GreenVolts will delay completing a 2-megawatt project to mid-2010 in order to improve the design of its concentrating solar power system.

When the company first announced its plan to build the power plant and sell the electricity to Pacific Gas and Electric two years ago, it had aimed to complete the entire project by the end of 2009. The San Francisco-based startup thought it could deliver the first megawatt of the project by the end of 2008 when it raised $30 million in series B last year (see Green Light post). 

The company has since determined that it should work on improving the design of its system in order to boost its performance and lower its cost, said GreenVolts' CEO Bob Cart via email. The company, founded in 2005, is building the project, called GV1, in Tracy, Calif., and has declined to reveal its cost. The company has installed some modules at the GV1 site to collect data.

"Instead of allocating a large amount of investment towards completing the project in 2008 using the first generation technology, we have decided to use those funds towards advancing the technology and putting a next generation system in place at GV1," Cart wrote.

GreenVolts' system uses an array of mirrors to concentrate the sunlight onto solar cells for generating electricity. The key component of the system is a dual-axis tracker called CarouSol by GreenVolts. The tracker sits low on the ground and tilts the mirrors to follow the sun's movement. The low profile makes the system easy to install and protects it from strong wind, the company said. The design of the CarouSol also reduces shadowing to a minimum.

Cart said his engineers are making changes to several parts of the system, including the mirrors and the receiver, which is made up of the solar cell, a lens and a device to dissipate heat. 

Until now, GreenVolts has been buying solar cells from other companies. But GreenVolts just signed a deal with the National Renewable Energy Laboratory to commercialize a solar cell technology developed by NREL (see Green Light post).

The company is licensing the patents for making inverted metamorphic multijunction (IMM) solar cells. Each cell has three layers of active materials for turning sunlight into electricity. The design originally was invented in the 1980s – NREL received the patent in 1987, said David Christensen, a senior licensing executive at the lab.

The lab's researchers have improved the design and received more patents since. Last summer, the lab's scientists said the version of IMM solar cell they had developed could convert 40.8 percent of the concentrated sunlight (326 times) that hit the cell into energy. Results from the lab tend to be higher than what can be achieved during commercial production, however. Multijunction cells can convert more light into power than traditional silicon solar cells, which may max out at 29 percent, but the exotic devices also cost more to make.

Once GreenVolts, whose first generation technology already can concentrate the sunlight 625 times, figures out how to mass-produce IMM solar cells, it intends to have them made for its own use, Cart said. He wouldn't say which manufacturers might make the cells for GreenVolts. How about selling the cells to other companies?

"It is premature to consider potential additional markets," Cart said.

GreenVolts isn't the only company that has licensed the IMM solar cell design to turn it into a commercial product. Emcore, a solar cell maker in Albuquerque, N.M., also has a similar development deal. Emcore won an award from the R&D Magazine last year for the solar cell technology it co-developed with NREL and the U.S. Air Force Research Laboratory. Emcore counts another concentrating solar power developer, SolFocus, among its customers.

NREL is kicking in $500,000 for the two-year project with GreenVolts. Cart said the company will provide "matching funds," and it already has the money. Commercializing a solar cell technology usually takes millions of dollars, Christensen said.

GreenVolts currently doesn't plan to use the IMM solar cells for its GV1 project, Cart said.

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