Road Map

Margin is the amount of energy from available resources that is above the expected demand in any given hour. Margin is used to understand where there might be a risk of not serving demand when requested. This is called "possible loss of load." Note that margins can also be calculated after an area imports energy from other areas. At WECC, we study the margins before transfers to understand the risk each area would have if the transmission capability disappeared. We then study risks after imports to determine whether the risks can be mitigated using outside help.

Margins can be shown for different periods by calculating a weighted average over time. The weighting used is the expected demand for that hour. This then gives information on the overall annual and monthly weighted average margins in an area.


The annual weighted margin is expected to be around 66% in 2020, slightly declining to 63% by 2029. The monthly weighted margin varies between 85% in the spring to just under 50% in the summer.

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Clicking a region on the map will change the charts to show that area's information. Clicking the same area again will switch the charts back to the overall Western Interconnection results.