Drivers of the energy transition: Fossil-free future through battery storage and Power-to-X

Migrating to photovoltaics and wind energy is only part of the way to the energy transition.  It is well known that some renewable energies can be volatile and therefore do not always provide a constant power supply. Against this background, storage systems and power-to-X technologies are essential building blocks on the way to climate neutrality, as they help stabilize the electricity grids and enable accelerated expansion of renewable energies. EnergyDecentral 2024, the leading trade fair for decentralized energy supply, will offer a comprehensive overview of current trends and developments. The exhibition will take place from 12 to 15 November, in Hanover, Germany in parallel with the EuroTier exhibition, which focuses on livestock technologies.

Against this backdrop, the key question posed at EnergyDecentral in November is: How much storage is needed for a successful energy transition? The International Energy Agency (IEA) assumes that a capacity of at least ten terawatt hours will be required by 2040 in order to achieve global climate targets. “As peak loads and the limited grid capacity of renewable energies are recurring issues, storage systems offer an excellent solution for driving forward their expansion,” says Marcus Vagt, project manager of EnergyDecentral, DLG (German Agricultural Society). Energy grid operators and solar and wind farms in particular have a high demand for buffering their energy volumes and feeding them into the grids at different times.

Hybrid power plants combine renewable power generation with battery systems at one location - a combination that contributes to grid stability and also offers a number of other advantages. “Generation and storage share the same infrastructure as well as the grid connection and can therefore be operated more economically,” explains Vagt. However, it is not only the large energy parks that are offered an alternative market model, for example when the German Renewable Energy Act (EEG) subsidy expires. In the early years of the energy transition, the main focus was on feeding electricity into the grid, but photovoltaics for self-generation is now an integral part of many producing farms. Without electricity storage, farmers often only use around 20 to 30 percent of their self-generated electricity; the rest is fed into the grid. An energy management system with storage helps them to optimize consumption and become self-sufficient.

Key players in mobile and stationary power supply

Batteries based on lithium-ion or lithium iron phosphate technology have established themselves on the market and are currently one of the most important pillars of the energy transition. They are the only way to make electromobility practicable. They combine a very high energy density with fast charging times. The disadvantage is that they lose capacity during charging, at low temperatures and over time. They are also questionable in view of the increased demand for valuable and increasingly scarce raw materials such as lithium and cobalt. Batteries with a sodium-based solid-state electrolyte could represent a promising alternative to established lithium-ion technology in the future, as sodium as a raw material is significantly more environmentally friendly, more readily available and cheaper than lithium.

A look at EnergyDecentral shows that there is not “the” one storage solution, but a variety of technologies. They make it possible to serve a wide range of applications - from power storage to capacity storage. Dr. Jan Girschik from Fraunhofer UMSICHT believes that redox flow batteries have an advantage here. The background: While the performance and storage capacity of conventional non-flow batteries such as lead-acid or lithium-ion batteries are in a fixed ratio to each other, these can be scaled independently of each other with redox flow batteries. The batteries can be recharged up to 20,000 times without loss of performance and the electrolyte is not explosive or flammable. This means that they can be operated for 15 to 20 years, which corresponds to the operating time of many wind and solar power systems.

Flow batteries as new beacons of hope

It is primarily vanadium flow batteries that are seen as the beacon of hope for the energy transition. Step by step, they are being developed towards the mass market. “They are primarily suitable for stationary energy storage and were developed by NASA in the 1970s with this aim in mind,” says Girschik, who heads the Battery Development Group at Fraunhofer UMSICHT. This is partly due to the relatively low energy densities of the electrolyte solutions in which the energy is chemically stored, but also “to properties such as deep discharge resistance and the almost non-existent self-discharge, which make the medium and long-term storage of large amounts of energy efficient in the first place.”

Girschik has optimized the fluid flow of the liquid storage media in the battery cells and developed design adjustments to the electrodes that can be adopted in already commercialized flow batteries with little conversion effort. As a result, he was able to reduce pressure losses in large-format vanadium flow batteries by up to 70 percent and prevent material-damaging deformations within the battery cells. The scientist hopes that this will make the provision of large-scale energy storage systems much more resource- and cost-efficient in future.

Improved sodium-sulphur batteries

Research into sodium-sulphur batteries (NAS batteries) is also becoming increasingly important as part of the energy transition. NAS batteries are stationary energy storage systems with a long service life and high energy content. They are used in various applications, such as stabilizing and optimizing the use of renewable energies, capping peak loads and load balancing as well as for emergency power supply.

One factor has hampered their economic use to date: they only work satisfactorily at temperatures above 250 degrees Celsius; at lower temperatures, too few charge carriers migrate from one pole to the other. A team led by Dr. Frank Tietz at Forschungszentrum Jülich has now found a way to ensure that enough charge carriers migrate even at room temperature. The researchers have significantly reduced the thickness of the electrolyte. In addition, the contact possibilities between the electrolyte and the two poles of sodium and sulphur have been optimized. “We have already achieved an energy density of around 46 watt hours per kilogram. Theoretically, a value of around 280 watt hours per kilogram would be possible with this cell structure,” says Aikai Yang, a doctoral student from China who developed the prototype. By comparison, current lithium-ion batteries have an energy density of between 100 and 250 watt hours per kilogram.

Green hydrogen for long-term storage

When it comes to the question of how renewable energy can be stored, however, it's not all about batteries at the exhibition grounds in Hanover. Other types of energy storage are necessary for the success of the energy transition and a functioning overall energy system. Hydrogen technology is one of the central key technologies for storing volatile renewable energies and for decarbonizing numerous sectors, particularly in the heat supply, transport and industry. With an extensive portfolio, the exhibitors at the trade fair grounds in Hanover provide solutions for the construction and operation of modules or entire plants along the H2 value chain. Industry experts and guests at EnergyDecentral will also be discussing the latest developments and trends in the field of hydrogen at the Expert Stage.

Due to its versatility, hydrogen is considered an important and forward-looking element of a decarbonized economy. However, it is only sustainable if it is obtained from renewable energies. “Green” hydrogen can be used to produce a climate-neutral fuel gas (power-to-gas) or a synthetic liquid fuel (power-to-liquid) by adding CO₂. The technologies known as Power-to-X (P2X) are therefore considered an important building block for an energy system based entirely on renewable sources. P2X complements existing storage technologies and makes it possible to store large amounts of energy in such a way that they can provide sufficient electricity and heat even during a dark doldrums.