LOLH. The number of hours per year where demand will exceed the generating capacity.
Loss-of-Load Hour (LOLH)
Loss-of-Load Hour (LOLH) is generally defined as the number of hours per year where system demand will exceed the generating capacity. LOLH is usually expressed in hours per year. Any outage caused by inadequate resources regardless of geographic extent or load interrupted (it could be 1 MW for a single customer or the loss of the whole area load) counts as a LOLH. An LOLH of 0.1 means that an hour of loss of load is expected for every 10 years. For a particular year, the resources available and load shapes for that year are used to calculate the metrics for that year.