For the energy transition, Germany is dependent on high-performance battery storage systems to provide electricity even when there is no wind and in the dark. However, the immense number of individual battery cells that are wired into these systems increases energy losses. Researchers in the KV-BATT project at the Faculty of Electrical Engineering at Dortmund University of Applied Sciences and Arts want to reduce these losses by increasing the voltage by a factor of ten to twenty.
A brief digression back to school days: electrical power describes how much energy is required in a certain period of time. It is stated as watts on every appliance. The voltage is specified by the socket, which in this country is 230 volts. This can then be used to calculate the strength of the current flowing through the cable. Amperage is power divided by voltage. With a 900-watt vacuum cleaner plugged into a socket, almost 4 amps of current flow.
"If twice the voltage were to come out of the socket - i.e. 460 volts - the current for the vacuum cleaner would only be 2 amps," calculates Prof. Dr. Stefan Kempen. He teaches electrical power engineering at Fachhochschule Dortmund and brings another decisive factor into play: resistance. "I can never get rid of it completely. Even a well-conducting copper cable has a small resistance," explains Prof. Kempen. And the higher the current, the higher the losses due to the resistance.
Resistance causes losses
None of this is a problem with vacuum cleaners. However, high-performance battery storage systems today have outputs of up to 100 megawatts - i.e. 100 million watts. Their voltage is around 1000 volts. According to the formula (power divided by voltage = amperage), currents of many thousands of amperes are generated. "Even the smallest resistors then generate enormous losses - twice over," says Prof. Kempen. This is because electricity is lost, which is released in the form of heat. As a result, the battery storage units have to be cooled. "This in turn requires new energy," explains Prof. Kempen.
The solution sounds easy: "We have to increase the voltage in order to minimize the losses - because the higher the voltage, the lower the current, the lower the loss," says Prof. Dr. Martin Kiel. He also teaches at the Faculty of Electrical Engineering and has driven the KV-BATT project forward with Prof. Kempen. Together, they now want to increase the voltage in the battery storage system by a factor of at least 10, perhaps even 20.
To this end, a real laboratory is currently being built in the Sauerland municipality of Ense in collaboration with the local municipal utilities. Two battery storage systems - one with the classic voltage of 1000 volts and one with a voltage of 10,000 to 20,000 volts.
"We will then not only see lower losses, but will also be able to test under real conditions how the high voltage affects the service life of the batteries and how we can improve the balance of the individual battery cells with good battery monitoring," says Prof. Kiel.
At the same time, standards and rules for the insulation distances between live parts are to be defined. While these have long been clarified for both direct current and alternating current up to around 1500 volts and have also been tested for overhead cables with more than 100,000 volts, there are no standards for direct voltage at medium voltage levels. "At 10,000 and 20,000 volts, rules for insulation are largely unknown," says Prof. Kempen. The design of suitable direct current switches is also not yet sufficiently defined.
Years of preparatory work
In recent years, the researchers at Fachhochschule Dortmund have already carried out a large number of calculations, developed their own modular battery storage assembly and successfully tested it in the university's own high-voltage laboratory under various environmental conditions ranging from temperature to humidity. "Now we want to finally test this system in the real laboratory," says Prof. Kiel. At the end of this year, the foundations should be in place on an industrial estate in Ense-Höingen. The real-world laboratory will then go into operation for two years in 2026.
The UAS researchers are confident that their approach will herald a small revolution in battery storage systems. This is because their modular assembly is significantly more compact than conventional systems thanks to its higher voltage and therefore lower resistance, does not require active cooling thanks to lower heat loss and should enable virtually maintenance-free operation. The modules can be easily connected in series in order to be adapted to the respective power requirements. The European patent procedure is running parallel to the real laboratory.
Background
The "KV-BATT-SYST(Opens in a new tab) " project is the follow-up project to "KV-BATT-TECH(Opens in a new tab) ", in which Fachhochschule Dortmund University of Applied Sciences and Arts developed the fundamentals of high-performance battery storage. In addition to Prof. Kempen and Prof. Kiel, the Fachhochschule Dortmund research team also includes research assistants Vanessa Steinkötter, Florian Leßmann and Marvin Sommer. Ense Werke GmbH, AEG Power Solutions from Warstein and WEISSGERBER Engineering from Dortmund are also involved in the practical test in the real laboratory. The project is funded by the Ministry of Business Studies, Industry, Climate Protection and Energy of the State of North Rhine-Westphalia.