A Water-Cooled Chip That Concentrates the Sun to Desalinate Water

Anyone who's dropped a cellphone in the bath knows that water and microelectronics don't usually mix well. But at IBM's Swiss lab in Zurich, marrying the two is becoming almost commonplace: microprocessors with water coursing through microchannels carved deep inside them are already crunching data in SuperMUC, an IBM supercomputer - with the heat that the water carries away used to warm nearby buildings.

And last week, on an unseasonally sunny Zurich rooftop, IBM went public before begoggled journalists with a demo of the technology's newest application: a solar energy-generating microchip array whose waste heat might one day drive desalination systems in arid areas like the Sahara. The firm has long promised this system, and it's still a work in progress, but it has now reached a form that can be demonstrated.

The trick with a concentrated photovoltaic (CPV) system like IBM's is to place a high-performance electricity-generating solar cell array at the focal point of a dish that collects sunlight (unlike a solar concentrator, which focuses a field of sun-tracking mirrors onto a steam generator that drives a turbine). In IBM's CPV system, water gushes through the base of the solar cells, cooling them to a temperature where they convert sunlight to electricity most efficiently. This beats regular solar power in two ways: it guarantees optimum efficiency and creates hot water that can be used for any purpose - with a multi-effect boiling desalination process being IBM's choice.

On IBM's rooftop, I donned ultra-dark goggles to watch Stephen Paredes, Bruno Michel and colleagues demonstrate their dazzling concept. A 1.5-metre mirrored dish concentrated the sun's energy by 150 times onto their prototype CPV chip, which has been engineered to maximise thermal contact with a water-cooled layer. It's fascinating to see their control rig: half of it is electronic but the rest, frankly, is plumbing - an interesting mix of disciplines indeed. Paredes's laptop showed the concentrator dish conversion efficiency to be about 18 per cent - respectable for a prototype, he says.

Their research aim now is to move towards 40 per cent efficiency or more with better-cooled CPV arrays that can cope with solar radiation 5000 times the sun's normal intensity. "We know how to engineer these cooling packages for computers so we're confident we can make this contribution to solar energy," says Michel.


A Water-Cooled Chip That Concentrates the Sun to Desalinate WaterNew Scientist reports, explores and interprets the results of human endeavour set in the context of society and culture, providing comprehensive coverage of science and technology news.