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Technology

Battery storage – securing the renewable energy supply

As the third pillar of renewable power generation, battery storage systems are indispensable for the use of new energies. Lithium-ion batteries from various manufacturers are used for this purpose, which can draw and store electricity directly from the power grid. The battery technology has been tried and tested over decades and is safe and reliable. Space-saving and optionally with visual protection, they are an integral part of the energy transition in Germany.

The challenge

Wind power and photovoltaic systems generate renewable electricity, but not at the same time as consumption. If the quantities of electricity generated do not exactly match the quantities of electricity consumed, the frequency in the power grid changes. As this frequency determines the rotational speed of the motors, it must remain constant at 50 Hz. If this does not work, the temporal imbalance in energy generation leads to wind turbines being switched off and to negative electricity prices on the exchanges. This is why battery storage is urgently needed as the third pillar of renewable energy supply.

The business basis

Battery Energy Storage Systems (BESS ) are electricity storage systems with voltage converters that can absorb and feed in electricity from the grid extremely quickly. This is done automatically by frequency measurement and control pulses to the inverters, which operate in the millisecond range. The climate-compliant battery energy storage systems compensate for power fluctuations in the grid and stabilize the frequency.

This electrical service is remunerated by the high-voltage grid operators TSOs such as TenneT GmbH. There are six daily auctions for this service, which are remunerated on a monthly basis. There is also a second business model for battery energy storage systems: electricity volumes are bought when electricity prices are negative and sold again when prices are positive. This trading takes place in the intraday trading segment.

The technology

At its core, a battery energy storage system consists of three components:

The battery consists of many battery cells with approx. 3.5 volts, which are connected together to form a battery module. Battery modules are often in a 19 inch device and are grouped together in a rack. Several battery racks are placed in a container and interconnected to the corresponding DC voltage, e.g. 1,000 volts DC. This is the input voltage for the inverter.

The inverter is the component that generates alternating current at a frequency of 50 Hz from the battery voltage – or converts alternating current (AC) into direct current (DC) in order to charge the battery.

The grid connection connects the system to the power grid. The inverters are connected via small 690 volt/20 kV transformers to a switch panel in a coupling station. From there it goes to a transformer station with 20/110 kV, which connects the control power to the high-voltage grid.

The battery

The containers are filled with battery racks containing battery cells from various manufacturers in Europe and Asia. Battery cells can be used for both mobile (e-cars) and stationary applications. We are manufacturer-independent and work with the best manufacturers in order to provide our customers with a good, reliable product.

The battery cells do not contain acid or other liquids, but consist of metal alloys and minerals. In the construction approval process, the substances are tested again for possible effects on the environment. The materials are mainly lithium, cobalt, manganese and nickel oxide to approx. 70 % and graphite, carbon, aluminum, copper.

The inverter

The bidirectional inverters are available in air-cooled or water-cooled versions. They are produced by well-known international manufacturers from the PV industry. We are also manufacturer-independent for this component.

The inverters consist of a separate metal housing that is mounted in a frame in the container. Live parts of the inverter are appropriately encapsulated and covered to prevent contact. The inverter units are suitable for outdoor installation.

The EMS energy management system, which communicates with the BMS battery management system and thus regulates the charging and discharging of the battery in order to stabilize the frequency, is used for control and regulation without the need for personnel. The marketer for the PRL service and trading on the intraday market has a 24/7 control room.

The grid connection

The grid connection is planned and installed by a specialized company with a license for medium and high voltage. Here, too, we are manufacturer-independent, even though we have been working with the same company for 30 years. This company has already built more than 120 substations in Germany and is responsible for the maintenance and servicing of more than 80 substations.

The infrastructure company is responsible for the foundations, including pile foundations if required, the construction roads, laying the cables, installing the transformers, connecting all components, installing the fence and creating a hedge.

We are constructing the entire battery energy storage system with two companies.

Emissions

During operation of the battery energy storage system, no air pollution occurs. In the planning permission process, all substances are tested for possible effects on the environment and noise tests are carried out.

Substances hazardous to water

The transformers used are filled with a special insulating oil and equipped with collecting basins.
The BESS systems can be installed in water protection areas.

A current project