NREL and Optony Collaborate on Developing Cost-Competitive Approach for Solar Electricity

July 14, 2008

If you combine thin-film solar cells with an optical system design, you’ll have a revolutionary concentrating photovoltaic (CPV) system. That is what the National Renewable Energy Laboratory (NREL) and Optony, Inc. are working on together. It’s a brand new approach. Instead of using silicon or gallium arsenide solar cells, the system will use thin-film solar cells to be developed during the collaboration, based on technologies originally developed at NREL that hold the world efficiency record for thin-film photovoltaic solar cells.

“We’re just embarking on this project with Optony, and this is our first attempt at merging a concentrator system with our next-generation converter technology,” says Scott Ward, a senior scientist at NREL specializing in concentrating solar power. “But we have reason to believe that it will lead to low-cost electricity.”

CPV systems create electricity using lenses or mirrors to concentrate sunlight on high-efficiency solar cells. The energy conversion efficiency of a solar cell is the percentage of sunlight converted by the cell into electricity. Even though they’re more efficient than thin-film cells, the silicon solar cells currently used for these systems are more expensive than those used for flat-plate PV systems. The multi-junction gallium arsenide-based solar cells now being considered for CPV systems are the most efficient at 40%. However, they require lenses or mirrors that focus the light around 500 to 1,000 times its strength, which has some disadvantages.

“If you’ve ever taken a magnifying glass to ants, it’s a lethal thing,” Ward says. “You can imagine what a hostile environment it is for a cell to operate under 500 to 1,000 suns concentration, and it’s expensive to create an optical system that will provide that kind of concentration ratio.”

Because there’s a lot of heat involved, you need a means to dissipate the heat away from the cell. This is difficult with silicon wafer cell technology, which is limited to the thermal properties of the cell. Thin-film cells, however, can be deposited into a variety of thermally conductive substrates. And they’re cheaper to manufacture than silicon cells.

“In this respect, thin-film cells are superior in design to the silicon solar cells,” says NREL Senior Scientist Miguel Contreras, who developed the thin-film cells with the world efficiency record. “The cheaper thin-film cells and low-cost optics should lead to a less expensive product or a lower dollar per watt of electricity.”

Dong Wang, the vice president of Optony, is working on-site at NREL as part of a joint team with Contreras and Ward. “The system will not only be cheaper to manufacture, but also more reliable,” Wang says.

For this joint project with Optony, Contreras and Ward are taking advantage of NREL’s many years of research in thin-film PV and concentrating solar power, bringing these two technologies together. For example, Ward says the characterization techniques developed for concentrator cells will be applicable to this project.  Contreras adds that NREL’s efforts in developing efficient thin-film cells will make a considerable contribution.

“The reason we’re working with NREL researchers is because we consider them to be the world’s experts in these solar technologies,” says PR Yu, president and CEO of Optony.

Because of this new approach’s great market potential, the joint project between NREL and Optony has received $250,000 from the Department of Energy’s Technology Commercialization Development Fund (TCDF). The TCDF Program has provided the NREL Technology Transfer Office with a total of $4 million to expand such collaborative efforts between NREL researchers and companies.

“With the additional funds provided by the TCDF, we can proceed with this research in an accelerated fashion,” Contreras says. Yu agrees that this financial support should help Optony speed up the commercialization process of its product.

The cooperative research and development agreement established between NREL and Optony includes three phases. During the first and second phases, they’ll design concentrating PV devices that are compatible with Optony’s optical system. The third phase will involve uniting the cells and Optony’s optical system into an interconnected array for studying and evaluating the new technology under real-world conditions at NREL’s Outdoor Testing Facility.

When Optony and NREL complete this project, they hope they’ll have a CPV product that will be directly transferable to a manufacturing environment.