Some big wind developers, like NextEra Energy Resources and even the Texas billionaire T. Boone Pickens, a promoter of wind power, have cut back or delayed their wind farm plans.

Renewable energy sources like biomass, which involves making electricity from wood chips, and geothermal, which harnesses underground heat for power, have also been slowed by the financial crisis, but the effects have been more pronounced on once fast-growing wind and solar.

Because of their need for space to accommodate giant wind turbines, wind farms are especially reliant on bank financing for as much as 50 percent of a project’s costs. For example, JPMorgan Chase, which analysts say is the most active bank remaining in the renewable energy sector, has invested in 54 wind farms and one solar plant since 2003, according to John Eber, the firm’s managing director for energy investments.

In the solar industry, the ripple effects of the crisis extend all the way to the panels that homeowners put on their roofs. The price of solar panels has fallen by 25 percent in six months, according to Rhone Resch, president of the Solar Energy Industries Association, who said he expected a further drop of 10 percent by midsummer.

(For homeowners, however, the savings will not be as substantial, partly because panels account for only about 60 percent of total installation costs.)

After years when installers had to badger manufacturers to ensure they would receive enough panels, the situation has reversed. Bill Stewart, president of SolarCraft, a California installer, said that manufacturers were now calling to say, “Hey, do you need any product this month? Can I sell you a bit more?”