Subject: [Homestead] thin, roll-up solar panel , attach to anything, cheap
Date: Sun, 02 Jan 2005 12:21:58 -0500
Only seven percent efficient, compared to rigid panel 20%, but at price
and versality in use, who cares at one Euro per watt. Forgot current
exchange rate, think a Euro is about $1.36.
The World's No.1 Science & Technology News Service
Pliable solar cells are on a roll
* 10:30 18 December 2004
* Exclusive from New Scientist Print Edition
* Fred Pearce, Uppsala
* Energy Research, European Union
* Eindhoven University of Technology
* Akzo Nobel
* Solar Century
Imagine wearing a jacket or rucksack that charges up your mobile phone
while you take a walk. Or a tent whose flysheet charges batteries all
day so campers can have light all night. Or a roll-out plastic sheet you
can place on a car's rear window shelf to power a child's DVD player.
Such applications could soon become a reality thanks to a light,
flexible solar panel that is a little thicker than photographic film and
can easily be applied to everyday fabrics. The thin, bendy solar panels,
which could be on the market within three years, are the fruit of a
three-nation European Union research project called H-Alpha Solar (H-AS).
The new solar panels will be cheap, too, because they can be
mass-produced in rolls that can be cut as required and wrapped around
clothes, fabrics, furniture or even rooftops. "This technology will be a
lot easier to handle than the old glass solar panels," claims Gerrit
Kroesen, the physicist from Eindhoven University of Technology in the
Netherlands who led the development team.
Kroesen's team has made its solar cells bendy simply by making them
thin. But this has involved a trade-off. While the best solar cells are
now working at efficiencies above 20%, the H-AS cells are only about 7%
efficient. The researchers think efficiency is worth sacrificing for a
cell that is going to be more generally useful, though they still hope
eventually to reach 10% efficiency.
Electron knockout
Conventional solar panels are made of pairs of sheets of semiconducting
silicon, doped with phosphorus and boron atoms. Electrons in the
phosphorus-doped (N-type) layer migrate across the boundary to occupy
holes left in the boron-doped (P-type) material, setting up a voltage
across the boundary between the two layers. When photons hit the silicon
in a cell they knock electrons out of its crystal structure, generating
a current that is collected by a mesh of metal contacts.
The H-AS solar panels are constructed in a similar way, but they are
made just 1 micrometre thick by depositing polymorphous silicon at high
pressures and temperatures. "Polymorphous silicon is as rigid as
crystalline silicon. But because it is less than a micrometre thick it
is flexible," Kroesen says. Today's solar panels are typically somewhere
between 4 and 10 millimetres thick.
The process of producing H-AS films involves temperatures of up to
200°C, which would melt a plastic substrate. So instead of depositing
the doped layers directly onto plastic they are first deposited onto
aluminium foil.
After the assembly has cooled, a plastic carrier layer is added
underneath it and the aluminium is removed and recycled. Contacts are
then added, followed by a protective plastic layer on top, too. This
sequence lends itself to continuous production on rolls of plastic film.
The Swedish and Dutch-owned company Akzo-Nobel, a partner in the H-AS
research, already has a pilot plant producing rolls of silicon cells 40
centimetres wide. A projected full-scale manufacturing plant would
produce panels at a cost of about 1 euro per watt. An A4-size panel sewn
onto the back of a jacket and costing less than 10 euros would charge a
mobile phone during a summer stroll. The company has not yet decided to
go ahead with the plant.
Jeremy Leggett, chief executive of the UK solar cell supplier Solar
Century, is impressed, describing the 1 euro per watt price point as
"breathtaking".
[Homestead] thin, roll-up solar panel , attach to anything, cheap,
tvoivozhd, 01/02/2005