In late 2015, Glendale Water & Power (GWP) decided to install a small-scale pilot energy storage system to evaluate how this nascent technology can be used in the utility’s electric system to meet the rapid fluctuations, if any, in its system load and demand. The utility sought the help of an existing energy marketing and consulting partner, Skylar Resources LP. Together, Skylar and GWP engineering evaluated several different applications for this technology, including the black start of generating units, support and management of solar intermittence, and mitigation of area control error (ACE).
After careful evaluation of several battery systems and working closely with reputed battery system and inverter companies to analyze different technologies, GWP agreed to Skylar’s recommendation to use a 2-MW battery energy storage system (BESS) as a pilot system. This pilot unit was used to evaluate the ACE application. A vacant lot adjacent to the newly built Grandview substation in northwest Glendale, California, U.S., was chosen for the location of the BESS. In March 2016, GWP executed a turnkey equipment supply agreement, whereby Skylar agreed to engineer, procure, construct and commission the BESS.
System Components
Skylar and GWP selected Saft Inc. with its Intensium Max+ 20M container for the battery system and ABB to supply the power conversion system (PCS). The Saft battery is a lithium-ion system rated at 950 kWh, capable of charging at 1 MW and discharging at up to 2 MW. It is housed in a 20-ft (6-m) International Organization for Standardization (ISO) shipping container with an integrated thermal management and fire-safety system.
The BESS is integrated with GWP’s supervisory control and data acquisition (SCADA) system for around-the-clock monitoring by GWP’s energy control center, while the thermal and fire systems are being monitored around the clock by a UL-listed fire systems company. Systems of this type are highly modular, with the smallest replaceable unit being a 14-cell Synerion 24M module rated at 2 kWh.
Within the Intensium Max+ 20M container, 28 Synerion 24M modules are arranged in series to create a 58-kWh energy storage system unit, which produces a 700-VDC output for PCS conversion. Each energy storage system unit includes a battery management module that manages the safe operation of the string. The container is built with 17 of these strings in parallel, which are coordinated by a master battery management module that collects operational data from each string and sends the aggregate data on to the PCS.
The ABB PCS is also modular, with 23 inverter modules for DC/AC conversion, each providing approximately 84 kW of AC power. The PCS has a control cabinet with graphic display module, communications media, auxiliary power and distribution, and a protection cabinet with AC breakers for grid isolation and DC breakers for battery isolation.
Operation Theory
The modularity of both the PCS and battery provides a high level of fault tolerance and availability of the system. The PCS has four-quadrant capability, meaning it can supply or absorb real power (megawatts) and be used to supply or absorb reactive power (megavolt-ampere). The heart of the BESS is the energy management system, which processes the ACE signal, grid data and battery inputs through dynamic operating algorithms to determine the required BESS output, while maintaining continuous communication with GWP’s SCADA system.
In ACE mode, the BESS control limits are set, which regulate power flow at the transmission interconnection point with the Los Angeles Department of Water and Power (LADWP) to help the GWP system operate within the scheduled power thresholds. This is accomplished by sending the ACE signal to the PCS, which manages the start and stop sequence of the inverters and battery lineup to either charge or discharge the stored power to operate within the control-error upper and lower thresholds of +8 MW/-8 MW, in accordance with the power exchange agreement between GWP and LADWP.
When operating in automated ACE mode, if the ACE is greater than +8 MW (that is, the actual power intake at the interconnection point is greater than the scheduled power), the BESS will source real power to the grid, thereby increasing internal generation and, consequently, lowering ACE to below +8 MW. On the other hand, if ACE is lower than -8 MW (that is, the actual power intake at the interconnection point is less than the scheduled power), the BESS will sink real power from the grid by increasing the internal system load and, consequently, increase the ACE to above -8 MW.
The PCS also manages the state of charge at an optimum level of 60%, while the ACE is within the limits. The pilot system is too small to correct the error fully at the point of interconnection to LADWP, but GWP’s intention is to operate the BESS in a scaled version of the ACE.
Construction Details
Skylar selected Beta Engineering to design, procure, construct and oversee the battery system installation and integration into GWP’s power grid. The designs were prepared by Beta based on GWP electrical engineering standards. Furthermore, all designs and specifications for the materials were reviewed, corrected as needed and approved by GWP electrical engineering prior to being installed.
Beta procured the power transformer from Virginia Transformer Corp., 69-kV breaker from General Electric (GE), and provided the engineering design and labor for installation and integration of all the components except for the new transmission line, which was constructed by GWP. To connect the BESS to GWP’s electric grid, the new 69-kV transmission line was built by reconstructing and reframing the existing 34.5-kV transmission line for 69-kV operation. Using a combination of both overhead and underground cables, the transmission line travels approximately 4 miles (6.4 km) from the Kellogg switching station to the Grandview BESS. The protection scheme for the new 69-kV line connecting the BESS to GWP’s electric grid was designed and implemented by GWP electrical engineering.
Skylar issued a notice to proceed with construction in November 2016. In summary, the main components of the BESS are as follows:
• 2-MW BESS, supplied by Saft
• 2-MVA PCS, supplied by ABB
• 2-MVA, 69-kV, 373-V power transformer, supplied by Virginia Transformer
• 69-kV gas-insulated substation breaker, supplied by GE
• A new 69-kV transmission line connecting the BESS to the Kellogg switching station, completed by GWP.
Challenges and Obstacles
Like most utility construction projects, this particular project had unique challenges and obstacles to overcome. Proper coordination between the GWP engineering team and Skylar as well as the timely support of Saft, Beta and ABB were key factors in completing the project.
One of the challenges was to get the system certified for fire protection and safety. Modifications were made to the system to meet the requirements of the Glendale fire department and around-the-clock monitoring of the fire system was incorporated.
Weekly project review meetings were held to discuss project challenges, identify solutions and document action items. Active coordination with local stakeholders — including the city of Glendale and the Glendale fire department — was crucial for the success of this project, which was commissioned in May 2017.
Lessons Learned
This pilot battery storage system has confirmed the ability of the battery to respond instantaneously to shifts in system load. With an energy storage system of sufficient size, GWP has unprecedented capacity to regulate its transmission system. Beyond future renewable integration, a future BESS of sufficient capacity also may serve as an emergency source of energy to start up generating units, mitigating the impact of potential unplanned disruptions in service. ♦
Jaime Reyes is an electrical engineering associate working in the substation engineering group at Glendale Water & Power. He was the project manager for the battery energy storage system project. Reyes holds a bachelor of science degree in electrical engineering from California State University.
