SAIDI
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| SAIDI | |
|---|---|
| Name | SAIDI |
| Caption | Typical SAIDI reporting dashboard |
| Field | Electrical power distribution |
| Introduced | 20th century |
| Related | SAIFI, CAIDI, ASAI, MAIFI |
SAIDI SAIDI is a widely used electric power reliability metric that quantifies the average outage duration experienced by customers over a given period. It is reported by utilities, regulators, and system planners to assess distribution performance and compare service continuity across territories and operators. The measure is central to regulatory reporting, investment planning, and customer communications in many jurisdictions.
Definition and meaning
SAIDI stands for the System Average Interruption Duration Index and expresses the average total duration of interruptions for each customer served. Utilities, such as Con Edison, EDF (Électricité de France), and Iberdrola, publish SAIDI alongside indices maintained by bodies like IEEE, NERC, and national regulators such as the Ofgem and the FERC. In reporting, SAIDI helps translate network events—ranging from localized faults to regional storms—into a single, comparable performance indicator used by organizations including Edison Electric Institute and World Bank energy projects.
Calculation and formula
SAIDI is calculated by summing the durations of all customer interruptions over a period and dividing by the total number of customers served. Utilities implement the formula when compiling outage databases maintained in systems like those from Siemens, Schneider Electric, or GE Grid Solutions. Regulators such as the Australian Energy Regulator and the California Public Utilities Commission require consistent calculation methods similar to procedures in IEC and IEEE Std 1366 guidance to ensure comparability.
Variants and related reliability indices
SAIDI is used with companion indices: SAIFI (System Average Interruption Frequency Index), CAIDI (Customer Average Interruption Duration Index), and MAIFI (Momentary Average Interruption Frequency Index). Other related measures include ASAI (Average Service Availability Index) and ENS (Energy Not Supplied), used by entities like CIGRE working groups and national utilities including E.ON, National Grid (Great Britain), and Tokyo Electric Power Company. Benchmarking reports from institutions such as the International Energy Agency often present SAIDI with these variants.
Applications and uses
Utilities use SAIDI for performance monitoring, capital planning, targeted reliability investments, and customer reporting. Regulators tie SAIDI to incentive mechanisms and penalty schemes in places overseen by Ofgem, FERC, Ontario Energy Board, and Energy Market Authority (Singapore). Financial analysts at firms like Moody's, S&P Global, and Goldman Sachs may consider SAIDI when assessing utility creditworthiness. Researchers affiliated with universities such as Massachusetts Institute of Technology, Imperial College London, and Tsinghua University employ SAIDI in studies of grid resilience and distributed energy resources.
Factors affecting SAIDI
SAIDI values are influenced by severe weather events like hurricanes and ice storms, utility asset condition, vegetation management, and crew restoration efficiency. Major historical events—e.g., Hurricane Sandy, 2011 Tōhoku earthquake and tsunami, and widespread blackouts such as the Northeast blackout of 2003—produce marked SAIDI increases for affected utilities including PSE&G and PG&E. Operational practices from companies like Duke Energy and RWE—including smart grid deployments from vendors like ABB and Hitachi Energy—also affect outage durations.
International benchmarks and standards
International standards and benchmarking efforts by IEEE, IEC, CIGRE, and regional regulators create guidance for SAIDI reporting. Comparative datasets published by agencies such as the European Commission, U.S. Energy Information Administration, and International Energy Agency allow cross-jurisdiction comparisons involving utilities like Enel and Statkraft. Some countries incorporate SAIDI targets into regulatory frameworks used by bodies such as the Australian Energy Market Commission and Brazilian Electricity Regulatory Agency.
Limitations and criticisms
Critics note that SAIDI aggregates diverse events into a single average, which can obscure distributional impacts among customers and the distinct nature of planned versus unplanned outages. Academics at institutions like Stanford University, University of Cambridge, and ETH Zurich have argued for complementing SAIDI with location-specific, resilience-focused metrics and customer-equity measures. Regulatory commentators referencing cases involving EnerNOC and smart meter rollouts caution that measurement inconsistencies, exclusions (major event days), and data quality issues can undermine cross-utility comparisons.