The Electric Transportation Energy Storage System (ETESS) is a new concept that integrates control logic for intelligently managing the charging of groups of plug-in electric vehicles with a small grid-connected electricity storage system.

Plug-in Electric Vehicles (PEVs) are coming and are forecast to become a significant share of the transportation sector in the future. The primary location for charging for most vehicles will be at a “home” location. But many PEVs, particularly BEVs, will need access to charge stations at other locations – at work, at shopping malls, in public parking garages, on city streets … everywhere. PEV charging loads will vary significantly during the day at these “park and charge” facilities. If the charging facility needs to keep its peak power demand below a power limit, it will need to actively manage the power allocation of each of the vehicles at the facility.

One challenge is to create optimization algorithms to allocate the available facility power to each PEV to keep the facility within its power constraints while minimizing any PEV customer disappointments. This is called intelligent Power and Energy Management (iPEM) logic. While the iPEM logic provides the capability to control the total facility power demand, it cannot add power, and this increases the risk that some vehicles will not get their requested energy transfer. However, if a grid-connected, energy storage system is placed within the facility, the iPEM algorithms can now take advantage of the energy storage capability to further improve the optimization. This integrated system of iPEM logic and energy storage is called the Electric Transportation Energy Storage System (ETESS).

Community Energy Storage (CES) is a new concept for grid storage that was developed by American Electric Power (AEP). A CES unit has a power of 25 kW with up to three hours of storage at rated power. It connects to the 240 volt secondary of the pad mounted transformer serving a group of homes. They are managed as a fleet by the utility to help manage the peak loads on the distribution feeder. In 2010, EPRI expanded on the CES concept to include units at power levels from 25 kW to 75 kW on single phase circuits and up to 200 kW on three phase circuits. They call it Distributed Energy Storage Systems (DESS) – Utility Padmount. The smaller CES-size units could be deployed in residential applications and the larger 75 kW to 200 kW DESS units could be deployed in commercial and industrial applications.
ETESS can also be thought of as just another DESS application, except it is connected to a group of charge stations at a parking facility rather than to homes or businesses. ETESS units can also serve the grid. They are individually and collectively capable of voltage and VAR support for the feeder, and can be managed as a fleet to provide frequency regulation or peak load management.

The objective of this project was to conduct a feasibility study of the ETESS concept. This report presents the results of this study. This report explores the technical and business issues associated with ETESS. It begins with an overview of energy storage for the grid, with a focus on distributed energy storage systems. Then the ability to communicate with PEVs and control the power demand during a charging session is explored. This establishes background for ETESS. Then the iPEM and ETESS concepts are introduced again. The balance of the report goes into more detail on the business issues and the technical performance of ETESS.