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Although other options exist, lithium-ion batteries are becoming the preferred way to store energy from renewable energy sources, helped by standards from the International Electrotechnical Commission (IEC).
One of the constant problems with renewable energy sources, such as wind power or solar PV, is that they have excess supply when the sun is shining or the wind is blowing, but can cause electricity shortages when the sun is setting or the wind is dropping. The way to overcome the intermittency of wind and solar power is to store it when there is excess supply for later use, or when there is a shortage.
Several technologies are used to store renewable energy, one of which is pumped hydro. This form of energy storage accounts for more than 90% of the current high-capacity energy storage on the planet. Electricity is used to pump water to reservoirs at higher altitudes during periods of low energy demand. When demand is higher, the water is routed through turbines at lower altitudes and converted back into electricity. Pumped storage is also useful for controlling voltage levels and maintaining power quality on the grid. It is a proven system, but it has drawbacks.
Hydropower projects are large and expensive, with prohibitive capital costs, and they have demanding geographic requirements. They need to be located in mountainous areas with an abundance of water. If the world is to meet net-zero emissions goals, it needs energy storage systems that can be located almost anywhere and at a large scale. IEC standards ensure that hydropower projects are safe and efficient. IEC Technical Committee 4 publishes a range of standards that specify hydro turbines and associated equipment. IEC Technical Committee 57 publishes core standards for the smart grid. One of its key standards, IEC 61850, specifies the role of hydropower and helps it interoperate with the power grid as it becomes digitalised and automated.
Lithium-ion batteries are getting better
Batteries are another obvious solution for energy storage. At the moment, lithium-ion batteries are the preferred choice. Utilities around the world have been increasing their storage capacity with super-sized lithium batteries – huge packs that can store 100 to 800 megawatts (MW) of energy. The Moss Landing energy storage facility in California is one of the largest in the world, with a total capacity of 750 MW/3,000 MWh.
Lithium batteries have dropped dramatically in price in recent years and have become capable of storing ever-increasing amounts of energy. Many of the advances in lithium batteries are due to the automotive industrys race to make smaller, cheaper and more powerful lithium batteries for electric cars. The power produced by each lithium-ion cell is about 3.6 volts (V). This is higher than standard nickel-cadmium, nickel-metal hydride and even standard alkaline batteries at about 1.5 V and lead-acid at about 2 V per cell, so fewer cells are needed in many battery applications. Lithium-ion cells are standardized by IEC TC 21, which publishes the IEC 62660 series on lithium-ion secondary cells for electric vehicle propulsion. TC 21 also publishes standards for renewable energy storage systems. The first, IEC 61427-1, specifies general requirements and test methods for off-grid applications and electricity generated by photovoltaic modules.
The second, IEC 61427-2, does the same but for grid applications, with power input from large wind and solar farms. “The standards focus on the proper characterisation of battery performance, whether it is used to power a vaccine storage fridge in the tropics or to prevent blackouts on nationwide power grids. These standards are largely chemically agnostic. They allow utility planners or end customers to compare apples to apples, even when dealing with batteries of different chemistries,” says Herbert Giess, an expert at TC 21.
IEC TC 120 was specifically created to publish standards in the field of grid-integrated electrical energy storage (EES) systems to meet grid requirements. An EES system is an integrated system with components, which may be already standardised batteries. The TC is working on a new standard, IEC 62933-5-4, which will specify safety test methods and procedures for lithium battery-based energy storage systems. IECEE (IEC System of Conformity Assessment Schemes for Electrotechnical Equipment and Components) is one of four conformity assessment schemes administered by the IEC. This scheme tests the safety, performance, interoperability of components, energy efficiency, electromagnetic compatibility (EMC) and hazardousness of batteries.
Concerns about safety and recycling
However, the disadvantages of using lithium batteries for energy storage are multiple and fairly well documented. The performance of lithium-ion batteries degrades over time, limiting their storage capacity. Issues and concerns have also been raised about recycling batteries, once they can no longer fulfil their storage capacity, as well as about sourcing the lithium and cobalt needed. Cobalt, in particular, is often mined informally, including by children. One of the main producers of cobalt is the Democratic Republic of the Congo. The challenge of energy storage is also being addressed through projects of the CIS Global Impact Fund. Li-ion recycling is one of the aspects being studied.
Finally, Li-ion is flammable and a significant number of Li-ion battery energy storage plants in South Korea caught fire between 2017 and 2019. While the causes have been identified, particularly poor installation practices, there was a lack of awareness of the risks associated with Li-ion, including thermal runaway.
IEC TC 120 has recently published a new standard that looks at how battery-based energy storage systems can use recycled batteries. IEC 62933-4-4 aims to “review the potential environmental impacts of reused batteries and define appropriate requirements.”
New battery technology
Other battery technologies are emerging, such as solid-state batteries, or SSBs. According to B2B consultancy IDTechEx, these are becoming the front-runners in the race for next-generation battery technology. Solid-state batteries replace the flammable liquid electrolyte with a solid-state electrolyte (SSE), which offers inherent safety advantages. SSEs also open the door to the use of different cathode and anode materials, expanding the possibilities for battery design. While some SSBs are based on li-ion chemistry, not all follow this path. The problem is that true BLUs, with no liquid at all, are a long way from being brought to market, even though they seem a promising alternative at some point in the future.
According to IDTechEx, the adoption of SSBs faces challenges such as high capital expenditure, comparable operating costs and high price. Clear value propositions must be presented for public acceptance. SSBs, even if they contain small amounts of liquid or gel polymers, may be accepted by the market as long as they offer the desired performance. Hybrid semi-solid batteries could provide a transitional path and offer better performance. In the short term, hybrid SSBs, which contain a small amount of gel or liquid, may become more common.
The race for the next generation of batteries is on. Although there are no standards for these new batteries yet, they are expected to emerge when the market requires them.
Author: Catherine Bischofberger
The International Electrotechnical Commission (IEC) is a global, non-profit organisation that brings together 174 countries and coordinates the work of 30,000 experts worldwide. IEC international standards and conformity assessment underpin international trade in electrical and electronic products. They facilitate access to electricity and verify the safety, performance and interoperability of electrical and electronic devices and systems, including, for example, consumer devices such as mobile phones or refrigerators, medical and office equipment, information technology, power generation and much more. |
