ENERGIES RENOUVELABLES
sol(ID)aires
Coproduction de chaleur et d'électricité
Photocell Provides Both Heat And Electricity
In 1969, scientists at the Ioffe Physico-Technical
Institute, St. Petersburg made heterostructured photoelectric cells
based on the elements of the third and the fifth group of the periodic
table (for example, gallium arsenide). Now the photocells can find application
not only in space, but also on Earth. To make them working the sunlight
is not necessary, because they can use radiation from any heated substance.
The ordinary dynamo with petrol drive also converts heat to electricity,
but the Ioffe scientists have offered a more sophisticated device.
If someone lives in the mountains, where there is
neither heat plants nor power lines, it is enough to have the photocell
super-heater and a gas cylinder to get warm, cook food and play on a notebook.
A device with a size about a small case works using a gas-jet, which heats
the emitter - a small metal plate - up to 1200-1400 oC. That
is not much hotter than burning coal. At such temperature the plate becomes
light-orange, but emits mainly long-wave radiation - with wavelengths higher
than 1 micron. The emitter is surrounded by photocells, which absorb this
light.
The photocell in the heater is a gallium-stibium
alloy. Such heterostructured conductor catches long-wave radiation, so
it gives a higher current than usual cadmium photocell, which can only
convert radiation with wavelengths of less than 1.1 micron. Stibium-gallium
photocell with a square of 2 sq. cm is able to produce 10A current. The
super-heater has 30 photocells in a series-connection and they give 12
V voltage. With such a source of electricity , one can use a notebook,
a small TV or an economic lamp.
Electricity is the main benefit of the device, but
it also heats well. The heated emitter radiates extensively, some part
of energy is taken by photocells, but about 70% of photons are reflected
back to the emitter. The device is being cooled by a fan, which drives
the hot air away from the heater and a room gets warm fast.
The physicists have made only a pilot device. It
costs much, but it is possible to choose such materials and dimensions
that it would be profitable to put it on a production line. It could be
of use for geological parties and polar explorers: with the photocell heater
you do not have to wind up a diesel engine at 40 C frost, just burn a gas-jet.
There are neither pistons nor crankshafts. There it is, noiseless, standing
in the corner, giving both heat and electricity.
Further information: Valeriy D. Rumyantsev, Professor of the Ioffe Physico-Technical
Institute, St. Petersburg, rumyan@scell.ioffe.rssi.ru
