Bill Totten's Weblog

Wednesday, October 11, 2006

Small is Useless

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 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 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 impossible.

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 {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 3,200 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 diametre 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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