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.

One company that clearly demonstrates the appeal of energy-efficiency businesses is EnerNOC, based in Boston. Its revenues increased from $60 million to $100 million last year, and it expects 60 to 70 percent growth this year. The company’s main business is basically a way to decrease peak demand for electricity, such as occurs in the afternoon on hot days. The company has created a network of electricity customers who allow their electricity use to be reduced, in response to a request from a utility, in return for discounts. As a result, utilities don’t have to build expensive new power plants to meet peak demands. The company also uses information from building management systems to detect “leakages, energy waste,” and other ways to reduce energy consumption. In one case, at Western Connecticut State University, electricity use was reduced up to 18 percent. Because the savings were “consistent and permanent,” local regulators granted the school the same renewable-energy credits that it would have received from installing solar panels or wind turbines.

In general, however, investors are concerned that profits from energy efficiency will be limited without regulatory changes. Aside from avoiding building new power plants by reducing peak demand, utilities have little incentive to reduce energy consumption: the more power used, the more money they make. Decoupling profits from power consumption could help, but this will be a challenge because of a patchwork of varying regulations across the country.

While low-capital ventures such as those that target energy efficiency are attractive, some high-capital businesses are still having success, particularly if they can attract foreign funding. Great Point Energy, based in Cambridge, MA, has developed a process for converting coal into natural gas. Its planned plants could cost as much as $1 billion each. Funding for such projects isn’t available in the United States, says Andrew Perlman, CEO of Great Point. But the company is drawing up plans for an approximately $100 million plant in China that will be funded by a power utility there. “We have a long way to go,” Perlman says. But once the first plant is built and the technology proven, the next plant will be much easier to finance, he says.