GERMANY: Flexibility of active and reactive power from HV distribution grid to EHV transmission grid


MITNETZ STROM, innogy, INESC TEC, Fraunhofer IEE, University of Kassel

Technical aspects
• Location: Eastern Germany: Parts of Brandenburg, Saxony and Saxony-Anhalt
• Supply area: 2,720 km²
• Installed capacity: 10.2 GW DER; > 8.5 GW RES
• Share of RES in consumption: 104%
• Grid connection points in scope of demo: 374 HV/MV substations, of which 99 with RES infeed; 16 TSO/DSO interfaces with 40 transformers
• Available flexibilities in the demo: 5.3 GW in HV grid, of which 2.9 GW wind and 1 GW solar
• Potential reactive power flexibility useable in demo: -350 Mvar to +280 Mvar

Innovative aspects of the demonstration
• Integrates new and improved forecasts for RES generation and load
• Schedule based co-optimising of grid in active and reactive power management
• Includes RES in schedule based congestion management and reactive power management coordinated between TSO and DSO
• Transforms optimisation results into control signals within automated processing for reactive power management

Main challenges
It is expected that by 2030 the share of RES will have increased by up to 65%. There is already a high RES share (~40% RES in Germany and ~100% in the demo region since 2017), especially wind power in north eastern Germany, which requires substantial redispatch measures to avoid overloading transmission and distribution assets. In 2017 congestion management costs reached a record €1.4 billion.
The redispatch potential in the transmission grid is reaching its limits due to the minimal capacity of conventional power plants and decreasing level of installed capacity in conventional plants. Therefore, emergency measures are used to curtail RES in the distribution grid. Redispatch potential can be increased by utilising DER and RES in the distribution grid.
This exacerbates the need for more efficient and coordinated congestion management processes for TSOs and DSOs. Otherwise, the DSOs may adopt congestion solutions that conflict with those put in place by the TSOs. There is also an increasing requirement for reactive power management. A
coordination mechanism is therefore needed that would enable the TSO to use reactive power flexibilities from the distribution grid.