IBM, which revolutionized the personal computer, is bringing its technological knowhow to solar through a new partnership with Airlight Energy, ETH Zurich and Interstate University of Applied Sciences Buchs NTB. The group recently won a three-year, $2.4 million grant from the Swiss Commission for Technology and Innovation to develop low-cost high-concentration photovoltaic thermal (HCPVT) systems.
Most concentrating solar power systems being developed today are either concentrating photovoltaic (CPV) or concentrating solar thermal systems that concentrate the sun’s heat on a transfer medium like water or molten salt and generate electricity via a steam turbine. But some companies are offering a combined CPV/solar hot water heating system, like Cogenra’s systems, but that’s a low-concentrating solar thermal system. Like a Swiss Army knife, the system that’s being developed is capable of multiple things — concentrating the sun 2,000 times, capturing 80 percent of the sun’s energy, desalinating water and even providing air-conditioning.
The researchers are planning to develop a 25-kilowatt system. "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," says Bruno Michel, manager of 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.”
The system uses a highly-reflective parabolic dish, much like a satellite dish to focus the sun’s light on a series of triple-junction high-efficiency PV cells. To keep them operating at high levels of efficiency and get the most out of the system, the cells are liquid-cooled, which provides more than enough heat to boil water, driving the desalination process.
The group is trying to solve a host of problems at once, particularly looking to Africa and the Middle East, where Europe has plans to develop massive solar projects and the primary source of water is the ocean, requiring desalination.
The system is still in prototype stages though. “The prototype HCPVT system uses a large parabolic dish, made from a multitude of mirror facets, which are attached to a sun tracking system. The tracking system positions the dish at the best angle to capture the sun's rays, which then reflect off the mirrors onto several microchannel-liquid cooled receivers with triple junction photovoltaic chips—each 1x1 centimeter chip can convert 200-250 watts, on average, over a typical eight hour day in a sunny region,” IBM says.
The liquid-cooled system that absorbs heat and draws it away is 10 times more effective than passive air cooling, according to IBM. “The coolant maintains the chips almost at the same temperature for a solar concentration of 2,000 times and can keep them at safe temperatures up to a solar concentration of 5,000 times.”
"The design of the system is elegantly simple," says Andrea Pedretti, chief technology officer at Airlight Energy. "We replace expensive steel and glass with low-cost concrete and simple pressurized metalized foils. The small high-tech components, in particular the microchannel coolers and the molds, can be manufactured in Switzerland with the remaining construction and assembly done in the region of the installation. This leads to a win-win situation where the system is cost competitive and jobs are created in both regions."
The ultimate goal is a CPV system with a levelized cost of energy under 10 cents per kilowatt hour, which is significantly less than where solar is at now, and a system that heats salt water to 90 degrees Celsius for a low-temperature desalination process. “Such a system could provide 30 to 40 liters of drinkable water per square meter of receiver area per day, while still generating electricity with a more than 25 percent yield or two kilowatt hours per day,” IBM explains. The system, it adds, can provide air conditioning through a thermal driven adsorption chiller.
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