The company created a subsidiary called ACCUmotive in 2009 to develop lithium-ion batteries. It built an energy-storage array that is now operated by German electricity joint venture Coulomb. The system's 96 lithium-ion "modules" boast a combined 500 kilowatt hours of storage capacity, which is used to stabilize the Saxony Kamenz power grid. There are plans to expand this installation to 3,000 kWh of storage capacity.
The Tesla Battery's cost $13,000 would pay most people's electric bills outright over it's life.
The Tesla's battery is also 53, 70 or 85 kWh whereas the average household uses around 1 kW (kWh/h) and certainly can get by with a few kWh of storage to handle its overproduction of solar during a day.
In the end, it's just economics. Does solar + battery pay itself back in lowered electricity bills? If it does, nothing else matters.
The most difficult thing in the world is to know how to do a thing and to watch someone else doing it wrong, without commenting. -- T.H. White