from new scientist
Why sustainable power is unsustainable
Renewable energy needs to become a lot more renewable – a theme that
emerged at the
Financial
Times
Energy Conference in London this week.
Although scientists are agreed that we must cut carbon emissions from
transport and electricity generation to prevent the globe's climate
becoming
hotter, and more unpredictable, the most advanced
"renewable" technologies are too often based upon non-renewable
resources, attendees heard.
Supratik Guha of IBM told the conference that sales of silicon solar
cells are booming, with 2008 being the first year that the silicon wafers
for solar cells outstripped those used for microelectronic
devices.
But although silicon is the most abundant element in the Earth's crust
after oxygen, it makes relatively inefficient cells that struggle to
compete with electricity generated from fossil fuels. And the most
advanced solar-cell technologies rely on much rarer materials than
silicon.
Rare metal
The efficiency of solar cells is measured as a percentage of light energy
they convert to electricity.
Silicon solar cells finally reached 25% in late December. But
multi-junction solar cells can achieve efficiencies
greater than 40%.
Although touted as the future of solar power, those and most other
multiple-junction cells owe their performance to the rare metal
indium, which is far
from abundant. There are fewer than 10 indium-containing minerals, and
none present in significant deposits – in total the metal accounts for a
paltry 0.25 parts per million of the Earth's crust.
Most of the rare and expensive element is used to manufacture LCD
screens, an industry that has driven indium prices to $1000 per kilogram
in recent years. Estimates that did not factor in an explosion in
indium-containing solar panels reckon we have
only a 10 year supply of it left.
If power from the Sun is to become a major source of electricity, solar
panels would have to cover huge areas, making an
alternative to indium essential.
Precious platinum
The
dream of the hydrogen economy faces similar challenges, said
Paul Adcock of UK firm Intelligent Energy.
A cheap way to generate hydrogen has so far proved elusive. New
approaches, such as using
bacterial enzymes to "split" water, have a long way to go
before they are commercially viable.
So far,
fuel cells are still the most effective way to turn the gas into
electricity. But these mostly rely on expensive platinum to catalyse the
reaction.
The trouble is, platinum makes indium appear super-abundant. It is
present in the Earth's crust at just 0.003 parts per billion and is
priced in $ per gram, not per kilogram. Estimates say that, if the 500
million vehicles in use today were fitted with fuel cells, all
the world's platinum would be exhausted within 15 years.
Unfortunately platinum-free fuel cells are still a long way from the test
track. A
nickel-catalysed fuel cell developed at
Wuhan University, China, has a
maximum output only around 10% of that a platinum catalyst can
offer.
A new approach announced yesterday demonstrates that
carbon nanotubes could be more effective, as well as cheaper, than
platinum. But again it will be many years before platinum-free fuel cells
become a commercial prospect.
Fuel vs food?
Biofuels, like ethanol fermented from maize, are the most infamous
examples of the doubtful sustainability of supposedly renewable forms of
energy. This time the non-renewable resource at risk is
the world's arable land,
Ausilio Bauen of
Imperial College London said at the meeting.
Again, there are potential solutions, but none that are ready for market.
Biofuels from
cellulose or even
lignin can be derived from inedible plant material and wood rather
than food crops. Algae, grown in outdoor tanks,
continues to attract attention, and
extracting biofuel from marine algae or seaweed could sidestep land
use issues altogether.
Renewable energy technologies remain the great hope for the future, and
are guaranteed research funds in the short term. But unless a second
generation of sustainable energy ideas based on truly sustainable
resources is established, the renewable light could be in danger of
dimming.
--
George Marshall,
Director of Projects,
Climate Outreach Information Network,
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