Batteries central to future grid storage

Batteries are set to play an increasing significant role in future grid energy storage

By Morand Fachot

Electricity is consumed as it is generated, supply must be reliable and demand must always be met. This requires spare capacity that can be ramped up rapidly and, ideally, storage. Utility-scale storage capabilities are still limited mainly to pumped hydro, but this is changing with the emergence of a new generation of advanced batteries that allow for storage on the grid. Standardization work by IEC TC (Technical Committee) 21: Secondary cells and batteries, is central to the future development of large-scale energy storage for the electric distribution network.

A123 systems nanophosphate EXT™ grid storage solution (Photo: A123 systems)
A123 systems nanophosphate EXT™ grid storage solution (Photo: A123 systems)

Current storage limitations

The characteristics of electricity generation, distribution and use are very specific. Electricity being consumed as it is produced there must be sufficient supply to meet variations in demand. At times of peak demand extra capacity must be available to respond rapidly. If demand cannot be met, the stability and quality of the power supply suffer and may result in brownouts or worse.

To balance demand and supply additional generation in necessary and a certain amount of storage may also be available, currently mainly in the form of pumped hydro, which makes up the bulk of electricity storage. However significant pumped storage might be, additional EES (electrical energy storage) sources are needed in the future.

The IEC works extensively on developing standards for EES technologies to provide safe and stable energy supply and to integrate electricity from intermittent renewable sources into the overall distribution grid.

Advanced batteries are set to play a major role in the future global EES landscape and in grid management. A May 2014 report from Navigant Research forecasts that the annual energy capacity of advanced batteries for utility-scale energy storage applications will grow at a CAGR of 71% from 2014 through 2023, from 412 MWh in 2014 to more than 51 200 MWh in 2023.

Fresh prospects from the new generation

A new generation of advanced safe, low-cost and efficient enough batteries to allow for storage on the grid has paved the way to the first instances of large-scale energy storage for the electric distribution network. However this introduction is still limited to high-value applications like frequency regulation and demand charge mitigation, according to clean technology markets consulting company Navigant Research. Navigant estimates that global revenue from next-generation advanced batteries, which include Li-ion (lithium ion), sodium metal halide, NaS (sodium sulphur), advanced lead-acid and flow batteries, will grow from USD182,3 million in 2014 to USD9,4 billion in 2023.

Finding the right chemistry for the right use

IEC TC 21 lists the key areas of battery standardization as SLI (starting, lighting, ignition) also named “starter” batteries, which supply electric energy to motor vehicles; automobile hybrid/electric vehicle cells; traction batteries; and the stationary batteries of the VRLA (valve-regulated lead-acid) type also known as sealed or maintenance-free batteries.

Beside stationary applications, VRLA batteries are used also in motorcycles and certain types of cars to reduce the risks of acid spilling. Lead-acid batteries are a proven and widespread technology and are still the preferred storage system to assure decentralized electric power in emergencies and in applications such as UPS (uninterruptible power systems).

Latest research in the stationary lead-acid battery market indicates a CAGR (compound annual growth rate) of 6,8% over the 2010-2017 period, with little threat from competing technologies during this period.

Nickel-based batteries, such as NiCd (nickel cadmium), introduced around 1915, and NiMH (nickel metal hydride) in service 80 years later, have a higher power density and a slightly greater energy density than lead-acid batteries. They are used in both stationary applications and in consumer electronics where they are being replaced in many cases by Li-ion and where NiCd batteries are being phased out on environmental ground. NiMH batteries are also extensively used in hybrid vehicles.

Li-ion is the primary chemistry used in batteries for consumer electronics, medical and defence applications, it is also emerging as a leading chemistry in utility-scale applications of batteries on the grid. The main advantage of Li-ion batteries is a very high energy density, but their main drawbacks are cost and safety issues (like overheating) that require constant monitoring.

To prepare International Standards for rechargeable batteries used in RE storage, TC 21 and TC 82: Solar photovoltaic energy systems, set up a JWG (Joint Working Group), JWG 82: Secondary cells and batteries for Renewable Energy Storage.

Let the current flow

TC 21 has broadened its scope to include technology and chemistry for flow batteries, which are starting to be deployed in the market and, as such need international standardization regarding performance, performance tests and safety.

Flow batteries are rechargeable batteries in which electroactive chemical components dissolved in liquids (electrolytes) stored externally in tanks are pumped through a membrane that converts chemical energy into electricity.

To develop standards for flow batteries that cover safety, performances, installation, terminology and other necessary requirements, TC 21 set up JWG 17: Flow battery systems for stationary applications, with IEC TC 105: Fuel cell technologies, as flow batteries and fuel cells share certain characteristics.

TC 21 current approved new work programme includes the development of International Standards for "flow battery systems for stationary applications" that cover general aspects, terminology and definitions, performance general requirement and method of test, and safety requirements.

The first ever grid-connected flow battery storage solution for use with renewables, a 50 kW EnStorage Inc. HBr (hydrogen-bromine) system providing up to 100 KWh of energy, was connected to a test site in southern Israel in April 2014.

A very broad remit

If the development of International Standards for batteries deployed in EES systems for utility-scale applications is currently attracting much interest, the performance and other characteristics of batteries used in a broad range of domains, such as consumer electronics, transport or medical equipment, are also the focus of a lot of attention (see e-tech May 2012 article on batteries for mobile devices and applications).

All International Standards for rechargeable cells and batteries, irrespective of type or application, or of size, from the tiniest cell to the largest array of batteries installed in EES systems, are prepared by IEC TC 21. These Standards cover all aspects depending on the battery technology, such as safety installation principles, performance, battery system aspects, dimensions and labelling.

Given the central role batteries play in so many systems and applications, a world without TC 21 standardization work for batteries is no longer conceivable.

A123 systems nanophosphate EXT™ grid storage solution (Photo: A123 systems) A123 systems nanophosphate EXT™ grid storage solution (Photo: A123 systems)
This 50 kW HBr flow battery system provides up to 100 KWh of energy (Photo: EnStorage Inc) This 50 kW HBr flow battery system provides up to 100 KWh of energy (Photo: EnStorage Inc)
8 MW Li-ion battery grid storage system in New York State (Photo: AES Corporation) 8 MW Li-ion battery grid storage system in New York State (Photo: AES Corporation)