IBM cools solar cells for water and power

Pumping water through micro-channels on the surface of a solar panel not only makes it more efficient but can also make seawater drinkable.

Concentrated photovoltaic (CPV) cells use lenses to focus large areas of solar energy onto a relatively small section of photovoltaic material, so it is not surprising that they can reach temperatures of 120 °C. These high temperatures make the cells less efficient, reducing the amount of electricity they can produce.

That is why keeping them cool is so important, says Bruno Michel, head of advanced thermal packaging at IBM's Zurich Research Laboratory in Switzerland. So with this in mind IBM has developed the "ultra-high concentrated PV", a hybrid solar panel that incorporates technology originally developed to help cool computer chips. The idea is to use water-filled microchannels to cool the cell - the hot water would then be used in desalination.

In arid areas where power generation is difficult this can solve two problems at once, producing electricity and clean water, says Michel. "Usually in areas with high solar irradiance there is little demand for heating," he says. "There is more demand for water."

One method of desalination uses hot water to distil seawater, evaporating it to remove the salt. This is expensive and you normally need to heat the water first. So it is far more energy-efficient to use water already warmed from cooling solar cells.

This is not the first hybrid of this sort, says Ian Tansley, chief technology officer of True Energy, an engineering firm specialising in renewable energy in Gwynedd, UK. "There have been some poorly designed incarnations of this on the market for some time ranging from a serpentine of pipes stuck to the back, to a stream of water trickling down the front," he says.

Michel claims IBM's approach is more efficient because each microchannel is etched onto the cell itself, which makes it better at cooling because the water is closer to the heat source. In tests, a 1-centimetre ultra-high CPV cell operated at between 70 to 90 °C, even with 5000 times the normal amount of solar radiation focused on it. This is five times as much as existing CPVs can handle.

Michel presented the findings at the International Conference on Concentrating Photovoltaic Systems in Las Vegas. He told our sister site New Scientist that IBM was working with a team at the Egypt Nanotechnology Research centre in Cairo to scale up the cell to a 10-square-metre prototype.