Friday, October 06, 2006

 

Small is Useless

Micro generation can’t solve climate change.

By George Monbiot. Published in New Scientist, 3rd October 2006

In seeking to work out how a 90% cut in carbon emissions could be achieved
in the rich nations by 2030, I have made many surprising findings. But
none has shocked me as much as the discovery that renewable micro
generation has been grossly overhyped. Those who maintain that our own
homes can produce all the renewable electricity and heat they need have
harmed the campaign to stop climate chaos, by sowing complacency and
misdirecting our efforts.


Last year, the environmental
architect Bill Dunster, who designed the famous BedZed zero-carbon
development outside London, published a brochure claiming that “up to
half of your annual electric needs can be met by a near silent micro
wind turbine”(1). The turbine he specified has a diameter of 1.75
metres. A few months later Building for a Future magazine,
which supports renewable energy, published an analysis of micro wind
machines. At 4 metres per second – a high average wind speed for most
parts of the UK - a 1.75 metre turbine
produces about 5% of a household’s annual electricity(2). To provide
the 50% Bill Dunster advertises, you would need a machine 4 metres in
diameter(3). The lateral thrust it exerted would rip your house to bits.


Turbulence
makes wind generators even less efficient. To avoid it, you must place
them at least 11 metres above any obstacle within 100 metres(4). On
most houses, this means constructing a minor hazard to aircraft. The
higher the pole, the more likely you are to inflict serious damage to
your house. In almost all circumstances, micro wind turbines are a
waste of time and money.


In his book Half Gone, Jeremy
Leggett, the chief executive of Solar Century, claims that “even in the
cloudy UK, more electricity than the nation currently uses could be
generated by putting PV roof tiles on all suitable roofs.”(5) This is a
big claim, so you would expect it to come from a good source: a
peer-reviewed journal, perhaps. Here is the reference Leggett gives:
“’Solar Energy: brilliantly simple’, BP pamphlet, available on UK
petrol forecourts”(6).


The Energy Technology Support Unit
(now Future Energy Solutions ) calculated that if solar electricity
could somehow achieve an efficiency of 12-15% at all points
of the compass, the “maximum practicable resource” in 2025 would be 266
terawatt hours (TWh) per year(7). Total electricity demand in the UK is
currently 407TWh(8). But Leggett’s claim is far more misleading than
this suggests.


The first reason is that solar panels facing
north are less efficient than solar panels facing south. The second is
that seeking to generate all our electricity by this means would be
staggeringly and pointlessly expensive – there are far better ways of
spending the same money. The International Energy Agency’s MARKAL
model gives a cost per tonne of carbon saved by solar electricity in
2020 of between £2200 and £3300. Onshore macro wind power, by contrast,
varies between a saving of £40 and a cost of £130 a tonne(9).


The
third problem is that the supply of solar electricity is poorly matched
to demand. In the UK, demand peaks on winter evenings. Even if we could
produce 407TWh a year from solar panels on our roofs, only some of it
could be used. There would be a surge of production in the summer,
during the middle of the day, and very little in the winter. While
solar panels might reasonably supply 5-10% of our electricity, the size
and inefficiency of the energy storage and standby power system
required makes a purely solar network impossible.


Similar
constraints affect all micro renewables: a report by a team at Imperial
College shows that if 50% of our homes were fitted with solar water
heaters, they would produce 0.056 exajoules of heat, or 2.3% of our
total demand(10); while AEA Technology
suggests that domestic heat pumps could supply only 0.022 eJ of the
UK’s current heat consumption, or under 1%(11). This doesn’t mean they
are not worth installing, just that they can’t solve the problem by
themselves.


Some campaigners accept that micro generators
can make only a small contribution, but argue that they are still
useful, as they wake people up to green issues. It seems more likely
that these overhyped devices will have the opposite effect, as their
owners discover how badly they have been ripped off and their
neighbours are driven insane by the constant yawing and stalling of a
windmill on a turbulent roof.


Far from shutting down the national grid, as the Green MEP Caroline
Lucas has suggested(12), we should be greatly expanding it, in order to
produce electricity where renewable energy is most abundant. This
means, above all, a massive investment in offshore windfarms. A recent
government report suggests there is a potential offshore wind resource
off the coast of England and Wales of 3,200TWh(13). High voltage direct
current cables, which lose much less electricity in transmission than
an AC network, would allow us to make use of a larger area of the
continental shelf than before. This means we can generate more
electricity more reliably, avoid any visual impact from the land and
keep out of the routes taken by migratory birds. Much bigger turbines
would realise economies of scale hitherto unavailable.


The electricity system cannot be run on wind alone. But surely it’s clear
that building giant offshore windmills is a far better use of our time
and money than putting mini-turbines in places where they will generate
more anger than power.

George Monbiot’s book Heat: how to stop the planet burning is published this week by Penguin.

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