Chinese researchers have presented a novel idea for solar-powered apparel that can control the body temperature of the wearer. The idea, which was developed by Ziyuan Wang and associates at Nankai University, blends cutting-edge flexible solar cells with electrocaloric devices. In a study published in the journal Science, the team outlines its methodology.

The goal of thermoregulating apparel is to maintain a pleasant and safe body temperature in a variety of settings.  In general, it can be divided into two groups: active and passive.  In order to maintain users' comfort, passive thermoregulation makes use of materials that take advantage of absorption, radiation, and the latent heat of phase transitions.

A key advantage of a passive approach is that an external power source is not needed. Passive thermoregulation, on the other hand, typically only works in one way, with clothing having a warming or cooling effect but not both, reports Physics World.

Active materials that use fluidic channels and coolant circulation to accomplish quick heating and cooling are typically used to provide bidirectional thermoregulation.  Batteries, which add weight and require recharging, are typically used to power these systems.  Although it has proven to be a considerable design issue, they might theoretically also be powered by solar energy collection.

“Because of their high energy consumption, it is difficult for active systems to maintain continuous thermoregulation of the human body for a long time through portable, sustainable energy-harvesting devices,” Xingyi Huang and Pengli Li at Shanghai Jiao Tong University write in a commentary article in Science that accompanies Wang’s paper.

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To tackle this challenge, Wang’s team drew from the latest advances in flexible organic photovoltaics. Today, these solar cells can maintain high conversion efficiencies even when contorted into different shapes.

“If such a highly efficient and flexible organic photovoltaic unit could be integrated with a proper thermal management system, then robust, self-sustaining, and thermoregulating clothing could be achieved,” Huang and Li predict.

Wang and associates developed a tiny wearable material in their work by attaching a flexible solar cell to a flexible electrocaloric module.  The latter is a device that reacts to applied electric fields by changing its temperature reversibly.

The electrocaloric module was able to cool the wearer's skin by up to 10 degrees in hot weather when the solar cell was exposed to sunlight.  A tiny, independent battery can be used to store any extra energy.  The wearable can be put into warming mode in the dark, using its stored energy to raise the wearer's skin temperature by up to three degrees. The device can accomplish thermoregulation over the course of a day.

Wang's team hopes that by incorporating this technology into wearable textiles, the invention may result in a new line of useful, solar-powered apparel that aids wearers in adjusting to difficult and complex situations.