New solar panels capture water from the air to cool themselves

 

As with human beings, solar panels can't perform well when overheated. The researchers have now discovered ways to create them to "sweat"--allowing the panels to cool and boost the power they produce.

It's "an easy elegant, effective, and elegant method of retrofitting existing solar cells to get immediate efficiency gains," says Liangbing Hu, an expert in materials science at the University of Maryland, College Park.

Presently around 600 gigawatts of solar power are available worldwide, supplying around 3% of all electricity needs. This capacity is projected to grow fivefold in the next 10 years. The majority of silicon cells convert sunlight into electricity. The typical silicon cell converts less than 20% sun's energy that strikes them into electricity. Most of the remainder turns into heat. This could warm the panels as high as 40 degrees Celsius. With any temperature that is over 25degC performance of the panels diminishes. In a field where scientists are fighting to get every 0.1 percent increase in efficiency for power conversion and even a one percent increase in efficiency is a financial benefit, according to Jun Zhou, a materials scientist at Huazhong University of Science and Technology.

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Researchers have demonstrated the possibility that cooling, solar panels using water could bring that advantage in the past. Nowadays, some companies offer water-cooled systems. However, these systems require plenty of accessible water and storage tank, pipes, and pumps, and it's not much use in extreme drought areas and countries with no infrastructure.

You can use an air-based water collector. Recent research has come up with materials that draw water vapor out of the air and then condense it into liquid water that can be consumed. One of the most effective is a gel that absorbs water vapor during the night when the temperature is excellent and the humidity high. The gel, a mixture of carbon nanotubes within polymers and the water-attracting calcium chloride salt, causes the liquid to condense into drops that the gel stores. If the temperature rises in the daytime and the gel is released, it releases water in the form of vapor. If it is covered with transparent plastic, the released liquid is kept inside, condenses back into the liquid, and is absorbed into storage containers.

Peng Wang, an environmental engineer at Hong Kong Polytechnic University, and his colleagues came up with alternative use of condensed water: cooling used for solar panels. Therefore, they applied a 1-centimeter thick sheet of gel on the surface of a conventional solar panel made of silicon. The idea was that, in the daytime, the gel would pull sunlight to evaporate the water is drawn from the air that night and release the vapor from the gel's bottom. The water would chill the solar panel as sweat evaporates from the skin cools us.

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The study found that how much gel they required depended on the conditions' humidity. In a desert with 35% humidity, one square meter solar panel would require one kilogram worth of gel to cool it down, while the humid zone with 80% humidity needed just 0.3 kilograms of gel for each square meter of the panel.

The result in both cases is that the solar panel's temperature decreased by 10 degrees Celsius. The panels' power output with cooling increased by 15 percent on average and as high as 19 percent in one outdoor test in which wind probably increased the cooling impact. Wang and his coworkers report the findings today in Nature Sustainability.

"The efficiency boost is substantial," Zhou says. He also points out that rain can dissolve the calcium chloride salt inside the gel, which could reduce its water-attracting properties. Wang agrees, but he points out that the gel's location under the solar panel is supposed to shield against rain. Wang and his team are developing a second-generation gel that won't break down, even if it's wet.

Another option for design, Wang says, is an arrangement that would capture and re-condense water after it has evaporated off the gel. The water, he claims, could be used to remove the dust that builds up on solar panels, thereby solving the power-sapping issue the same while. In addition, the water could be used to store water for drinking, meeting a pressing need in the desert areas.