Once again, Elon Musk is looking several moves into the energy future. Solar City is marketing DemandLogic(TM), technology recently developed by Tesla. This is a battery backup device that allows a user of solar energy to cut their demand charge by saving some of their energy for use after the sun goes down to cut their peak demand (see this video and this cut sheet or this one, to better understand demand charges). In so doing they can substantially reduce their electric bill. This also helps solve a problem that otherwise might limit the introduction of renewable energy sources such as solar.
In the Southwest, as penetration of renewable energy increases there is considerable concern about the sudden change in supply as the sun goes down. This has resulted in what is referred to as the Duck Curve. By reducing the demand peak and smoothing the ramp, the negative impact of renewable energy is substantially reduced. While demand logic will be a money saver throughout the country, in the Southwest it contributes by expanding the practical expansion of use of renewable energy.
More press on DemandLogic Here: