EWE is planning to build a battery storage facility with a capacity of 120 megawatt
The Lower-Saxony-based utilities provider and network operator EWE is planning to build a saltwater redox flow battery in a salt cavern. When finally completed, the massive storage facility will be able to provide a major city like Berlin with power for an entire hour.
The EWE gas storage facility in the East Frisian community of Jemgum/ @ EWE
The energy supplier and network operator EWE, which is based in the Lower-Saxon city of Oldenburg, wants to use so-called salt caverns in Lower-Saxony to house a massive redox flow battery. These salt caverns are cavities in the massive layers of salt that are located under the ground there. Up to now, such caverns have been used to store strategic reserves of oil and gas. The caverns are created by first drilling a borehole from the surface, water is then pumped in and a part of the rock salt is then washed out. This is relatively inexpensive. The spaces that are created in this way can be several hundred metres high and up to 60 metres wide.
In the future, these cavities will also be used to store green electricity that is not immediately used. Up to now, however, such cavities have only been considered as compressed air reservoir or as storage space for electrolytical hydrogen that has been produced using excess green electricity. These kinds of cavities offer the perfect conditions for such a facility as they are by and large air and water tight. This type of storage is complex, however, and in particular then requires a generator once again with which to convert the previously stored mechanical or chemical energy into electricity.
Polymers swim in salt water
The development of a saltwater battery by the scientists at the Friedrich-Schiller University Jena led the Oldenburg-based company to the idea to no longer convert the electricity into mechanical and chemical energy beforehand, but to instead store it directly as electrochemical energy. This has been made possible by the fact that the researchers in Thuringia have further developed the previous concept with the saltwater operated redox flow battery.
While the concepts that have been available on the market up to now still use lithium and graphite as anode and cathode materials, the researchers in Jena have focussed on using polymers dissolved in saltwater. This approach is fundamentally similar to the structure of plexiglass and polystyrene, which are respectively complemented with functional units, allowing them to absorb or emit electrodes. “What is new about our battery system is that it is significantly cheaper to manufacture, but still reaches almost the same capacity and performance as traditional metal- and acid-based systems”, says Martin Hager, who, in joint cooperation with Ulrich S. Schubert and Tobias Janoschka, developed the principle of the new battery.
The use of affordable membranes
A further aspect is that the plastic particles are contained in an aqueous sodium chloride solution. Sodium chloride is, in turn, the primary component of rock salt, in other words the material that the layers of salt consist of. This means that such salt caverns can be directly used to create these redox flow batteries. The pipes in which the two electrolyte liquids are contained could then simply be installed in the borehole that has already been drilled as it is, an aspect that further drastically lowers the price for this type of energy storage facility.
The technology used also suppresses the price. This is because, on the one hand, – as is the case in the vanadium redox flow storage facilities – no more expensive and also environmentally hazardous heavy metals are used for the electrolyte. On the other hand, these heavy metals are also not dissolved in aggressive media such as sulphuric acid. The sulphuric acid has the result that in the stack of the redox battery, where the exchange of electrodes takes place, specialised and expensive separators need to be installed. The saltwater batteries in contrast only require inexpensive cellulose or fleece membranes.
The redox flow battery in the salt cavern is intended to store solar and wind energy that cannot be used immediately and then give off this energy again at a later time when required. This means that an expansion of the grid is not required/ @ EWE
Only suitable for large-scale applications
However, up to now this technology exists only as a prototype. The containers for the electrolyte are roughly the size of a rain barrel. A lot of research work is still necessary in order to achieve the size that is being striven for with such a salt cavern. That being said, these prototypes reach up to 10,000 charging cycles without any significant loss of capacity. However, the energy density of the system is still extremely low at ten watt-hours per litre. The researchers in Jena are nevertheless already working on a larger and better performing solution.
This is still not a significant problem, however, as the battery is not intended for mobile use and there is a lot of space in the salt caverns, which means that the energy density does not play a decisive role. The amount of power that a storage facility of this kind can contain – that consists of two medium-sized caverns – is sufficient to provide a city with a multi-million population like Berlin with enough electricity for an hour”, calculated Peter Schmidt, Managing Director of EWE Gasspeicher. The wholly-owned subsidiary of the Oldenburg-based utilities provider is responsible for the entire project, because they already operate eight such salt caverns in which natural gas is stored.
The battery generating plant should be in place by 2023
The first step does, however, look relatively humble. The Oldenburg-based company will first use large plastic containers into which the electrolytes are filled and which are connected to a battery via a stack. EWE will erect these containers before this year is out on the grounds of the gas storage facility in Jemgum in East Friesland, in order to test this technology on a large scale. “We still have a number of tests to carry out and quite a few issues that still need clarifying until we will be able to use the storage principle in underground caverns in accordance with the research work done at the University of Jena”, states Ralf Riekenburg, who is responsible for the overall project at EWE, when explaining the slight detour taken. “But I am assuming that we can have a cavern battery in operation by the end of 2023.”
When everything functions, the energy storage market and the market for control energy could be fundamentally altered, something of which the Managing Director Peter Schmidt is convinced. This is because the storage facility will not only help to regulate short-term fluctuations in the energy supply grid, but also supply energy over a longer period of time, in case energy derived from photovoltaic systems and wind farms is insufficient. The researchers have at least achieved an energy density of 100 milliamperes per square centimetre, which is sufficient to quickly take energy out of the grid system and store it or feed it back into the grid when required, which is especially necessary for the provision of control energy. Such large storage facilities can even solve the energy grid problems that those regions are battling with in which many large solar power plants and wind turbines are currently located. This solution on a large scale also has the potential to be very inexpensive compared to lithium-ion battery power stations.
The future of our energy supply requires a change of approach, as global energy needs are growing and reserves of fossil fuels are limited. At the same time, greenhouse gas emissions need to be severely reduced if a drastic climate change is to be counteracted.
In order to meet these requirements, it is necessary to strike an intelligent balance between energy conservation, energy efficiency and expanding the use of renewable energy sources. To do this, closely knit systems are needed that are able to provide electricity and heat flexibly, efficiently and as directly as possible.
EWE is the first Group to focus definitively on this trend and which supplies energy in such a sustainable way across all core competencies.