With each percent more electricity generated from wind and solar power, it is becoming increasingly clear: more storage is required for the energy transition. In particular, different storage systems are needed – not just different types of batteries, but also hydrogen. This is the only way to offset fluctuations, cope with periods in which little to no energy is generated, and keep the network stable.
"Make hay while the sun shines." People have heeded this wisdom for many years. For example, around 11,000 years ago, our ancestors started to preserve grain and meat and to build up reserves for the winter and hard times. The first storage containers were made of ceramic; we now use granaries, cooling appliances, and canned goods. Today, we need to apply this wisdom to another important commodity: energy. Here, too, the aim is to store surpluses in order to compensate for subsequent bottlenecks.
We will have to contend with such bottlenecks in future, as our energy supply is changing. Until now, power plants have always generated enough energy to keep supply and demand in balance. However, we have primarily burned fossil fuels to achieve this and emitted harmful greenhouse gases into the atmosphere. To keep global warming below 2 °C, as outlined in the Paris Agreement, Germany is expanding its renewable energy supply. The aim is for renewable energy to account for 80 % of electricity consumption by 2030. In 2023, renewables accounted for more than half (52 %) of electricity consumption for the first time.
But wind and solar energy are volatile. They can neither supply energy at the push of a button nor constantly. “We have to be prepared for the fact that electricity generation will in future be less controllable and plannable than it is today. But with wind and solar power, we will always generate more energy than is actually needed at the time. We need to store this surplus to get through the night and periods where there is a lack of wind or sun as well as to keep the power grid stable in the short term. We therefore need more and different types of storage,” says Prof. Dirk Witthaut from the Institute for Climate and Energy Systems (ICE-1).
Battery storage systems are seen as the best technological and economic means of storing electricity generated from renewable sources efficiently and with as little loss as possible. During storage and subsequent reconversion into electricity, 80–90 % of the original energy is recovered. Battery storage systems already compensate for fluctuations in the power grid, thus ensuring a steady and stable electricity supply. This involves fluctuations in the seconds range as well as in the minutes and hours range. “These fluctuations also exist without renewables, but they may occur more frequently in future as a result of the renewable energy expansion, as there will be fewer conventional power plants that can provide energy at short notice with their generators and flywheels,” explains the grid stability expert.
However, Germany needs large capacities in order to achieve greenhouse gas neutrality by 2045 as planned. According to an analysis by the Institute of Climate and Energy Systems (ICE-2), around 156 gigawatt hours of electricity storage capacity is needed for short and medium-term electricity storage alone, i.e. for storing electricity in the seconds range right up to several days. Battery storage accounts for around 97 gigawatt hours of this, with the rest being provided by pumped-storage plants.
We are still a long way from achieving these figures. At the end of 2023, the capacity of the roughly 1.1 million stationary battery storage systems amounted to 11.6 gigawatt hours. Although in 2023 the number of newly installed systems in Germany doubled for the sixth time in a row, these are mainly smaller home storage systems with a maximum of 20 kilowatt hours that are being connected to the grid, i.e. storage systems for private photovoltaic systems. Large battery storage systems with over 1,000 kilowatt hours, such as those used by companies to secure their own energy supply and charge their own electric vehicles, have rarely been installed to date. Power grid operators require systems in the range of several megawatt hours. This can be used to compensate for major fluctuations, for example when a wind farm briefly generates significantly more electricity during strong gusts or the output of a large photovoltaic field drops because the sun is obscured by clouds.
Lithium-ion batteries are currently the dominant battery type on the market in all sizes – from small mobile electronic devices such as smartphones and batteries for electric cars to stationary electricity storage systems. Lithium-ion batteries are considered to be very efficient, have a high energy density, and a long service life. For Prof. Martin Winter, founding director of the Helmholtz Institute Münster (IMD-4, HI MS) and the MEET Battery Research Center of the University of Münster, this type of battery sets the benchmark. “And this relatively new technology is still a long way from reaching its optimum level,” emphasizes the battery expert.
Nevertheless, he believes it is wrong to focus only on this battery type: “Some requirements for stationary and mobile storage systems may be better met by other battery types that are not yet as technologically mature.” Competition also helps to keep prices low, Winter adds. “After a rapid price increase in 2021/22, the price of lithium has fallen again significantly. This is because sodium-ion batteries have now been declared ready for the market and are already being used in small electric car prototypes,” he explains.
However, sodium-ion batteries have a lower energy density. To store the same amount of energy as a lithium-ion battery, they have to be heavier and larger than the latter. But they have a further advantage: sodium is readily available, inexpensive, and is relatively environmentally friendly to extract by comparison. This is often not the case with lithium. There are fewer areas with large deposits of lithium and its extraction is viewed critically in many cases due to the associated environmental damage. This also applies to two other components that are used in both lithium-ion and sodium-ion batteries: nickel and cobalt.
