Modelling hydropower in detail to assess its contribution to flexibility services in the European power system

Abstract

Decarbonizing the energy mix is a promising strategy to mitigate climate change and reach long term emission reduction targets. Intermittent renewable energy sources (iRES) such as solar PV and wind (offshore and onshore) are expected to have a vital role in future low carbon energy systems. As the share of iRES increases, so do the flexibility requirements from complementary technologies to ensure system adequacy. Hydropower is regarded as a key contributor for system adequacy by providing flexibility and the full range of ancillary services. This study assesses the effects of different yearly water inflows (rainfall years) on the ability of hydropower to generate and store electricity in a European low carbon energy system with 59% iRES penetration in the year 2050. This is done using the hourly power system simulation software Dispa-SET developed by the European Commission. Three rainfall years are investigated: a high flow year, an average flow year and a low flow year. Each rainfall year is simulated using short-term and long-term optimization of the storage of the hydropower storage levels, leading to a total of six scenarios. Only the long-term optimization considers seasonal variation of water inflows for the simulation. Results show that different rainfall years affect electricity production of hydro plants by up to 4%. This translates into a maximum of 7% variation in annual variable production costs. The long-term optimization of reservoir levels results in increased electricity production (1- 2%) and decreased variable costs (5 - 7%), compared to the short-term optimization. Key mechanisms contributing to the results are: (1) a production shift from gas turbines (GT) to pumped hydro storage plants (PHS), storage hydro plant STO) and other power generators, (2) iRES curtailment reduction, (3) storage hydro plant spillage reductions. Based on this study, hydropower has a key role as a flexibility provider in an energy system with 59% iRES penetration. The different rainfall years have a limited impact on the total hydroelectricity production but they translate into a significant reduction of variable costs in the system. The added value of the long-term optimization lies in providing insight on the potential savings that can be achieved if seasonal variations of water inflows are considered for the dispatch of hydropower plants