Sustainable energy storage systems could replace lithium-ion batteries
With growing concerns in the EU about China’s influence in the renewable energy sector, leaders are being cautioned against becoming overly dependent on Chinese lithium-ion batteries. As the EU aims to achieve net-zero emissions by 2050, it will increasingly rely on volatile renewable energy sources, significantly raising the demand for energy storage capacities.
The Group of Seven (G7) major industrial nations now plan to increase global electricity storage capacity by 6.5 times by 2030, according to a draft joint declaration by their energy ministers to promote renewable energy. Policymakers, industry leaders, and scientists face the challenge of successfully implementing this initiative.
A stable energy supply must be guaranteed at all times. Europe is expanding wind and solar parks, yet there is a lack of grid capacity to transport the electricity to where it is needed. Negative electricity prices arise in situations where the supply of electricity from renewable energies significantly exceeds the demand. Large-scale storage systems can shift the availability of electricity from periods of surplus to periods of shortage, thereby avoiding curtailment, especially of wind farms.
Lithium-ion batteries have long been considered the market-leading energy storage technology due to their high energy density. However, they are more performance-oriented than long-term capacity storage. Typically, lithium-ion batteries cannot store energy for much longer than eight hours. The future renewable energy system will be subject to significant fluctuations. No single storage technology can meet all needs alone. Therefore, a mix of technologies is required, with long-duration energy storage (LDES) gaining importance.
Long-term energy storage is gaining in importance
According to BloombergNEF, lithium-ion batteries will lose their market leadership in energy storage to newer technologies, some of which are already price-competitive. The average investment costs for thermal energy storage and compressed air energy storage are $232/kWh and $293/kWh, respectively. In contrast, lithium-ion batteries cost $304/kWh for systems with a runtime of four hours.
However, BloombergNEF notes that the costs for long-duration energy storage (LDES) are unlikely to decrease as rapidly as the costs for lithium-ion batteries this decade. This is because lithium-ion batteries are widely used in both the transportation and energy sectors, and these scaling effects will drive down the technology’s costs.
In Europe, long-duration energy storage (LDES) has better competitive chances for various reasons. These include cost considerations as well as issues of energy security. There is a focus on technologies that do not rely on lithium and China. Additionally, lithium is not inherently sustainable. When considering the entire value chain, the methods for extracting and processing lithium have significant ecological and social impacts. Furthermore, lithium batteries can occasionally ignite. Safety concerns are one reason why large energy providers are looking for energy storage systems that can operate for decades without the risk of a “dangerous event”.
Public net electricity generation in August 2023
A significant expansion of electricity storage could significantly reduce the investment pressure on expensive gas power plants and provide substantial added value for climate protection and the economy if the regulatory framework is right. This is demonstrated by a study commissioned by the companies BayWa r.e., ECO STOR, enspired, Fluence, and Kyon Energy at Frontier Economics. The main reasons are clear. They lie in saving fossil gas and avoiding CO2 and the corresponding CO2 costs. Additionally, there are marketing opportunities for storage and the provision of system services. With energy storage, existing grids can be better utilized, and future grid expansion can be significantly reduced.
In fact, Germany should have long since invested in pumped storage power plants. However, not a single new one has been connected to the grid since 2003. Pumped storage and hydrogen storage are well-suited for storing energy over very long periods, but they require an enormous amount of time and cost-intensive expansion. There are other long-duration energy storage (LDES) technologies such as thermal energy storage, compressed air energy storage, and redox flow batteries. While we are still in the early stages of commercialization with LDES technologies, China is already developing gigawatt-hour-scale projects, thanks to favorable political conditions.
New technologies based on pumped storage plants
New, sustainable approaches driven by startups worldwide are interesting. These durable systems operate without fossil fuels and chemicals and are relatively flexible in site selection.
- The energy storage system of Energy Vault® is based on the principle of gravity storage, similar to pumped storage systems. The system consists of a tall tower made up of a series of modular concrete blocks. These blocks are lifted and stacked using excess energy, thereby storing potential energy. When energy is needed, the concrete blocks are lowered by gravity. As they descend, they drive generators that convert the potential energy back into electrical energy. The entire process is controlled by specialized software. In the Jiangsu province of China, such a storage system with 25 megawatts / 100 megawatt-hours is scheduled to be operational in 2024. After the initial investment for construction and installation, the operating costs are relatively low, and there are no costs for chemical materials or complex recycling processes.
- Another idea comes from RheEnergise. RheEnergise uses a special fluid that is about two and a half times denser than water. The system consists of two reservoirs, an upper and a lower one, connected by pipelines. Like a pumped storage power plant, this system also utilizes the principle of gravity. Due to the higher density of the fluid used, the system can store more energy per unit volume than water. The higher density of the fluid also allows operation with smaller height differences between the reservoirs, which further facilitates site selection. The system has a lower ecological footprint and can be integrated into the natural landscape without major interventions.
- The energy storage system from Hydrostor is based on compressed air energy storage (CAES) technology. The Canadian start-up uses excess electrical energy from renewable sources to compress air in underground caverns or constructed reservoirs. During compression, the compressed air displaces water in the caverns, which is pumped into a separate reservoir. When energy is needed, the compressed air is released from the underground caverns. The released air is directed through a turbine, which converts the kinetic energy of the expanding air into electrical energy. The water displaced during energy storage flows back into the caverns when the compressed air is released, closing the cycle. Hydrostor has improved the traditional CAES system by integrating water displacement and using modern technologies to increase efficiency.
- The energy storage system from Rondo Energy stores energy in the form of heat instead of electrical energy. This heat is stored in special, high-temperature-resistant materials such as bricks. Excess energy from wind or solar power is used to heat the storage materials to high temperatures of up to several hundred degrees Celsius. When energy is needed, the stored heat can be utilized in various ways depending on the application. The heat can be directly fed into industrial processes that require high temperatures. Alternatively, the heat can be used to generate steam, which drives turbines and is thus converted back into electrical energy. The system has a high efficiency since electrical energy is directly converted into and stored as heat. Heat losses are minimal, and the storage materials have a long lifespan. The technology can be scaled for various applications, from small industrial processes to large power plants.
- The energy storage system developed by the team at the Massachusetts Institute of Technology (MIT) uses an innovative combination of supercapacitors and carbon cement. Electrical energy is stored in an electric field. An electrolyte between two layers of carbon cement stores the energy. During charging, ions accumulate at the electrodes in the electrolyte, creating an electric field. During discharging, the ions flow back, and the stored energy is released. Because the material is so strong, it could be used as part of the concrete foundation of buildings. A 3.5-meter-wide block of the material could store about 10 kWh of energy, which is equivalent to the average daily electricity consumption of a household.
- Northvolt’s Treepower energy storage system is an innovative concept that uses biomass and other organic energy storage materials from sustainable sources. These materials are used to produce electrodes and other components for batteries. These cells have similar properties to conventional batteries but have a smaller environmental footprint. The use of biomass and organic materials reduces dependence on rare and environmentally harmful raw materials such as lithium or cobalt.
The further development and testing of these sustainable storage concepts will be crucial to optimize the technologies and increase their market acceptance. The benefits of these systems are clear: if they work, they could surpass lithium-ion batteries in many applications. The German government is increasingly focusing on gas power plants and hydrogen as energy storage solutions.
It remains to be seen which energy storage technologies will ultimately prevail.
Doris Höflich, Market Intelligence Senior Expert
Sources:
- Fachzeitschrift Recharge
- PV Magazin
- BloombergNEF Research
- Frontier Economics
