The environmental friendliness and low generation cost of renewable energies – such as wind and solar energy – means their use is increasing worldwide. The amount of energy produced by these sources generally fluctuates; i. e. due to weather conditions, the generation capacities vary considerably over short periods of time, and also seasonally. The higher the share of wind energy and photovoltaics in an electrical grid, the greater the bottlenecks in supply.
Ultimately, the most sustainable option for avoiding supply bottlenecks is storage facilities that feed energy surpluses back into the grid at times when the performance of renewable energy sources is low. Time periods from milliseconds to minutes (short-term), hours to days (medium-term) and days to weeks (long-term) must be compensated.
Mechanical, electrical and electrochemical processes can be used for storage. All these processes have been established on a large scale for decades, but have specific technological advantages and disadvantages. Mechanical storage facilities are pumped storage facilities, for example, which are inexpensive and reliable, but which have a major impact on nature, are usually bound to geological formations and therefore cannot be used in a completely decentralized manner. Electrical storage devices such as capacitors have very low energy densities and are particularly suitable for high performance and short storage times.
Electrochemical storage devices such as double-layer capacitors, batteries and fuel cells can cover the entire required time range and are also highly modular, scalable and can be used decentrally. For all storage facilities, the levelized cost of energy is of particular interest in addition to investment and operating costs, which is why long service life and low investment costs also enable low energy costs. Although significant cost reductions for electrochemical technologies have been achieved in recent years, this type of storage is currently usually too expensive (compared to fossil energy sources) for a broad range of stationary applications but has the potential for further cost reductions.