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New System Could Help Make Supply of Renewable Electricity More Stable

Grid operators need to do more than just distributing the electricity produced by photovoltaic plants and wind farms. They have to ensure a regular quality of supply as well. It is a complex issue to achieve this with the available components and systems.

Credit: Panthermedia/ Jean-Luc Cochonneau

Currently, researchers from FAU are developing a hybrid compensation plant system together with partners from the fields of energy supply, science and business. To this end, the researchers have combined an energy storage element and an extremely powerful converter that can control the form of the signal in the power grid in a single system. The goal is to reduce the number of individual systems. The collaborative project received EUR 2.5 million in funding from the Federal Ministry for Economic Affairs and Energy (BMWi).

Not all electricity is the same

Photovoltaics and wind power play a key role in the production of electricity. These types of energy facilities are commonly based at decentralized locations in rural areas. However, it takes a complex system of transformer stations and distribution networks to provide sustainably produced electricity to all consumers.

For example, solar power plants feed the direct current they produce directly into the low-voltage and medium-voltage network through power converters, which turn the direct current into alternating current. However, the conversion process generates harmonic currents that distort the voltage, damaging the signal in the distribution network and as a result, the quality of the electricity, which in turn can have a major effect on the functioning of machines and equipment.

Combined in a single system

Network operators offer system services to ensure the quality of the electricity they deliver. These services are enhanced by energy held in reserve to offset unexpected additional requirements at short notice. Then, the energy reserves are replenished during performance peaks. However, operators have used the required systems only as individual elements.

Researchers who work under the direction of TU Dortmund have now combined energy reservoirs and system services 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," describes Ralf Böhm, research associate at the Institute for Factory Automation and Production Systems (FAPS), whose team designs the key control technology that combines the individual components of the system together to form a whole.

The system is supplied with a flywheel energy storage system and a battery as well as a freely adjustable current converter that can affect the form of voltage signals. Flywheel energy storage systems are employed to produce large amounts of energy available at short notice, whereas a so-called redox flow battery, a complex liquid chemical battery, with high capacity is perfect for storing energy for a long period of time and releasing it when required.

In the future, the researchers are looking to test the compensation system using a demonstration model set up in the medium voltage distribution network of the Haßfurt public utility company. As part of the HYBKomp collaborative project, the Federal Ministry for Economic Affairs and Energy has provided development funds of EUR 2.5 million, of which EUR 400,000 have been allocated to FAU.

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