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6 December 2006


Spectrolab’s new terrestrial solar cell smashes 40% efficiency barrier

Boeing subsidiary Spectrolab Inc has achieved a new record in terrestrial concentrator solar cell efficiency. Using concentrated sunlight, the company has demonstrated a photovoltaic cell that converts 40.7% of the sun's energy into electricity, as verified by the U.S. Department of Energy's National Renewable Energy Laboratory (NREL).

"This solar cell performance is the highest efficiency level any photovoltaic device has ever achieved," said Dr David Lillington, president of Spectrolab. "The terrestrial cell we have developed uses the same technology base as our space-based cells. So, once qualified, they can be manufactured in very high volumes with minimal impact to production flow."

According to the U.S. Department of Energy’s (DOE) Alexander Karsner, assistant secretary for Energy Efficiency and Renewable Energy, this ‘new milestone in sunlight-to-electricity performance’ was achieved with the help of DOE funding (via NREL's High Performance Photovoltaics program). Kasner added that the breakthrough could lead to systems with an installation cost of only $3 per watt, producing electricity at a cost of 8-10 cents per kilowatt/hour.

The majority of solar cell modules available today do not concentrate sunlight, and so only achieve an efficiency of around 18%. But using an optical concentrator, sunlight intensity can be increased. Spectrolab’s new solar cell is ‘multi-junction’, allowing it to capture more of the solar spectrum. In a multi-junction cell, individual cells are made of layers. Each layer captures part of the sunlight passing through the cell, so that the cell receives more energy from the sun’s light.

Multi-junction cells offer an advantage over silicon cells in concentrator systems because fewer solar cells are needed to achieve the same power output.

The DOE has been working on multi-junction gallium arsenide-based solar cell devices since the early 1980s. By 1994, the DOE’s NREL had demonstrated a 30% efficient multi-junction cell. These cells attracted interest from the space industry, and today most satellites utilize them.

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

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