With increasing efficiency of solar cells, their use becomes more popular
Solar power has started replacing conventional power in some areas even as
researchers persevere in developing
more efficient solar cells to tap this
clean source of almost limitless energy
(New Scientist, Vols 145, 146, Nos 1969, 1974).
In Germany, bus stops, shelters,
parking ticket machines and speed
warning signs powered by photovoltaic cells are beginning to appear all over.
Explains Alexander Mayr-Benz of
Mabeg, which manufactures solar photovoltaic cells, "Photovoltaic systems
are much cheaper and pay for themselves within 2 years." Installing conventional power lines for such street structures, on the other hand, works
out to be expensive.
The solar panels store the solar
energy during the day and deliver light
at night. Light-emitting diodes and
low-energy lamps are used which
sparingly use the power stored in the
panels. For instance, the background
lighting for a half-metre square information panel in a bus stop uses only 1.3
watts.
Meanwhile, scientists from
London's Imperial College report the
development of a device to enhance
the efficiency of conventional solar
photovoltaic cells. Called the "quantum
well", the device is an extremely thin
layer of a semiconductor sandwiched
between 2 layers of another.
Conventional solar cells are junctions
between 2 layers of a semiconductor,
each layer having different qualities
because of being doped with different
impurities.
The new device, its developers
Keith Barnham, Jenny Nelson and Paul
Griffin, hope would ultimately increase
the eff iciency of a solar cell to the theoretical limit of 31 per cent calculated by physicists- Solar cells available commercially show an efficiency of about 20 per cent.
"We have all the elements to turn a
20 per cent efficient cell into one with
22 per cent efficiency," says Barnham,
adding that there's still "an awful lot of
optimisation to do."
In a 1993 experiment, Barnham and
his team were able to raise the efficiency of an aluminium gallium arsenide
solar cell from the 9 per cent then attainable to 14 per cent by incorporating 50 quantum wells of gallium arsenide.
Development Organisation and the
Central Research Institute of Electric
Power industries, are exploring drill
holes to depth "s of 2 lcm, where temperatures reach around 200c.
But it is Australia that is the hot spot
for hot rock research. Among the reasons for a high HDR potential in
Australia are: the heat generating capacity of the Great Artesian Basin, in which 80 per cent of the country's resources
are concentrated, is twice normal levels;
and the presence of vast sedimentary
basins of coal and shale which provide
insulation for the heat-holding rocks.
Also, the technologies required to
develop HDR, such as well-logging,
drilling, hydraulic stimulation and seismic monitoring are well established
methods in Australia. "Advances in
these technologies should contribute to
overall cost reductions," contends Wyborn.
In fact, it has been estimated that
HDR technology can meet Australia's
energy needs for thousands of years to
come and as economically as the current
available energy resources.
A feasibility study of HDR technology
would soon be conducted in Hunter
Valley, New South Wales, an area which
has rich coal reserves. Several Australian
organisations and large companies are
sponsoring the project, which could also
lead to the setting up of a demonstration plant.
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