The need to store electrical energy from renewable sources for use when a fixed power source is unavailable has led to many technological developments in the design of batteries over the years.
Sodium-sulphur (NaS) batteries are long-duration stationary batteries for many large-capacity grid applications. NaS provides superior functions and performance features possible only 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, need sophisticated and innovative technologies to stabilize the grids, avoid congestions and transmission deferral. Renewable energy plants require stable long-lasting storage technology that can cycle energy on a daily basis.
The rise of renewables
Concerns about burning fossil fuels to power our networks and the global commitment to CO2 targets have driven the demand for electricity generation from clean renewable energy sources, which has resulted in the acceleration of developments in biomass, PV, hydro- and wind-powered generation. Efficiencies have improved dramatically, and these “clean” technologies can now be used at utility-scale to power the networks.
The need for stationary batteries
However, the amount of electricity from renewable energy sources varies according to the weather and daytime. Power from a PV panel falls significantly when a cloud moves between the sun and the panel, and disappears completely at sunset. Wind turbines generate power while the wind is blowing, but if the wind falls – or blows too hard – the output is reduced. To provide a continuous and reliable supply of electricity, engineers design batteries to store surplus electricity while the sun shines and the wind blows for use after sunset or when the wind drops.
A better option
NaS technology has long been a standard choice for utility-scale batteries with installations dating back to 2000 still in operation. Offering significant advantages over competitive technologies, NaS batteries have a high energy density, offer high charge/discharge efficiency, long cycle life and long service life. NaS batteries are made from inexpensive, environmentally benign materials, and are recyclable post-operational life. NaS batteries can even be used as peakers, in place of diesel or gas-fired generators, because they can 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.
Lower environmental impacts
Unlike many other rechargeable batteries, which are made from rare and volatile materials, NaS batteries are built from environmentally benign materials and are easily and safely disposed of, and potentially recyclable post-operational life. NaS batteries also offer higher energy and longer life than other technologies do for certain utility-scale applications.
How do NaS batteries work?
NaS batteries are high-temperature batteries operating at between 290 and 340°C. They use a solid electrolyte, which is unique among the common secondary (i.e. rechargeable) cells. One electrode is molten sodium and the other molten sulphur. The chemical reaction between them produces an electric current.
Stationary NaS batteries are extremely useful in electric power grids where they 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 can also be useful for back-up in the event of power outages since 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 6 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 life span.
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 4000 MWh globally. This gives NaS batteries a longer proven track record than any other utility-scale battery technology, and up until 2018 NaS was the world’s most specified utility battery technology from a single supplier.
For more information on NaS batteries, contact Aaron at Altum Energy (firstname.lastname@example.org)