Page 81 - Alternative Energy Systems in Building Design

CRYSTALLINE, AMORPHOUS, THIN-FILM, AND SUN-TRACKER TECHNOLOGIES 57

CONCENTRATOR TECHNOLOGIES

Concentrator-type solar technologies are a class of PV systems that deploy a number
of lenses to concentrate and focus solar energy on semiconductor material used in the
manufacture of conventional PV solar cells.
The advantage of these types of technologies is that for a comparable surface area
of silicon wafer, it becomes possible to harvest considerably more solar energy. Since
silicon wafers used in the manufacture of PV systems represent a substantial portion
of the product cost, by using relatively inexpensive magnifying concentrator lenses, it
is possible to achieve a higher-efficiency product at a lower cost than conventional PV
power systems.
One of the most efficient solar power technologies available commercially for large-
scale power production is a product manufactured by Amonix. This concentrator tech-
nology has been specifically developed for ground installation only and is suitable only
for solar farm–type power cogeneration. The product efficiency of this unique PV solar
power concentrator technology, under field test conditions in numerous applications
in the United States (determined by over half a decade of testing by the Department
of Energy, Arizona Public Service, Southern California Edison, and the University of
Nevada, Las Vegas), has exceeded 26 percent, nearly twice that of comparable conven-
tional solar power systems. At present, Amonix is in the process of developing a mul-
tijunction concentrating cell that will augment solar power energy production efficien-
cy to 36 percent.

Why concentration? Before PV systems can provide a substantial part of the world’s
need for electric energy, there needs to be a large reduction in their cost. Studies con-
ducted by the Department of Energy (DOE), the Electrical Power Research Institute
(EPRI), and others show that concentrating solar energy systems eventually can
achieve lower costs than conventional PV power systems. The lower cost results from
the following.

Less Expensive Material Because the semiconductor material for solar cells is a
major cost element of all PV systems, one approach to cost reduction is to reduce the
required cell area by concentrating a relatively large area of solar insolation onto a rela-
tively small solar cell. The solar power concentrator technology developed by Amonix
deploys low-cost Fresnel lenses to focus sun power onto the cells, which reduces the
required cell area and material by nearly 250 times. A 6-in wafer used in a flat-plate PV
system will produce about 2.5 W, but will produce 1000 W in the Amonix system.
Higher Efficiency Concentrating PV cells achieve higher efficiencies than do non-
concentrating PV cells. Flat-plate silicon cells have efficiencies in the range of 8–15
percent, whereas the Amonix concentrating silicon cell has an efficiency of 26 percent.
Concentrating multijunction cells presently under development are expected to achieve
efficiencies greater than 34 percent.
Further increased annual energy production is achieved by the incorporation of a
two-axis sun-tracking system. All high-concentration system technologies require a
sun-tracking control system. A computerized tracking system periodically adjusts the