It may seem contradictory, but soon you may be able to cool your home with sunlight. Israeli company SolCold has developed a high-tech paint based on a process called 'laser cooling' to offset the cost – economically and environmentally – of using air conditioning in hot summer months.
Laser cooling is the process by which hitting specially designed materials with a laser can cool them by up to 150ºC. The molecules in these materials "absorb photons whose light is of one frequency while spontaneously re-emitting higher-frequency photons, which also carry more energy," according to New Scientist. Since energy is lost in this exchange, the temperature of the material goes down.
Sunlight isn't as powerful as a laser, but Yaron Shenhav of SolCold decided to see if he could adapt this laser cooling process so it worked with the sun.
“Heat from a building could be absorbed and re-emitted as light,” Shenhav told New Scientist. “As long as the sun is shining on it, it would be continuously cooled. It’s like putting a layer of ice on your rooftop, which is thicker when there is more sun."
To do this, SolCold created a material that could do the same trick using several frequencies of scattered light, instead of the concentrated frequency of a laser. The resulting paint is composed of two layers: the outer layer filters out some of the sun’s rays and the inner layer completes the heat-to-light conversion, cooling itself below the ambient temperature and, subsequently, the home living beneath the paint.
The paint tested well in the lab, with some caveats. So far it works better on metal roofs than concrete, and is more successful over rooms with low ceilings than high ones. However, simulations have shown that the paint can make a top-floor room up to 10ºC cooler than a room without it.
SolCold will begin testing the paint on buildings in the next two years. As it stands now, the paint isn't cheap – about $300 to coat about 1000 square feet – but Shenhav thinks the early adopters will be shopping malls and stadiums, where energy consumption soars. Shenhav told New Scientist that applying the paint to buildings like that could cut air conditioning costs by 60 percent, saving money and carbon emissions. It could also reduce the occurrence of "heat islands," which are areas with already-high temperatures that get even hotter with the constant use of air conditioners.
But, New Scientist notes, the paint could prove useful beyond Earth, too. Though the temperatures are freezing in space, there is no air to carry heat away from objects. Currently, reflective fabrics are used to deflect radiation from the sun, and internal heat exchangers to get rid of excess heat produced by equipment. But SolCold's tech paint could change that.