Mar. 11--Alternative energy is today's hot topic, but some businesses in the area have been working with it for a long time.

First Reserve Corp., a Greenwich-based private equity firm founded in 1983 that specializes in the energy industry, has made investments in many alternative energy companies and interests, such as BlueSource LLC, a Utah-based firm that sells greenhouse gas offsets to retail and wholesale buyers, and Gamesa Energia, a Spanish solar company. Other alternative-energy firms within its portfolio include Industrial Power Generation Co., a Richmond, Va.-based landfill waste-to-energy company, and Osage Bio Energy, a Virginia-based company that constructs barley-fed ethanol and protein feed production facilities in the southeastern United States.

"Renewable energy is one of the fastest-growing segments in the broader energy industry, and we expect various forms of clean energy to account for an increasing share of the fuel and power mix," said Glenn Payne, director of First Reserve Corp. He said the company sees opportunities in wind, solar, barley ethanol and waste as viable economic alternatives to carbon-dioxide-emitting alternatives.

"We see tremendous growth potential, but as with all of our investments, we will be very selective," he said.

A cluster of alternative energy companies supplying equipment, expertise and capital to the power industry has begun taking shape in Fairfield County. Officials would like to see their number

grow as the country strives to decrease its dependence on fossil fuels.

"The drivers for alternative energy are economic development, the environment and security," said Patricia Downs, executive director of the Office of Strategy and Policy for the state Department of Economic and Community Development. "If you look at all three, the additional creation of alternative energy sources is critical because we don't want to rely on foreign sources of energy. We need to develop our own."

Alternative energy is expected to become a key sector industry in Connecticut and a major focus of the Obama administration, Downs said.

"It will have its place, and it will keep growing as the demand increases," she said.

Alternative energy firms in lower Fairfield County include Alternative Energy Solutions and Enel North America Inc. LLC, both in Stamford; Anderson Electric Power Systems in Greenwich; and Westport Solar Consultants and Pacific Capital Resources, both in Westport, according to the Business Council of Fairfield County. EnerNOC, a Boston-based alternative energy company, has an office in Stamford.