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Problem: Solar energy technology offers a clean
renewable alternative to conventional energy production. The main
barrier to implementation of solar technology in electrical power
production is the cost and availability of the materials used.
Solution: Concentrator Photovoltaic systems concentrate
the sun’s energy onto a relatively small surface limiting the amount of
expensive materials required to build these systems.
Concentrator PV systems are not new. There is a Concentrator
PV power plant that has been operating in the Mojave Desert for over 25
years. This older design takes up a tremendous amount of space
and is not practical for most applications. The following article
describes a new design that is much more efficient and can be used in a
relatively small amount of space.
The following article was reprinted from Parc Research, an independent research laboratory.
Concentrator PV (CPV)
The prevalent approach for generating solar electricity is through
PV (photovoltaic) systems that use semiconductor PV material to convert
sunlight directly into electricity. In fact, grid-connected PV is the
fastest-growing energy technology in the world.
Silicon-based flat-plate PV—which produces electricity by having
sunlight directly strike panels tiled with sheets or wafers of
expensive PV cell material—has dominated the market. However, silicon
feedstock shortages and rising wafer prices have highlighted the need
for technologies—such as non-silicon thin-films or CPV (concentrator
PV)—which reduce the use of silicon or other semiconductor PV
materials. Semiconductor material costs often dominate the costs of the
total installed PV system, and are considered one of the best
opportunities for lowering overall costs and increasing the
competitiveness of solar with conventional fossil fuel-derived
electricity.
CPV approaches, on the other hand, offer an effective, practical way to keep solar cell conversion efficiencies high while keeping semiconductor material costs down.
Although thin-film solar technologies are fabricated with cheap
roll-to-roll processes, they are limited by: more use of scarce and
expensive source materials (e.g., gallium and indium); modest
efficiencies; and reliability issues. CPV approaches, on the other
hand, offer an effective, practical way to keep solar cell conversion efficiencies high while keeping semiconductor material costs down.
PARC recently signed a broad agreement with California-based
start-up SolFocus to jointly develop CPV systems that can deliver
low-cost, reliable solar energy. SolFocus' CPV solutions can
potentially: advance the market beyond current flat-plate silicon PV
and its underlying cost limitations; deliver both short- and
long-term cost advantages; position PV to compete with conventional
electricity; and open large new markets for clean solar energy.
How It Works
CPV (concentrator PV) technologies use relatively inexpensive optics
such as mirrors or lenses to “concentrate” or focus light from a
relatively broad collection area onto a much smaller area of active
semiconductor PV cell material. CPV systems must be pointed directly at
the sun because they work by focusing sunlight onto a targeted area,
and therefore require trackers which follow the sun’s trajectory
throughout the day.
Since the PV semiconductor material usually dominates the costs of
the solar PV system, reducing the amount of PV material required to
capture a given amount of sunlight leads to substantially lower system
cost and resulting cost per watt of output. For higher concentrations
that reduce PV material use by 100-1000 times more, it can be
cost-effective to use higher efficiency cells that increase the
electricity generated from a given collection area—even though this PV
material can cost up to ten times more than silicon.
Currently, the most efficient approach is multi-junction cells which
achieve up to 40% conversion of the sun’s energy into electricity by
using stacked layers of III-V compound semiconductor materials to
capture more of the solar spectrum. In addition to enabling more
electricity from a given amount of sunlight, multi-junction cells
obtain even higher efficiencies at higher concentration levels.
Partnerships & Product Roadmap
With strong early contributions in non-imaging optical design from
researchers at the University of California at Merced, SolFocus' CPV
solutions build on PARC expertise in optical system design,
optoelectronics, and advanced materials and processes for electronic
packaging.
SolFocus won the grand prize at the 18th NREL Industry Growth Forum held in November 2005 by the Department of Energy’s National Renewable Energy Laboratory).
SolFocus, strengthened by its mutually beneficial partnerships, has
already developed two low-cost CPV module designs—Gen 1 and Gen 2:
- Up to 2 MW (megawatts) of the Gen 1 design will be installed in
2006-2007 at pilot sites including California, Hawaii, and Shanghai,
China.
- The Gen 2 design, which further improves performance and reduces
costs at higher volume production, will be available for test
installations 2007.
- Both modules are targeted for rooftop- and field-installed solar electricity systems.
SolFocus won the grand prize at the 18th NREL Industry
Growth Forum held in November 2005 by the Department of Energy’s
National Renewable Energy Laboratory). SolFocus CEO Gary Conley was
recognized at this event as the Clean Energy Entrepreneur of the Year
(2005).
Solution Features
Advantages Compared to Flat-plate PV:
- *Requires only 1/1000th of the expensive, active semiconductor
material as other PV *systems to generate the same amount of
electricity from the sunlight falling on a given area
- *Lowers the cost of solar electricity to less than half what is available today
- *Operates at nearly double the efficiency of most flat-plate PV
Both CPV Modules:
- *Enabled by highest-efficiency cells available—triple-junction cells approaching 40% at over 500-sun concentration
- *Employ non-imaging optics
- *Use glass—can easily meet 30-year lifetime requirements
- *Use dry, passive cooling—no liquids or fans
- *No moving parts in module—avoids mechanical failure in module
- *Fully “enclosed”—no exposed mirrors or open fire hazards
- *Use mirrors or reflective elements which allow purely reflective
light entry—avoids the *chromatic aberration of lens-based concentrators
- *Use minimal components—have a number of “double-purposed” materials
- *Have one-quarter the focal length of other systems—makes them extremely compact
- *Assembled with high-throughput, automated technology
One person has commented on this article.  1. reflector /concentratorsVery interesting! I've been looking for several years at a way to inexpensively produce a parabolic concentrator using easily available materials, and also a concentrator that produces a tight parallel high concentration beam to carry for some distance. I was unaware of the advantages and availability of the more efficient cells you mention. If you have an interest, I'll share details, if not, keep up the good work. Best, Jeffrey Greene J! Reactions • General Site LicenseCopyright ©2006 S. A. DeCaro |
