A few days ago, Musk acquired SolarCity — the California based firm providing solar power systems for homes, businesses and governments — to unite two of his businesses and create the world's only integrated sustainable energy company. It will integrate electric charging with Tesla cars, home batteries with solar roofs and rooftop solar panels. It will sell different solar products as a single offering, such as hooking up Tesla's energy storage solution, called Powerwall, with SolarCity's solar panels, and enable Tesla cars to make money even when people aren't using it.