December 8, 2006, St. Louis, MO--Boeing's wholly owned subsidiary Spectrolab has developed a solar cell, used with a concentrator, that reaches a record efficiency of 40.7%. The U.S. Department of Energy's National Renewable Energy Laboratory (NREL; Golden, CO) verified the milestone.

"The terrestrial cell we have developed uses the same technology base as our space-based cells," said David Lillington, president of Spectrolab. "So, once qualified, they can be manufactured in very high volumes with minimal impact to production flow."

High-efficiency multijunction cells have a significant advantage over conventional silicon cells in concentrator systems because fewer solar cells are required to achieve the same power output. This technology is aimed at reducing the cost of generating electricity from solar energy as well as the cost of materials used in high-power space satellites and terrestrial applications.

"These results are particularly encouraging since they were achieved using a new class of metamorphic semiconductor materials, allowing much greater freedom in multijunction-cell design for optimal conversion of the solar spectrum," said Richard King, principal investigator of the high-efficiency solar-cell R&D effort. "The excellent performance of these materials hints at still higher efficiency in future solar cells."

Currently, Spectrolab's terrestrial concentrator cells are generating power in a 33 kW full-scale concentrator system in the Australian desert. The company recently signed multimillion dollar contracts for its high-efficiency concentrator cells and is anticipating several new contracts in the next few months.

An eye on costs
When compared to conventional high-efficiency solar cells used without concentrators, the potentially reduced cost (per quantity of power produced) of a higher-efficiency concentrator-based solar cell such as the Spectrolab cell must be balanced against the increased cost of using a solar concentrator, which consists of a parabolic, paraboloidal, or other mirror and usually a motor-driven mirror-pointing system (and often a solar-cell cooling system as well).

For many photovoltaic installations, even the greater than 40% efficiency of the Spectrolab cell--in comparison to the 15% efficiency of conventional nonconcentrator solar cells--may not be enough to offset the added cost and complexity of a solar-concentrator system. In addition, as prices of solar cells come down (as thay have been doing), the cost of a solar-concentrating and mirror-pointing system will become a larger portion of the cost of the total installation. Developments in large-scale manufacturing of solar-concentrator mirrors and mechanical components, resulting in economy of scale, will be necessary to counter this problem.

Applications in space, such as electrical power for satellites, are entirely different; here, even small reductions in weight and size add up to dramatic reductions in cost due to savings in launch costs.

Development of the Boeing Spectrolab high-efficiency concentrator-cell technology was funded by the NREL's High Performance Photovoltaics program and Spectrolab.