Customer application
Intelligent Control of a Battery Swarm

The “SchwarmSpeicher Allgäu” swarm battery system stabilizes the low voltage network in and around the Bavarian town of Kempten. For monitoring and controlling the distributed storage systems, egrid, the specialist for intelligent distribution grids, relies on WAGO controllers, due to flexibility, reliability and service quality.

The concrete box the size of a garage, located among multi-family units, tennis courts and swimming pools to the west of Kempten, could be a conventional local network transformer station. But what’s hiding behind the metal door is neither a transformer nor a medium voltage switchgear, but 36 lithium ion battery packs, stacked to form a black wall – one of five large batteries spread throughout the greater Kempten area that the local network operator, AllgäuNetz, uses to ensure the stability of the distribution network.

And that is necessary, since, as in many other regions, the low voltage network in Kempten and the surrounding areas has come under significant pressure in recent years. The reason: the significant increase in feed-in of electricity from renewable energies. A clear example is the number of days on which electricity on the medium voltage level was fed back: Until a few years ago, this was very rare, but since 2017 it has already occurred more than a hundred times.

Intelligent Network Hardening

But now, instead of laying new lines at great cost, the network operator has decided to invest primarily in intelligent measures for hardening the existing grid – above all in a system of distributed storage batteries. This battery system supports the local grid with sophisticated algorithms, as well as communication, measurement and control technology from WAGO. The batteries, each with a capacity 500 kilowatts, were installed specifically where a great deal of electricity is fed into the grid and withdrawn again with a time delay.

The swarm storage system, christened “SchwarmSpeicher Allgäu,” went online at the end of 2017. The design, planning and operation of the battery system were handled by egrid applications & consulting GmbH, a joint venture of Allgäuer Überlandwerke and Siemens specializing in consulting services related to the design of intelligent distribution networks.

36 lithium ion battery packs, stacked to form a black wall: The local network operator, Allgäuer Überlandwerke, uses a total of five of these large batteries spread throughout the greater Kempten area to ensure the stability of the distribution network. For management of the swarm storage system, egrid relies on multi-purpose operation. This makes it possible to exploit different earnings sources. “The most important function of the system is to supply primary control power. We generally also support the local network with this,” explains egrid Managing Director Bernhard Rindt. Furthermore, the storage systems occasionally absorb peaks that arise during grid use. The battery packs also serve as an emergency power system. This allows the network operator to invest less money in procuring and operating diesel generator sets, which normally handle this.

With the right energy management framework, even more operating modes will be possible in the future – for example in the context of “Demand Side Management” (DMS) or providing reactive power.

Better Together

Why did egrid create a system of storage batteries with intelligent control instead of installing isolated large batteries? “The swarm storage system offers a series of advantages right away. For example, it is much easier to keep the individual batteries at the optimal state of charge of forty to sixty percent. To do this, the system preferentially activates whichever battery is right at the upper or lower limit of this range,” explains Rindt. Furthermore, it is easier to get a handle on the heat build-up of the batteries in the system, which extends their lifespan. And last but not least, the availability increases: If one of the battery packs is no longer working properly, or maintenance work needs to be performed, the four remaining storage systems can make up the capacity shortfall.

The individual plants are monitored and controlled from a control room that is staffed around the clock. Both negative and positive control energy are provided automatically according to the frequency deviations, which are measured on site. However, egrid has also implemented additional control algorithms to ensure that the batteries are kept at the optimal state of charge by exploiting degrees of freedom. If the storage systems are to be used for capping peak loads in the grid, the system is operated from the control center in an alternative operating mode.