New analysis shows the cyclones that ravaged parts of the upper North Island in April proved a boon for parts of the electricity industry.
Besides swamping the town of Edgecumbe, they left North Island hydro dams brimming over with water.
Mercury's turbines have been whirring to make the most of the water, its chief executive Fraser Whineray says. Photo: 123rf
This happened as the South Island was running dry, and official records show lots of power flowed profitably, from companies in the North Island to customers in the South.
They show one of the big winners from this situation was Mercury - the old Mighty River Power.
Its chief executive Fraser Whineray said company turbines had been whirring to make the most of the water.
"We have had three cyclones come though the North Island, Cyclones Debbie and Donna and Cook," he said.
"Obviously that means there is a lot of water (in hydro lakes) that we have to process through the turbines."
This has boosted profitability so much the company had to tell the stock exchange of a $10 million jump in earnings on two separate occasions in the last month.
"We have lifted guidance a couple of times because of the expectations of additional rainfall and therefore extra hydro production," Mr Whinneray said.
"We are now at about $520m when we started off at under $500m."
These figures were earnings before interest, taxation, depreciation, amortisation and financial variations.
While autumn storms lashed the North Island, drenching people but filling bank accounts, the story in the South island was exactly the opposite.
They harmed Meridian Energy, which usually has a hard time in winter because water that should be flowing into its hydro dams is locked up as snow in the mountains.
But low autumn rains this year made it worse.
The editor of Energy News, Gavin Evans, said Meridian had lots of customers in the South Island, and not enough electricity, and so was forced to buy high priced electricity from the North island.
"Meridian has the bulk of their custom in the South Island," Mr Evans said.
"Not only do they supply the smelter but half their retail customers are in the South Island as well.
"So when they are in the market to supply those customers, they are paying really high prices."
Earlier this month, Meridian confessed its woes to the Stock Exchange, admitting lower water storage and lower water inflows into its hydro lakes.
It was generating 19 percent less electricity than in the same month last year and paying 30.4 percent more for the electricity it bought from other people.
Another company involved in this situation is Genesis Energy, which is burning coal and gas at Huntly to generate power and send it southwards.
Unlike the other companies, it has been keeping quiet about the situation and its CEO, Marc England, would not even discuss profitability.
"I am not in a position to disclose our earnings," he said.
"The cost of coal and gas is quite high and we have a carbon charge on top of that, so depending on prices in that market, our margins vary considerably.
"This is good news for Genesis but we are not disclosing - obviously we are in a closed period and our results will come out in August."
Despite that, Gavin Evans said he thought Genesis would still do well.
"When lakes are low, they get to run all the Huntly units really hard, and the industry is paying a premium for those supplies so they [Genesis] will tend to come out of it better."
The fourth big company, Contact Energy was also affected, recording a big drop in hydro generation and a big jump in gas-fired electricity.
For New Zealand as a whole, winter power woes are still regarded as manageable.
However, Transpower has nudged up its own level of watchfulness once more.