Small may be beautiful

Micro power generation on a grand scale is one of those utopian visions that sound great in theory, but have very little going for them in practice. Millions of on-site generation units can never provide large volumes of clean electricity with anything like the efficiency and security of a centralised power system. Yet the rose-tinged illusion of cheap and secure "decentralised generation" replacing the power systems of today crops up with monotonous regularity to seize the headlines and the attention of politicians.

This summer has been no exception. The advent in Britain of two reports extolling the virtues of small scale generation, one from Greenpeace and the other from the New Economics Foundation, a think-tank (page 8), have provided ample fodder for newspapers in the silly season. Stories of how household units -- rooftop windmills in particular -- can revolutionise today's power supply systems for the better have been rampant in Britain in the summer months. The press excitement even spread to the European continent.

Proponents of the vision of micro-scale energy self-sufficiency were galvanised into action by two events. First came the announcement by Centrica, Britain's largest energy supplier, of a program offering customers 1 kW wind turbines for an estimated £1500. Second, the UK government extended its fondness for democracy via "public consultation" by inviting submissions on a potential strategy for micro generation.

Even Danish newspapers -- in a country so well practised in home power that its journalists should know better -- got carried away by the thrill of supposed discovery in Britain. "Everybody can have their own mini-wind turbine," stated one of many headlines. "Put a wind turbine on the house," said another. The press fuss met with a scathing response from the well respected Danish association of wind turbine owners. "Take a deep breath and a good look at how such a unit can live up to its promises," said the association, pointing out that paying £1500 for an annual generation of 1000 kWh is a poor deal compared with the £230-£270 investment required in a large wind turbine to gain the same amount of wind power. The association began life 30 years ago campaigning -- in the name of common sense and efficient use of the resources available -- for the right to feed power to the grid rather than into individual household installations. It won the argument hands down and since then efficiencies have improved with the gradual replacement of many small individual turbines close to property with larger machines on better sites.

Advocates of micro generation frequently use the spread of laptop computers as an analogy for how reductions in size lead to compact, efficient and cheap solutions. But while shrinking a computer does not compromise the ability of electrons to do their job, the same cannot be said of power generation. Units for extracting energy from liquids or gases cannot be miniaturised without also minimising power output. The same is true for solar panels. Generation units can be made smaller as power outputs come down, but they cannot become smaller and produce more power more cheaply. In fact, the reverse is invariably the case.

Small gas turbine units are much less efficient than larger units -- and they cost more per kilowatt of output. Small wind turbines are only slightly less efficient than larger units but, being closer to the ground, intercept lower wind speeds, so generate less electricity. The price of today's micro wind units needs to come down fivefold if they are to be cost competitive with utility scale wind. It might happen, but it would not enable householders to become self-sufficient in green power. The sun does not shine at night, the wind does not always blow. "Fuel cells with combined heat and power," say the visionaries. But that is an inefficient way of generating either heat or electricity and ignores the difficulties of ensuring a good match between electricity and heat demands. Storage or back-up is essential, but it is tricky and expensive.

But bigger is better

Enthusiastic micro power householders will learn to their cost that families are inefficient users of energy -- demand ranges from a few watts (when the sun and the wind could be working overtime and producing lots of power) to about 10 kW (when the sun and the wind could be taking a break). Without also investing in copious back-up and storage, or relying on the grid, there can be no security of supply.

It all gets very expensive. If the visionary self-sufficient village is to pay back its investment in micro power, it must avoid having to turn its costly purchases off for much of the time. That requires selling excess power to the grid for a healthy price, which leaves the shared power system that we all pay for buying relatively expensive electricity it could get more cheaply from utility scale wind generation.

In niche applications, powering telecommunications, railway signalling, road signs and remote communities, micro wind has a serious role and a potentially huge market. But centralised networks evolved for a reason: individual generation of electricity is hugely inefficient -- it costs more for less. Piecemeal generation is particularly wasteful of intermittent renewable resources. They need robust centralised systems to absorb their ebbs and flows among the ups and downs of demand. Micro wind generation on a grand scale means more pollution and higher electricity bills. To embrace it as a solution to mainstream power supply would divert investment from utility scale wind to designer wind. The beneficiaries would be nuclear, coal and gas.

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