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Dispatch Algorithm Issue Corrected

July 7, 2022

A minor modelling deficiency in the IESO’s energy market dispatch software caused, under certain conditions, the derates of generation facilities to not be considered in the final 5-minute interval (interval 12 of hour ending 24) of the real-time unconstrained sequence. This resulted in a limited impact on the market price from late 2016 until this issue was corrected in April 2022.

It is estimated that this issue would have reduced market prices on average by ~$0.40/MWh in the final dispatch hour of approximately 230 days. The IESO determined that this issue arose as a result of a software change on November 29, 2016. Once the concern had been identified and confirmed, a solution was implemented on April 7, 2022.

There was no impact to reliability as the constrained schedule that is used to dispatch supply resources was not affected. The IESO continues to review this matter along with any additional controls that may be required to prevent similar issues in the future. 


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