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NGK’s NAS sodium sulfur grid-scale batteries in depth

NAS grid-scale batteries. image: NGK.
Japan-headquartered NGK Insulators is the manufacturer of the NAS sodium sulfur battery, used in grid-scale energy storage systems around the world. ESN spoke to Naoki Hirai, Managing Director at NGK Italy S.r.l.

What is the history of NAS batteries and how have they progressed from early R&D to commercialisation?

Originally, the principle of the sodium sulfur battery was released in the United States, and it led to various trials in the US, Europe as well as Japan for the development of the battery to be utilised for electric automobiles or energy storage systems.

NGK started the development of the Beta Alumina electrolyte utilising the expertise of fine ceramic technologies in 1984, and extended it to the development of NAS (sodium sulfur) battery in 1989, jointly with TEPCO (Tokyo Electric Power Company).

It resulted in the only success of commercialisation in 2002. Up to now NAS is the most-used large scale battery in the world.

What are the applications NAS batteries are suitable for?

NAS batteries can store large amounts of energy and discharge for long durations, and can be configured for large-scale deployments. Therefore NAS batteries are suitable for energy type applications, such as energy shifting of renewables from off-peak to peak time, transmission and distribution (T&D) network management, and load levelling. Also NAS batteries can be used for ancillary services additionally to stack the benefits and the income.

What are some of the advantages of NAS batteries in comparison to other technologies for storing energy?

Heading the list of the NAS battery's advantages are long discharge times, six hours and more, large capacities available from 10s to 100s of megawatts, and long life; rated at 15 years, 4,500 cycles at 100% DOD (depth of discharge). The batteries' advantages also include compact design, it is easy to expand the system size as much as needed, they are quick to install and require minimal maintenance. In addition, NGK’s NAS battery systems are the only grid-scale battery storage with over 10 years of commercial operation. And in total cost per kWh, the NAS battery is less expensive than other technologies, such as lithium-ion or redox flow batteries.

Where have NAS batteries been deployed so far?

NGK’s NAS batteries are currently being used by 190 locations in Japan, North America, Middle East and Europe, providing an overall capacity of 530MW and 3700MWh for load levelling, renewable energy stabilisation, transmission and distribution network management, in microgrids and for ancillary services.

For example, 108MW of NAS battery systems are being used by Abu Dhabi’s main utility for grid-scale demand management to operate thermal generation efficiently. In Italy, 35MW NAS facilities operated by the transmission operator Terna, store the surging supply of wind energy generated in the south of that country for transmission across the grid to the large power users in the north, thereby reducing transmission congestion and the curtailment of wind generation in the Italian grid. And in Japan, a 50MW/300MWh NAS batteries system was delivered to optimise the balance of supply and demand of power by absorbing excess solar PV generation to avoid limiting the output from solar facilities.

Who are the primary customers for these batteries at the moment?

The main customers are utility companies, transmission and distribution system operators, renewable energy producers and big electricity consumers such as factories and shopping malls.


Heading the list of the NAS battery's advantages are long discharge times, six hours and more, large capacities available from 10s to 100s of megawatts, and long life; rated at 15 years, 4,500 cycles at 100% DOD."

Are the manufacturing processes for the NAS battery all done by NGK Insulators, or are some parts or equipment sourced from other companies?

NGK manufactures the key component of NAS technologies, the solid electrolyte made of Beta Alumina ceramic. The mass production of the Beta Alumina electrolyte was quite challenging but NGK succeeded in designing the electrolyte to realise high performance and in establishing the manufacturing process to assure its high quality. Because of the difficulty of development and mass production of Beta Alumina electrolyte, NGK is the only manufacturer of NAS technology.

Also NGK manufactures not only the Beta Alumina electrolyte but also NAS cells, modules and systems as containerised solutions in NGK’s own factory that has 150MW production capacity per year with well automated facilities.

It’s impressive that that 300MWh project in Japan was completed in six months. What are some of the challenges in executing a project that quickly?

NGK have developed the containerised NAS battery to achieve the quick turnaround requested by customers. The containerized NAS battery is incorporated with battery modules and controllers into the standard ISO container at NGK’s factory. The container size is 20 feet which is the most popular size. The container is easy to ship and unload at the site.

Previously, NGK delivered an “Enclosure type” solution and it was necessary to perform on-site assembly of the enclosure, battery modules and controllers. However, by incorporating these components in advance, the on-site assembly is streamlined and the construction period is shortened by one-third from previous designs.

There are several main uses for energy storage, including renewables integration and ancillary services. For which do you expect to see the most growth and demand for NAS batteries?

Since NAS batteries can store large amounts of electricity and can provide very fast response - within 1 millisecond of an electronic command, we think both uses have potential for NAS batteries. From a service provider's point of view, multiple revenue sources are a must-have condition to secure economic feasibility in energy storage projects. In this regard, we think a mixture of both uses is now common in the industry.

We often hear that microgrids using energy storage will be important in developing economies, where grids do not exist or are not reliable. What are the advantages of the NAS batteries in these settings?

NAS batteries can provide essential functions for smaller grids, such as microgrids, island grids, and grids in remote locations. These functions include support for higher levels of renewables, time shifting and stabilisation of wind and solar, voltage (VAR) support, frequency regulation, protection against frequency collapse during contingencies, black start energy and backup power. NAS batteries allow fossil and biomass generators to be operated at a fixed output setting that minimizes fuel use and emissions. With NAS batteries result is a greener grid with lower operating costs and higher reliability.

NAS batteries have been deployed in many different regions of the world. Which countries are the most exciting markets, and why?

The UK is definitely a leader. Obviously, the 200MW tender of Enhanced Frequency Response (EFR) services to the grid drew huge attention last year. It was a big moment for the battery storage industry. NAS batteries are always ready for future rounds of frequency response procurements and new services that might come in future. Ireland, Germany and Italy are exciting markets as well. In Ireland, wind curtailment is a potential opportunity for NAS batteries. In Germany, primary control reserve (PCR) is one of potential, and in Italy, the transmission system operator (TSO) is now running various kinds of battery storage systems including NAS batteries and we expect more to come.

In addition, Middle East has big potential for expansion of the NAS battery market. Solar PV continues to expand rapidly and the price of PV plants is getting drastically lower. We believe hybrid systems of solar PV and NAS batteries could be competitive solutions in this region.

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