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Asunto:[CeHuNews] 40/06 - Micro generation can't solve climate change by George Monbiot.
Fecha:Lunes, 16 de Octubre, 2006  02:14:51 (+0000)
Autor:Alexander von Humboldt <cehumboldt>

CeHu News 40/06

Micro generation can't solve climate change

by George Monbiot

Published in New Scientist (October 03 2006)

In seeking to work out how a ninety per cent 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 diametre 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 four metres per second
- a high average wind speed for most parts of the UK - a 1.75 metre turbine
produces about five per cent of a household's annual electricity {2}. To provide
the fifty per cent Bill Dunster advertises, you would need a machine four metres
in diametre {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 eleven 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 photovoltaic roof tiles on all suitable
{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"

The Energy Technology Support Unit (now Future Energy Solutions) calculated that
if solar electricity could somehow achieve an efficiency of twelve to fifteen
per cent at all points of the compass, the "maximum practicable resource" in
2025 would be 266 terawatt hours per year {7}. Total electricity demand in the
UK is currently 407 terawatt hours {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 GBP 2200 and GBP 3300. Onshore macro wind power, by contrast, varies
between a saving of GBP 40 and a cost of GBP 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 407
terawatt hours 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 five to ten per cent of our electricity, the size and inefficiency of the
energy storage and standby power system required makes a purely solar network

Similar constraints affect all micro renewables: a report by a team at Imperial
College shows that if fifty per cent 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 exajoules of the UK's current heat consumption, or under one per cent
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
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 3,200 terawatt hours {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.


1. Bill Dunster Architects, 19th March 2005. Zedupgrade: an introduction to
refurbishment systems for existing homes.

2. Derek Taylor, Winter 2005/6. Potential outputs from 1-2 metre diameter wind
turbines. Building for a Future, special wind power feature. This is extracted
from the graph, and describes output at an average annual windspeeds of four
metres per second. The previous article in the same edition, by Nick Martin,
explains that in built-up areas "Very few installations are likely to experience
more than the equivalent of four metres per second average windspeed".

3. Nick Martin, Winter 2005/6. Can We Harvest Useful Wind Energy from the Roofs
of Our Buildings? Table 2. Building for a Future, special wind power feature.

4. ibid.

5. Jeremy Leggett, 2005. Half Gone: oil, gas, hot air and the global energy
crisis, page 201. Portobello Books.

6. ibid, note 253, p290.

7. Energy Technology Support Unit, 1999. New and renewable energy: prospects 
in the UK for the 21st century - supporting analysis, page 141. ETSU, Harwell.

8. Department of Trade and Industry, DUKES, Table 5.2.

9. Republished by Department of Trade and Industry, 2003. Energy White Paper -
Supplementary Annexes, page 7.

10. Jeremy Woods, Robert Gross and Matthew Leach, December 2003. Innovation 
in the renewable heat sector in the UK: Markets, opportunities and barriers. 
Centre for Energy Policy and Technology, Imperial College, London.

11. Future Energy Solutions, AEA Technology, April 2005. 
Renewable Heat and Heat from Combined Heat and Power Plants, page 39.

12. Caroline Lucas, 4th August 2006. Let's shut down, not melt down.

13. Department of Trade and Industry, 2005a. 
Offshore Renewables - the Potential Resource.

Copyright (c) 2006

Bill Totten

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