Arizona Public Service Tests World's Most Efficient Solar Cells
Nov 01 - The Tribune
Nov. 2--Arizona Public Service has started testing the world's most efficient solar cells at its Solar Technology and Research Center in Tempe. The cells, which covert sunlight directly into electricity, have the potential to revolutionize the industry by making solar energy more cost-competitive with conventional energy sources, said Peter Johnston, manager of technology development for APS.
The new photovoltaic technology was developed by the Spectrolab division of
The Boeing Co., and similar systems have been used to power spacecraft,
including the Mars Rovers. The APS test is the first time it has been
demonstrated as part of a utility's electricity grid.
"It's small, a one kilowatt system, but it's the world's first,"
Johnston said.
The new device uses concentrating triple junction solar cells, which are
composed of three layers of semiconducting material, each of which extracts
energy from a different part of the solar light spectrum. The efficiency is
further enhanced by a system of mirrors that concentrates the sunlight by 500
times onto each cell. That is about twice the concentration of existing
photovoltaic systems, Johnston said. As a result, the new system is expected to
be about 50 percent more efficient at converting sunlight into electricity than
other technology APS has tested to date, he said.
The silicon cells APS has been testing at the STAR center have about a 20
percent efficiency rating, meaning that about 20 percent of the sun's energy is
converted to electricity. The new cells, which are made of layers of gallium
indium phosphide, indium gallium arsenide and germanium, have a conversion
efficiency of about 32 percent, Johnston said.
Eventually Boeing hopes to increase that efficiency to 50 percent, he said.
Increasing the efficiency of solar cells is important to bringing down the cost
of solar energy. To date the cost per kilowatt of electricity produced from
sunlight has been about four times greater than electricity produced from
conventional sources such as coal. The new system may cut that cost in half,
making solar still twice as expensive but closer to being competitive,
especially if conventional sources of fuel continue to increase in price,
Johnston said. The system is less costly because fewer cells are needed, which
reduces the amount of expensive semiconducting material that is used, said Dr.
Raed Sherif, manager of terrestrial photovoltaic activity at Boeing Spectrolab.
APS plans to continue testing the system for about a year and will install
improved cells as they are developed. The purpose is to test the reliability of
the technology, which could encourage more utilities to give it a try, Sherif
said. Because triple junction solar cells have functioned successfully in the
extreme temperatures of space, Sherif believes they will prove reliable on
Earth, even in the intense heat of sunlight concentrated 500 times. "We
don't think the performance will degrade, but that is one of the things we need
to demonstrate," he said.
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