Best practice site visit - NAS Battery Energy Storage System – Csillebérc (HU)

In December 2024 the StoreMore team visited a location utilizing Sodium-Sulfur (NAS) battery technology in Csillebérc. The purpose of the visit was to gain first-hand insights into the operational characteristics, performance, and potential applications of NAS batteries, specifically within the context of the StoreMore project.

It is important to note that this particular installation was selected due to its status as the first and longest-operating NAS battery system in Hungary. As such, it provides a valuable opportunity to gain insights into the long-term performance and operational characteristics of this technology in the Hungarian context.

Sodium-Sulfur (NAS) Battery Technology: An Overview

Sodium-Sulfur (NAS) batteries are a type of high-temperature molten salt battery that employs sodium metal as the anode, sulfur as the cathode, and a solid ceramic electrolyte to separate the two. This unique combination of materials results in several distinct characteristics that differentiate NAS batteries from other energy storage technologies.

Operating Principle:

NAS batteries operate at high temperatures (around 300°C), which allows for the use of molten sodium and sulfur as active materials. During charging, sodium ions migrate from the anode to the cathode through the solid electrolyte, combining with sulfur to form sodium polysulfides. During discharge, the process is reversed, with sodium ions moving back to the anode, generating electrical energy.

The solid electrolyte, typically made of beta-alumina, is a key component of the NAS battery. It allows for the passage of sodium ions while preventing direct contact between the sodium and sulfur, which would cause a short circuit and damage the battery.

Key Characteristics:

NAS batteries exhibit several unique characteristics that differentiate them from other battery technologies:

High Energy Density: NAS batteries offer a high energy density, allowing for compact and efficient storage of large amounts of energy.
Long Cycle Life: With proper operation and maintenance, NAS batteries can achieve a long cycle life, typically exceeding 15 years or 4,500 cycles.
Fast Response: NAS batteries can respond quickly to changes in grid demand, making them suitable for applications requiring fast frequency regulation and voltage support.
High Efficiency: NAS batteries exhibit high round-trip efficiency, meaning a significant portion of the stored energy can be recovered during discharge.
Long Duration Storage: NAS batteries are well-suited for long-duration energy storage applications, enabling the storage of energy over extended periods.
Environmental Benefits: NAS batteries are environmentally friendly, with no harmful emissions during operation.

Construction and Design:

NAS batteries typically consist of several key components:

Battery Cells: Individual battery cells contain the sodium anode, sulfur cathode, and solid electrolyte.
Battery Modules: Multiple battery cells are connected in series and parallel to form battery modules, increasing the overall capacity and voltage of the system.
Battery Container: Battery modules are typically housed in insulated containers to maintain the operating temperature and ensure safety.
Power Conversion System (PCS): The PCS converts the DC output of the battery system to AC power for grid connection and controls the charging and discharging processes.
Thermal Management System: A thermal management system is essential to maintain the optimal operating temperature of the battery cells.

Applications:

NAS batteries have a wide range of applications in the energy sector, including:

Grid Stabilization: Balancing supply and demand, providing frequency regulation, and maintaining grid stability.
Renewable Energy Integration: Storing excess energy from renewable sources such as wind and solar power to ensure a consistent and reliable power supply.
Peak Shaving: Reducing peak demand by discharging energy during peak hours and charging during off-peak hours.
Microgrid Applications: Providing reliable power supply and grid support for isolated communities and microgrids.
Backup Power: Serving as a backup power source for critical loads during grid outages.

Advantages of NAS Batteries:

High energy density and long cycle life
Fast response and high efficiency
Suitable for long-duration energy storage
Environmentally friendly with no emissions
Modular design allows for flexible system scaling

Challenges and Considerations:

High Operating Temperature: Maintaining the high operating temperature requires careful thermal management.
Safety Considerations: Handling molten sodium requires careful safety precautions.
Capital Cost: The initial capital cost of NAS battery systems can be significant.

Despite these challenges, NAS batteries offer a promising solution for addressing the growing demand for energy storage and grid modernization. Continued research and development efforts are focused on improving the cost-effectiveness, safety, and overall performance of NAS battery technology.

Potentials in StoreMore

The inclusion of sodium-sulfur (NAS) battery technology in the Analysis and Cataloguing of Energy Storage Solutions activity within the StoreMore project offers significant potential. The A1.3 Energy Storage Outlook has already recognised NAS technology as a viable long-duration energy storage solution, highlighting its technical feasibility, high energy density, and long operational lifespan. Given these strengths, the Csillebérc NAS battery installation provides an excellent real-world case study to enrich the project's catalogue of sustainable energy storage solutions.

NAS batteries stand out for their unique combination of sustainability and performance. Their hermetically sealed design eliminates emissions during operation, ensuring minimal environmental impact. Furthermore, their recyclability, with recoverable sodium and sulfur components, aligns well with StoreMore’s emphasis on environmental assessment. The robust thermal management system, while energy-intensive, is integrated into the overall high round-trip efficiency (85–90%) of the technology, making it competitive with other advanced storage solutions. Evaluating NAS batteries in-depth as part of A1.5 would also allow the consortium to explore their CAPEX implications, particularly in scenarios where long-duration storage and grid stabilisation are prioritised.

By incorporating NAS technology into the StoreMore analysis, the consortium could provide a well-rounded view of its capabilities, limitations, and potential environmental and economic benefits. This would enhance the value of the Catalogue of Sustainable Energy Storage Solutions by offering decision-makers a proven, scalable, and durable alternative to conventional lithium-ion systems. Including NAS technology could also bolster the modelling and optimisation tools developed in subsequent activities, ensuring that the StoreMore project addresses a broader spectrum of real-world storage needs.

Conclusions

The Csillebérc NAS battery site visit demonstrated the remarkable capabilities and potential of sodium-sulfur technology in addressing modern energy storage challenges. Its high efficiency, long-duration capacity, and environmentally friendly design underscore its suitability for renewable energy integration and grid stabilisation. The system’s robust monitoring, control, and safety protocols, combined with its modular and low-maintenance nature, make it a prime candidate for broader adoption in energy storage projects across the Danube region and beyond.

As the StoreMore project continues to evaluate and catalogue sustainable energy storage solutions, incorporating insights from this site visit into its activities will provide valuable real-world context. The NAS battery’s proven durability, emission-free operation, and recyclability align seamlessly with StoreMore’s goals of fostering sustainability and innovation in energy storage.

The full report is available here.