WP6 – Grid Integration

An appropriate inverter control design for the plant, while adhering to the unique characteristics of the proposed setup, will first have to be laid out in compliance with all requirements for its operation at the EU power grid. These requirements especially encompass the relevant network codes set by the ENTSO-E as well as national grid codes and ensure the compatibility as well as a grid-stabilizing behavior of all devices operating in the transmission network. The second design aspect will focus on creating a converter that is compliant with the turbine characteristics in all operation scenarios considered in this project. The resulting grid-side control will be implemented in a simulation model to be used for further grid integration studies in the tasks below. Depending on the performance class of the system, the design and the standard to be applied are also taken into account.

This task is worked on in close collaboration with parts of WP3. In a first step, historic mains frequency measurement data are processed to form profiles for expected loads on devices participating in Frequency Restoration Services. These data are utilized in WP3 to determine operation profiles and technical characteristics of the proposed plant setup that fuel the further studies on grid stability of the plant performed in this task 6.2. The considered effects will be twofold: On the one hand, the proposed setup will be capable of long-term energy provision with several applications of interest. For instance, the plant could be enabled for peak shaving local offshore wind energy. This mode of operation ensures that peaks in local wind energy output otherwise overstraining grid transport capacity can be compensated such that the combined hybrid wind and hydro plants operate their mainland grid connection to maximize energy output. On the other hand the plant is capable of providing support on the short-term range, which involves major grid support and stabilization in reaction to any failures and emergency situations within the European transmission grid. Based upon an assessment of the abilities of the plant, such as the capability of the proposed setup to provide flexibility in varying gradients and durations, the capability of the plant to serve as provider of the relevant operational reserves (FCR, FRR, RR) are evaluated.

Furthermore, since the plant inherently serves as an energy storage system, promising features of an expanded control concept would involve black-start capability and grid-forming behavior. The former would enable the plant to serve as an independent voltage reference used to restart the grid after a major power outage. For this capability, grid-forming behavior is a requirement. This mode of control would also permit the provision of inertia, which is currently discussed as a requirement of a grid deemed to operate in a stable fashion with severely reduced shares of fossil generation. On the basis of the results from the other work packages, it is evaluated whether the requirements for a grid-forming control system are given for the pumped storage power plant and if this control can be used here. If this is the case, a suitable control system is implemented and its contribution to inertia and black start capability is examined.

Parts of the work packages in this project are concerned with enabling the power plant to provide required and optional operational services to the grid. Many of these services are tendered on market-based platforms to ensure provision of the most cost-effective bidder. The potential revenue that can be achieved using a storage power plant therefore varies based on the individual market conditions. Against this background, this task utilizes the results from the previous work packages to perform an economic evaluation based on the calculation of the Levelized Cost of Storage and Energy Storage on Investment of the proposed concept. Based on these, this work seeks to propose a strategy to maximize financial revenue by comparing individual gains for each service and to estimate the cost-effectiveness of revenues achieved with providing services on markets that are best suited to the technical and economic abilities and constraints of the proposed storage plant concept.