Client Duke Energy

Location Notrees, Texas (USA)

Sectors Utilities

The Challenge

Re-power lead-acid batteries to power a grid

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 their 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?

Our experts had just the answer.


Project fact file

50 Milliseconds

Maximum reaction time to provide high power output.

1 MW


0.25 MWh


The Solution

Hybrid storage proposal to revitalise old batteries

Younicos proposed a novel method of overcoming the problems associated firstly, with switching from two very different battery chemistries and also, converting to 100% li-on. This innovative approach would furthermore allow the Notrees site to operate on the old system during the transitional phase.

The Younicos control platform operated both chemistries in parallel by harnessing sophisticated control methods, with our experts using their deep understanding of operating characteristics to simultaneously manage 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 for many more years to come.


The Aggreko Difference

Hybrid storage solution for an electric power company in Texas

The Impact

Increased viability and rapid response for renewable energy methods

Our energy storage solutions have helped prove the viability of batteries and the impact they can have for renewable energy sources. Unpredictable changes in customer demand have so often caused intermittency problems for cleaner energy, but by providing an option to store energy during non-peak generation periods and even send it back to the grid, energy storage increases the value and practical application of wind power.

 When commissioned in 2012, the Notrees site 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, Notrees automatically deploys its full capacity in less than half a second after a frequency deviation event, providing nearly 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. 


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 ,
Duke Energy Renewables 

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