NYT: In the garage of Peter Rive’s San Francisco home is a Tesla Motors lithium-ion battery pack. It is not connected to Mr. Rive’s electric Tesla Roadster sports car, but to the power grid. The California Public Utilities Commission has awarded $1.8 million to Mr. Rive’s company, SolarCity, a residential photovoltaic panel installer, to research the feasibility of storing electricity generated by rooftop solar arrays in batteries. As rooftop solar systems provide a growing …