Energy Storage as a Distribution System Upgrade Alternative
By Roger Lin
The use of energy storage as an alternative to traditional wires and substation upgrades can be an attractive option for utilities. Energy storage can support distribution system operation in lieu of upgrading the entire distribution circuit, which could be difficult due to restrictions or constraints in certain environments. Depending on the conditions, storage could be a more effective and less expensive option; use of energy storage will also help the utility more effectively use the existing transmission or distribution capacity. This can be a valuable option compared to upgrading the capacity for peak hours, especially if they occur infrequently over the course of an entire year. However, beyond the upfront comparative cost-to-benefit analysis, there can be other challenges that arise after the decision to install storage is made, especially when deploying it in dense urban environments.
One historical example of this was at a distribution circuit located in Southern California. This particular distribution circuit was overloaded during peak hours of some days, which required the utility company, Southern California Edison, to study a circuit upgrade. This 12.47kV circuit, which was located in a dense urban area in the city of Orange, was evaluated to understand how an energy storage solution might be a more effective alternative to a traditional distribution circuit upgrade. This energy storage system would perform functions like peak shaving – essentially relieving stress on the circuit during peak hours – but also would have the ability to provide reactive power and voltage regulation to help maintain efficiency and reliability of the electricity network. Ultimately, a 2.4-megawatt, 3.9-megawatt-hour energy storage system was deemed to be the optimal size to relieve the overloaded distribution circuit.
The selected site for the energy storage system ended up being located on the property of one of Southern California Edison’s customers in a dense industrial area of the city, and from there connected directly to the distribution circuit. This available site, which itself was an easement on the property, had a number of unique challenges. The easement was only about 1,600 square feet in a trapezoidal shape, had a gas service line running through the center of it, a medium voltage duct bank along one boundary line, and water lines cutting through one corner of the easement. In addition, there were concrete walls along two of the site boundaries which would further restrict movement and complicate installation procedures.
In the past, typical installations of energy storage at the megawatt scale had been done in one or more containerized packages, essentially shipping container-sized batteries. In this case, for a 3.9-megawatt-hour energy storage system, the container would have to be roughly 53 feet long. However, due to the geometry of the site, the size of container needed would not fit in its entirety in the site and still allow other equipment to be installed such as transformers, switchgear, and power conversion systems or inverters. Thus a repackaging of the contents of the energy storage container was required. Fortunately, the energy storage system’s design used modular energy storage rack components to allow flexibility for multiple physical configurations of the racks. These racks could not only be installed in standardized shipping containers, but could just as easily be installed inside specially-designed rooms inside either pre-existing or new construction buildings, or within custom enclosures.
Ultimately, the solution for the energy storage system was the installation of a mechanical electrical equipment room, or MEER, to fit the needs for both the amount of energy storage required and the space requirements of the available site. This MEER was designed to contain all the energy storage rack components, DC isolation switches, control hardware, a battery thermal management cooling system and safety equipment, including an automated fire suppression system. External to the MEER were the power conversion system (PCS), switchgear, and 12kV/480V transformer.
Due to the high energy density of the underlying storage technology, and with clever layout and proper design of the energy storage system, all components were able to fit into the 1,600 square foot trapezoidal easement despite the underground interferences and site restrictions.
The business of maintaining grid capability sufficient to meet the electricity needs of the surrounding population is starting to change. In the past, only upgrades to transmission and distribution wires and substation capacity were seriously considered. Today, energy storage is a viable non-wires option available to utility companies for supporting their networks, adding a powerful new option to their toolkit. The utility in this previous example is considering how to make subsequent installations of energy storage as routine and commonplace as transformers and switchgear. While standardization of energy storage is desirable, flexibility in system design and configuration is equally important especially when presented with a challenging site. This configurability, along with system energy density, is a key to enabling storage installation in almost any location in the grid – at generation, transmission, and distribution sites, or even at commercial and industrial customer sites behind the meter.
Roger Lin, Director of Product Marketing at NEC Energy Solutions, leads all product management and marketing activities for the company. Focusing on grid energy storage solutions as well as battery systems for commercial and industrial applications, he has over ten years of experience in energy storage technologies and applications. In past roles he was responsible for several successful development efforts ranging from high power energy storage systems for hybrid buses to core lithium ion cell technologies at A123 Systems. Prior to joining NEC, he held roles in early stage venture capital fund YankeeTek Ventures, and business development and materials science research and development at Saint-Gobain. Roger received an M.S. in Materials Science and Engineering from MIT, a B.S. in Ceramic Engineering from Rutgers University, and is an inventor on nine United States patents.