Reliability & Outages
Keeping the lights on
How reliable is the electricity supply, and how does that vary between the 29 distribution companies?
This page uses the Commerce Commission's information disclosure data: SAIDI (minutes off supply per customer per year) and SAIFI (interruptions per customer per year). The layout follows the US Energy Data reliability page.
Same sections, same order as US Energy Data: Reliability & Outages ↗, so the two can be read side by side. Where New Zealand data cannot support a chart, the slot stays and says why.
Explore grid reliability
The US page opens with a combined explorer for outage duration and frequency by state.
Chart not available for New Zealand
We have not built a combined explorer. The charts below cover the same measures one at a time, by distributor.
Outage frequency, excluding major events
How often does the average customer lose power in a normal year? Normalised SAIFI caps major event days so storms do not swamp the underlying network performance.
Compared with the US: Commerce Commission normalisation caps class B and C interruptions on major event days at each distributor's quality-path threshold. The US uses IEEE 1366 major event days; the idea is the same, the threshold is not.
Outage frequency, excluding major events
Normalised SAIFI by distributor, interruptions per customer.
Loading chart…
Outage frequency, including major events
The full picture: all interruption classes including Transpower, generation and third-party events, with nothing capped.
Outage frequency, including major events
System average interruption frequency index, interruptions per customer.
Loading chart…
Outage frequency: with and without major events
The gap between the two lines is what storms and other major events add on top of routine faults. Pick a distributor to see how exposed its network is.
Outage frequency: with and without major events
Normalised versus all-class SAIFI, by distributor.
Loading chart…
Outage duration, excluding major events
How many minutes is the average customer without power in a normal year? Normalised SAIDI caps major event days.
Outage duration, excluding major events
Normalised SAIDI by distributor, minutes per customer.
Loading chart…
Outage duration, including major events
All classes, uncapped. Cyclone Gabrielle in 2023 and the 2024 definition change both leave a mark.
Outage duration, including major events
System average interruption duration index, minutes per customer.
Loading chart…
Outage duration: with and without major events
Normalised versus uncapped minutes per customer for a chosen distributor.
Outage duration: with and without major events
Normalised versus all-class SAIDI, by distributor.
Loading chart…
Outage duration by utility type
The US compares investor-owned, public and cooperative utilities.
Chart not available for New Zealand
New Zealand's 29 distributors are a mix of consumer trusts, council-owned companies and listed companies, but the Commission's disclosures do not carry an ownership field and we have not added one. The individual-distributor chart below is the closest view.
Outage duration by individual utility
Every distributor over time. Rural networks with long overhead lines (Top Energy, The Lines Company, Westpower) sit well above urban ones (Wellington Electricity, Vector). Use the Chart tab and add distributors to compare.
Outage duration, including major events
System average interruption duration index, minutes per customer.
Loading chart…
Planned and unplanned SAIDI
National ICP-weighted minutes per customer.
Loading chart…
Outage duration vs electricity sources
Do places with more wind and solar have more outages?
Chart not available for New Zealand
Reliability is reported by distributor and generation by Electricity Authority network region. The two geographies overlap but do not match one to one, and New Zealand's generation mix is set nationally by the hydro system rather than by region, so the US-style scatter would not mean much.
Change in outage duration vs change in electricity sources
Has adding renewables changed reliability?
Chart not available for New Zealand
Same geography mismatch as above, and the disclosure series only starts in 2013.
Change in outage duration vs demand growth
Does fast load growth strain the network?
Chart not available for New Zealand
Distributor SAIDI and regional demand could be joined through the distributor names, but the 2024 definition change breaks the SAIDI trend that the scatter needs. Left out until the Commission publishes a back-cast.