A cool idea for solar-powered cold-storage is about to make refrigeration a lot more affordable, practical and environmentally friendly in off-the-grid and partially-electrified areas of the world.
Birth of a ‘cool’ concept
The system is an energy-efficient hybrid refrigerator that combines conventional compressor-created cold air with clean, quiet cooling generated by thermoelectric technology and photovoltaic solar panels. The concept is the brainchild of MIT graduate Sorin Grama and Sam White, an entrepreneur with business-and-funding savvy. In 2007, the pair founded Promethean Power Systems, Inc. According to its website, the objective of the Cambridge, Mass.-based firm is to “develop a complete, stand-alone rural refrigeration system that stimulates businesses, reduces dependency on fossil fuels and increases the quality of life in emerging markets by enabling its users to reliably store food, vaccines and other perishable items.
“Thermoelectric cooling is basically a semiconductor chip that creates heat on one side and runs cold enough to create ice on the other,” White explains in a Nov. 7, 2008, interview with a newspaper called India New England. The problem with thermoelectric technology is its inefficiency, White says, noting that it uses twice the amount of power to produce the same amount of cooling as a conventional refrigerator. To date, that inefficiency has limited the use of thermoelectric technology to small consumer-electronic applications. However, Grama and White say they have overcome this obstacle by developing proprietary “smart” controls that enable their cooling system’s compressor, thermoelectric modules and solar panels to work together synergistically.
Reporter Chris Nelson reports the “how-to’s” of the Promethean system in his India New England article: “Early in the morning and late in the afternoon, when the sun’s rays are less intense, the solar panels can’t produce enough electricity to run the compressor. But they can generate just enough juice to run the thermoelectric modules, which produce cold air until the compressor kicks in,” the article explains. “That usually happens around midday,” it continues, “when the sun is at its highest point in the sky and the solar panels are cranking out plenty of electricity. But even then the compressor won’t use all of the power generated, so the thermoelectric modules will use the excess to provide extra cooling.” White adds that, during periods of extended cloudiness, the system uses a small generator to backup its solar panels. The result he says, is a cooling system that utilizes 20 percent less power while creating the same amount of refrigeration as a compressor alone.
White and Grama were first rewarded for this cool concept in 2007, when it captured second prize and $10,000 in MIT’s annual graduate-level business-plan competition. The pair followed that victory with a trip to India where they cased out and confirmed the need for such a product. Following that trip, they built and tested a laboratory-scale, 60-liter chilling unit. In September 2008, they reportedly began constructing a 500-liter system with funding from Quercus Trust, a private investment firm located in Newport Beach, Calif. The larger system will be tested in India sometime during 2009, White indicates. The pair say they’ll sell their system for about $17,000. That’s nearly $5,000 more than the cost of a conventional diesel-powered unit but – unlike diesel systems – Promethean technology requires no additional fuel charges, Grama says. Their system also features extremely low maintenance costs, he says. Because it involves no moving parts, there’s little to break down and a remote-monitoring unit that enables anywhere-any time remote diagnosis, further reduces maintenance expense, he claims.
“As a result,” Grama says on the firm’s website, “our system can provide cooling power at an operating cost that is 66 percent lower than the operating cost of conventional units.”