Low-wattage thinking

New Scientist
Saturday 30/9/2006, Page: 24

Small-scale renewable power schemes may sound great, but this flawed idea could wreck our chances of stopping global warming, argues George Monbiot

TO PREVENT global temperatures rising by 2 °C above pre-industrial levels, the rich nations must cut their carbon emissions by 90 per cent by 2030.

In seeking to work out how this might be done, I have made many surprising findings, but none has shocked me as much as the discovery that renewable micro-generation - whereby people generate their own electricity with devices on their houses or in their gardens - has been grossly over-hyped. Those who say we can produce all the electricity we need and heat our homes from renewable sources have harmed the campaign to stop climate chaos, by sowing complacency and misdirecting our efforts.

Here's an example of how misleading the rhetoric over microgeneration can be. 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". 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. In winds of 4 metres per second - higher than average for most of the UK - a 1.75-metre turbine produces about 5 per cent of an average household's annual electricity. To provide the 50 per cent Dunster advertises, you would need a machine 4 metres in diameter, which would rip the side off your house.

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

What about micro solar power? In his book Half Gone (Portobello Books, 2006), Jeremy Leggett, who is chief executive of the solar energy company Solarcentury, 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". This is a big claim, so you would expect it to come from a good source - a peer-reviewed journal, perhaps. But the reference Leggett gives is "SolarEnergy: brilliantly simple, BP pamphlet, available on UK petrol forecourts".

The estimate is contradicted by the European consultancy firm Future Energy Solutions, formerly the Energy Technology Support Unit, which calculated that if solar electricity could somehow achieve an efficiency of 12 to 15 per cent at all points of the compass, the "maximum practicable resource" in the UK in 2025 would be 266 terawatt-hours per year. Total annual electricity demand in the UK is currently 407 TWh.

Leggett's claim is even more misleading than this suggests. For a start, solar panels facing north produce less power than solar panels facing south. Furthermore, seeking to generate all our electricity this way would be staggeringly and pointlessly expensive; there are far better ways of spending the money. The International Energy Agency's MARKAL model puts the cost of saving carbon using solar electricity in 2020 at between £2200 and £330o a tonne. Its estimate for onshore macro wind power, by contrast, ranges between a saving of £4o and a cost of E130 a tonne. A third problem is that solar electricity supply is poorly matched to demand. In the UK, demand peaks on winter evenings.

Even if we could produce 407 TWh a year from solar panels on our roofs, most of it would be wasted.

What about the argument from some campaigners that even though micro-generators can make only a small contribution, they still wake people up to green issues? It seems more likely these 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 the ill-sited windmill.

What's the alternative? Far from replacing the national grid with more localised power supplies, as the Green MEP Caroline Lucas suggests, we should be greatly expanding it to carry renewable energy from places where it is most abundant. This means, above all, a massive investment in offshore wind farms. A recent UK government report suggests England and Wales have a potential offshore wind resource of 3200 TWh. High-voltage direct current cables would allow us to make use of a larger area of the continental shelf. This means we can generate more electricity more reliably avoid spoiling the view from the land and keep out of birds' migration routes

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.