# Dutch student offers new insights into power-generating windows

##### July 9, 2012

On 5 July Jan Willem Wiegman graduated from TU Delft with his research into power-generating windows. The Applied Physics Master’s student calculated how much electricity can be generated using so-called luminescent solar concentrators. These are windows which have been fitted with a thin film of material that absorbs sunlight and directs it to narrow solar cells at the perimeter of the window. Wiegman shows the relationship between the colour of the material used and the maximum amount of power that can be generated. Such power-generating windows offer potential as a cheap source of solar energy. Wiegman’s research article, which he wrote together with his supervisor Erik van der Kolk, has been published in the journal Solar Energy Materials and Solar Cells.

Windows and glazed facades of office blocks and houses can be used to generate electricity if they are used as luminescent solar concentrators. This entails applying a thin layer (for example a foil or coating) of luminescent material to the windows, with narrow solar cells at the perimeters. The luminescent layer absorbs sunlight and guides it to the solar cells at the perimeter, where it is converted into electricity. This enables a large surface area of sunlight to be concentrated on a narrow strip of solar cells.

The new stained glass

Luminescent solar concentrators are capable of generating dozens of watts per square metre. The exact amount of power produced by the windows depends on the colour and quality of the light-emitting layer and the performance of the solar cells. Wiegman’s research shows for the first time the relationship between the colour of the film or coating and the maximum amount of power.

A transparent film produces a maximum of 20 watts per square metre, which is an efficiency of 2%. To power your computer you would need a window measuring 4 square metres. The efficiency increases if the film is able to absorb more . This can be achieved by using a foil that absorbs light particles from a certain part of the solar spectrum. A foil that mainly absorbs the blue, violet and green light particles will give the window a red colour. Another option is to use a foil that absorbs all the colours of the solar spectrum equally. This would give the window a grey tint. Both the red and the grey film have an efficiency of 9%, which is comparable to the efficiency of flexible .

Wiegman’s research has also shown the importance of a smooth film surface for the efficient transport of light particles to the perimeter of the window as they are then not impeded by scattering between the film and the window surface.

The research into power-generating is in keeping with the European ambition to make buildings as energy neutral as possible. Luminescent solar concentrators are a good way of producing cheap .

Explore further: Researchers boost solar concentrator efficiency

More information: Publication: "Building integrated thin film luminescent solar concentrators", Solar Energy Materials and Solar Cells, Volume 103, August 2012, pages 41–47.

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##### antialias_physorg
5 / 5 (1) Jul 09, 2012
It would be great if the windows were switchable.
When you're not home the window could switch to opaque on the backside (guiding all light towards the solar cells at the rim) and while you're at home you could switch to transparent with still a modicum of light going to electricity generation.

Small scale energy harvesting seems to be the future.
##### Shootist
1 / 5 (2) Jul 09, 2012
Small scale energy harvesting seems to be the future.

Only because it is seen as fashionable among the nattering class.

##### El_Nose
not rated yet Jul 09, 2012
place grey windows in bedrooms and large windows facing the street. Solves problems
##### antialias_physorg
5 / 5 (1) Jul 09, 2012
Stuff is becomeing more energy efficient.

Consider how much energy cell phones/laptops used a couple of years ago and how much they use now for the same usage profile.
It's not inconceivable that we'll get low power applications (like e-readers, cell phones, etc. ) that will not require a charging device at all - merely scavenging energy off the environment when not in use.

Certainly for embedded sensors and the like a self-charging/harvesting approach is a major boon. You wouldn't want lay down a network of cables throughout a concrete structure - just to power all the sensors that will give you information on material fatigue. What you really want to do is just throw in a handful of them when pouring the concrete and have them relay information whenever they have gathered enough energy to send a short burst of data.

Similarly the appliances in your home will get (and have gotten) more energy efficient. Hopefully to the point where you won't need a grid connection at all.
##### xX_GT_Xx
not rated yet Jul 09, 2012
Neat idea. Not terribly practical as a commercial product though.

How are you going to make use of the power? What are people supposed to do, wire their windows up to their home or office? Did window installation just become the job of an electrician?