The continuing economic recession has abruptly halted a number of large solar and biofuels projects. But while green-technology companies dependent on such capital-intensive projects have foundered, things look brighter for other ventures, such as those that require little in the way of expensive equipment and facilities, or those that have managed to attract foreign investment. Those were some of the conclusions of clean-tech investors who gathered at this week's GoingGreen East conference in Boston.

As the credit markets have tightened, many capital-intensive projects have stalled. For example, OptiSolar, a company based in Hayward, CA, has sold planned solar-farm projects because it couldn't raise money to expand manufacturing. Corn-ethanol plants are being shut down and some sold in bankruptcy proceedings for a fraction of their value. Meanwhile, some next-generation biofuels companies, such as Mascoma, based in Boston, have put plans for new plants on hold.

Projects requiring hundreds of millions of dollars have fallen from favor, says Jim Matheson, a general partner at Flagship Ventures. Don Wood, managing director at Draper Fisher Jurvetson, says that his firm is turning to businesses that require smaller plants, such as those that desalinate water and cost only $10 million.

Perhaps the biggest winners will be companies with technologies to improve energy efficiency. Wood says that in the coming years, "efficiency is where you'll get the highest marginal return on investment," in large part because costs are low. Some such ventures take advantage of cheap sensors, communications hardware, and software packages to monitor and control energy use both in buildings and on the electricity grid, says Chuck McDermott, a general partner at Rockport Capital. He says that sensors are cheap enough now that they can be distributed throughout a building, even in the ductwork. A pair of sensors on each side of an air filter in a heating system can detect when the filter needs to be changed to save energy. Sensors and controls on appliances will allow homeowners and utilities to reduce energy use.