Renewable energy companies have long been on a journey to the promised land, with the European sector almost doubling in 2007. But this year has begun in retreat, with most stocks down 20-30 per cent from their December peaks, led by the solar panel manufacturers. In part this reflects a broader change in attitudes to risk as markets’ wobble.

But there may also be a reassessment of the heroic assumptions share prices embody. Société Générale, for example, takes the forecasts of the trade body, EPIA, for growth for the solar power market out to 2030, and then assumes that operating margins can be sustained at a hefty 20 per cent. Even then the bank finds that bellwethers Q-Cells and SolarWorld are overvalued.