The system uses day-night temperature differences to extract water from the air while slightly increasing electricity generation by cooling solar panels
A three-month trial in Saudi Arabia has shown that a solar panel add-on system can harvest water without using any electricity by exploiting the day-night warming and cooling of solar panels. In fact, the system slightly increases the electricity-generating efficiency of the panels by keeping them cooler.
“I am confident that the system can be manufactured economically,” says Peng Wang at the country’s King Abdullah University of Science and Technology. “We are looking forward to working with potential industrial partners to speed up this process.”
The new approach uses a layer of hydrogel placed under each photovoltaic panel and encased in a metal box. During the night, the box is open to allow the desert air to flow through it where the hydrogel absorbs water vapour.
During the day, the box is closed. The sun warms the solar panel, and thus also the hydrogel underneath it, making the water evaporate from the gel. The humidity in the closed box gets so high that the water condenses on the metal and can be drained from the box.
During the trial, from May to June 2021, a small prototype system produced 0.6 litres of water per square metre of solar panel per day.
The basic idea isn’t new. Several other teams have developed water harvesters that also exploit day-night temperature changes. But Wang says his team is the first to create an integrated system that extracts water while also generating electricity.
One advantage of using the add-on is that no extra land is required. Another is that electricity generation increased slightly – by nearly 2 per cent – because the transfer of heat to the hydrogel and water-harvesting box cools the solar panels. High temperatures reduce the efficiency of solar panels.
The cooling effect can be increased by leaving the condensation box open during the day. Although this stops water extraction, in the trial it boosted electricity generation by up to 10 per cent. Wang envisages creating flexible systems that could switch between water extraction and higher solar panel electricity generation as needed.
In the trial, the team used water from the panel to irrigate a small patch of plants. Wang hopes large-scale systems could produce food, water and electricity all at once.
However, the design is still at an early stage. During the trial, the team manually opened and closed the condensation boxes. The hydrogel also deteriorated somewhat, so a more stable water-absorbing material is needed, Wang says.
A company called Sundrop Farms is already using solar power to allow it to grow tomatoes in a desert region in Australia. However, its greenhouse system relies on this power to desalinate seawater pumped from the nearby coast.
Journal reference: Cell Reports Physical Science, DOI: 10.1016/j.xcrp.2022.100781
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