As energy storage becomes an increasingly integral part of a renewables-based system, interest in and discussion around non-lithium (and non-pumped hydro) technologies increases. A team of experts from CENELEST, a joint research venture between the Fraunhofer Institute for Chemical Technologies and the University of New South Wales take a deep dive into redox flow batteries.
In the last 15 years, the increase in renewable energy sources such as photovoltaic and wind energy has accelerated significantly. At the same time, manufacturing and installation costs, especially for PV systems, have fallen significantly, making this energy source one of the cheapest and cleanest forms of energy, depending on the location. With the increase of fluctuating renewable energies in an electrical grid, the need for compensation possibilities at times when renewable energies are not available increases . One possibility is the use of electrochemical energy storage such as lithium-ion, lead-acid, sodium-sulphur or redox-flow batteries. Additionally, combinations of hydrogen electrolysis and fuel cells can be used . Batteries can be adapted in a flexible and decentralised manner depending on the respective requirements and are scaleable from a few kW/kWh for e.g. domestic storage up to systems of several MW/MWh for grid storage. The different types of electrochemical energy storage systems have different physical/chemical properties, which affect the cost of the system. It is important to note that the cost of the storage system over its lifetime (levelised cost of storage – LCOS) is a critical factor used in selecting the most suitable system for a particular application . For example, the investment costs for lead-acid batteries are significantly lower than for all other technologies, but the service life is very short.
Technologies with similar investment costs at higher lifetimes result in a lower levelised cost of storage, but to be precise additional factors such as recycling, energy efficiency and maintenance costs have to be considered. A battery with a high efficiency, low recycling effort, low investment and maintenance costs and great freedom of scalability to meet the requirements of the application would be an ideal system. In electrical networks there are different storage time requirements: short-term storage, medium-term storage and long-term storage. The shorter the storage time, the more suitable are physical storage devices such as capacitors. Batteries are suitable for applications ranging from a few minutes to several hours. In addition, mass storage systems such as electrochemical hydrogen generation (power-to-gas) are particularly suitable for long-term storage of several weeks.
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