To solve this problem, excess electrical energy can be stored in batteries. When these batteries are discharged, they release electrical outputs with steady amplitudes and frequencies.

However, the best energy-storage devices present challenges of their own. In particular, they typically work at voltages of under 10 Volts, and can only be charged and discharged at rates below 100 millivolts per second. Their energy storage efficiency drops drastically to under 2% when charged with pulsed electricity at voltages higher than 100 Volts, which is typical of recent mechanical energy harvesters. This performance can be enhanced by installing extra power management modules – but these only add complexity to energy-storing devices, resulting in considerable losses during energy conversion.

A team led by Dr Jiantong Li at the KTH Royal Institute of Technology has developed a new energy-storage device that overcomes these challenges. Using a flexible, electrically conducting polymer, the team’s device is made up of tiny batteries called ‘micro-supercapacitors’, or MSCs. Crucially, the team’s choice of polymer enables them to print large grids of MSCs directly onto paper using organic inks.

To test their design, Li’s team printed an array of 100 MSC cells in a grid pattern spanning 3.5 cm long, and 2.4 cm wide. The design demonstrates substantial improvements on the performance of existing energy-storing devices. It can handle output voltages as high as 160 Volts; and also works extremely quickly: charging and discharging at up to 30 Volts per second.

The team then used the device to capture and store high-voltage pulses from a generator powered by falling water droplets. The device can also capture 62% of the maximum energy harvested by the generator, making it vastly more efficient than existing batteries.

With its highly compact arrangement, combined with its simple manufacturing process, the MSC array is ideally suited for sustainable energy storage. If their vision is achieved, it could ultimately accelerate the rollout of renewable energy worldwide.