Storage technology at RWE

Description

The large storage system was installed on open ground directly beside the Köpchenwerk pumped storage power plant, which was built in 1930 and is now a listed building. Synergies with the infrastructure of the pumped storage plant can be utilised on the grounds: Besides a medium voltage connection, an operational team with many years of experience in the intermediate storage of electrical energy and working with the technology used crews the location.

RWE commissioned the company BELECTRIC, a globally leading specialist in energy storage systems, for the design and construction. The Group drew on the technology and expertise of SAE for the telecontrol equipment and implementation of a control algorithm compiled inhouse for the charging and discharging control of the battery storage system. The result is an automated storage system, which provide a balancing power of up to 7000 kW at fluctuating network frequency by a an imbalance of feed-in and feed-out – all in a matter of seconds: If electricity is fed from the network into the battery, the transformer steps down the AC voltage to 330 V for the storage. The three converters of the system works as rectifiers, in this way converting the 3-phase AC voltage to DC voltage and charging the battery.

In each of the overseas shipping containers weighing 30 tonnes respectively, a total of 552 battery modules with 100 lithium-ion cells each from the automotive industry then store this energy. The battery modules are the core of the large storage system. If the battery is discharged again and the current flows back into the network, the converter convert the 900 V DC voltage back, with a total output of 7000 kW, back to AC voltage. The voltage for the medium voltage network is stepped up to 10 kV in the transformer. The battery storage system is connected to the network via a four-wire medium voltage switching station: The load flows proceed from and to the battery storage system via the transformer in three fields. One field contains the outgoing circuit to the medium voltage network.

Feed-in and feed-out management in relation to frequency

When RWE Supply & Trading markets primary balancing power, operation of the battery storage system is then oriented towards compensating the fluctuating loads cases and helping to stabilise the network effectively. To this end, charging and discharging commands must be realised taking into account the frequency for optimal network capacity utilisation and the optimal load factor of the battery. RWE has developed its own algorithm to automatically take account of these factors, which SAE IT-systems has integrated in the telecontrol software: The control therefore functions automatically but can also be realised ad hoc by the control centre, if required .

Communication in and with the storage system

The telecontrol from SAE IT-systems also forms the central communication node between the battery storage, central control station and power station application planning/ dispatch. Several remote terminal units of type net-line FW-5-GATE and FW-50 are used here.
The power station application planning/dispatch can remotely read out key parameters for the primary control output, the operating status if the battery, frequency data and the available input and output power and/or duration via the SAE telecontrol. This data can also be important for maintenance of the large storage system.
Thanks to the telecontrol connection, RWE can monitor and analyse yield data, technical and regulatory restrictions of the storage system, allowing it to respond to trends. An FW-5-GATE is used as a protocol converter for reliable disconnection of the IP networks for the process control of the energy management system and central control network of the RWE. This converts the IEC 60870-5-104 and IEC 60870-5-101 protocols bidirectionally, thereby generating a “serial gap” – a media break as an insurmountable hurdle for attacks from subordinate networks.

The available output of the battery storage system is reported at the transmission system operator Amprion and marketed by RWE Supply & Trading from Essen. Supply and demand on the primary control energy market can therefore be balanced.
RWE is also utilising the jointly developed telecontrol solution from SAE for the control in the following battery storage projects, like the system in Hoppecke.

“Storage technologies are the link between modern networks and volatile generation from renewable energies.”
Frank Amend, Management Belectric