exchanged when liquids turn to vapor and vice versa -- the process that cools you 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... If what you want to do is heat or cool, using solar energy this way is probably more efficient -- and certainly cheaper -- than converting it first into electricity... In the developing world, solar powered ice makers allow locals to store the village's food or medicine without any electricity. For example, in May charitable organization, Heifer International, set up three solar ice makers in remote areas of Kenya. Each will be able to keep 26.5 gallons (100 liters) of milk chilled. More than 500 members of two dairy cooperatives are expected to benefit directly. Most of the interest in such solar refrigeration in Western countries comes from the commercial, not residential, sectors. Cost is one reason -- absorption chiller systems typically cost $7,000 to $10,000 per ton of cooling; one-ton window air conditioners from big box retailers start around $250 -- but companies can save on electric bill as well as enjoy a more benign environmental image."