Hydropower modelling Vientiane January 24. 2018
Head, dh Energy from hydropower Hydropower plants transforms the potential energy in water to electricity. Energy is calculated by the following equation: E = η ρ g Q dh When η (efficiency), ρ (=1000 kg/m³) and g (=9,81 m/s²) are constant, generated power only depends on head (dh) and turbine flow (Q). 2
How does mitigation measures affect hydropower generation and revenue? Reduced flow through the turbines - Loss of water due to minimum flow, sediment flushing etc. - Loss of water due to reservoir operations that increase the flood loss - Reduced generation and revenue Reduced head (lower head water level and/or higher tail water level) - Reduced head due to flushing/slucing or other environmental concerns - Reduced generation and revenue Generation at times when the power price is low - Reduced revenue 3
Types of hydropower plants Reservoir - No active reservoir: Run-of-river hydropower Outflow = inflow Water is lost during floods - Reservoir: Daily, weekly, monthly, seasonal or annual storage Water is saved to be used when needed Head - Low head <30 m - Medium 30 200 m - High head >200 m 4
Types of models Many different models can be used for hydropower modelling. Choice of model depends on types of hydropower plant, and what output is needed. Types of models: - Hydraulic models ISIS, HEC-Ras, MIKE11 Good for: Low-head schemes, hydropower plants with challenging hydraulics Disadvantages: Large and complicated models, (often) no in-model hydropower calculation - Water balance models IQQM, HEC-ResSim, MIKE Basin Good for: Multi-purpose projects, larger river basins Disadvantages: No hydraulics in the model, some models not suited for all hydropower operation - Hydropower production models MaxHydro, Optipower, Powel Optimal Hydropower Good for: Production planning and forecasting, optimizing revenue Disadvantages: No hydraulics in the model, models often do not take into account other water uses - Spreadsheet models Good for: Simple systems Disadvantages: Not suited for complex systems 5
Hydraulic model example: MIKE 11 Hydraulic model - Based on Navier-Stokes equations - Fully dynamic model River is defined by crosssection profiles - From terrain model - Calibrated to observed data Operation rules defined in structures (dams) in the river network - Flexible, but may require (a lot) of programming Output: Flow and water levels - Power generation calculated separately 6
Water balance model example: HEC-ResSim The reservoir system is built using a network of elements (junctions, routing reaches, diversion, reservoirs) Based on water balance equations - Level pool assumption Goals and restrictions can be added to the different elements Not a hydraulic model - Capacity curves, tailwater curves, travel time etc. must be specified in the model - Input from a hydraulic model will improve the results Output: Flow and water levels - Power generation calculated separately or - Power generation calculated in the model 7
Hydropower production models Different types of models: - Hydropower planning models Water balance models, more focused on HPP - Hydropower operation models Long term or short-term Usually includes forecasting (hydrological model) 8
Spreadsheet models: Excel Sometimes, complicated models are not needed Spread sheet models may be a good alternative if - Limited number of HPP - Only concerned about power generation - No optimization of water uses 9
Which model to choose? Several existing power plants in the same river basin. Several reservoirs - Power planning model if hydropower is the only consideration - Otherwise: water balance model Two high-head run-of-river HPPs - Spreadsheet model Cascade of low-head run-of-river HPPs - Hydraulic model 10
Hydropower modelling. What data is needed? 1. Data series for inflow Q - Usually daily data for 30 years - For large reservoir schemes, or when the variation in flow is small, weekly or monthly data may be ok - For very small (<5 MW) run-off-river plants, hourly data is better 2. Efficency curves for electro-mechanical equipment η - Turbines, generators, transformers 3. Reservoir volume curves (if reservoir scheme) dh, Q 4. Tailwater curve (if large variation in tail water level) dh - In the Mekong, the variation in TWL can be more than 10 meters, which may be 50% of the head! 5. Hydropower key data dh, Q - Max and minimum turbine flow - Design of waterways 6. Information about other water uses and mitigation measures dh, Q 7. Power tariffs 11
Modelling of run-of-river HPPs (from case study) 12
Modelling of reservoir schemes (example reservoir modelling) 13