kapacitetsmargin

Kapacitetsmargin, or capacity margin, is a metric used in power system planning to express the amount of spare generation capacity available relative to expected demand. It describes the difference between total available capacity and forecast peak demand, typically as a percentage, and can also be stated as an absolute megawatt value.

The conventional formula is capacity margin = (C − P) / P × 100%, where C is the total available capacity that can be dispatched and P is the forecasted peak load. Capacity should reflect realistic operability, including maintenance outages, forced outages, fuel availability, and other constraints. In practice, margins are influenced by factors such as weather, outages, and the variability of non-synchronous generation like wind and solar.

Interpretation is that a higher cap margin implies greater reliability and a lower risk of supply shortfalls, but at the cost of maintaining and operating more capacity. A lower margin increases the probability of shortages during extreme conditions or unforeseen outages. Many planning methodologies set target margins to meet a specified reliability standard, sometimes expressed as a probability of adequacy or a reserve requirement.

Relation to reserve margin and planning: capacity margin is closely related to reserve margin and is often used interchangeably in planning contexts. Some frameworks distinguish a planning reserve margin (a target value) from the realized reserve margin (actual available capacity during operation). Location and timing are important, as margins can vary across regions and seasons.

Applications and limitations: The metric informs investment decisions, capacity auctions, and interconnection planning. However, capacity margin does not by itself capture transmission constraints, intra-hour variability, or market design details, and relies on forecast accuracy for both supply and demand.