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 olar energy could get a mega-boost, effectively gaining
a threefold improvement over conventional technology, with a
system being developed at the Department of Energy's Oak Ridge
National Laboratory (ORNL).
 The
"full-spectrum solar energy system" harnesses the clean
and abundant energy found in sunlight and uses that energy more
efficiently than is possible with traditional solar energy systems.
The technology departs from conventional approaches that focus
on using solar energy for a single purpose, such as to generate
power.
"Instead
of inefficiently converting the visible light found in sunlight
into electricity only to reconvert a sizeable portion back into
interior light, it makes more sense to just collect and distribute
the light directly," said Jeff Muhs, a researcher in ORNL's
Engineering Technology Division. "By using the visible portion
of the light spectrum, we can reduce the amount of electricity
we consume for lighting commercial buildings. We can use the
other portions of the spectrum to generate electricity."
Interior lighting
is the single largest user of electrical power in commercial
buildings, accounting for more than a third of all of the electricity
consumed commercially in the United States.
The system
being developed by Muhs and industry partners uses novel roof-mounted
two-axis tracking concentrators that separate the visible and
infrared portions of the sun's rays. Using large-diameter optical
fibers, it distributes visible light to interiors of buildings.
The system converts infrared, or non-visible, portions of the
solar spectrum into electricity.
The most economical
photovoltaic cells today use silicon-based materials, and the
conversion efficiency of these devices is relatively low in most
portions of the visible light spectrum.
"Our
approach leverages the benefits of concentrating photovoltaic
cells in the near-infrared portion of the spectrum, where they
are generally more efficient," Muhs said.
Models developed
at ORNL and independently verified by Antares Engineers &
Economists suggest that the overall efficiency and affordability
of solar energy can be improved by as much as threefold in commercial
buildings when compared to conventional solar technologies.
To effectively
use the visible light from the sun for interior lighting of commercial
buildings, it must be combined with artificial light yet still
maintain uniform lighting -- even when the amount of sunlight
changes. Muhs has dubbed this combination of natural and artificial
light "hybrid lighting."
The benefits
of hybrid lighting include the elimination of glare and variability,
better utilization of direct sunlight, the reduction of architectural
intrusion and the reduction of energy consumption during peak
demand.
"Hybrid
lighting is poised to compete with conventional day lighting
and conventional solar technologies as the preferred use of solar
energy in commercial buildings," Muhs said. "Integrated
with full-spectrum solar energy systems, it offers even further
advantages."
Industry partners
agree that the potential for commercial application of a full-spectrum
solar energy system is significant.
"Assuming
our goal remains the same, and utility deregulation continues
at its ever-increasing pace, full-spectrum approaches like this
that take a holistic view of solar energy are the future of solar
energy," Muhs said. "The ultimate goal of reducing
greenhouse gas emissions using solar energy hasn't changed. We're
just rethinking how best to do it in commercial buildings where
lighting loads and energy costs are high during peak demand periods."
Other prospective
partners, including Translight LLC of Pomfret, Conn., share Muhs'
optimism. "Our analyses indicate that there is a realistic
opportunity to achieve simple pay-backs of less than five years
using this hybrid approach to solar energy," said Hanafi
Fraval, director of Translight, a manufacturer of large-core
optical fibers.
The ORNL-led
initiative is also receiving support from the Solar Energy Industries
Association in Washington, D.C., and Duke Solar in Raleigh, N.C.
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