Clever solution: Organic solar concentrators collect and focus different colours of sunlight. Solar cells can be attached to the edges of the plates. By collecting light over their full surface and concentrating it at their edges, these devices reduce the required area and therefore cost of solar power. Image demonstrates how light is concentrated at the edges.
Credit: MIT
SYDNEY: New technology could turn your windows into solar panels or improve the efficiency of existing solar cells, reducing the cost of solar power, says a new report.
Today in the U.S. journal Science, engineers at the Massachusetts Institute of Technology, in Boston, U.S., describe how to turn a window into a solar concentrator, by painting it with a mix of organic dyes and setting small solar cells around the edges.
Fibre optic principles
Study co-author Jon Mapel said the organic dyes use the same principles as fibre optics to focus light from all over the glass onto the silicon-based solar cells at the edges. This provides the cells with ten times as much energy as they could collect on their own.
The system is so simple to manufacture that the team expects it to be on the market within three years, and Mapel has started a company with co-authors Michael Currie and Shalom Goffri to commercialise the technology.
Mapel said that currently the cost of solar-generated energy is the main barrier to its wider use. "Solar power is really an engineering problem waiting for an elegant solution to reduce the costs," he said.
The organic solar concentrator (OSC) developed by the MIT team has a conversion efficiency of 6.8 per cent, meaning that 6.8 per cent of the energy collected by the OSC is converted into electricity. This is lower than silicon or thin film panels, which have efficiencies of 14 and 10 per cent respectively. However, because expensive silicon-based cells are only a small part of the OSC, the electricity produced should be cheaper.
Mobile mirrors
Most concentrators use mobile mirrors that track the sun and focus the rays onto a solar cell, but the moving parts are expensive. In the 1970s engineers tried using organic dyes as concentrators, but too much light was lost on way to the solar cells at the edge.
The MIT team found that the secret was using specific ratios of component dyes, which each absorb a particular wavelength of light. Mapel said that, as well as using the dye for window-like panels, existing solar panels could be retrofitted with a layer of the concentrator to improve their efficiency.
Silicon cells are usually the most expensive part of a solar panel, so the MIT team was trying to develop cells that used cheaper organic compounds as semiconductors. The cells they developed had superior optical qualities, but their electrical properties couldn't match silicon-based cells.
"The [concentrator] was an effort to divide and conquer: to use the organics for their optical properties and inorganic semiconductors for their electrical properties," Mapel said.
However, Martin Green, a leading photovoltaics expert at the University of New South Wales in Australia, thinks Mapel and his colleagues are being overly optimistic. "The projected… efficiency is not yet high enough for major commercial impact," he commented.
