In 2020, researchers tested a self-moistening hydrogel mat under solar panels; it cooled them by at least 10°C and boosted output by up to 19%

Solar panels often lose power as they heat up in the sun. A 2020 study titled 'Photovoltaic panel cooling by atmospheric water sorption–evaporation cycle,' published in Nature Sustainability, tested a solution for this: a gel that sucks up water from the air at night, then gently releases it as vapor during the day. Solar cells are more efficient when they stay cool, and at high temperatures a panel's electricity-generating efficiency decreases; existing fixes like fans, water sprays, or reflective coatings typically require extra energy and constant maintenance. The study found this cooling effect lowered panel temperatures by at least 10°C in lab tests. In outdoor field tests in Saudi Arabia over two seasons, this one change increased electricity output by 13% to 19%, according to the paper.

How the gel actually works

The team behind this study, from KAUST and Hong Kong Polytechnic University, created this gel from a cocktail of polyacrylamide, carbon nanotubes, and the salt calcium chloride. They applied a thick layer to the underside of a standard solar panel. At night, the gel pulls moisture directly out of the air, like salt left out in a humid kitchen gets damp. The following day, when the panel heats up, the stored water evaporates off the gel. This absorbs heat and cools the panel, much like sweat cools human skin. In laboratory tests, the system achieved a steady cooling power of 295 watts per square metre, enough to keep the panel significantly cooler during peak sun hours.


A newer version pushes efficiency further

Since that original study, a separate KAUST team led by Qiaoqiang Gan, with researchers including Saichao Dang and Huangyu Fang, has developed a related but distinct hydrogel: lithium chloride salt embedded in a cross-linked sodium polyacrylate network, described in a 2025 paper in Materials Science and Engineering: R: Reports. Attached to the rear of the panel, like the original gel, the material is designed to be cheaper and easier to manufacture at scale than earlier hygroscopic composites. In an outdoor test at the KAUST campus in Thuwal, Saudi Arabia, over 21 days, the composite reversibly absorbed and released water without failure, and at 38°C ambient temperature it reduced panel temperature by up to 14.1°C, increasing power conversion efficiency by 12.9 percent. The team also found that panels with this cooling layer lasted more than twice as long as uncooled panels under the same test conditions. KAUST researchers estimate the approach could reduce the overall cost of producing solar electricity by 18%, but this is based on their own modeling, not a full-scale deployment.

Making the technology cheap enough to matter

A cooling layer is only useful if it can be manufactured affordably. In a separate research project examining a self-adhesive hygroscopic composite published in Materials Science and Engineering: R: Reports, a hydrogel made of lotus root powder and lithium chloride was used, both of which are cheap and readily available materials. This hydrogel attaches directly to the panel surface without adhesives or additional fasteners. The researchers conducted the outdoor study at the KAUST campus in Thuwal, Saudi Arabia, over 21 days from July 12 to August 2, 2022.

Why this matters for your rooftop

Rooftop and utility-scale solar installations are growing rapidly across the world, and every extra percentage point of efficiency counts. A panel that operates 10°C to 14°C cooler can generate significantly more electricity from the same patch of roof or land without the need for a larger installation or additional hardware. That kind of gain adds up over the life of a solar system, which typically runs 20 to 25 years, whether for a homeowner paying a monthly power bill or a city trying to hit clean energy targets. This is especially relevant for places that already experience extreme heat, as hotter climates tend to have the largest efficiency losses from overheating panels in the first place. Large solar farms in these regions need a low-maintenance solution, and a quiet passive cooling layer with no pumps, fans or power source could fit that need.

It's worth being clear that none of these hydrogel coatings are on roofs yet. They are still technologies at the research stage, tested in labs and small outdoor trials rather than commercial products. Cost, rain durability and long-term performance in various climates still need further testing before manufacturers can build this into panels at scale. But the core idea, a gel that can self-regulate its water supply to cool a panel without any input of electricity, is a potential answer to a problem that has long depended on complex, power-hungry solutions. With solar power on the rise, small efficiency improvements like this could be just as important as improvements to the panels themselves.