Tesla Motors [NSDQ:TSLA] CEO Elon Musk caused quite a stir when he tweeted that the company was preparing to unveil a "major new product line" that was "not a car." Most of the speculation quickly turned to stationary batteries that could be used to power a house or business. Those rumors were confirmed last night when Musk unveiled a new line of batteries under the Tesla Energy brand at the company's design studio in Hawthorne, California.