Transmission system operator TenneT and Daimler AG through its wholly owned subsidiary Mercedes-Benz Energy GmbH have researched and tested the feasibility of innovative system services in the transmission grid as part of a joint development partnership.
The results are groundbraking: Automobile battery storage systems can take over tasks from large-scale power plants and make a significant contribution towards power grid stabilisation and system recovery.
The joint study was carried out within the framework of the Enera project as part of the “Smart Energy Showcases – Digital Agenda for the Energy Transition” (SINTEG) funding programme by the German Federal Ministry for Economic Affairs and Energy. The project partners have shown that automobile battery storage systems that use a lithium-ion basis can be used for highly dynamic system support and system recovery – specifically for a black start in power plants and to support mass inertia. Ultimately, this can help to compensate for the loss of conventional energy generation.
For the development partnership, the prototype of a battery storage system made up of automotive batteries with a total connected load of approx. 1 megawatt (MW) and a storage capacity of 750 kilowatt hours (kWh) was installed at the test centre in Kamenz. These are second-life and replacement batteries.
Electricity production is becoming considerably more volatile due to the increasing in-feed of weather-dependent forms of renewable energy. In the power grid, generation and consumption need to be balanced in order to maintain a frequency of 50 Hertz. If this is not the case, frequency deviations can occur.
The masses of large-scale power plants, which rotate in synchronisation with the grid frequency of 50 Hertz, ensure that these fluctuations are dampened so that the system responds to these deviations in a more inert way. This is important, as frequency deviations can only be compensated with a delay through primary balancing power. Without the inert masses in the grid, the frequency would change so quickly that no compensation through balancing power would be possible. This would lead to ever-greater frequency deviations, which in the worst-case scenario could cause power failures.
At the Mercedes-Benz Energy test lab in Kamenz, the project partners have now shown that automobile battery storage systems can respond to a changing frequency in less than 100 milliseconds. This means they can replace the inert masses in large-scale power plants.
The project partners have also shown that battery storage systems can be used to start up energy generating assets and even entire power stations, for example after a large-scale power failure. Today, diesel power units are used to restart turbines in power stations (rotating masses) and supply power to auxiliary units. The development study shows that this can also be done with battery storage systems – with virtually no losses and in a process that is much better for the environment. The energy storage system acts as a kind of “starter battery for the energy supply” and restarts the inert rotating masses of a power station. The necessary energy, around 2-4% of the rated capacity of a power station, is retrieved from the energy storage system if needed. To prove this, the project partners constructed a test grid in Kamenz and restored it after a simulated power failure using the automobile battery storage system.
In the next phase of the development partnership, the project partners will work together to define the requirements that will enable a tender process for the future system service by TenneT.