Expected Unserved Energy (EUE)

Expected Unserved Energy measures the amount of load, in megawatt hours, that is statistically expected to go unserved over a planning horizon due to insufficient capacity or transmission. While LOLE counts the frequency of shortfalls, EUE quantifies their magnitude, providing planners with a more granular view of reliability risk. Utilities use EUE to evaluate how different portfolios mitigate both brief and prolonged scarcity events.

EUE is derived from the same probabilistic simulations used for LOLE but integrates the depth and duration of each shortage. When a scenario produces a deficiency, the deficit megawatts are multiplied by the length of the event and aggregated across all samples to produce an energy metric. This allows planners to compare portfolios that may have identical LOLE values but vastly different consequences when outages occur.

The metric has gained prominence as climate events create multi day disruptions, highlighting the need for resources that can sustain output beyond a single peak hour. Regulators incorporate EUE thresholds into resource adequacy filings, prompting developers to provide storage duration data, fuel security plans, and flexible operating strategies during procurement.

Because EUE can be monetized by multiplying unserved energy by the value of lost load, it provides a transparent cost benefit lens for transmission upgrades, storage procurement, and resilience investments. Sponsors that demonstrate meaningful EUE reductions often secure higher accreditation or bonus scoring in competitive tenders.