Transpower says New Zealand's largest hydro lake, Lake Pukaki, is near its maximum levels so there will be spills to ensure it remains safe. Photo: 123RF
The South Island hydro lakes are currently so full that water is being spilt, less than four months since levels were at record lows.
In August Transpower said hydro storage was at just 55 percent, among the lowest levels in around 90 years of historic records, which sent prices soaring.
Incoming Meridian Energy chief executive Mike Roan said New Zealand's largest hydro lake, Lake Pukaki is now near its maximum control levels so there will be spills to ensure it remains safe.
He said it was not unusual at this time of year, with summer storms in the area bringing large amounts of water.
"At times it doesn't rain, and as most of New Zealand's electricity system relies on hydro-generation when it doesn't rain what we tend to do is use gas, and if it gets really dry we use coal as well to make electricity.
"When that occurs because you are using a high-cost product, you tend to see the price of electricity rise. But when you have full hydro lakes like we do today you tend to see that price come off to the very low levels that you see today and around Christmas.
"So it's a good time of year, and I think we are fortunate that we have a lot of renewable electricity from hydro generation."
Since the 1960s, New Zealand had relied on hydro storage to make most of the country's electricity, and while electricity consumption has grown considerably since then the amount of storage has not increased by much, he said.
Waikato University hydro power scientist Earl Bardsley said this showed the real need to increase storage capacity.
If the water had been able to be stored, it could have helped keep power prices down if there was another dry period next winter, he said.
"It is an unfortunate consequence of our system where we only have limited storage to tide us through to next winter.
"If we have another dry winter, we would very much like to have that water that we have lost generating power. On the other hand, we might have a wet summer - we just don't know what will happen as yet."
The scrapped Lake Onslow project in Otago should be looked at again as a solution to increase storage capacity, Bardsley said.
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