Scientists announced a collaborative project to develop a cost-effective photovoltaic system capable of concentrating solar radiation 2000 times before converting into useful energy (electricity and heat), with a very high efficiency.

IBM Research, Buchs University of Applied Sciences, the supplier of the Airlight Energy technology, as well as scientists from ETH Zurich are trying to develop this new photovoltaic system.

The system called “high concentration photovoltaic thermal” (HCPVT) will be able to provide electricity, drinking water and air conditioning in isolated locations. It will mainly be able to focus on average the equivalent of 2000 suns, with an efficiency that can collect 80% of the incident radiation.

Replace expensive materials

Scientists plan to use a large dish, consisting of a multitude of mirrors, in order to concentrate the sun’s rays on triple-junction photovoltaic cells mounted on modules cooled microchannels. The system should be able to directly convert more than 30% of sunlight into electricity and recover effectively – over 50% – the residual heat.

“Achieving a high conversion efficiency with a low-cost system is the main challenge of this project,” said Aldo Steinfeld, professor and director of the Laboratory of solar technology to PSI. His team based at the Institute of Energy Technology at ETH develops the optical design of the subsystem of the solar concentrator. This includes the monitoring system (tracker) of parabolic concentrator and the secondary reflector. “Advanced digital techniques will be applied to optimize the optical configuration and a uniform solar flux than 2,000 suns focused on the photovoltaic cell,” said Aldo Steinfeld.

The Aquasar technology

Once aligned, the sun rays are reflected on a mirror comprising a plurality of triple junction photovoltaic arrays, cooled by a liquid. Each chip of one square centimeter (1×1) can convert heat into electricity (200-250 watts) during a typical eight-hour day in a sunny area. The receiver has more than one hundred chips and delivers 25 kilowatts of electrical power. PV chips are mounted on micro-structured substrates where a refrigerated a few tens of micrometers is enough to absorb heat liquid flows. Liquid cooling technology called ‘Aquasar’ is already implemented in the data center.

The cost of a complete system would reach $250 per m2, three times less than an equivalent system. The levelized cost of energy would be less than 10 cents per kilowatt-hour (kWh).

The prototype

With an integrated approach to HCPVT, scientists are trying to both eliminate the problems of overheating of the solar chips by redirecting the energy to desalinate water and cool air. Water at 90°C passes through a membrane filter, where it is vaporized and desalinated. Such a system could provide between 30 and 40 liters of drinking water per day per square meter, enough to power a small city in running water in addition to electricity.

A HCPVT prototype is currently being tested at the IBM Research Laboratory in Zurich. The project is funded to the tune of 2.25 million Swiss francs by the Swiss Commission for Technology and Innovation (CTI).

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