Road Map

Studying every hour of every year, we can calculate the number of hours in which the expected margin between availability and demand falls below the threshold margin. These are the hours in which available resources may not meet the system demand entirely, also known as loss-of-load hours (LOLH).

The charts below show the total LOLH by year (upper), then by the monthly breakout (middle), and the hours in which loss of load is occurring (lower).


Most of the hours in which the expected margin falls below the threshold margin occur in the summer months. All hours experience some risk, with hours 18 and 19, which immediately follow the evening peak demand, seeing the highest risk.

Page Tip

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.