Solar power system with oasis effect

Water and plant growth in the shade of a solar power system: the artistic representation shows what the newly developed concept could look like in a mature form. © Renyuan Li

Photovoltaics ingeniously combined with water production: Researchers present a system that supplies solar power and, thanks to an absorbent hydrogel, can also tap water from the desert air to supply crops. The scientists say that the concept could thus develop into a sustainable and cost-effective strategy to provide people in remote dry regions with energy, water and food.

The sun burns down from the sky all day and dries everything – in addition to the lack of power sources, the water shortage is a major problem in many desert regions. But there is actually plenty of water there too – in the form of water vapor in the air. Relative humidity can rise to over 60 percent, especially at night. Transforming this water treasure into usable liquid has long been a goal of researchers. Peng Wang’s team from the Saudi Arabian King Abdullah University of Science & Technology in Thuwal has already developed promising concepts. In their current study, they now make it clear that modules for generating solar power can be effectively combined with the use of humidity.

They call their newly developed system “Water-Electricity-Crop Co-Productionsystem” (WEC2P). It consists of a photovoltaic module that supplies solar power when exposed to sunlight. As is well known, this area gets hot in the glow of the sun. It’s also a factor that limits effectiveness—red-hot solar cells deliver less power. In their concept, the researchers have now used the waste heat from the solar module as an energy source for water production: it heats units of a special hydrogel that are located directly under the solar module surface. As a result, the hydrogel releases water that it has absorbed from the humidity during the night.

Electricity from the sun – and water from the air

Wang and his team had previously developed this special hydrogel. It consists mainly of the inexpensive salt calcium chloride. This non-toxic substance has an extremely high affinity for water: it can absorb so much humidity from the surrounding air that it eventually turns into a liquid solution. To keep it in shape, the researchers connected the salt to a polymer. This material can thus absorb large amounts of water and still remain firm – it forms a so-called hydrogel. It can then release the stored water again in the form of steam by heating it. This can then be condensed and collected.

With the WEC2P system, the whole thing works like this: During the cool, humid desert night, the hydrogel units under the solar panel are exposed to the air and thereby absorb moisture from it. During the day, the sunshine brings the solar cells to generate electricity and heats them up. The waste heat is transferred to the underlying hydrogel units, which means that they sweat out their stored liquid, so to speak. The resulting vapor then condenses in a sloping metal box that seals the system at the bottom. There it can finally pearl into a collection vessel and be used.

Plants grow in the desert

The device, which the researchers built to demonstrate the concept, has a solar panel that is 60 centimeters long and 30 centimeters wide. For their experiments, they combined it with a plant breeding box in which 60 water spinach plants were cultivated for two weeks. They were supplied exclusively by the water collected from the air in the plant. As the evaluations showed, in addition to generating electricity, the system had supplied two liters of water in the two weeks. The researchers report that the plants in the propagation box grew and thrived splendidly.

As they emphasize, there is another possible use of the system in addition to water production: it can be used to cool the solar cells. To do this, the condensation tank is simply opened during the day so that the moisture from the hydrogel units can effectively provide cooling by perspiration. As a result, the solar panels cooled by up to 17 degrees Celsius and thus increased electricity generation by up to almost ten percent, reports the scientists.

However, they apparently see the more important application as the combination of energy and water generation: “Part of the world’s population still has no access to clean water and green electricity, and many of them live in rural areas with a dry climate,” says Wang. “Ensuring that everyone on earth has access to clean water and affordable clean energy is part of the Sustainable Development Goals set by the United Nations. I hope our design can evolve into a decentralized power and water system to light homes and water plants,” says Wang. In order to turn the previous proof-of-concept design into an actual product, the team now plans to increase the water absorption capacity of their hydrogel even further.

Source: Cell Press, Article: Cell Reports Physical Science, doi: 10.1016/j.xcrp.2022.100781

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