SUPERIOR TECHNOLOGY Stationary energy storage

Sodium-sulphur (NaS) batteries are used for many large-capacity grid applications as the NaS battery system boasts unrivaled function and performance, which has been made possible from decades of research, design, testing, demonstration, advanced manufacturing and over 20 years of proven commercial operation. Energy storages for stationary applications provide additional power for spinning reserve and energy for peak-shaving. Sophisticated technologies are needed to stabilise grids and to elude congestion as well as transmission deferral.

The Better Option

Offering significant advantages over competitive technologies, NaS batteries have a high energy density and charge/discharge efficiency, as well as a long cycle and service life. These batteries can be used as peakers, in place of diesel or gas-fired generators, because they supply reliable power for six hours at a time. This application saves money and offers the utility carbon tax savings due to the elimination of gas or diesel exhaust. The batteries are built from environmentally benign materials and are easily and safely disposed of.

HOW DO THEY WORK?

NaS batteries operate at high temperatures between 290°C and 340°C. They use a solid electrolyte, which is unique among the common secondary (ie rechargeable) cells. One electrode is molten sodium and the other molten sulphur. The chemical reaction between them produces an electric current.

Specific Benefits

Stationary NaS batteries meet specific requirements for reliability of power supply and voltage stabilisation on power grids. As such, they can provide power stored up from off-peak times to meet peak demand, effectively adding capacity on the grid (peak-shaving). They are useful for back-up in power outages as they offer a steady supply of current for an exceptionally long time. When used in a microgrid, NaS batteries offer both storage and smoothing of output from variable renewable energy sources.

Typical NaS battery units are housed in a 20ft standard sea freight container and are equipped with six large NaS modules, an airconditioned control cabinet with the Battery Management System (BMS) and are ready for easy installation and DC-voltage connection to the Power Conversion System (PCS). The total number of NaS containers depends on the power and capacity requirements, lifetime and load profile of the application. Typically, the charge/discharge efficiency in the 85% range provides efficient use of energy, with slow linear degradation over an extended lifespan.

NaS battery systems have been deployed for over 20 years, at more than 200 projects worldwide, with a total installed capacity of more than 580MW and 4 000MWh globally.

The Longevity And Brevity Of Batteries

A battery’s value is in its lifespan – the longer it lasts, the higher the return on investment will be (as replacement costs are not added over the total project period). The battery lifespan should match the optimal financial period of a project. Specifying a battery without an established lifecycle is a risk, which may have financial implications. Battery degradation affects the performance and lifespan of a battery and it may need to be replaced.

ENERGY VS POWER

Energy batteries are used in applications that require a reliable, longterm supply of power at the rated output (eg mobile phones laptops. Power batteries provide short bursts of high-power energy and are found in automotive, industrial, and rapid-charge applications.

HIGH-ENERGY OR HIGH-POWER DENSITY?

Energy storage systems that have a high-energy density store a lot of energy in a smaller amount of mass. High-energy density does not mean high-power density. A system with a high-energy and low-power density operates for a relatively long period (eg a mobile phone’s battery power will last for most of the day before it requires a recharge.)

High-power density systems provide large amounts of current based on their mass (eg a tiny supercapacitor may have the same power output as a large battery but due to its size, it will have a higher-power density. High-power density systems recharge faster as their energy release is faster (eg a camera flash needs to be small to fit inside a camera but requires a higher-power output for the flashtube.)

Performance And Reliability

Storage technologies vary, they are not commodities, so their application, lifespan, risk factors must be well understood before an investment is considered.

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