Improving Grid Stability and Integrating Wind Energy: 

Younicos Battery Park # 1

Name of Project:
Improving Grid Stability and Integrating Wind Energy: 
Younicos Battery Park
Notrees, TX  
Wind + Storage  
Duke Energy  
Duke Energy  
Funded in part by US Department of Energy, Office of Electricity - ARRA Grant  
Operational since 2012


Duke Energy is using Younicos controls 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 constructed by Duke Energy in 2012, and is the largest wind-integrated storage resource in North America. The integrated facility at Notrees provides 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 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.


In 2016 it was determined to replace the advanced lead-acid batteries with lithium-ion, in two phases. To ensure that the Notrees BESS could continue to perform as a single storage unit that would rely on the coordinated operation of two very different battery chemistries, Younicos proposed a hybrid storage solution for the repowering. Applying sophisticated control methodologies to an advanced understanding of the operating characteristics of different battery chemistries, the Younicos control platform operates both chemistries in parallel while simultaneously managing the operation of the entire facility as a single unit on the ERCOT grid. The innovative control strategies manage various battery conditions such as different thermal constraints, different battery balancing requirements and different warranty conditions. This ensures optimal performance of both lead-acid and lithium-ion chemistries.


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 near-instantaneous 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.

Under the Younicos controls approach, the existing Notrees batteries have been gradually replaced over the course of 2016. In the process, the remaining life of the existing lead-acid technology was utilized as newer lithium-ion is implemented on a phased basis.

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