Duke Energy, the largest electric power holding company in the United States, is using Younicos control technology to manage operations for a 36 megawatt Battery Energy Storage System (BESS) at the site of Duke Energy’s 153 MW Notrees wind farm in West Texas. The Notrees BESS, funded in part by a U.S. Department of Energy Smart Grid award, was initially constructed by Duke Energy in 2012, and remains the largest wind-integrated storage resource in North America. The integrated facility at Notrees has been providing environmentally friendly and flexible capacity to the Electric Reliability Council of Texas (ERCOT), which operates the grid and manages about 75% of the deregulated market in the state. The BESS is located in a 20,000-square-foot building adjacent to the wind farm substation. It is tied in at distribution-level to the wind farm’s 34.5kV system, and connects to the ERCOT grid through the same point of interconnect as the wind farm.





To maintain its high level of performance and extend the ability of the system to continue to provide fast-acting stability to the ERCOT-grid for years to come, Duke Energy decided to re-power the batteries, which had been using advanced lead-acid technology since 2012. This presented a challenge: how to continue to run the existing site to capture the remaining life of the existing batteries, while introducing newer lithium-ion technology to replenish capacity as the lead acid capacity degrades.





To ensure that the Notrees BESS could continue to perform as a single storage unit, relying initially on the coordinated operation of two very different battery chemistries before being converted to 100% li-on, Younicos proposed a hybrid storage solution for the re-powering. Applying sophisticated control methodologies to an advanced understanding of the operating characteristics of different battery chemistries, the Younicos control platform operated both chemistries in parallel, while simultaneously managing operation of the entire facility as a single unit on the ERCOT grid. The innovative control strategies managed various battery technology conditions, such as different thermal constraints, battery balancing requirements and warranty conditions. During this period, the control platform ensured optimal performance of both lead-acid and lithium-ion chemistries.

While continuously operating under Younicos controls, the remaining Notrees lead-acid batteries were eventually replaced. The facility is now running on 100% lithium-ion, ensuring optimal performance or many more years to come.

“Duke Energy Renewables was a pioneer in its early installation of the Notrees Battery Park, one of the largest in the nation. Investing in updated technology will extend the life of the project, enhance performance, and expand the value it provides to the ERCOT market.”


Jeff Wehner, Vice President Operations, Duke Energy Renewables



The inherently fast response of energy storage resources provides ancillary services for enhanced grid-management to facilitate increased penetration of clean renewable energy. It also reduces grid instability caused by unpredictable changes in customer demand. Furthermore, by providing an option to store energy during non-peak generation periods and return it to the grid when needed, energy storage increases the value and practical application of wind power. When commissioned in 2012, the Notrees BESS was the first resource to operate in ERCOT’s Fast-Response Regulation Service (FRRS) program. This ancillary service enables the grid operator to call upon fast-acting resources, such as energy storage, to provide an immediate response when a frequency excursion occurs. Managed by the Younicos controls platform, the Notrees BESS automatically deploys its full capacity in less than half a second after a frequency deviation event, providing nearly instanta neous feedback of frequency changes or other unexpected events. Such a rapid-response-resource has a much more immediate impact on addressing frequency events than conventional generators, which are limited by their ramp rate in how fast they can respond to a signal from ERCOT.




battery park is the largest wind-integrated system in North America.



of commissioning and actively participating in ERCOT’s FRRS market.



maximum reaction time to provide high power output.




The Younicos control technology platform is unmatched in its ability to provide high power output within 50 milliseconds accurately and precisely without infringing upon safety protocols. Tailored specifically to meet the performance objectives of the end-user, Younicos Control Technology can manage multiple BESS applications simultaneously, while also prioritizing how the system responds based on real-time conditions. The versatility of the platform supports utilization of multiple battery technologies and power electronics devices, enabling the development of scalable, flexible real-time energy management options, engineered specifically to meet customer needs and local grid operator rules.