DENA Study – Ancillary Services 2033

The German Energy Agency (DENA) has released a techno-economic study to investigate the effect of high penetration of Renewable Energy Sources (RES) on the need for ancillary services in Germany. As RES are connected to the electricity grid via power electronic converters, this causes a different behavior compared to the current power generators  in terms of system inertia, primary, secondary and tertiary reserves, reactive power support, short circuit power support, grid restoration and operational security. In addition, the study tries to identify to what extent these ancillary services can be delivered by RES and smart grid technologies such as distributed energy resources (demand response, distributed storage,…), along with challenges to integrate them into the ancillary services market. The study is divided in five main parts, where the key findings are discussed below.

Frequency support – The study concludes that there will be sufficient inertia in 2033. Even in the case without any conventional power plant connected to the German grid, the inertial response of the European generators will be sufficient to react to a power outage of 3000 MW. On the other hand, it is concluded that some of the existing and planned power plants have to be dedicated as must-run to provide primary reserves. The study also concludes that alternative technologies such as large scale battery storage systems can be an economically more feasible alternative to must-run power plants in terms delivering primary reserves.

Due to the variable generation profile of PV and wind power plants, the amount of required secondary and tertiary power reserves is expected to increase significantly. It is stated that pumped storage hydro power plants, wind power plants and demand response can provide the necessary reserve power, which in turn requires an adjustment of prequalification standards for providers of these reserves.

Voltage support – Power electronic converters of wind and solar power plants  are able provide reactive power for voltage support, even in the case without any active power generation, as long as they are connected to the network. The reactive power requirements can be met in case of additional investments in the communication infrastructure. This way, transmission system operators can remotely activate reactive power sources in nearby  distribution grids to satisfy the reactive power needs in the transmission grid.

Short circuit power –  On average, the short circuit power of the transmission grid is going to increase with 20%, but not exceed current highest and lowest levels. The circuit power in distribution grids can be unacceptably low without contribution from the transmission grid, according to the study. This will become a limitation when operating microgrids. High wind and solar generation in distribution grids can result in situations where no conventional power plant is connected to the distribution grid decreasing the short circuit power drastically.

Grid restoration – The study concludes that grid restoration will still be possible but will require much more coordination between conventional and distributed generation, as well as demand to safely restore the electricity grid after an incident.

Grid operation – The most important findings of this analysis belong to the operational security of the electricity grid. In future, a clear defined and standardized interface between transmission grid and distribution grid operators, as well as electricity markets will be necessary to coordinate the interaction of the transmission grid and flexible distribution grid in the operational time frame.

Due to increasing flexibility and the increasing number of control possibilities, the system has to be automated in every layer to be able to deal with this complexity. The future challenge will be to develop automated operation and planning principles which are market based and are able to find the optimum between network expansion and operational security. Therefore the regulatory framework has to be adapted to master these future challenges.

In conclusion , it is very important that the provision of ancillary services is clearly defined during the implementation of smart grid mechanisms, and the resulting communication infrastructure. The design must also foresee the possibility of fast intervention of grid operators in cases where the system is operated close to its stability limits. Therefore, the interface between smart grids,  markets  and the resulting communication structure has to be designed from a regulatory perspective as soon as possible to enable the provision of ancillary services by smart grids.

> The full study can be found at www.dena.de/en/projects/energy-systems/dena-system-services-study-2030.html