Indium window generates electricity from rain

In an experiment simulating rainfall, the window generated 8.3 watts per square meter (W m-2) from a single raindrop. In a proper downpour, that is a substantial amount of electricity. The project led by Professor Seung Hwan Ko pursues an even more ambitious goal: the window is intended to enable not only net-zero energy buildings—i.e., those that generate as much energy over the course of a year as they consume—but buildings with a positive energy balance. Once the technology is mature, it can also make an important contribution to the energy transition.

The scientists’ invention is nothing less than a multifunctional, intelligent window. It has several additional capabilities that go beyond generating electricity in bad weather. For example, the window can defrost itself in mist or frost through a process known as Joule heating. The window is also useful in hot weather, as it cools interior spaces. Its layered structure of silver and indium tin oxide reflects a large portion of infrared thermal energy without losing transparency. In this way, the window combines a mini power plant, a cooling system and an anti-frost device in one.

The “secret” behind the window’s power generation is the so-called triboelectric effect. “Tribo” derives from the Greek word for “to rub”, so triboelectric nanogenerators (so-called TENGs) are devices that generate electrical charge by bringing together and separating two different materials. This type of power generation is becoming increasingly widespread. One example is fitness trackers and medical monitoring devices worn on the body that recharge through movement. Here, too, transparent yet flexible indium tin oxide plays a central role.