The Palo Alto, California, company pledged to leave the fate of the deal up to a majority vote of "disinterested" shareholders at both Tesla and SolarCity, meaning Musk wouldn't have a say. Musk's argument for combining Tesla and SolarCity primarily revolves around a battery system that stores solar energy in homes and businesses trying to minimize their dependence on the power grids run by utilities. Tesla introduced the battery, called "Powerwall," 14 months ago, providing the first inkling that it planned to be more than just an auto maker. Musk believes both Tesla and SolarCity will be better off if their products are united under one roof and a common brand. SolarCity already is selling the power-storing batteries as part of an agreement that Tesla expects to generate $44 million in revenue this year, according to SEC documents.