Waste heat from solar panels can now go to work rather than to waste. So instead of heat going into the air, they can use it to produce clean water. As solar panels don’t like heat, this approach might also help cool the panels themselves, thereby improving their efficiency. Two birds, one stone - electricity and fresh water.
Good solar panels can have an efficiency rating of about 20% at about 25°C. This can lower as the panel gets hotter. If you apply water on to panels, then this can have a cooling affect that improves panel output. Although they dont mention it as a side benefit specifically by the KAUST team, it seems that it could be.
A driver behind this development is that a lot of water is in use to keep solar farm panels clean. The other is that the typical desalination process uses a lot of electricity. The “what if” moment is, could a single device both desalinate and make electricity? What if the 80% of sunlight that goes to waste on a solar panel, could indeed make clean water too?
The team came up with a design for a device that has water channels arranged in a ‘stack’. These have porous hydrophobic membranes and heat conduction layers that hold them apart. They then place this underneath a solar panel. The waste heat from the solar panel causes seawater to vaporise in the top channel. The membranes allow the steam vapour to pass through which then condenses in clean water channel below. When the vapour condenses, heat gives off which the thermal conduction layers use to repeat the process.
The multi stack system extracts as much energy as it can from the available sunlight to produce clean water. The current design has three separate ‘stacks’ that pass energy from one level to the other. So far the device has produced 1.64 litres of clean water per square meter of solar panel, per hour. In fact this is more than twice that of other typical solar stills which only have a single stage process. The activity happening below the solar panel does not affect its electrical output.
The use for this concept is far and wide. We can all imagine the possibilities of having the ability to purify water and make electricity from one device.