Monday, April 29, 2013

Two-For-One: A New Solar Dish Delivers Low-Cost Electricity Along With Fresh Water

By Jeff Spross on Apr 29, 2013 at 10:41 am

One challenge that continues to hound solar power is the efficiency with which it converts sunlight into electrical power. Right now, that efficiency ranges from 10 to 30 percent, while much of the rest is lost as waste heat. But Swiss researchers associated with IBM have built a new solar dish, called the High Concentration PhotoVoltaic Thermal system (HCPVT), that tackles the waste heat problem by using it to generate fresh water.

The dish itself is covered in small mirrors, which concentrate sunlight on a small module of photovoltaic cells. That design puts the dish at the leading edge of efficiency, converting 30 percent of the received solar radiation into electricity and providing 25 kilowatts of power. But it also means the solar module faces an enormous concentration of heat. To keep it from melting, the HCPVT employs a liquid coolant system that IBM first developed for its high-performance computers, and that’s 10 times more effective than traditional passive air cooling.

The liquid keeps the solar cells operating safely at up to 5,000 times the normal solar concentration by drawing away the waste heat, after which the heated coolant is used to vaporize salty water in a desalinization system. As a result, the HCPVT is able to recover half the waste heat and put it to productive use.
According to IBM, the HCPVT is built from unusually low-cost materials, meaning the per area price of setting it up is significantly lower than comparable solar systems, as is the cost per kilowatt hour:
“We plan to use triple-junction photovoltaic cells on a micro-channel cooled module which can directly convert more than 30 percent of collected solar radiation into electrical energy and allow for the efficient recovery of an additional 50 percent waste heat,” said Bruno Michel, manager, advanced thermal packaging at IBM Research. “We believe that we can achieve this with a very practical design that is made of lightweight and high strength concrete, which is used in bridges, and primary optics composed of inexpensive pneumatic mirrors — it’s frugal innovation, but builds on decades of experience in microtechnology….
With such a high concentration and a radically low cost design scientists believe they can achieve a cost per aperture area below $250 per square meter, which is three times lower than comparable systems. The levelized cost of energy will be less than 10 cents per kilowatt hour (KWh). For comparison, feed in tariffs for electrical energy in Germany are currently still larger than 25 cents per KWh and production cost at coal power stations are around 5-10 cents per KWh.
Just one square meter of receiver area in the HCPVT system can provide 30 to 40 liters of drinkable water per day — about half the needed daily amount for the average person, according to the United Nations. The researchers think a large array of the dishes could produce enough fresh water to sustain a town. On top of that, the system can even provide air conditioning, using an absorption chiller rather than the standard compression chiller:
The HCPVT system can also provide air conditioning by means of a thermal driven adsorption chiller. An adsorption chiller is a device that converts heat into cooling via a thermal cycle applied to an absorber made from silica gel, for example. Adsorption chillers, with water as working fluid, can replace compression chillers, which stress electrical grids in hot climates and contain working fluids that are harmful to the ozone layer.
The prototype is being tested at IBM research facilities in Zurich, and the project was recently awarded a three-year, $2.4 million grant from the Swiss Commission for Technology and Innovation. The long-term vision is to build arrays in areas of southern Europe, Africa, the Arabic Peninsula, South America, Australia, and the southwestern United States — places that are remote, dry, and in need of both affordable sustainable energy and greater supplies of drinking water.

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