Energy supply security could hardly be a more pressing concern for nations everywhere right now. But even before the Iran war, the situation was becoming acute as more of the world’s energy generation shifts from fossil fuels to renewables.
Oil, natural gas and coal may be finite resources but they can be stored in their natural state while energy generated by solar and wind systems are infinite but require a long duration energy storage (LDES) solution to keep supply and demand in balance across the grid, as a result of their intermittency.
A world of renewables
The share of renewables in global electricity generation is expected to expand from 32% in 2024 to 43% by 2030, while the share of variable renewable energy (VRE) sources is set to almost double, reaching 28%, according to the International Energy Agency (IEA). At the same time global electricity demand is on course to grow at least 2,5 times as fast as overall energy requirements through to 2030, by which time renewables and nuclear will generate half of all electricity supply.
The IEA highlights grid congestion as “a critical bottleneck” in many regions, “slowing the deployment of new electricity generation, storage and demand.” The organization also stresses that meeting the increasing demand for electricity requires annual investment in grids to rise by 50% by 2030, with storage of “an increasingly weather-dependent mix of power generation sources” a priority.
What are the existing storage solutions?
Two principal technologies for energy storage are already in operation. Pumped hydro and battery energy storage systems (BESS) are seen by investors as pivotal low-carbon systems that complement renewable energy assets.
With pumped hydro, water is pumped uphill when energy is cheap and released to drive turbines and generate power when energy is expensive. It remains the only technology capable today of storing gigawatt (GW), let alone terawatt (TW) hours. Many nations have opted to either modernize and reinvest in existing systems, such as this example in Wales, or are planning entirely new projects. A proposed development in Scotland would more than double Great Britain’s existing electricity storage capacity and, if it gets the go-ahead, would be the first large-scale pumped storage project in the country for more than 40 years.
Yet conventional pumped hydro is not suitable for countries that lack mountainous geography or large water reservoirs. (For more on the disadvantages of large hydro projects, read The potential of small hydropower | IEC e-tech) In these situations, lithium-ion batteries are the preferred form of energy storage. But there are disadvantages to using batteries too. Traditional lithium-ion batteries are limited by capacity (typically 4–6 hours) and lifespan caused by constant charge-discharge cycles.
“Batteries have improved dramatically, but struggle to scale to the levels required for national grids,” says Tony Sample, Chair of IEC TC 82, the technical committee which develops standards for solar photovoltaic (PV) systems. “Longer-term storage solutions – such as hydrogen – will be essential, particularly for sectors like aviation where electrification is impractical.”
Widely used for many applications, lithium-ion batteries have other disadvantages, including their reliance on critical minerals and the risk of thermal runaway. Consequently, the search for new or enhanced LDES is moving at pace. Each approach comes with trade-offs in cost, efficiency, and scalability.
According to Christian Noce, Chair of IEC TC 120, the IEC technical committee which prepares standards for electrical energy storage (EES) systems, “an EES system is highly complex with multiple subsystems and components. That’s why IEC TC 120 adopts a system‑level approach to create a common framework for grid‑connected EES systems that makes design, operation, and safety more consistent and more efficient.”
The pros and cons of flow batteries
Flow batteries are a type of rechargeable battery that uses two different chemical solutions (electrolytes) to store energy. These electrolytes are stored in external tanks. The technology is scalable as the energy storage capacity can be increased by augmenting the size of the tanks. It is also safer than lithium-ion, with no risks of explosion.
Valued at USD 1,22 billion in 2026, the global market for the technology is projected to hit USD 2,88 billion by 2034. Current commercial flow batteries are based on vanadium and zinc-based chemistries. Future commercial deployments include projects in Sweden, while construction is underway on Europe’s largest flow battery at Laufenburg, Germany, capable of over 1,6 GWh storage capacity and an output exceeding 800 MW.
A novel type of flow battery has been developed in the Netherlands and makes use of a saltwater solution that produces acid and a base fluid when charged and then stored in separate reservoirs. One Aquabattery is claimed to last for 20 years and store energy for up to 100 hours. But flow battery technology requires a high initial investment in tanks and electrolytes and provides low energy density compared to Lithium-ion. (For more on the pros and cons of redox flow batteries, read: Go with the flow: redox batteries for massive energy storage | IEC e-tech).
Is compressed air energy storage a contender?
Although compressed air energy storage, or CAES, is a technology currently used at only two sites worldwide, there are plenty of projects in the pipeline, including in Germany, Arizona and South Australia, as well as the UK.
CAES works by compressing ambient air and storing it under pressure underground using surplus or off-peak power. During peak power times, the air is heated and therefore expands. This in turn drives a turbine, generating power that can be exported to the grid. CAES systems can store and produce power on average for 8 hours up to 12 hours. Variants include Advanced CAES and Liquid CAES. According to this paper in ScienceDirect, however, several drawbacks are hindering the technology’s wider adoption, ranging from high capital costs and site-specific restrictions, to regulatory processes.
