Friday, May 11, 2007

Solar Power at Half the Cost

A new roof-mounted system that concentrates sunlight could cut the price of photovoltaics.

By Kevin Bullis

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Cheaper solar: This solar concentrator uses mirrors and lenses to focus light, reducing the amount of semiconductor material needed and cutting costs. The rectangular module is mounted with the same hardware as conventional flat solar panels.
Credit: Soliant Energy, Inc. Patent Pending

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•	View a slideshow of solar concentrator images and schematics.

A new mechanism for focusing light on small areas of photovoltaic material could make solar power in residential and commercial applications cheaper than electricity from the grid in most markets in the next few years. Initial systems, which can be made at half the cost of conventional solar panels, are set to start shipping later this year, says Brad Hines, CTO and founder of Soliant Energy, a startup based in Pasadena, CA, that has developed the new modules.

Concentrating sunlight with mirrors or lenses on a small area cuts the costs of solar power in part by reducing the amount of expensive photovoltaic material needed. But while concentrated solar photovoltaic systems are attractive for large-scale, ground-based solar farms for utilities, conventional designs are difficult to mount on rooftops, where most residential and commercial customers have space for solar panels. The systems are typically large and heavy, and they're mounted on posts so that they can move to track the sun, which makes them more vulnerable to gusts of wind than ordinary flat solar panels are.

Soliant has designed a solar concentrator that tracks the sun throughout the day but is lighter and not pole-mounted. The system fits in a rectangular frame and is mounted to the roof with the same hardware that's used for conventional flat solar panels. Yet the devices will likely cost half as much as a conventional solar panel, says Hines. A second-generation design, which concentrates light more and uses better photovoltaics, could cost a quarter as much. He says that a more advanced design should be ready by 2010.

The Soliant design combines both lenses and mirrors to create a more compact system. Each module is made of rows of aluminum troughs, each about the width and depth of a gutter. These troughs are mounted inside a rectangular frame and can tilt in unison from side to side to follow the sun. Each trough is enclosed on top with a clear acrylic lid. Inside each trough, a strip of silicon photovoltaic material runs along the bottom. As light enters, some of it reflects off the inside surface of the trough and reaches the strip of silicon. The rest of the incoming light is focused on the strip by a lens incorporated into the acrylic lid.

As a solar concentrating system, this design has a few drawbacks. Because the troughs are mounted close together, they shade each other during parts of the day, decreasing the total amount of electricity produced. They can also only track from side to side, which makes it impossible for them to follow exactly the arc of the sun across the sky. This second problem will be addressed in the second-generation design, in which each trough will be divided into sections, each of which can pivot from side to side and also up and down.

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Solar Power at Half the Cost

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