Client Duke Energy

Location Notrees, Texas (USA)

Sectors Utilities

The Challenge

Finding the right energy storage answer

In 2013, a major solar farm was installed in Texas. OCI Solar Power decided to look at incorporating energy storage into the mix, and turned to a local expert, Younicos, to launch its first energy storage initiative.

The Younicos track record includes the construction of the first battery storage system in Texas, the 36 megawatt Notrees Energy Storage System, which is
still the largest renewables integrated storage facility in North America and was instrumental in proving the benefits of fast-responding storage assets to the Texas market.

The customer was confident that this record of successful performance meant that Younicos was the premier choice for delivering a storage solution tailor-made for the Texas market. The customer wanted to install the storage system alongside its solar farm, taking advantage of existing equipment and interconnection facilities.

In order to preserve the versatility of the system, it was important to select a chemistry that could reliably participate in the markets for energy storage today, namely Fast- Frequency-Regulation- Service (FRRS).

Another requirement was to provide other services, such as solar power ramping, to smooth the intermittency of the colocated solar farm output, as well as future services such as Firm Frequency Response (FFR).


Project fact file

50 Milliseconds

Maximum reaction time to provide high power output.

1 MW


0.25 MWh


The Solution

Flexible, configurable energy storage to perfectly meet demand


Performance, reliability and ease of installation and maintenance were key considerations for the project team. Our compact Y.Cube solution was the ideal system to meet all requirements.

Two 3 x 3 metre Y.Cube enclosures were installed side-by-side on a 90 square-metre concrete slab next to the solar farm control house, and tied into the existing 34.5 kV bus.

Both Y.Cubes, along with the transformer and other electrical equipment, were all installed by a single forklift in a cost-effective and speedy installation. Each Y.Cube enclosure contains the LG-Chem battery racks, two Y.Converters 250, Younicos’ proprietary power electronics solution, along with HVAC, fire suppression and auxiliary load equipment, all managed by the Younicos control platform.

The unique configurability of the Y.Cube solution, which allows the user to build the system with more choice than offered by a standard ‘one-size-fits-all’ 40-foot-container, enabled the customer to optimise both the operational size and footprint of the storage system.


The Aggreko Difference

We are energising the viability of battery storage

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 our 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