Smart window manages light flow and energy generation

Dan Rogers - 20 May 2010

A smart electronic window that can alter levels of light filtration and generate energy has been developed at the Eindhoven University of Technology.

The dye-based glass uses thin strips of photovoltaic (PV) material, fitted to the edges of the glass, to absorb redirected sunlight and generate energy.

The windows consist of a liquid crystal material and fluorescent dye encapsulated in glass. The dye absorbs sunlight and directs it towards the edges of the glass. The level of light passing through the window can also be controlled, either automatically or using a switch.

An electrical current could also be applied to alter the opacity of the glass itself, meaning the amount of light coming through the glass can be altered throughout the day.

The research team in the Netherlands is speaking to glass manufacturers and architects about making the technology suitable for the market, where it could be used in office buildings or vehicles.

Michael Debije, senior researcher in the Polymer Technology group at the university, comments: 'We're in contact with several companies in the Netherlands regarding test projects, or façade installations.

'Within the year, we'll have some functional devices for outdoor and lifetime testing in place.'

Lifetimes

Lifetime trials of the window will be key to establishing market uses, as long-term operation of decades may be required for some applications, such as listed buildings. It is lifetime issues that have hindered the progress of organic PVs in building-integrated energy markets.

However, the liquid crystal and dye materials used suggest longer-term operation will be possible in future trials.

'Recently, there has been a lot of work using laser dyes, which have lifetimes measured more in decades, so multi-year operation is quite possible.'

Materials

Debije explains: 'A control pad or push button could be used to apply a low voltage across the device to change light absorption. This could be used in office buildings - in the dark state the window could generate maximum power, and use no energy - during the daytime it could be adjusted to allow light into the building and still generate power at lower output.'

The research group has already produced devices to test the smart window's performance, though it has used orange and yellow materials so far. A blue version has recently been added, and Debije says grey-blue versions are being prepared to make the material more suitable for commercial purposes.

The transmission range for the windows - which dictates the lowest and highest level of light absorption and brightness allowed by the dye material - is being optimised, to expand to 10-70%.

Manufacturing is also being considered: glass producers are speaking to the research team about how to easily integrate the PV strips on the edges of the glass panels.

Debije adds: 'Window frames could be adapted. This would make it easy to adopt, as it should not be a major change in the way they make frames, apart from having some wiring. However, the ideal would be to include it as part of the glass, so these devices could be retrofitted.'

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