Windmill 'best deal in alternative energy'

The finding takes into account the usual criticisms of wind as a resource – variability and intermittency – as well as the state-organised bonuses to be earned from producing electricity from it.

It assumes wind speeds of 5.5-6.5 metres per second at hub height, which would be typical for hills in the English Midlands. A Yorkshire uplands site would expect a little more.

However, wind only tops the chart for a single largish turbine, 50 metres high and capable of 330 kilowatts of output, which should bring in an 18 per cent return on an investment of around 80,000, according to Carter Jonas.

Ten megawatts of wind investment would come further down the table, with 15.3 per cent projected returns, because payments for electricity for the national grid are weighted in favour of smaller projects. A little 11kw turbine would make as much, in percentage terms, as a 10mw wind farm.

Carter Jonas stresses that the best solution depends on circumstances and its calculations are only a rough guide. But the results are an interesting challenge to popular perceptions.

A small hydro plant, at 50kw, would come a close second overall. And a 1mw anaerobic digester, running on a mix of manure and energy crops generated on-site, would come third, despite widespread disappointment at the tariffs set for digester-driven electricity before the election – now under review.

Charles Hardcastle, renewable energy expert at Carter Jonas in York, was one of those who protested to the Department of Energy and Climate Change that their tariff was likely to discourage farmers from investing in digesters. He said this week that he was not sure if the figures produced by the company's national team had fully taken into account the cost of refurbishment or replacement of the engines which turn digester gas into electricity.

He added: "Although a wind turbine could show the best return on paper, they do rank high in terms of risk and sites need to be fully assessed to ensure all potential constraints, such as planning, wind availability and grid connections, can be overcome."

The Carter Jonas Energy Index can be found at http://www.carterjonas.co.uk/~/media/Publications/energy-index.ashx/

CW 17/7/10