Thermal energy storage is underused
Thermal energy storage technologies are being commercially deployed, including at Ciudad Real in Spain. The plant, under construction, will use a closed-loop system of molten salts and steam. The salt transfers heat to water to produce superheated steam which then flows through a steam turbine to produce electricity on demand. The developer claims this will provide LDES from 8 hours to 8 days and that the solution is scalable to large-scale deployment of 300 MW and beyond. Another claim is that the system has a lifespan of 25 to 35 years without degradation.
Thermal energy storage is also one of the main selling points of concentrated solar power (CSP) systems. These plants store excess heat energy gathered during the day (For more on the potential of CSP for energy storage, read Concentrating solar power for cheap energy storage | IEC e-tech).
The Noor solar plant in southern Morocco, which claims to be the world’s largest CSP facility, has a generation capacity of more than 580 MW – enough to provide electricity to more than 1,1 million Moroccans even after sunset. One of the disadvantages of CSP thermal energy storage is the high initial cost to build a facility. Building and maintaining concentrating solar collector fields in harsh, often desertic conditions is too often more expensive than other forms of renewable energy like solar PV energy and wind. Despite this, researchers say the CSP market is experiencing robust expansion and growing at 8,3% a year to reach USD 5,4 billion by 2034.
Hydrogen is becoming an option
Renewable energy can also be converted into hydrogen for longer term storage via electrolysis. An advantage of hydrogen is that it can be used as a fuel in its own right, for powering aviation and shipping, for example, or converted back into electricity. Hydrogen can also be stored and transported in liquid ammonia form making it particularly suitable for transportation over long distances, according to researchers at Fraunhofer.
Unlike lithium-ion batteries, hydrogen can be stored in large quantities for extended periods without significant energy losses. Furthermore, so called green or low-carbon hydrogen, produced using renewable electricity via electrolysis, presents an “especially compelling” case as it supports both decarbonization and energy security. But the cost of electrolysis and the lack of existing infrastructure remain a problem. (For more on low-carbon hydrogen, read How can hydrogen decarbonize industry? | IEC e-tech)
Technology agnostic and future-proof standards
Even though battery energy storage was the most commercially mature technology when IEC TC 120 began its work in 2012, the committee has purposefully built system‑level standards that can accommodate any EES storage technology, including pumped hydro, flow batteries and more. It develops standards that fall under five key areas: terminology (published as IEC 62933‑1); unit parameters and testing methods (IEC 62933‑2); planning and installation (IEC 62933‑3); environmental considerations (IEC 62933‑4) and safety (IEC 62933‑5).
“The important point is that the efficiency of a storage system depends not only on the particular technology but on the system architecture,” Noce explains. “A lithium‑ion cell in a phone or car may last a few hundred cycles before the user replaces the device. In a grid‑connected storage system, that same chemistry must deliver several thousand cycles. The system context changes everything.”
Specific international standards for flow batteries are developed by IEC TC 21 which produces standards for secondary cells and batteries. The IEC 62932 series specifies the performance of flow batteries for stationary applications and testing electrolyte for vanadium flow batteries.
The TC also develops standards for the safety and performance of lithium cells, as well as for the repurposing of, say, lithium-ion batteries initially used for EVs, in energy storage systems. In 2024 it published IEC 63330-1, which provides general requirements for the repurposing of secondary cells, modules, battery packs and battery systems, that are originally manufactured for other applications such as EVs.
Testing and certification plays an important role in the safety and performance of batteries. One of the IEC four conformity assessment systems administered by the IEC, IECEE (the IEC System for Conformity Assessment Schemes for Electrotechnical Equipment and Components) offers a broad certification service portfolio that includes battery safety, battery performance, battery safety when installed in end products, energy efficiency, EMC and hazardous substances.
Innovation in the field of energy storage is rapid, with proposals for standardizing new kinds of storage technologies received by the IEC every day. Noce says, “If standards are written too narrowly around today’s technologies, they become barriers for the technologies of tomorrow. The challenge is to remain technology agnostic. That is essential if we want to avoid creating obstacles for future innovation.”
As a result, the IEC looks fit and ready to tackle future requirements in this very innovative sector.
Author: Adrian Pennington
The International Electrotechnical Commission (IEC) is a global, not-for-profit membership organization that brings together 174 countries and coordinates the work of 30.000 experts globally. IEC International Standards and conformity assessment underpin international trade in electrical and electronic goods. They facilitate electricity access and verify the safety, performance and interoperability of electric and electronic devices and systems, including for example, consumer devices such as mobile phones or refrigerators, office and medical equipment, information technology, electricity generation, and much more.
