Even as Barack Obama promised to “harness the sun and the winds and the soil to fuel our cars and run our factories” in his inaugural address, investors were fleeing the businesses that seek to profit from this green future. A basket of US-listed companies in the field, the WilderHill Clean Energy index, has lost almost 70 per cent of its value over the past eight months. The mismatch between government enthusiasm and investor sentiment might seem strange. After all, more than almost any other business, renewable energy relies on taxpayer support.

Making money from clean energy has become harder for a variety of reasons. The falling cost of “dirty” energy is a key culprit. Expensive fossil fuels had lessened the need for subsidies to make technologies such as photovoltaic and wind energy viable. But that gap has now widened. Meanwhile, the credit crunch has sapped funding for capital-intensive projects, such as wind farms. It has also made transferable tax credits less of an incentive and strained state budgets in eco-friendly places such as California. Private patrons, such as car companies planning green vehicles, are also more cautious.