"There have been some big changes in both the market and policy dynamics since we made our investment that, I think, on balance, are not terribly positive for BrightSource," said Dan Reicher, executive director of the Steyer-Taylor Center for Energy Policy and Finance at Stanford. Mr. Reicher oversaw an early investment in BrightSource in 2008 when he was director of climate and energy initiatives at Google. (The company went on to invest $168 million in Ivanpah.)
"Clean tech investing is way off," he said.
Still, experts say, BrightSource's solar thermal technology — which focuses sunlight from mirrors onto 2,200-ton boilers 339 feet in the air to make steam that drives turbines to produce electricity — may have an advantage over conventional panels, which convert sunlight directly into electricity.
The increase in renewable sources of energy, which produce intermittently, coming into the grid, has also increased the need for other services crucial to reliable operation, services that solar thermal plants could provide. Those needs include the ability to start and stop quickly, at any season or hour, when human operators give the order.
Utilities pay power plants for some of those jobs, and some conventional generating stations earn a significant income, in addition to what they receive for producing energy. Around the country, coal plants — of which there are fewer and fewer — were well suited to that work. And government regulators can simply require utilities operating on the grid to show that they have the ability to accomplish some of those jobs, which industry executives call "ancillary services."
"In the future, there will be money to be made from technologies and systems that contribute to integrating and balancing renewables on the grid," said Samuel Thernstrom, the executive director of the Energy Innovation Reform Project, a nonprofit in Washington that evaluates electricity policy. "That's going to be an increasing issue as the percentage of renewables on the grid increases."
Ivanpah could stabilize voltage but has little storage, though it does have natural gas backup. At the dedication, Mr. Ramm said that in the future, BrightSource's boilers would use molten salt to store the heat longer. Last year, Arizona Public Service opened a solar thermal plant, Solana, that lets customers brew their morning coffee with the previous afternoon's sunshine.
At the California Independent System Operator, the company that manages the grid on a moment-to-moment basis, Stephen Berberich, the president and chief executive, said that "on an apples-to-apples basis, it is more expensive than photovoltaic, but it has a heck of a lot more capabilities than photovoltaic does."
Another expert, Ron Binz, an energy consultant based in Denver and the former chairman of the Colorado public service commission, said that storage would indeed be needed as intermittent renewables grew. But solar thermal plants were not the only way to meet that need, he said, and a competition would follow. "You can't look at any element of this without looking at all the others," he said.
As for the federal loan guarantee program, the government has already changed its approach, looking to emphasize a range of cleaner technologies, especially in fossil fuels and nuclear power.
To that end, Mr. Moniz encouraged the crowd of industry executives to pursue new projects that would qualify for the loan guarantees. "Bring them on," he said. "We're ready."