Adjustment of generation is still the principle means of providing flexibility services and the core topic of the HydroFlex project. In this context, understanding the time scales of flexibility is important. These range from millisecond responses due to electrical faults all the way to yearly and even decade scale changes due to economic, technological and population development. Different mechanisms have evolved to cope with this range of time scales.
Physical requirements, commonly imposed by TSOs, related to protection settings, requirement to inertia and turbine governor parameters and performance characteristics of voltage regulator are used to secure the shortest time scales. Intra-day markets and day ahead markets are used to balance the hourly and diurnal variation, and financial markets (future markets) are put in place to balance the intermediate scale. The long-term development, such as grid development plans and capacity expansions, resides in the borderland between the TSO-level, regulatory bodies as well as political decision. Nevertheless, in a commercial, deregulated power market, reliable predictions regarding the types of markets that will exist in the future as well as reliable prediction of future pricing is critical for anyone considering investment in new.
During the last decades, several models for predicting wholesale electricity prices have been developed. The models vary in time resolution and geographical resolution but are in general based on minimizing the cost of producing the predicted consumption in a future time interval. Models to predict future prices for flexibility services have so far been quite limited. Within the HydroFlex WP2, a novel approach for investigating flexibility requirements is under development. The basic principle is to combine a traditional market model with a detailed simulation of failure events. For each hourly equilibrium load, failure events are injected, and a time domain simulation is performed in order to see if the system is able to stabilize itself again and the required dynamic response of the hydropower plants in the system. Initial results are encouraging, but there remains significant development and testing before concluding.