Communion Of Dreams

Orange windows?
July 16, 2008, 7:17 am
Filed under: MetaFilter, MIT, Predictions, Science, tech

Currently, there are two fundamental problems with solar power:

1. Manufacturing. Photovoltaics are difficult and expensive to manufacture, with exacting quality standards. Minor imperfections can ruin the electrical circuit of a cell or even a whole panel of cells.

2. Efficiency. To get maximum efficiency from solar panels, they should be mounted so as to be optimally oriented towards the sun. Ideally, they would track the sun across the sky during the course of the day, and account for seasonal variation in the sun’s path. Such tracking mechanisms are expensive to build and maintain.

Well, researchers at MIT seem to have come up with a simple way of addressing both problems.

MIT opens new ‘window’ on solar energy

Cost effective devices expected on market soon

Imagine windows that not only provide a clear view and illuminate rooms, but also use sunlight to efficiently help power the building they are part of. MIT engineers report a new approach to harnessing the sun’s energy that could allow just that.

The work, to be reported in the July 11 issue of Science, involves the creation of a novel “solar concentrator.” “Light is collected over a large area [like a window] and gathered, or concentrated, at the edges,” explains Marc A. Baldo, leader of the work and the Esther and Harold E. Edgerton Career Development Associate Professor of Electrical Engineering.

As a result, rather than covering a roof with expensive solar cells (the semiconductor devices that transform sunlight into electricity), the cells only need to be around the edges of a flat glass panel. In addition, the focused light increases the electrical power obtained from each solar cell “by a factor of over 40,” Baldo says.

(Video here.)

What they have done is to solve a basic problem with using a flat pane of glass to concentrate light around the edges of the pane, thanks to research done on lasers and LEDs. The difficulty with this approach in the past was that light energy would be ‘lost’ in passing through the glass, making such a system inefficient. But Baldo and his fellow researchers discovered that a simple application of dye or paint – they literally used orange automotive paint – on the surface of the glass did the trick. The light is absorbed by the color on the surface, then re-emitted within the pane at a particular wavelength which passes easily through the glass matrix to the edges of the pane.

This innovation is exciting for several reasons. First off, it is fairly cheap to apply such a dye to the surface of the glass, and it really doesn’t matter if there are imperfections – they’ll just disrupt the light absorption at that point, not interfere with the functioning of the photovoltaic cells. Secondly, it eliminates the need for elaborate tracking systems – any light which hits the glass is concentrated at the edges of the pane. So all you need to do is rim the edges of the glass with photovoltaic cells, and you maximize your energy gain.

A side benefit will be that the application of this technology to large buildings will generate electricity while at the same time reducing the heat load from solar radiation through windows. Say you make your windows such that they allow 25% of the light striking them to enter the building, the rest being captured for electricity generation (this can be done by controlling the amount of dye on the surface of the glass – such as is done today with tinted windows). That 25% is still plenty sufficient to help with natural illumination, but means that you won’t need to run air conditioning systems nearly as much to offset the heat load. (I just picked 25% at random – I think that the actual amount needed for illumination would be less – architects and engineers would be be able to factor this into any building’s design specs).

Of course, it could well mean that windows in our near-term future show up as being orange. Maybe I’ll need to drop such descriptions into Communion of Dreams next time I do some editing . . .

Jim Downey

(Via MeFi.)

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