How does Fast Reserve BESS ensure ultra-stable supply? 

Thursday, September 19, 2024

ITALY: Danfoss grid converter technology is at the heart of Terna's Fast Reserve pilot project. For this project, system integrator Loccioni created a 12.6 MW energy storage system on behalf of a major national multi-utility. Excellent performance is assured by the liquid-cooled VACON® NXP Grid Converter. It ensures rapid grid intervention in less than 200 ms and an overall battery energy storage system (BESS) efficiency of 90%.

The European Green Deal is an EU strategic policy initiative that aims to transform Europe into a sustainable economy by progressively reducing greenhouse gas emissions. In recent years, this initative has significantly boosted awareness of sustainability, energy transition, and electrification. To comply with decarbonization objectives and promote a sustainable energy transition, stakeholders in the energy sector aim to increase the proportion of renewables in the energy mix.

One of these players is Terna, operator of the national electricity transmission grid in Italy. As the entity responsible for ensuring a stable and high-quality power supply, Terna launched a tender for the construction of a fast reserve unit.

The situation: Not your usual BESS

“Fast Reserve” is a pilot energy storage system aimed at providing an ultra-fast frequency regulation service to stabilize the 50 Hz mains. This stabilization mitigates load variations which could otherwise lead to sudden unwanted disturbances, especially as a result of abrupt and unexpected insertions. With the contribution of power converter manufacturer Danfoss, and system integrator Loccioni, the pilot project led to the creation of a 13.64 MVA battery energy storage systems (BESS), located in a combined-cycle power plant of an important national multi-utility.

Matteo Marchetti, head of Loccioni Energy, explains, "Since "Fast Reserve" was a pilot project, there were no benchmarks or previous experiences available on which to capitalize. However, we had the experience of over 20 years of work with electricity storage and energy flow management (with the creation of micro-grids for us and for several customers) and our approach to measuring to improve, also guided us in this adventure. The design specifications stipulated that the storage system, capable of 12.6 MW of power and 7 MWh of energy, would ensure very fast, almost instantaneous response times, with the ability to plug into the grid in a time interval t < 200 ms under any load condition over the entire range of the available nominal power: from -12.6 MW, in full absorption, to +12.6 MW, in full delivery".

The challenge: High efficiency and fast response

As well as providing a storage system for surplus energy production, battery energy storage systems (BESS) play a fundamental role in stabilizing the frequency of the electricity distribution network. Here, the response time of the system is a critical element: ensuring an instantaneous insertion of BESS into the grid is vital to ensure the quality and stability of power supply.

Considering that the response time of a traditional BESS is typically around 1 second, we can well understand the innovative scope of the "Fast Reserve" pilot project, with load insertion transient to be contained in less than 200 ms over the entire power range, from -100% to +100%.

The next major challenges were efficiency and reliability. It is well known that storage systems deliver high efficiency, but in this case the design specifications required particularly high values. Another challenge posed by the project was limited space.

One of the reasons we chose Danfoss power converters, especially the liquid-cooled VACON® NXP Grid Converter, is the high efficiency of 98%, which is really top-notch. It is also thanks to this characteristic, as well as the careful design of the entire system, that we have been able to achieve such high levels of efficiency overall. If we think that the efficiency of a combined-cycle power plant is typically in the order of magnitude of 60%, it is easy to understand how the 90% achieved by the Fast Reserve pilot project that we have implemented together with Danfoss is of value for all. It also helps us understand the enormous potential that electric technology, if well exploited, can have in store for the future.
Matteo Marchetti of Loccioni Energy

The solution: A benchmark in scalability and compactness

The scalability of the VACON® NXP Grid Converter used in the application has allowed the designers to think in highly modular terms. They have achieved a high rationalization of the plant architecture, optimizing the available space, and they manage the entire system with a single controller.

The Fast Reserve system is housed in 6 containers stacked in pairs, forming three separate units.

The lower containers house lithium-ion batteries (these are LG JP3 units with 715-1000 V DC), while the upper containers house two twin electrical panels, each of which contain 2 liquid-cooled VACON® NXP Grid Converter 640-1100 V DC units in an open configuration (IP00). In total, 12 pcs VACON® NXP Grid Converter are installed.

Inside each container, the panel layout has been carefully optimized to occupy minimal space. The liquid-cooled VACON® NXP Grid Converter modules proved to be an exceptional ally, as they are more compact in size compared to similar solutions on the market, such as air-cooled modules.

Benefits of VACON® NXP Grid Converter

Suitable for a DC input of up to 800 V, with AC output of 520 A
A built-in sine filter ensures high power quality with a nice AC sine wave
A common-mode filter equalizes the differences between the system's common mode voltage, which arise when transforming
A low-complexity, lightweight system with no need for a separate transformer
Performs well at low loads

The outcome: Exceptional reliability and rapid response

The system has been in continuous operation for more than a year without a hitch or alarm ever appearing. With its exceptional reliability, this system is now a benchmark of reference in the electrification sector, which is destined to grow steadily in the coming years.

The overall efficiency of the system is exceptional, reaching the threshold of 90%. This number refers to the entire energy cycle: the two stages of conversion, charge and discharge, the intermediate phase of energy maintenance and the entire chain of dissipations related to system components such as transformers, cooling systems, and auxiliaries.

The collaboration between Danfoss and Loccioni went far beyond the normal customer-supplier relationship, which in turn enabled Loccioni to achieve optimal results far beyond the project requirements. Tests carried out during functional testing and then in the field certified the ability of the system to guarantee response times of less than 160 ms in the most critical condition: in the switch from -12.6 MW to +12.6 MW, thus ensuring performance 20% higher than specified.

Danfoss has helped us in every possible way, both in terms of delivery and technical support. Their availability and flexibility have allowed us to work side by side in achieving a common goal, and customer satisfaction.
Matteo Marchetti of Loccioni Energy

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