# Infinia Raises $50M for Stirling Solar Infinia, a company that has spent the past 25 years working on stirling engines, just announced this afternoon that it has raised a Series B round of$50 million. Why is it raising such a sizable round now? The company, which is backed by a who’s who of entrepreneur investor firms in Vinod Khosla’s Khosla Ventures, Bill Gross’ Idealab and Paul Allen’s Vulcan Capital, says it will start selling its stirling engine product for solar thermal power plants by the end of this year and will use these funds to make that happen.

The stirling engine is a centuries-old technology that uses an external heat source, runs quietly, can be greenhouse gas-free and can be more efficient than an internal combustion engine. Inventors have been working on the technology since the stirling engine arrived, but stirling engines are still not used in the mainstream, just for very niche applications.

Infinia’s solar thermal stirling product is an intersection of several cleantech trends: more and more solar thermal power plants are getting ready to come online over the next few years, and with the concern over climate change, startups are working on stirling engines as an alternative to the traditional internal combustion engine.

Infinia’s CEO J.D. Sitton tells us that the company’s stirling engine can provide 3 kilowatts of AC to the user, and for the solar market it can convert sunlight to AC electricity at a rate of 24 percent — that’s pretty high. Sitton says its customers will be solar asset developers, likely in Spain and the U.S., and that the company’s technology will bring down the costs of making stirling engines.

The solar thermal company with the most power plants coming online in the U.S., Stirling Energy Systems, already uses a concentrator dish attached to a stirling engine designed to convert sunlight to electricity. Other inventors like Dean Kamen (mind behind the Segway) are working on stirling engines to power vehicles (Kamen’s built a stirling engine scooter).

Infinia’s round was led by GLG Partners and included new investor Wexford Capital, as well as existing investors Vulcan Capital, Khosla Ventures, EQUUS Total Return, Idealab and Power Play Energy. The company raised a $9.5 million Series A round in June of 2007 from Idealab, Khosla, and Vulcan, as well as a$3-4 million angel round before that from undisclosed investors.