The cost of commercial solar panels has fallen substantially in recent years; in fact, it has fallen by half since 2012. The International Energy Agency predicts that by 2040, renewable energy sources will contribute to at least 40% of global energy generation.

Researchers in China’s Soochow University have partially overcome one of the classic drawbacks of solar panels, that they do not function in rainy conditions. The solar panel incorporates a triboelectric nanogenerator (TENG), which allows the panel to generate energy in sunshine and in rain.

The friction of raindrops sliding on the cell causes electrons to be “knocked off” and therefore generates an electric charge. Once raindrops hit the topmost layer, it loses an electron and becomes positive, while the surface of the PDMS film becomes negative. This leads to the buildup of differential charge between the negative surface and the positive raindrop, which can be trapped and conducted to the lower layer by the nanogenerator. The newest structure of this hybrid solar panel incorporates a heterojunction silicon solar cell, and a TENG device made of paired polymer layers. They are grooved in a manner identical to a DVD, which is necessary for capturing sunlight on rainy days.

TENG output peaks at about 33nA in short circuit current, and 2.14V at peak open-circuit voltage. This combination of high current and voltage optimizes energy gathering efficiency in a wide range of weather conditions.