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New windows double as solar panels

Steve Connor
Friday 11 July 2008 15:46 BST

A new type of solar panel that allows light to pass through it like a pane of glass has been invented by scientists who said that it is 10 times more powerful than conventional methods of producing energy from sunlight.

The discovery raises the prospect of using ordinary domestic windows to generate electricity with minimum structural alterations, although scientists have not yet worked out how much it would cost to convert a domestic home to a solar-powered generator.

Instead of coating the entire solar panel with solar cells - the expensive semiconductor devices that turn the energy of sunlight into electricity - the new solar panel works on the principle of concentrating the light, and the energy, at the edges of a pane of glass where it can be collected by the solar cells.

Scientists from the Massachusetts Institute of Technology (MIT) in Boston said that the “solar concentrator” is made from a film of organic molecules that can be coated on to glass window panes or other surfaces exposed to sunlight. This allows light to pass straight through the window even though it is being used to generate power.

It also means that the expensive solar cells need only be placed around the edges of the collecting area, so that there is little need to track the movements of the Sun for generating maximum power, as well as reducing overall costs.

“Light is gathered over a large area [like a window] and gathered, or concentrated, at the edges. The cost of photovoltaic power can be reduced with organic solar concentrators,” said Professor Marc Baldo, the leader of the research team at MIT.

Existing solar concentrators using in commercial solar generators have to track the movements of the Sun during the day to generate the highest optical intensities. This often involves expensive mobile mirrors and are difficult to maintain, Professor Baldo said.

“In addition, solar cells at the focal point of the mirrors must be cooled, and the entire assembly waste space around the perimeter to avoid shadowing neighbouring concentrators,” he said.

The MIT solar concentrator involves a mixture of two or more dyes that are painted onto a pane of glass or plastic. These dyes absorb light across a range of different wavelengths, which is then re-emitted at a different wavelength and transported across the pane to the waiting solar cells at the edges.

Jon Mapel, one of the MIT scientists who worked on the project, said that the trick was to improve the efficiency of the process, which ultimately leads to better performance and lower costs.

“We made it so the light can travel a much longer distance. We were able to substantially reduce light transport losses, resulting in a tenfold increase in the amount of power converted by the solar cells,” Dr Mapel said.

Solar power is seen as one of the greenest sources of energy but it has been dogged by the relatively high costs of installing photovoltaic cells on houses and buildings, which can take years to pay off in terms of energy savings.

Their efficiency in low-light conditions is also a problem for countries such as Britain were sunlight is a rare commodity in the coldest months of winter.

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