Solar PV Gets Into Hot Water For Greater Efficiency

Cogenra Solar has seemingly been gaining momentum with its unique system of combing concentrating photovoltaics and concentrated solar thermal to produce both electricity and hot water, but the company might have competition on the distant horizon.

Technology giant IBM’s research division in Zurich marked Earth Day by announcing it will develop, with various European collaborators, a hybrid solar power system. There are important differences between the IBM prototype and Congenra’s system, but the basic concept is the same: make electricity with PV, and don’t lose the heat. As with Cogenera, IBM says by doing so it can put 80 percent of the collected solar energy to use.

IBM hybrid solar pv solar thermal

Prototype of system under development in Switzerland (image via IBM Research)

We’ve written about the success Cogenera has had selling its system to California wineries, who use large amounts of hot water in cleaning barrels and other equipment in the winemaking process. But more recently, Greentech Media reported that Johnson Controls will use Congenra’s system to power its YORK absorption chillers in the U.S. Southwest, where air conditioning is a huge electricity suck on sunny days. The Johnson Controls deal is one that reporter Herman K. Trabish said could move Cogenra’s system “to the big time.”

How the Cogenra system works (image via Cogenra Solar)

How the Cogenra system works (image via Cogenra Solar)

But back to IBM: The company says the system it will help develop over the next three years with a $2.4 million grant from the Swiss Commission for Technology and Innovation, could be used with such chillers, too. But IBM mentions another interesting possible use:

(T)he 90 degree Celsius water will be used to heat salty water that then passes through a porous membrane distillation system where it is vaporized and desalinated. Such a system could provide 30-40 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 — a little less than half the amount of water the average person needs per day according to the United Nations, but a large installation could provide enough water for a town.

Meanwhile, of course, the system would be producing electricity thanks to a parabolic dish focusing sunlight exceeding 2,000 suns on triple-junction photovoltaic cells. That would put to use about 30 perecent of the collected energy. The system captures an additional 50 percent – heating the salty water in the desal scenario – by mounting the PV chips “on micro-structured layers that pipe liquid coolants within a few tens of micrometers off the chip to absorb the heat and draw it away ten times more effective than with passive air cooling.”

“The design of the system is elegantly simple,” said Andrea Pedretti, chief technology officer at Airlight Energy, which is working with the IBM researchers on the project. “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.”

Here’s a short video from IBM Research explaining their system:

Pete Danko is a writer and editor based in Portland, Oregon. His work has appeared in Breaking Energy, National Geographic's Energy Blog, The New York Times, San Francisco Chronicle and elsewhere.