America's Production Tax Credit - equal to about 1.8 cents per kilowatt hour - stands out in the renewable subsidy world because it is so short term. Each year, it goes through an annual renewal vote by the US Congress - typically after the 12 month period has expired. As such it is a very difficult calculation to make for investors with no long term pricing support. It expires at the end of this year.

So news that Gamesa Energy USA, a subsidiary of Gamesa Corp - a big player in the wind world - has sold the rights to its Allegheny Ridge wind farm to an Australian firm, Babcock & Brown deserves attention. Clearly a company who accounts in Euros may not be too thrilled to have dollar assets over the next year or so. The dollar does seem set to go south. But it is also symptomatic of something much bigger.

Earlier this week, Goldman Sachs announced that it was putting up for sale Horizon Wind Energy. Many view this as Goldman (and they won't comment) predicting the top of the market and some concern that the PTC will not renewed.

As a rule, I'm against subsidies. But if you're going to have them in place to achieve long-term changes, then they themselves have to be long-term. 1 year just isn't enough for an investment in wind turbines which when installed, may take 10 years to pay for themselves. Viewed from afar, the state programmes of Renewables Portfolio Standards appear to be far more effective than the federal PTC.