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Reserve Margin Planning Reserve Margin The primary metric used to measure resource adequacy, defined as the difference in resources (Anticipated or Prospective) and Net Internal Demand, divided by Net Internal Demand, shown as a percentile. Anticipated Prospective (Anticipated Resources – Net Internal Demand) Net Internal Demand (Prospective Resources – Net Internal Demand) Net Internal Demand Reference Margin The assumptions and naming convention of this metric vary by subregion. The Reference Margin Level can be determined by using both deterministic and probabilistic (based on a 0.1/year loss of load study) approaches. In both cases, system planners use this metric to quantify the amount of reserve capacity in the system above the forecasted peak demand needed to ensure sufficient supply to meet peak loads. Establishing a Reference Margin Level is necessary to account for long-term factors of uncertainty involved in system planning, such as unexpected generator outages and extreme weather impacts that could lead to increased demand beyond what was projected in the 50/50 load forecasted. In many subregions, a Reference Margin Level is established by a state, provincial authority, ISO/RTO, or other regulatory body. In some cases, the Reference Margin Level is a requirement. Reference Margin Levels can fluctuate over the duration of the assessment period, or may be different for the summer and winter seasons.
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