Solar Concentrator Borrows Water Cooling from IBM Supercomputer

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IBM Research

Flat photovoltaic panels have come to dominate the global solar market thanks to a dramatic drop in panel prices over the past five years. A Swiss start-up, using technology that IBM Research–Zurich developed for one of its supercomputers, is challenging the status quo with a dish-shaped solar concentrator that produces both electricity and hot water.

The start-up, Airlight Energy, developed the dish and has created a spin-off company—called Dsolar for “dish solar”—and plans to release the concentrator in 2017. It will be targeted at off-grid communities in areas like deserts that get a lot of direct sunlight but want for both electricity and hot water. In developed countries, the 10-meter-high concentrator can be used for on-site power generation at corporate campuses or hotels, says Ilaria Besozzi, business development manager at Airlight Energy.

The parabolic dish, which automatically reorients to track the sun throughout the day, is made up of 36 elliptical reflectors that concentrate light onto very efficient, multijunction solar cells to produce electricity. These types of cells use materials tuned for different wavelengths and in this device will be able to convert about 30 percent of sunlight into current, says IBM.

Typically, the solar cells exposed to concentrated sunlight are air cooled. Airlight Energy hopes to increase the electrical output—and produce hot water—by using liquid cooling. Behind each set of solar cells is a structure that houses IBM’s water-cooling technology, which is now used in its SuperMUC supercomputer in Germany. Water flows through a network of small tubes, or “microchannels,” etched into a layer of silicon to wick away the heat from the solar cells, says Bruno Michel, the manager of advanced thermal packaging at IBM Research–Zurich. In supercomputers, the liquid coolers are attached directly to the processors, where most of the heat is generated, says Michel.

Because the dish uses active cooling, the solar cells should be able to withstand a very high concentration of light—the equivalent of 2,000 suns—and still operate for 25 years. The higher concentration has the side effect of heating the cooling water to about 90 ºC. At that temperature, the water can be used to power desalination systems or, oddly enough, a particular type of heat-driven cooling system, Michel says. In full sunlight, the dish is designed to generate 12 kilowatts of electricity and 20 kW of heat.

Concentrated photovoltaic (CPV) systems have been around for decades, and the technology offers, at least in theory, a number of advantages. They can generate more power in a given amount of space and offer higher conversion efficiency than flat panels can. In fact, by generating both heat and electric power, Airlight Energy says it converts 80 percent of sunlight into usable energy. But the cost of CPV technology and its complexity have kept it from becoming commonplace with utilities.

To keep costs low, Airlight Energy is using two materials not normally used in solar concentrators. Rather than have glass mirrors to concentrate light, the mirrors will be made of the same thin plastic foil used to wrap Swiss chocolates, says Besozzi. The main structure of the dish will be made of a specialized concrete, which can be precisely molded, doesn’t shrink, and costs far less than metals or plastic building materials, Airlight Energy says.

Engineering a system to simultaneously generate electricity and process the thermal energy will be difficult, says Sarah Kurtz, principal scientist at the U.S. National Renewable Energy Laboratory. For example, if the heat-driven cooling fails, the dish needs to quickly steer away from the sun or transfer the heat in another way. Using thin-film mirrors lowers the cost, but first-of-a-kind systems are typically expensive. “The challenge is to reduce the cost of the other components, but at 2,000 times concentration, this is feasible,” she says. Having IBM’s technology behind the product gives it commercial credibility, notes Matthew Feinstein, an analyst at Lux Research, in Boston. Traditionally, CPV systems were targeted at utilities, but many industrial companies, such as data center operators and manufacturers, can easily make use of the solar dish’s thermal energy, he adds. Still, “commercialization and early adoption have always been a challenge for unique solar technologies,” he says.

This article was updated on 16 October 2014.

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