Grid operators need to do more than simply distribute the electricity generated by wind farms and photovoltaic plants. They also have to ensure a consistent quality of supply. Achieving this with the available systems and components is a complex issue.
Not all electricity is the same
Wind power and photovoltaics play a major role in the generation of electricity. Such energy facilities are frequently based at decentralised locations in rural regions. However, it takes a complex system of distribution networks and transformer stations to deliver sustainably produced electricity all the way to the consumer.
Solar power plants, for instance, feed the direct current they generate directly into the medium-voltage and low-voltage network via power converters, which transform it into alternating current. However, the conversion process produces harmonic currents that distort the voltage, impairing the signal in the distribution network and therefore the quality of the electricity, which in turn can have a significant impact on the functioning of equipment and machines.
Combined in a single system
Network operators provide system services to ensure the quality of the electricity they provide. These services are supplemented by energy held in reserve to offset unforeseen additional requirements at short notice. The energy reserves are then replenished during performance peaks. However, operators have to date made use of the required systems only as individual elements.
Researchers working under the lead of TU Dortmund have now combined system services and energy reservoirs in a hybrid compensation system. ‘The aim of our project is to extend the potential fields of application of battery storage systems and reduce the number of facilities needed to provide system services,’ explains Ralf Böhm, research associate at the Institute for Factory Automation and Production Systems (FAPS), whose team designs the important control technology that joins the system’s individual components together to form a whole.
The system is equipped with a flywheel energy storage system and a battery in addition to a freely adjustable current converter that can influence the form of voltage signals. Flywheel energy storage systems are used to make major quantities of energy available at short notice while a so-called redox flow battery – a complex liquid chemical battery – with its high capacity is ideal for storing energy over the long term and releasing it on demand.
The researchers want to test the compensation system in the future using a demonstration model installed in the medium voltage distribution network of the Haßfurt public utility company. The Federal Ministry for Economic Affairs and Energy has provided development funds of EUR 2.5 million(US $2.96 million) as part of the HYBKomp collaborative project, of which EUR 400,000(US $474 million) have been allocated to FAU.
Image credit: By Dirk Ingo Franke – photo taken by Dirk Ingo Franke, CC BY-SA 1.0, https://commons.wikimedia.org/w/index.php?curid=60611