Irrigating plants while generating solar power?

Solar power, by nature, usually works best in dry places, so there are plenty of scientists around the world who are generating clean water with energy from the Sun. But what if you could use a photovoltaic (solar) panel to make both water and electricity?

A group of Saudi Arabian researchers have developed a photovoltaic system that not only generates water from thin air – it cools the solar panels and makes them more efficient in the process.

The system works by putting a solar panel on top of a specially made hydrogel (a super-absorbent gel made of water-loving polymers). These are mounted on a metal container.

The hydrogel absorbs water vapour from the surrounding air. Then, when heated, it releases the water again. Solar panels heat up while generating electricity, so the hydrogel under the photovoltaics releases water into the container, where it can be collected.

Even better: by absorbing this “waste heat”, the hydrogel cools the solar panels down a little and makes them up to 9% more efficient.

The researchers have trialled their system, called WEC2P, in the hot Saudi Arabian June weather. The results are published in a paper in Cell Reports.

The precise amount of water (and electricity) generated depended on the amount of sun available each day – seasonal variation, clouds and dust storms all affected it.

After 30 days, a 30cm × 60cm solar panel made 3.4 litres of water. That’s not very much, but it’s enough to irrigate some spinach, for instance.

Which is exactly what the researchers did: they set up a spinach patch in a plastic plant-growing box. The researchers planted 60 seeds in a reservoir of reclaimed water that had already been collected by the solar panels, and then connected the box to the system so it could provide them with an extra 150ml a day (occasionally topped up by another source when the solar panels didn’t generate enough water). The box was fitted with a cooling system to prevent the interior heating to over 50°C, but it didn’t need to be used for the course of the experiment.

In total, 57 of the 60 seeds sprouted, and the plants grew to 18cm high after 16 days – which is when they hit the top of the box and the experiment had to end.

“A fraction of the world’s population still doesn’t have access to clean water or green power, and many of them live in rural areas with arid or semi-arid climate,” says Professor Peng Wang, a researcher in environmental science and engineering at the King Abdullah University of Science and Technology, and senior author on the paper.

“Our design makes water out of air using clean energy that would’ve been wasted, and is suitable for decentralised, small-scale farms in remote places like deserts and oceanic islands.”