ors, including
lead sulphide, lead telluride and cadmium selenide. What's more, Klimov says
his group has identified two new materials that are less toxic and have band
gaps better matched to the solar spectrum than lead selenide, though he will
not identify the materials as he has yet to publish the work.
photon can generate multiple charge carriers, the overall power efficiency of
solar cells could be dramatically increased. The world record for a
ground-based cell is 24.7 per cent, achieved by a device made in Australia
at the University of New South Wales. Klimov predicts that the multiple-carrier
generation could one day yield a cell with double that efficiency,
approaching 50 per cent. Ellingson is slightly more conservative, but
he still projects efficiencies around 45 per cent. With more work, the chips
cranking out extra electrons in New Mexico and Colorado could one day bring a
bright solar future for us all.
is not the only useful form of energy that ultra-efficient solar cells might
generate. They could also be used to induce a chemical reaction that creates
fuel. While this approach is not strictly dependent on a cell in which each
photon yields more than one current-carrying electron, the additional charge
carriers would help by accelerating the reaction.
compelling scenario, nanocrystals could be immersed in water, and the current
flowing out of the solar cell would break down the water molecules into
hydrogen and oxygen. As with direct production of electricity, the benefit of a
multiple-exciton solar cell would come through more efficient exploitation of
the solar energy that hits it, says chemist Nathan Lewis of the California
Institute of Technology in Pasadena.
the basis for fuel-cell vehicles that would operate emissions-free and require
no gasoline. Oxygen from the air would react with hydrogen in the presence of a
catalyst to produce electricity, with water as a by-product. Calls for a move
to a hydrogen economy, however, tend to gloss over the fact that producing
hydrogen requires energy - and if that energy comes from fossil fuels the
environmental benefit of hydrogen power is questionable. Using solar energy to
generate the hydrogen would overcome this objection.
more, there are other ways of putting a solar fuel generator to work. "I'd
rather do like the plants do," says Lewis. "Use sunlight to convert
water and carbon dioxide into ethanol or methanol." These liquids are more
compatible with existing fuelling stations than hydrogen. Whatever the product,
Lewis says, "making a multiple-exciton-per-photon solar cell for any
purpose would be a major tour de force".
of Nanosolar Cell: http://www.newscientist.com/data/images/archive/2553/25531601.jpg
Letters photon article: http://pubs.acs.org/cgi-bin/abstract.cgi/nalefd/2006/6/i03/abs/nl052276g.html
Review Letters article: http://scitation.aip.org/getabs/servlet/GetabsServlet?prog=normal&id=PRLTAO000092000018186601000001&idtype=cvips&gifs=yes
Debate Over Wind Power Creates Environmental Rift
BARRINGER, New York Times, June 6, 2006, http://select.nytimes.com/mem/tnt.html?emc=tnt&tntget=2006/06/06/us/06wind.html&tntemail1=y
OAKLAND, Md. Dan Boone has no doubt that his crusade
against wind energy is the right way to protect the Allegheny highlands he
loves. Let other environmentalists call him deluded at best, traitorous at
worst. He remains undeterred.
For four years or more, Mr.
Boone has traveled across the mid-Atlantic to make every argument he can muster
against local wind-power projects: they kill birds and bats; they are too
noisy; they are inefficient, making no more than a symbolic contribution to
Wind farms on the empty
prairies of North Dakota? Fine. But not, Mr. Boone insists, in the mountainous
terrain of southwestern Pennsylvania,
Virginia, areas where 15 new projects have been proposed. If all
were built, 750 to 1,000 giant turbines would line the hilltops, most
producing, on average, enough electricity to power 600 homes.
Wind projects are in the
midst of a huge growth spurt in many parts of the country, driven by government
incentives