Covid-19 has left a mark on New Zealand's energy consumption, which is yet to return to business as usual.
The national grid operator Transpower said it was sharing its data and experiences with international counterparts, as the pandemic changed energy use and consumption patterns around the world.
Transpower operations manager Stephen Jay said the most valuable lesson learned from the experience was the way the industry pulled together to manage through the crisis.
"The security of providing (uninterrupted service) through lockdown was challenged in terms of the expertise, the capability, the logistics of repair and enhancement, and you need to get done to secure the energy supply," he said.
"We did a lot of collaboration across the industry to make sure that we were sharing information, and there were no surprises in terms of how we were reacting."
The changes were not just because mostly everyone was locked-down in their homes when the country entered alert level 4 on 25 March 2020, but because most businesses and industries had to shut down for more than a month during that initital period.
Most regions had usage drops of between 15 and 20 percent during level 4, with Napier experiencing the biggest drop with the shutdown of Pan Pac Forest Products, while Invercargill had the lowest drop of any region as the Tiwai aluminium smelter continued to operate throughout the crisis.
Not surprisingly, the drop in level 4 demand saw New Zealand's renewable energy supply reach its highest level in modern history to 91 percent, compared with 88 percent in the pre-Covid era.
The Auckland based-lines company Vector said there had been a material change in the region's power usage during level 4 alert.
"(The) impact of Covid-19 . . . resulted in lower electricity network volumes and therefore revenue, driven by a significant drop in commercial sector consumption as well as an impact on the wider business," the annual report says, adding the pandemic adversely impacted the group's undelrying profit by about $10 million.
"With restrictions in place under Covid-19 alert levels 3 and 4, electricity volumes across our network decreased by approximately 10 percent leading to a fall in revenue for the period."
The company said residential use had returned to near normal levels, just prior to the most recent community Covid outbreak in August, but commercial use had yet to return to previous levels.
At the start of alert level 4, volume across Vector's electricity network fell 15 percent on the previous three-year average, while gas use dropped 22 percent.
For the first time, Auckland's weekday commercial loads across both gas and electricity networks resembled those of a typical weekend.
Residential consumption during level 4 increased by about 13 percent, with people working and studying from home.
Morning peak use also shifted to later in the day, with usage peaking at midday for the first time on record.
However, it said once the country entered the level 1 alert level, residential trends largely returned to normal.
The industry was still crunching the data to see how the changes might inform transmission management in the future.