The deal represents a needed boost in credibility for Stirling, which has come under fire from environmentalists who question Stirling's role in the 150-mile Sunrise Powerlink proposed by San Diego Gas & Electric Co.

Under an agreement with SDG&E, the Arizona startup with 40 employees plans to develop a power plant, consisting of 12,000 solar energy dishes, near El Centro at an estimated cost of $400 million.

Overview Background: Stirling Energy Systems was founded in 1996 to develop solar energy technology that uses mirrors shaped into 38-foot dishes to concentrate the sun's heat to 1,300 degrees. The heat energy powers an engine, which uses thermodynamics to generate about 25 kilowatts of electricity, or enough to power 12 to 15 homes. The barrel-shaped engine requires no fuel or water and emits no exhaust. What's happening: The first phase of Stirling's Imperial Valley project calls for building 12,000 solar dishes covering roughly three square miles. That would generate about 300 megawatts, or enough to power roughly 300,000 homes. The future: Environmentalists say they are skeptical of the Stirling proposal. They doubt that the company can move from its prototype models to large-scale production in time to enable San Diego Gas & Electric to meet a statewide mandate that requires it to use renewable energy for 20 percent of its total power supply by 2010.

The plant would generate enough electricity for nearly 300,000 homes in San Diego, and it represents the first step in a three-phase renewable energy project that SDG&E has cited as a key reason for the $1.5 billion transmission line.

Environmental opponents of Sunrise, on the other hand, have condemned Stirling's proposed solar facility as a “desert mirage.”

Details of Stirling's agreement with NTR were presented at a sunny news conference yesterday morning in Balboa Park. Representatives of Stirling and NTR said the Irish conglomerate has invested $100 million to acquire a 52 percent stake in Stirling.

“It's a great solar day in San Diego,” said Bruce Osborn, Stirling's chief executive.

He said NTR's initial investment will help Stirling commercialize its technology, expand to about 100 employees and complete preliminary work related to its proposed solar facility in the Imperial Valley.

“Those who act first and anticipate and adapt stand the best chance of reaping the rewards,” said NTR chief executive Jim Barry, who traveled from Dublin for the announcement. “In California, solar is clearly a critical resource.”

Founded 30 years ago, NTR initially specialized in developing toll road projects in Ireland. Since then, the company has expanded to 3,500 employees and has focused on developing renewable energy and waste management businesses in Europe and the United States. NTR posted fiscal 2007 revenue equivalent to more than $711 million.

As an investment, NTR's little bit of Irish green also will help “green the grid” in San Diego, said Mike Niggli, chief operating officer for SDG&E.

The investment helps to “pave the way for development of a vast renewable energy source in the Imperial Valley,” Niggli said.

Under a 20-year contract signed in 2005, SDG&E agreed to buy all power produced by a 300-megawatt solar power plant Stirling has proposed to build about 10 miles west of El Centro.

Electricity generated by the project would be sent to San Diego via the Southwest Power Link, an existing 500-kilovolt transmission line that runs parallel to Interstate 8.