An expanding array of state-of-the-art and emerging technologies are opening new opportunities to improve and/or to reduce the costs to generate, deliver and use electricity. One of these technologies is modular electricity storage (MES). In this book, the specific utility application addressed is the use of MES to reduce the cost of electricity delivery by reducing the cost of electricity transmission and distribution (T&D) equipment. Specifically, MES would be used to defer expensive improvements or capacity additions to T&D equipment by providing modular capacity additions as needed.