The Commerce Commission will be taking a "closer look" into how Hawke's Bay lines company Unison let its standards slip - ending up as one of the nation's most unreliable.
Annual electricity distribution company summaries, released by the Commerce Commission, show Unison ranked in the top five of the nation's lines companies when it came to the value of its regulatory asset base ($586 million), regulatory profit ($39.5m), line charge revenues ($152.8m), as well as the fifth highest number of customers (112,781) and the fifth largest amount of energy delivered (1615GWh).
However, Unison placed 21st (out of 29) when it came to outages.
The average time of outages per customer rose 45 per cent over a three-year period to six hours and 12 minutes.
The average number of outages experienced by customers rose 15.5 per cent to an average of 3.04 outages.
A Commission spokesperson said Unison had earlier this year self-reported it was in breach of its quality standards for the 2017/18 year.
"This trend in declining reliability was picked up in the performance summaries and we will be taking a closer look at the causes of this breach.
"We have not noted anything else in the performance summaries that raises significant concerns about Unison's performance at this stage."
Unison did not respond to requests for comment.
In 2018 Unison, which operates lines distribution networks across Hastings, Napier and Taupo, also had the fourth longest line length in New Zealand - a total of 9245km.
Commerce Commission deputy chairwoman Sue Begg said with three full sets of summaries now published, the data allowed for stronger year-on-year comparisons across both the sector as a whole and individual lines companies.
"The purpose of these summaries is to shine a light on lines companies' performances and with a third set of data now published there are some interesting trends emerging," Begg said.
"Through our own analysis when comparing the data sets, we have seen that overall demand has increased over the past year in terms of total energy delivered, peak demand, network capacity and customer numbers.
"Across the sector, capital expenditure has increased by 16 per cent and operational expenditure is up 5 per cent, which is significantly higher than the 3 year average.
"In 2018, total revenue has also increased by nearly 4 per cent; however lines companies' collective return on investment has dropped 1 per cent and regulatory profit decreased by nearly $100m (12 per cent)."