Evaluation of a Hydro Power System Production Planning Model

Sammanfattning

This study evaluates two different optimization models for production planning of a hydropower system. The study focuses on the model Flow Optimization for River System Analysis (FORSA) and compares it to HydroProdPlan (HPP). The primary objective of this thesis is to asses the impact of head dependency on power production of a hydropower optimization system and investigate the accuracy and limitations of a linearized production function based on a first-order Taylor approximation. This study concerns with the Lule river system and applies multiple scenarios to investigate differences in revenue, turbine-level production, reservoir dynamics, operating decision and computational performance. The head independent HPP model assumes a constant head meanwhile the head dependent FORSA model includes the head dependency through a linear approximation of the production function. The difference between FORSA and HPP were within a percent in aggregated river revenue. Significant differences could be observed at the turbine level, particularly for stations with a large head variability. The FORSA model showed a more realistic reservoir management behavior compared to HPP. This study also highlighted the limitations of the linearization approach. The Taylor approximation produced unrealistic results under special circumstances, such as negative production and positive production at zero discharge. The inaccuracies were effectively corrected through a FORSA built-in post-processing step that restored the realism of the production. The sensitivity analysis demonstrated that the linearization primarily affects the production magnitude rather than the timing of the discharge decisions. The sensitivity analysis also highlighted the limitations of using one turbine efficiency curve across all heads, leading to some forbidden discharge operating points for different heads. Overall, the findings indicate that the head dependency plays an important role in an accurate hydropower modeling system, especially for a fine temporal resolution. Although the simplified production planning models may provide reasonable aggregate results, the hourly production of turbine-level and reservoir dynamics accuracy is sacrificed. The FORSA model with the Taylor approximation approach offers a computationally efficient and applicable solution for hydropower production planning without unit-commitment and must-be-on conditions.