BrightSource Energy said it raised $150 million in a fourth round of financing, bringing the total the firm has raised so far to more than $300 million.

The financing will be used for two purposes: to help BrightSource build solar thermal power plants in the U.S. Southwest to serve customers like Pacific Gas & Electric and Southern California Edison, and to expand internationally.

International. There's a word you haven't heard much from BrightSource. Rival eSolar has already taken the international route, signing deals to provide equipment and intellectual know-how to power providers in China, South Africa and India. China could be a lucrative market, although to date, it has yet to produce a domestic powerhouse in this industry like Suntech in photovoltaic solar panels. A number of Chinese companies make solar thermal water heaters but not solar thermal power plants or solar thermal power plant equipment. Sources, however, have told me that the government is interested -- very interested -- in seeing the market expand.

So to are some solar thermal power plant developers. Solar thermal equipment is expensive. Chinese equipment manufacturers could help bring down the price, one developer told me at the recent Solar Industry Summit. Potentially, BrightSource could enter deals to build power plants overseas or enter into joint ventures with local companies; First Solar has cut deals like this in China to build photovoltaic power plants. (PV panels harvest energy by effectively stripping electrons from sunlight. Solar thermal plants are like big tea kettles: they harvest heat from the sun, mostly to boil water.)

Like the solar panel industry, the solar thermal industry is in the midst of consolidation. Last year, Siemens bought Solel, one of the older companies in the business, for $410 million, while Areva, the French company known for nuclear, bought struggling startup Ausra.

Among the startups that popped up in the early part of the decade, three seem to be doing well: BrightSource, eSolar, and Stirling Energy Systems. BrightSource has signed contracts to build solar thermal plants that will produce 2.6 gigawatts of electricity for major California utilities. It has also struck an alliance with Bechtel to help build these plants. It hasn't been easy. Regulators have squeezed the size of its Ivanpah, California plant. BrightSource's power plants will be based on tower technology: mirrors will direct heat to a water tank in the sky to produce steam. The success to date, and the company's vivid history, is why we put founder Arnold Goldman in the Greentech Hall of Fame.

Stirling uses a Stirling engine that generates hot air. It and sister company Tessera Solar are building power plants in California and Arizona.

Meanwhile, eSolar has a power tower similar to BrightSource but a different business model. It largely gave up on trying to build power plants. Instead, it now concentrates on making equipment and selling it to power plant builders or licensing the technology.