Maximize Megawatt Production
Performance Indicator Summary
Performance indicator: Maximize Megawatt Production
Technical Workgroup: Hydropower TWG
Research by: Hydropower TWG, Established flows for power formulas
Modeled by: The Power entities provided models to the PFEG for implementation in the Shared Vision Model.
Activity represented by this indicator: Generation of hydropower
Link to water levels: In general higher water levels on Lake Ontario call for higher outflows. This will provide for more megawatt production. However, if flows are too high, they can exceed the capacity of the plants. At the Moses-Saunders and Beauharnois power plants, higher outflows will lower the operating head which is a factor in megawatt production. However, due to regulation requirements in Lake St. Francis, Hydro Quebec must keep Lake St. Francis within a 30 cm (11.8 in) range.
Importance: Maximizing megawatt production is a goal of all the hydropower entities. Because Hydro Quebec does not perform peaking operations at Beauharnois, this PI is critical to their operations. Plans that reduce megawatt production will cause the price of electricity to all users to increase due to the nature of the electricity markets. This is discussed in detail in the contextual narrative. Also, the foregone electricity will be made up by alternate sources that are more expensive and contribute to reduced air quality.
Performance Indicator Metrics: For the Hydro Quebec plant at Beauharnois-Ceders, typically, total inflow in excess of 7500 cms (265,000 cfs) exceed the point of best efficiency. The incremental water is turbined at 50% efficiency at Beauharnois or at Ceders. Above 9000 m³/s (318,000 cfs) , the water is spilled. These numbers are subject to important adjustments according to maintenance of units. The predictability of outflows from Lake Ontario through the year is of primary importance for production optimization.
For Moses-Saunders, flows lower than 7930 cms (280,000 cfs) are allow for peaking. Flows in excess of 8540 cms (302,000 cfs) will exceed the best efficiency point when all 32 units are in service.
Temporal Validity: Valid for the entire year.
Spatial Validity: Valid for outflows at the Moses-Saunders and Beauharnois generating stations.
Links with hydrology used to create the PI algorithm: Hydropower production is a function of the river flows and operating head. For HQ, river flows at Beauharnois-Ceders include the Lake Ontario outflows as well as the flows from local tributaries which may be very high during the spring freshet. The levels downstream of Beauharnois are also affected by the inflows from the Ottawa river, and other local tributaries. The head is defined as the difference between the water level immediately upstream of the power station (forebay) and immediately downstream (tailrace) of the plant.
Algorithm: A computer program was provided to the PFEG for implementation in the Shared Vision Model and takes into account the local hydraulic parameters, the rating curves for the units, ice and other operating constraints.
Validation: The formulas to determine power have been modeled and field tested. For Moses-Saunders, they have been validated by the Gauging Committee and approved by the International St. Lawrence River Board of Control. They are the basis for the rating tables used by the power entities in measuring outflows and reporting to the International Joint Commission.
Documentation and References: Rating tables used by the power entities have been in operation since inception of the project. Moses-Saunders tables are accepted by the IJC. They have been updated and tested as generating units have been upgraded.
Risk and uncertainty assessment: This PI is objectively measurable. There is risk that a selected plan may negatively impact hydropower's ability to operate at best efficiency. The impact would be measurable and therefore there is little uncertainty with this PI.
In the production evaluation models, a fixed equipment maintenance program was used for all the simulations, while this program can be adjusted in reality. Tests were made and showed that this hypothesis is acceptable to compare the plans as long as the plans have a similar level of predictability and stability. If it was the case, the maintenance program could be adjusted in a similar way regardless of the plan that is eventually implemented. Nevertheless, we know that the flow predictability and stability is not the same for all the plans and these factors are covered by two other PI.