We've been seeing a lot of transparent or even white solar panels lately that act as windows and parts of a building's facade while they generate energy. The idea of using energy-generating and energy saving technologies as part of the building itself is becoming more popular and for good reason. These technologies not only save energy, but are also aesthetically pleasing.

The latest in these types of technologies are smart windows that tint themselves to block out the sun and keep the building cooler. Earlier versions of these types of windows have needed an external power source to work, but a new version from researchers at Nanyang Technological University in Singapore generates its own energy and even makes a surplus that goes back to the building.

The window consists of two glass panes that are filled with an oxygen-carrying liquid electrolyte. The two panes are each wrapped in a conductive coating and an electrical wire links the panes together to create a circuit. One of the panes is coated in a pigment known as Prussian Blue that gives the glass its blue tint when it is fully charged.

© Nanyang Technological University

The window can turn the cool-blue tint in bright daylight to block out as much as 50% of the light to keep the building cool, while during the evening and night, reverts back to glass and it has a pretty neat way of achieving this tint.

"Our new smart electrochromic window is bi-functional; it is also a transparent battery,” Professor Sun Xiaowei explained. “It charges up and turns blue when there is oxygen present in the electrolyte – in other words, it breathes.”

When the electrical circuit between them is broken, a chemical reaction starts between Prussian Blue and the dissolved oxygen in the electrolyte which turns the glass blue. When the electrical circuit is closed, it discharges the battery and turns the glass into a colorless white. The color changes happen within seconds. In a real-world application, the window would be controlled by a switch.

The research team also used a small section of their device to power a red LED, proving that the window could also find use as a transparent, self-rechargeable battery for low-power electronics.