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Posted: Apr 22, 2013
The power of 2000 suns
(Nanowerk News) Together with scientists of IBM Research, the Buchs University of Applied Sciences and Technology and the supplier of solar power technology, Airlight, scientists of ETH Zurich are to research and develop a new photovoltaic system. The so-called “High Concentration Photovoltaic Thermal” (HCPVT) system will deliver electricity, fresh water and cool air in remote locations and shall be capable of concentrating, on average, the power of 2000 suns, with an efficiency that can collect 80 percent of the incoming radiation and convert it to useful energy.
This novel High Concentration Photovoltaic Thermal can accommodate a 2,000-fold concentration of sunlight and convert 80 percent of the radiation into usable energy.
Replace expensive material
The scientists plan to use triple-junction photovoltaic cells on a microchannel cooled module which can directly convert more than 30 percent of collected solar radiation into electrical energy and allow for the efficient recovery of waste heat above 50 percent. They try to achieve this with a practical design that is made of concrete trackers, primary optics composed of inexpensive pneumatic mirrors, and structures made of concrete. The design of the system is simple – a large parabolic dish, made from a multitude of mirror facets, is attached to a tracking system that determines the best angle based on the position of the sun.
“Reaching high efficiency with a low cost system is the main challenge in this project”, says Aldo Steinfeld, professor for Renewable Energy Carriers at ETH Zurich. Together with his group at ETH’s Institute of Energy Technology, he will develop the optical design of the solar concentrator sub-system. This includes the sun-tracking parabolic concentrator and the matching secondary non-imaging reflector. “Advanced ray-tracing numerical techniques will be applied to optimize the optical configuration and reach uniform solar fluxes exceeding 2000 suns at the photovoltaic cell”, explains Aldo Steinfeld.
Using Aquasar technology
Once aligned, the sun’s rays reflect off the mirror onto several microchannel-liquid cooled receivers with triple junction photovoltaic chips – each 1x1 centimeter chip can convert 200-250 watts, pretty constant, over a typical eight hour day in a sunny region. The whole receiver combines more than hundred chips and provides 25 kW electrical power. The photovoltaic chips are mounted on microstructured substrates that pipe liquid coolants within a few tens of micrometers from the chip to absorb the heat and draw it away 10 times more effectively than with passive air cooling. Using hot water cooling Aquasar technology as already implemented for Datacenters, the estimated cost per aperture area is 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).
Schematic of the High Concentration Photovoltaic Thermal. (click image to enlarge)
Prototype is being tested
With the HCPVT packaging approach scientists can both eliminate the overheating problems of solar chips while also repurposing the energy for thermal water desalination and cool air. The 90 degree Celsius water will pass through a porous membrane distillation system where it is then vaporized and desalinated. Such a system could provide 20 liters of drinkable water per square meter of receiver area per day. “The integration of several novel components, e.g. the faceted concentrator, the secondary optics, and the microchannel heat exchanger, makes the HCPVT system unique”, says Aldo Steinfeld.
Scientists envision the HCPVT system providing sustainable energy and fresh water to locations around the world. A prototype of the HCPVT is currently being tested at the IBM Research lab in Zurich. The project is funded by the Swiss Commission for Technology and Innovation (CTI) with 2.25 million Swiss Francs.