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Oorja Protonics, a secretive Fremont, Calif. start-up developing fuel cell systems that run on alcohols like methanold and ethanol, has just raised $15 million in a second round of funding, according to a regulatory filing cited by PE Week.

Alcohol-based fuel cells are still in the early stage of development, but they’ve already been introduced for commercial use in laptops, camcorders, MP3 players, mobile phones, and other devices. There’s an overview in the Space Review, which among other things, mentions potential application of these fuel cells in space.

The company raised $5.52 million from Sequoia Capital last year, which we mentioned was a first sign that Sequoia is turning attention to the alternative energy sector. This time, it brings in two of its “coat-tail” investors, DAG Ventures and Artis Capital.

DAG has made a business of partnering with other high profile investors, and investing alongside them even if DAG has to invest a little later. Artis is a hedge funds with close (family) ties with Sequoia. McKenna Capital also invested.

Update: Sunil Paul is also an investor.