There is only so much heat—or cold—that the human body can take. This can be a problem in extreme environments, from subzero polar temperatures to the ruthless heat of the Sahara, and it doesn’t stop at Earth. Maintaining temperature is also an issue for astronauts. The vacuum of space is a gargantuan freezer, and exposure to direct sunlight out there can be just as brutal as the cold.

Clothing tech that regulates body temperature usually goes only one way: heating or cooling. It also tends to be bulky and needs substantial energy that eventually drains any batteries. What if there was a system that both heat and cool while running on a constant renewable energy source?

A team of researchers, led by Ziyuan Wang of Nankai University in Tianjin, China, has created a flexible, solar-powered device that can be incorporated into clothing and regulate the body by actively heating or cooling the skin. It also works continuously for 24 hours and only needs sunlight to recharge.

“To achieve the required sustainability and flexibility as well as light weight, the thermal-management unit for the body must be highly efficient in transferring energy and have a low energy consumption,” the team said in a study recently published in Science.

Batteries not included

Wang’s new system combines the power of a solar cell with that of an electrocaloric device. Solar cells, also known as photovoltaic cells, are made of materials that are semiconductors, which can absorb energy from sunlight and convert it to electricity. In this case, the photovoltaic material used is a flexible polymer.

The other component is an electrocaloric device that changes temperature when placed in an electric field applying the field will heat the material, while removing it will cool it.

The system developed by Wang and his colleagues is made of a type of polyvinyl. This flexible material functions as an insulator, integrating a solar cell outside the polyvinyl with an electrocaloric device underneath. When exposed to sunlight, the solar cell did exactly what it was expected to by turning sunlight into electrical energy. This electricity is then transferred to the electrocaloric device, where (assuming the device is in cooling mode) the appearance of an electric field will heat the device. Enough power is produced by the solar cell to keep the entire system going, and any extra energy is kept in a separate energy storage device.

Turn it up or turn it down

Whatever energy stored during the day becomes especially useful after the sun goes down. In the dark, the system automatically taps into energy from the storage attachment to keep going through the night.  Heating and cooling modes can be easily switched as it gets hotter or colder. And, when the system runs out of energy, there is no need to plug anything in—exposure to direct sunlight for 12 hours will recharge it.

“With these two working modes, bidirectional controllable thermoregulation for cooling and warming can be implemented as needed,” the researchers said in the same study.

So how can an explorer, astronaut, or anyone in an extreme environment wear this device? Wang proposes a suit with heating-cooling panels attached to the front and back of the chest, arms and legs. Because the panels are so flexible and lightweight, a garment like this would not weigh down someone facing blistering heat.

While this thermoregulatory tech may not be available yet, Wang is hopeful that it could be a significant breakthrough for those who have to work in extreme environments, even astronauts who have to brave the freezing darkness to go out on a spacewalk.

Science, 2023.  DOI:  10.1126/science.adj3654