NTU team's 'smart' window scores a first in energy use

Invention generates its own electricity, helps save power
By Carolyn Khew, The Straits Times, 17 Dec 2014

THIS is a window that can block out sunlight by day and charge your mobile phone by night without requiring an external power source.

In a first, scientists from Nanyang Technological University (NTU) have invented a "smart" window which can act as a rechargeable battery as well as darken or brighten a space without the need for an external power source.

Instead, the window is powered by a chemical reaction between dissolved oxygen in the electrolyte and a pigment called Blue Prussian, which gives the glass its blue tint.

The window, which took lead scientist Sun Xiaowei and four other scientists from NTU four years to develop, was recently featured in peer-reviewed scientific journal Nature Communications.

The self-powered window contains liquid electrolyte held between two glass sheets that make up one window. The liquid electrolyte acts as a conduit for ions to pass from one glass sheet to the other so as to generate electricity.

One sheet is coated with the blue pigment while the other is attached to a thin strip of aluminium foil. Both sheets are connected by electrical cables to form an electrical circuit.

At night, the window can function as a battery. The electricity can be used to charge low-powered devices, such as mobile phones or LED lights, by connecting a cable to the window.

Talks have begun with companies to commercialise the product, said Prof Sun from the School of Electrical and Electronic Engineering at NTU, adding that commercialisation can take two years.

"Our technology is very attractive as a zero-sum consumption smart window," said Prof Sun. "Building owners and even common households can reap energy savings right from the outset and over the long term."

Some windows on the market are retrofitted with tinted film to block out sunlight, but these cannot be brightened at night to enable the surroundings to be seen more easily. Those that can be brightened require an external power source.

Citing figures from the US Green Building Council, Prof Sun estimated that electrochromic or "smart" windows are 44 per cent more efficient than windows which are unable to adjust the amount of light entering a space.

The "smart" windows help save energy, for example, via air-conditioning to keep a room cool by filtering light coming in.

According to the Energy Efficiency Programme Office website run by various government agencies, air-conditioners rank among the top three energy-sapping appliances, alongside water heaters and refrigerators or freezers.

Prof Sun estimates his window would be lower in cost than other smart windows on the market, as the raw materials needed are cheaper. Other smart windows cost around US$50 (S$66) to US$100 per square foot.

When contacted, Mr Eugene Tay, founder and director of Green Future Solutions, a sustainability consultancy, said buildings here usually use blinds or double-glazed windows to reduce the amount of heat entering the building.

When asked if building owners would be keen to use the self-powered window as an alternative, he said: "If it helps to reduce the heat coming in, generates electricity and is affordable, I don't see why not."