The pros and cons of batteries for energy storage

The time for rapid growth in industrial-scale energy storage is at hand, as countries around the world switch to renewable energies, which are gradually replacing fossil fuels. Batteries are one of the options.

One of the ongoing problems with renewables like wind energy systems or solar photovoltaic (PV) power is that they are oversupplied when the sun shines or the wind blows but can lead to electricity shortages when the sun sets or the wind drops. The way to overcome what experts in the field call the intermittency of wind and sun energy is to store it when it is in oversupply for later use, when it is in short supply.

Various technologies are used to store renewable energy, one of them being so called “pumped hydro”. This form of energy storage accounts for more than 90% of the globe's current high capacity energy storage. Electricity is used to pump water into reservoirs at a higher altitude during periods of low energy demand. When demand is at its strongest, the water is piped through turbines situated at lower altitudes and converted back into electricity. Pumped storage is also useful to control voltage levels and maintain power quality in the grid. It's a tried-and-tested system, but it has drawbacks. Hydro projects are big and expensive with prohibitive capital costs, and they have demanding geographical requirements. They need to be situated in mountainous areas with an abundance of water. If the world is to reach net-zero emission targets, it needs energy storage systems that can be situated almost anywhere, and at scale.

IEC Standards ensure that hydro projects are safe and efficient. IEC Technical Committee 4 publishes a raft of standards specifying hydraulic turbines and associated equipment. IEC TC 57 publishes core standards for the smart grid. One of its key IEC 61850 Standards specifies the role of hydro power and helps it interoperate with the electrical network as it gets digitalized and automated.

Li-ion batteries are improving

Batteries are one of the obvious other solutions for energy storage. For the time being, lithium-ion (li-ion) batteries are the favoured option. Utilities around the world have ramped up their storage capabilities using li-ion supersized batteries, huge packs which can store anywhere between 100 to 800 megawatts (MW) of energy. California based Moss Landing's energy storage facility is reportedly the world’s largest, with a total capacity of 750 MW/3 000 MWh.

The price of li-ion batteries has tremendously fallen over the last few years and they have been able to store ever-larger amounts of energy. Many of the gains made by these batteries are driven by the automotive industry's race to build smaller, cheaper, and more powerful li?ion batteries for electric cars. The power produced by each lithium-ion cell is about 3,6 volts (V). It is higher than that of the standard nickel cadmium, nickel metal hydride and even standard alkaline cells at around 1,5 V and lead acid at around 2 V per cell, requiring less 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 the propulsion of EVs. TC 21 also publishes standards for renewable energy storage systems. The first one, IEC 61427?1, specifies general requirements and methods of test for off-grid applications and electricity generated by PV modules. The second, IEC 61427-2, does the same but for on-grid applications, with energy input from large wind and solar energy parks. “The standards focus on the proper characterization of the battery performance, whether it is used to power a vaccine storage fridge in the tropics or prevent blackouts in power grids nationwide. These standards are largely chemistry agnostic. They enable utility planners or end-customers to compare apples with apples, even when different battery chemistries are involved,” TC 21 expert Herbert Giess describes.

IEC TC 120 was set up specifically to publish standards in the field of grid integrated electrical energy storage (EES) systems in order to support grid requirements. An EES system is an integrated system with components, which can be batteries that are already standardized. The TC is working on a new standard, IEC 62933?5?4, which will specify safety test methods and procedures for li-ion battery-based systems for energy storage.

IECEE (IEC System of Conformity Assessment Schemes for Electrotechnical Equipment and Components) is one of the four conformity assessment systems administered by the IEC. It runs a scheme which tests the safety, performance component interoperability, energy efficiency, electromagnetic compatibility (EMC) and hazardous substance of batteries.

Concerns raised over safety and recycling

However, the disadvantages of using li-ion batteries for energy storage are multiple and quite well documented. The performance of li-ion cells degrades over time, limiting their storage capability. Issues and concerns have also been raised over the recycling of the batteries, once they no longer can fulfil their storage capability, as well as over the sourcing of lithium and cobalt required. Cobalt, especially, is often mined informally, including by children. One of the most important producers of cobalt is the Democratic Republic of Congo. The challenge of energy storage is also taken up through projects in the IEC Global Impact Fund. Recycling li?ion is one of the aspects that is being considered.

Lastly, li-ion is flammable and a sizeable number of plants storing energy with li?ion batteries in South Korea went up in flames from 2017 to 2019. While causes have been identified, notably 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 which looks at how battery-based energy storage systems can use recycled batteries. IEC 62933?4?4, aims to “review the possible impacts to the environment resulting from reused batteries and to define the appropriate requirements”.

New battery technology

Other battery technologies are emerging, including solid state batteries or SSBs. According to B?to?B 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 benefits. SSEs also open the door to using different cathode and anode materials, expanding the possibilities of battery design. Although some SSBs are based on li?ion chemistry, not all follow this path. The problem is that true SSBs, with no liquid at all, are very far from market launch, even if they look like a promising alternative at some point in the future.

According to IDTechEx, “The adoption of SSBs faces challenges, including high capital expenditure, comparable operational costs and premium pricing. Clear value propositions must be presented to gain public acceptance. The market may embrace SSBs, even if they contain small amounts of liquid or gel polymers, as long as they deliver the desired features. Hybrid semi-solid batteries could provide a transition route, offering improved performance. In the short term, hybrid SSBs, containing a small amount of gel or liquid, may become more common.”

The race is on for the next generation of batteries. While there are yet no standards for these new batteries, they are expected to emerge, when the market will require them.

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