Startup Tests Cool Roof Coating
Israeli startup SolCold has recently begun testing a new type of coating designed to help keep buildings—among other structures and industries—cool in the presence of sunlight.
SolCold reports the coating was developed after researchers contemplated the idea of harnessing the sun's radiation in a reverse method—meaning, instead of radiation heating up buildings, it would actually help to cool them down.
Made up of four layers, the coating includes: a reflective IR emission layer at its base; a flexible, transparent, and thermal conductive layer; a layer of active cooling particles; and a confidential top layer. The company adds that the cool roof coating also utilizes an anti-strokes fluorescent patent technology.
The resulting combination reportedly creates an active cooling effect with zero implementation and maintenance.
SolCold designed a two-layer material that absorbs some particles of light—then uses them to conduct a reaction that turns heat into a cooling mechanism.— Tatiana Hürlimann (@solar1408) April 26, 2022
According to reports, the coating works by reflecting most sunlight, but allows some particles of light to breakthrough. The second layer of material then reacts to the specific radiation let in and emits particles of light at a higher frequency, thus causing the material to lose energy and get cooler.
“It’s continuously maintaining the lower temperature, not only on the coating, but penetrating below, so we can actually cool down the interior,” SolCold Founder Yaron Shenhav told Fast Company.
The company recently applied the coating to car roofs for concept testing. In its study, SolCold found that a white car covered with the coating was as much as 25 degrees Fahrenheit cooler than a non-coated white car sitting in the sun in the middle of the day. A black car was reported to be 34 F cooler.
“Each year you can read tragic stories about babies forgotten inside parked cars who die because temperatures are too high,” Shenhav said. “Our technology, which cools without the need for electricity, dramatically drops the temperature within cars, potentially saving lives.”
In upcoming tests, Konnect, Volkswagen Group’s innovation hub in Tel-Aviv, plans to apply the coating on one of its electric concept cars which it believes might help the vehicles travel further on a single battery charge thanks to a reduction of energy used for air conditioning.
Should testing continue to be successful, Shenhav estimates that when the coating is applied to buildings, it could cut the energy use from air conditioning by as much as 60%. In the future, he hopes that the coating could be used on buildings in countries where few people can currently afford air conditioning systems.
The issue with that though, is that the technology, as it is currently designed, is reported to be expensive: In pilot tests, it costs around $100 per square meter. Next year, the startup is aiming to have production costs land around $30 per square meter. That number is still out of reach for widespread use in developing countries, however.
“We’ll still need to wait a few years before it can be affordable [in developing countries],” Shenhav said.
While the largest future potential for the coating is on the roofs of homes and buildings, the startup has plans to first implement the coating with products from the automotive, telecom and defense, and even clothing industries.
Other Cool Coatings Research
Earlier this year, scientists from the Lawrence Berkeley National Laboratory announced their development of an all-season smart-roof coating, designed to keep homes warm during the winter months and cool throughout the summer without consuming natural gas or electricity.
“Our all-season roof coating automatically switches from keeping you cool to warm, depending on outdoor air temperature. This is energy-free, emission-free air conditioning and heating, all in one device,” said Junqiao Wu, a faculty scientist in Berkeley Lab’s Materials Sciences Division and a UC Berkeley professor of materials science and engineering who led the study, at the time.
“Our new material – called a temperature-adaptive radiative coating or TARC – can enable energy savings by automatically turning off the radiative cooling in the winter, overcoming the problem of overcooling.”
According to Berkeley Lab, the problem with current cool roof systems, most notably reflective coatings, membranes, shingles or tiles that have light-colored or darker “cool-colored” surfaces, is that they still naturally emit some of the absorbed solar heat as thermal-infrared radiation. Because of this, heat is also radiated in the winter months and can lead to increased heating costs.
To find a more effective alternative, researchers looked to metals, as the material is typically a good conductor of electricity and heat.
Results from the study revealed that the average household with TARC installed on the roof could save up to 10% in electricity usage and reflected around 75% of sunlight year-round. The thermal emittance of the material, however, was high (about 90%) when the ambient temperature was warm (above 25 C or 77 F), promoting heat loss to the sky. In cooler temperatures, the thermal emittance switched to low, and further promoted the retention of heat from solar absorption and indoor heating.
The coatings research has since been published in the journal Science and was primarily supported by the Department of Energy Office of Science and a Bakar Fellowship.
In July 2021, India-based startup company ReMaterials designed a roofing alternative with the goal of keeping homes cooler: modular roofing panels that are made from paper and wood waste.
The Modroof design utilizes cardboard (manufacturing and agriculture) waste and what the company calls natural binders that might a lightweight option that helps insulate the home. A waterproof coating is also added to the material, which has a metal structure and an air gap.
Company testing shows that the roof can make an 18-degree F difference inside the home.
ReMaterials also claims that the combination of materials also helps combat the heavy rain season as traditional metal roofs suffer from corrosion while concrete roofs crack. And, in terms of price, the Modroof falls somewhere in between the two and are easier to install, according to the company.
That same year, in April, engineers at Purdue University announced what they called “the whitest paint yet”—a cool coating that aims to reduce buildings’ needs for air conditioning.
The team initially created an ultra-white paint last October, and have been pushing to reformulate it for even “cooler” properties. The team recently published a paper about its findings in the journal ACS Applied Materials & Interfaces.
The researchers have gone so far as to say that this white is closest thing available to an equivalent of “Vantablack,” which absorbs up to 99.9% of visible light. On the flip side, the new whitest paint reflects up to 98.1% of sunlight, compared to 95.5% in the researchers’ previously developed ultra-white paint. Typically, white coatings expect to reflect 80-90% of sunlight.
To test the cooling traits of the paint, researchers used thermocouples to demonstrate outdoors that the paint can keep surfaces 19 degrees Fahrenheit cooler than the ambient surroundings at night, and 8 degrees F below their surroundings during high noon. Reportedly, the paint even works in winter climates.
Patent applications for this paint formulation have been filed through the Purdue Research Foundation Office of Technology Commercialization. This research was supported by the Cooling Technologies Research Center at Purdue University and the Air Force Office of Scientific Research through the Defense University Research Instrumentation Program. The research was performed at Purdue’s FLEX Lab and Ray W. Herrick Laboratories and the Birck Nanotechnology Center of Purdue’s Discovery Park.