gap. Battery storage appears to be most promising due to im- provements in technology as well as economies of scale. Storage tends to make the net demand profile flatter and, as such, is ex- pected to improve reliability. In addition, most battery storage devices can respond in subsecond time scales. Hence they can be valuable as enablers of fast controls in a smart grid. Storage of various sizes can be distributed throughout the grid ranging from end-use customer premises to major substations and cen- tral power stations. This can alleviate congestion in both trans- mission and distribution.