IEEE Spectrum November, 2014 - 22

superComputer CooLiNg
for pHotoVoLtaiCs
A start-up is using a system designed to cool a
supercomputer to increase the efficiency of solar
Flat photovoltaic panels have
come to dominate the global solar
market thanks to a dramatic drop in
panel prices over the past five years. A
Swiss start-up, using technology that
IBM Research-Zurich developed for one
of its supercomputers, is challenging
the status quo with a dish-shaped solar
concentrator that produces both electricity and hot water.
The start-up, Airlight Energy,
developed the dish and has created a spin-off company-called
Dsolar for "dish solar"-and plans
to release the concentrator in 2017.
It will be targeted at off-grid communities in areas like deserts that
get a lot of direct sunlight but
want for both electricity and hot
water. In developed countries, the
10-meter-high concentrator can be
used for on-site power generation
at corporate campuses or hotels,
says Ilaria Besozzi, business development manager at Airlight Energy.
The parabolic dish, which automatically reorients to track the sun throughout the day, is made up of 36 elliptical
reflectors that concentrate light onto
very efficient, multijunction solar cells
to produce electricity. These types of
cells use materials tuned for different
wavelengths and in this device will be
able to convert about 30 percent of sunlight into current, says IBM.
Typically, the solar cells exposed to
concentrated sunlight are air cooled.
Airlight Energy hopes to increase the
electrical output-and produce hot water-
by using liquid cooling. Behind each set
of solar cells is a structure that houses
IBM's water-cooling technology, which
is now used in its SuperMUC supercom22

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puter in Germany. Water flows through
a network of small tubes, or "microchannels," etched into a layer of silicon
to wick away the heat from the solar
cells, says Bruno Michel, the manager
of advanced thermal packaging at IBM
Research-Zurich. In supercomputers,
the liquid coolers are attached directly
to the processors, where most of the heat
is generated, says Michel.

supErsolAr: A cooling system originally
designed for an IBM supercomputer would let a
photovoltaic system produce both 12 kilowatts
of electricity and 20 kW of heat.

Because the dish uses active cooling,
the solar cells should be able to withstand a very high concentration of light-
the equivalent of 2,000 suns-and still
operate for 25 years. The higher concentration has the side effect of heating
the cooling water to about 90 ºC. At that
temperature, the water can be used to
power desalination systems or, oddly
enough, a particular type of heat-driven
cooling system, Michel says. In full sunlight, the dish is designed to generate 12
kilowatts of electricity and 20 kW of heat.
Concentrated photovoltaic (CPV) systems have been around for decades, and

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the technology offers, at least in theory,
a number of advantages. They can generate more power in a given amount
of space and offer higher conversion
efficiency than flat panels can. In fact,
by generating both heat and electric
power, Airlight Energy says it converts
80 percent of sunlight into usable energy.
But the cost of CPV technology and its
complexity have kept it from becoming
commonplace with utilities.
To keep costs low, Airlight Energy is
using two materials not normally used
in solar concentrators. Rather than have
glass mirrors to concentrate light, the mirrors will be made of the same thin plastic
foil used to wrap Swiss chocolates, says
Besozzi. The main structure of the dish
will be made of a specialized concrete,
which can be precisely molded, doesn't
shrink, and costs far less than metals
or plastic building materials, Airlight
Energy says.
Engineering a system to simultaneously generate electricity and
process the thermal energy will
be difficult, says Sarah Kurtz, principal scientist at the U.S. National
Renewable Energy Laboratory. For
example, if the heat-driven cooling
fails, the dish needs to quickly steer
away from the sun or transfer the
heat in another way. Using thin-film
mirrors lowers the cost, but first-ofa-kind systems are typically expensive.
"The challenge is to reduce the cost of the
other components, but at 2,000 times
concentration, this is feasible," she says.
Having IBM's technology behind the
product gives it commercial credibility,
notes Matthew Feinstein, an analyst at
Lux Research, in Boston. Traditionally,
CPV systems were targeted at utilities, but
many industrial companies, such as data
center operators and manufacturers, can
easily make use of the solar dish's thermal
energy, he adds. Still, "commercialization
and early adoption have always been a
challenge for unique solar technologies,"
he says. -m a rtin l a monica
A version of this article appeared online
in September.

iBm reSearCH-ZuriCH

nEwS

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