Researchers at the Institute of Energy Technologies (IET-1) are therefore looking for new or improved active materials for the cathode of sodium-ion batteries, for example, which should use as little cobalt and nickel as possible. Such work fits in perfectly with the Federal Ministry of Education and Research’s umbrella concept for battery research. The concepts outlines that Germany must reduce its dependence on regions of the world, some of which are politically unstable, and achieve greater technological sovereignty when it comes to battery technologies. In order to achieve these goals, Prof. Winter believes that application-inspired basic research is essential. He is therefore critical of current cuts to battery research (see interview).
According to Winter, six criteria are crucial when selecting battery types: sustainability, cost, energy content, performance, service life, and safety. “The type of battery we should use is dependent on the criteria that a battery storage system needs to fulfil. With electric cars, for example, the focus is more on the volume and weight of the battery; with stationary batteries there is a greater focus on cost,” Winter explains. Scientists at the Helmholtz Institute Münster and at the institutes on the Jülich campus are therefore researching various types of batteries. These include lithium-ion and sodium-ion batteries, solid-state batteries, metal–air batteries, and redox flow batteries (see examples).
However, new battery storage systems alone will not be sufficient for the energy transition. “Batteries are needed to compensate for fluctuations in electricity consumption throughout the day or as a reserve for hours, or perhaps even a few days, but not for seasonal storage over weeks or even months. Other solutions have to be used in such cases,” Prof. Winter emphasizes.
Prof. Andreas Peschel, director at the Institute for a Sustainable Hydrogen Economy (INW-4), agrees: “We need batteries, but they are not suitable for bridging periods of several days in which little or no energy can be generated. They are also not suited to replacing current winter storage facilities for natural gas in a climate-friendly way.” Hydrogen-based solutions are particularly recommended for long-term energy storage. The electrical energy is converted into chemical energy by using it to produce hydrogen from water in electrolysis plants. The stored energy can be released again in fuel cells.
Hydrogen can be used directly as an energy carrier as well as a reaction partner in power-to-X technologies. These technologies convert electricity from renewable sources into fuels or raw materials for industry. Synthesis products such as methanol, ammonia, and special liquid organic compounds known as liquid organic hydrogen carriers (LOHCs) are particularly important here. They can be used to store energy at normal temperature and pressure, or at only slightly increased pressure, and their energy density per volume is significantly higher than that of pure hydrogen. “Such hydrogen carriers can be handled in a similar way to traditional fossil fuels and can be easily transported from overseas by ship, for example,” explains Peschel.
However, a lot of research and development work is still needed when it comes to hydrogen. Peschel and his colleagues at INW are working together with partners on innovative technologies that should enable the switch to hydrogen as an energy carrier. This should help make it easier to transport, store, and use hydrogen. The aim is to develop hydrogen-based solutions that are compatible with existing infrastructure. The researchers are also investigating how hydrogen can be recovered from chemical hydrogen storage and integrated into various applications, for example as a fuel or in the chemical industry.
This research forms part of the Helmholtz Cluster for a Sustainable and Infrastructure-Compatible Hydrogen Economy (HC-H2). In the cluster, INW and its partners seek to transform the Rhenish mining area into a hydrogen model region. At the beginning of March 2024, the first of several planned demonstration projects was put into operation: a fuel cell system from Robert Bosch GmbH at the Hermann-Josef-Krankenhaus (HJK) in Erkelenz. In combination with an LOHC storage technology that has yet to be installed, the system is expected to cover 20 % of the hospital’s electricity and heating requirements. “This is an order of magnitude that allows us to scale the technology for larger requirements and other applications, for example for industry and commerce,” explains Peschel.
Other Jülich institutes are also working on hydrogen and power-to-X technologies. Jülich experts are even putting the energy transition to the test on a small scale on their own campus. The findings of the Living Lab Energy Campus (LLEC) project are to be used as a blueprint for residential and industrial areas. Various storage technologies such as large batteries and hydrogen are used to combine electricity, heat, and chemical energy, for example. The mobility sector is also involved by using batteries from electric cars as intermediate storage. If many people succeed in making their electric cars available as energy storage for the public grids in future, it is likely that significantly fewer new stationary battery storage systems would need to be installed. Jülich researchers from ICE-2 estimate that electric cars could cover almost two thirds of the 97 GWh of battery storage capacity that is required by 2045. For this to be possible, however, regulatory hurdles for feeding electricity from the vehicle battery into the grid first need to be removed and attractive business models developed. There are still many unanswered questions here.
In principle, however, Jülich experts are clear on the fact that we need different storage technologies and more storage for a climate-neutral energy system. This can help to keep the power grid stable and nobody has to worry about being left in the dark during periods of little energy. And who knows, perhaps the electricity reserves in the cellar will become just as common for future generations as the freezer filled with peas, pizza, and bread rolls is for us today.
Text: Frank Frick/Christian Hohlfeld | images: Forschungszentrum Jülich/Ralf-Uwe-Limbach, Forschungszentrum Jülich/Sascha Kreklau; illustrations: Jens Neubert
