Researchers in China have developed solar-powered clothing for thermoregulation. [Image: NASA]
Space explorers, desert trekkers and polar scientists often find themselves in places where environmental temperatures change rapidly between extreme hot and cold. Now, scientists in China have devised a solar-powered clothing system for keeping adventurous humans comfortable during these temperature cycles.
The proof-of-concept thermoregulatory clothing incorporates a flexible organic photovoltaic panel that powers bidirectional electrocaloric devices transferring heat to or from the wearer’s skin (Science, doi:10.1126/science.adj3654). Researchers at Nankai University, China, say that the wearable system can keep a person comfortable for 24 hours with 12 hours of exposure to sunlight.
The need for thermoregulatory clothing
Passive and active thermoregulatory systems already exist for use in jobs as diverse as astronauts on spacewalks to actors wearing heavy costumes at warm-weather theme parks. However, cooling vests based on circulating fluids require mechanical compressors, and thermoelectric devices based on the Peltier effect―heating and cooling at the junction of two different conductors―demand large amounts of energy. Many passive systems can only warm up or cool down the wearer, not both.
Battery-powered thermoregulatory systems can provide short-term comfort management but not all-day performance. Yet the need for longer-term thermoregulation exists, from spacewalks lasting eight or 10 hours to polar expeditions of multiple days.
Design and performance
The Nankai clothing system gets its power from a flexible organic photovoltaic panel with an effective area of 25.2 cm2 and a thickness of only 180 μm; it provides 5.75 V. The electrocaloric panels in the system are made of a flexible polymer that exhibits large adiabatic temperature changes near room temperature. The scientists also incorporated an energy-storage system to store some of the solar energy during the day to power the system at night.
The research team designed panels with the photovoltaic material on top (exposed to the outside world) with the electrocaloric panels on the bottom (near the wearer’s skin). A voltage control system allows the user to switch between heating and cooling modes depending on the environment and personal comfort. The scientists tested out the panels’ energy-generation capabilities under simulated sunlight ranging from 55 to 100 mW/cm2 as well as actual daytime sunlight in summer. (In Earth orbit, astronauts would get 136.7 mW/cm2 of power from the sun.)
The solar-powered panels maintained human skin temperature between 32.0 and 36.0°C.
The solar-powered panels maintained human skin temperature between 32.0 and 36.0°C ― a warm-weather comfort zone―while outside temperatures ranged from 12.5 to 37.6°C. The relative sizes of these panels could be tailored for harsher environments. For example, a typical spacesuit might have an outside surface area of about 1.85 m2, but the Nankai researchers estimate that it would take only about 1.12 m2 of photovoltaic paneling to provide an astronaut with all-day comfort.
“The integrated device of Wang et al. opens many possibilities for developing actively controlled, self-powered and wearable localized thermal-management systems and expanding human adaptation to harsh environments,” write Xingyi Huang and Pengli Li, Shanghai Jiao Tong University, China, in a related article published alongside the paper. “It is possible to imagine a future of all-weather thermal management that is not limited by an energy supply and where extra collected energy might even power electronic devices under special conditions.”