Hydropower modelling - Home » Mekong River Commission · •Many different models can be used for hydropower modelling. Choice of model depends on types of hydropower plant, ...

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Hydropower modelling

Vientiane January 24. 2018

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Energy from hydropowerH

ead

, dH

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 poweronly depends on head (dH) and turbine flow (Q).

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How does mitigation measures affect hydropowergeneration 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

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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

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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

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Hydraulic model example: MIKE 11

• Hydraulic model- Based on Navier-Stokes

equations- Fully dynamic model

• River is defined by cross-section 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

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Water balance model example: HEC-ResSim

• The reservoir system is built using a network of elements (junctions, routingreaches, 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 willimprove the results

• Output: Flow and water levels- Power generation calculated

separately or- Power generation calculated in the

model

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Hydropower production models

• Different types ofmodels:

- Hydropower planning models▪ Water balance models,

more focused on HPP

- Hydropower operationmodels▪ Long term or short-term

▪ Usually includesforecasting (hydrologicalmodel)

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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

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Which model to choose?

• Several existing power plants in the same river basin. Severalreservoirs

- 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

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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, Q4. 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, Q7. Power tariffs

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Modelling of run-of-river HPPs

(from case study)

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Modelling of reservoir schemes

(example reservoir modelling)