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Hydropower Area Equivalents

Reduced Models for Efficient Simulation of Large-Scale Hydropower Systems

Time: Thu 2023-04-27 13.00

Location: Kollegiesalen, Brinellvägen 8, Stockholm

Language: English

Doctoral student: Evelin Blom , Elkraftteknik

Opponent: Arild Helseth, SINTEF

Supervisor: Professor Lennart Söder, Elkraftteknik

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QC 20230403


With over 4000 TWh yearly electricity production worldwide, hydropower plays an important role in many power systems. Unlike many other renewable energy sources, hydropower has a certain degree of controllability and high levels of flexibility over several time scales. This flexibility is estimated to be integral for the transition of the energy systems towards more variable renewable energies and thus reducing greenhouse gas emissions. 

Given the important role that hydropower currently plays and is expected to play in future power systems, accurate models of hydropower are vital. As hydropower electricity production is a non-convex function of the discharge with for example non-linear head dependencies and forbidden zones of operation, detailed models of real hydropower systems quickly become computationally heavy. Even linear models with high numbers of interconnected stations are often too complex for large-scale power system models. For this reason, reduced or aggregated models of hydropower are commonly used to simulate its operation in different power system models. 

Due to the temporal and spatial connections in many hydropower systems with large rivers, the aggregation of hydropower can pose significant challenges. This means that aggregation from historical data might not be good enough to accurately simulate the hydropower operation. However, accurate reduced models of hydropower are still needed for long-term current and future studies of energy systems worldwide. In this thesis, the basic assumption is that the simplified reduced hydropower model should mimic the real hydropower operation. Thus, instead of aggregating the existing hydropower stations within a certain geographical area, one computes a new hydropower area Equivalent model with the aim to match the simulated power production of a more Detailed model of the real hydro system in that area. 

In this work, the area Equivalent models are calculated by computing the model parameter values. Here, this is mainly done based on a bilevel optimization problem formulation. In this thesis, different methods to compute the area Equivalents are proposed together with different model formulations and bilevel problem formulations. These are all compared using case studies of Swedish hydropower systems. Moreover, a Baseline aggregation method is outlined and compared to the developed area Equivalents. 

The studies presented in this thesis highlight the potential trade-offs in the accuracy of the area Equivalent model. Some problem formulations give a higher accuracy in hourly power production, others in peak power production or total power production over the simulation period. All area Equivalents perform better than the Baseline aggregation. In general, the average error in hourly power production is reduced by 50% using the area Equivalent compared to the Baseline aggregation. Moreover, they all successfully reduce the simulation time compared to the reference Detailed model with over 96%.