QUOTE : SolarCity is a key part of what can be thought of as the unified field theory of Musk. Each one of his businesses is interconnected in the short term and the long term. Tesla makes battery packs that SolarCity can then sell to end customers. SolarCity supplies Tesla’s charging stations with solar panels, helping Tesla to provide free recharging to its drivers. Newly minted Model S owners regularly opt to begin living the Musk Lifestyle and outfit their homes with solar panels. Tesla and SpaceX help each other as well. They exchange knowledge around materials, manufacturing techniques, and the intricacies of operating factories that build so much stuff from the ground up.