One of the persistent problems with renewable energy sources, such as wind energy systems or solar photovoltaics, is that there is an oversupply when the sun shines or the wind blows, but can lead to electricity shortages when the sun sets or the wind falls. The way to overcome the variability of wind and solar energy is to store it when there is an oversupply, for later use, or when there is a shortage.
Various technologies are used to store renewable energy, including pumped hydropower. This form of energy storage accounts for more than 90% of the world’s current high-capacity energy storage. Electricity is used to pump water to reservoirs at higher altitudes during periods of low energy demand. When demand is greatest, the water is passed through lower turbines and converted back into electricity. Pumped storage is also useful for controlling voltage levels and maintaining power quality in the electrical grid. It is a proven system, but there are disadvantages.
Hydropower projects are large and expensive, have prohibitive capital costs and have demanding geographic requirements. They should be located in mountainous areas with an abundance of water. If the world is to achieve net-zero emissions goals, it needs energy storage systems that can be located virtually anywhere and at scale. IEC standards ensure that hydropower projects are safe and efficient. IEC Technical Committee 4 publishes a series of standards specifying hydraulic turbines and associated equipment. IEC TC 57 publishes core standards for the smart grid. One of the most important IEC 61850 standards specifies the role of hydropower and helps it work with the electricity grid while digitalizing and automating it.
Li-ion batteries are getting better and better
Batteries are one of the obvious other energy storage solutions. For now, lithium-ion batteries are the favored option. Utilities around the world have been ramping up their storage capabilities using super-sized lithium batteries, huge packs that can store anywhere from 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.
The price of lithium batteries has fallen dramatically in recent years and they are capable of storing increasingly large amounts of energy. Much of the profits generated by these batteries are due to the auto industry’s race to build smaller, cheaper and more powerful lithium batteries for electric cars. The power produced by each lithium-ion cell is approximately 3.6 volts (V). It exceeds that of standard nickel-cadmium, nickel-metal hydride, and even standard alkaline cells by about 1.5 V and lead-acid by about 2 V per cell, requiring fewer cells in many battery applications. Li-ion cells are standardized by IEC TC 21, which publishes the IEC 62660 series on secondary Li-ion 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 PV modules.
The second, IEC 61427-2, does the same, but for applications on the electricity grid, with energy input from large wind and solar farms. “The standards aim to properly characterize battery performance, whether used to power a vaccine storage refrigerator in the tropics or to prevent power outages in national power grids. These standards are largely chemistry agnostic. They allow utility planners or end customers to compare apples to apples, even if different battery chemistries are involved,” says TC 21 expert Herbert Giess.
IEC TC 120 was specifically designed to publish standards in the field of grid-integrated electrical energy storage systems (EES) to support grid requirements. An EES system is an integrated system with components, which can be batteries that have already been standardized. 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 systems operated by the IEC. It carries out a program that tests the safety, interoperability of performance components, energy efficiency, electromagnetic compatibility (EMC) and hazardous substances of batteries.
There are concerns about safety and recycling
However, the disadvantages of using lithium batteries for energy storage are numerous and quite well documented. The performance of Li-ion cells degrades over time, limiting their storage capacity. Issues and concerns have also arisen over the recycling of the batteries once they can no longer fulfill their storage capacity, and the required sourcing of lithium and cobalt. Cobalt in particular is often mined informally, including by children. One of the major producers of cobalt is the Democratic Republic of Congo. The challenge of energy storage is also being addressed through projects in the IEC Global Impact Fund. Recycling li-ion is one of the aspects that is being considered.
Finally, Li-ion is flammable and a significant number of power stations that store energy with Li-ion batteries in South Korea burned down between 2017 and 2019. Although the causes have been identified, particularly poor installation practices, there has been a lack of awareness of their consequences. the risks associated with li-ion, including thermal runaway.
IEC TC 120 recently published a new standard that looks at how battery-based energy storage systems can use recycled batteries. IEC 62933-4-4 aims to “assess the potential impact on the environment due to recycled batteries and define appropriate requirements.”
New battery technology
Other battery technologies are emerging, including solid-state batteries, or SSBs. According to B-to-B consultancy IDTechEx, these will be the frontrunners in the race to the next generation of battery technology. Solid state batteries replace the flammable liquid electrolyte with a solid state electrolyte (SSE), which offers inherent safety benefits. SSEs also open the door to the use of different cathode and anode materials, expanding the possibilities of battery design. While some SSBs are based on Li-ion chemistry, not all follow this path. The problem is that real SSBs, without any liquid, are still far from market introduction, even if they appear to be a promising alternative at some point in the future.
According to IDTechEx, SSB adoption faces challenges including high capital expenditure, comparable operating costs and premium pricing. Clear value propositions must be presented to gain public acceptance. The market can embrace SSBs even if they contain small amounts of liquid or gel polymers, as long as they provide the desired properties. Hybrid semi-solid batteries could provide a transition route and better performance. In the short term, hybrid SSBs, which contain a small amount of gel or liquid, may become more common.
The race is on for the next generation of batteries. While there are no standards yet for these new batteries, they are expected to emerge when the market demands them.
Author: Catherine Bischofberger
The International Electrotechnical Commission (IEC) is a global non-profit membership organization that unites 174 countries and coordinates the work of 30,000 experts worldwide. International IEC standards and conformity assessment are the basis of international trade in electrical and electronic goods. They facilitate access to electricity and verify the safety, performance and interoperability of electrical and electronic devices and systems, including, for example, consumer equipment such as mobile phones or refrigerators, office and medical equipment, information technology, electricity generation and much more.
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