New solar
cells see the light
A new generation of more efficient solar
cells is on the horizon.
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MUCH MORE EFFICIENT: The next generation
of solar cells will be two to three times more energy efficient
than today's solar cells, says Associate Professor Turid Worren,
here standing in front of a wall of solar cells at NTNU's
electrical engineering building.
Photo: Gorm Kallestad/Scanpix
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Today’s solar cells have an efficiency of
17 per cent, where 100 per cent means that all the energy from sunlight
is converted to electricity. There are two types of solar cells,
known as first- and second-generation cells. The most important
difference between the two is the production price. First-generation
cells are built of single crystals of silicon, and are expensive
to produce,while the production of secondgeneration cells is far
less expensive. The drawback of second-generation cells is that
they sacrifice efficiency for cost, as compared to firstgeneration
cells. However, because the cost is so much lower, the price per
produced watt is also reduced.
Now, a new project at NTNU is taking part
in the search for third-generation solar cells. Associate Professor
Turid Worren is head of a project that will make a test model of
the solar cells by the end of the year. The efficiency of the new
cells should be beyond anything that has been produced in Norway
to date.
LITTLE INTEREST
SO FAR
“Theoretically, we might reach efficiencies of 60 per cent
or higher. In practice we hope for 40 per cent efficiency at the
start. Even at that level, the energy efficiency will be 2 to 3
times higher than today’s solar cells”,Worren says.
NTNU is the only institution in Norway where
this kind of research is conducted. Worldwide, just a few groups
are working on this new type of solar cell; otherwise, interest
in the field has been limited.Worren says fossil fuels are to blame.
“I am convinced that a new generation of
solar cells would have been available already, if not for cheap
fossil energy”, she says.
QUANTUM DOTS
The new solar cells are based on what are called ‘quantum
dots’. All solar cells use semiconductors to absorb sunlight, but
today's cells are unable to absorb very much of the infrared heat
radiation from the sun. The new solar cells being developed have
pyramid-shaped semiconductor dots in addition to conventional semiconductors.
These dots absorb a portion of the infrared light that the other
parts of the solar cells do not capture.
The project uses new technologies and is
partly financed by NTNU’s Nanolab. The longterm goal is to produce
solar cells using this new technology.
BEAUTIFUL CELLS
“Using these kinds of solar cells, we could build solar cell
power plants in sunny places in the developing world.At our latitudes,
the most realistic use of this technology would be to cover buildings
with aesthetic building elements that integrate solar cells", Worren
explains. People would accept this approach if the cells were decorative
enough,Worren says. “Solar cells can be beautiful, and a good alternative
to decorative stone and window glass”, she says.
90,000 ROOFTOPS
On a worldwide basis, the installation of new solar cell
plants (measured as the amount of energy produced) increased by
63 per cent from 2003 to 2004, with much of the increase due to
political involvement. It is estimated that by 2010, the number
of solar cell plants will have tripled compared to 2004. In Norway,
solar cells are mainly used for mountain cottages and lighthouses,
where it can be difficult to connect to the power grid.
“If we could cover 0.3 per cent of Norway’s
land area with solar cell plants, we could produce 120 terawatt
hours, which corresponds to our entire electricity consumption in
2002”, Worren says.
“That means that it is physically possible
to handle Norway’s total energy consumption with power from solar
cells, but that is neither necessary nor desirable. One alternative
could be to produce just one per cent of Norway's electricity consumption
using solar cells. That would correspond to a solar cell area of
some 90,000 roofs, each measuring 100 square metres”, she says.
SILICON SHORTAGES
Another factor that makes the production of more efficient
solar cells interesting is the lack of raw materials for the current
technology. Most solar cells have an active portion made of a thin
wafer of silicon. The solar cell industry is currently experiencing
a silicon shortage. The search for other ways to produce silicon
has begun, but increased efficiency in silicon use will also be
an important component of solar cell production.
By Tore Oksholen
Contact: Turid Worren, Department of Physics,
NTNU
Tel: +47 73 59 18 42, Email: turid.worren@ntnu.no
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