The flexible, washable device can be screenprinted onto clothing and consists of three main parts: sweat-powered biofuel cells; motion-powered devices called triboelectric generators, and energy-storing supercapacitors.

Biofuel cells that harvest energy from sweat are located inside the shirt at the chest. Devices that convert energy from movement into electricity, called triboelectric generators, are positioned outside the shirt on the forearms and sides of the torso near the waist.

They harvest energy from the swinging movement of the arms against the torso while walking or running. Supercapacitors outside the shirt on the chest temporarily store energy from both devices and then discharge it to power small electronics.

Harvesting energy from both movement and sweat enables the wearable microgrid to power devices quickly and continuously. The triboelectric generators provide power right away as soon as the user starts moving, before breaking a sweat. Once the user starts sweating, the biofuel cells start providing power and continue to do so after the user stops moving.

“When you add these two together, they make up for each other’s shortcomings,” said co-first author Lu Yin. “They are complementary and synergistic to enable fast startup and continuous power.”

The entire system boots two times faster than having just the biofuel cells alone and lasts three times longer than the triboelectric generators alone.

The wearable microgrid was tested on a subject during 30-minute sessions that consisted of 10 minutes of either exercising on a cycling machine or running, followed by 20 minutes of resting.

The system was able to power either an LCD wristwatch or a small electrochromic display - a device that changes colour in response to an applied voltage - throughout each 30-minute session.

“We’re applying the concept of the microgrid to create wearable systems that are powered sustainably, reliably and independently,” Yin added.

“Just like a city microgrid integrates a variety of local, renewable power sources like wind and solar, a wearable microgrid integrates devices that locally harvest energy from different parts of the body, like sweat and movement, while containing energy storage.”

Each wearable provides a different type of power. The biofuel cells provide continuous low voltage, while the triboelectric generators provide pulses of high voltage.

In order for the system to power devices, these different voltages need to be combined and regulated into one stable voltage. That’s why the device uses supercapacitors which act as a reservoir that temporarily stores the energy from both power sources and can discharge it as needed.

In January this year, a team demonstrated a film that effectively evaporates sweat from skin while using the moisture to power wearable electronics.