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In Dunedin yesterday with Climate Change Minister James Shaw, Mr Parker said he knew Project Onslow was unpopular with some conservationists.
The project would destroy habitat around the Central Otago lake, including a wetland, Mr Parker said.
But without Project Onslow, the country would not be able to break away from its use of fossil fuels.
"People should not just dismiss it out of hand, because I don’t know another route to net zero, and I’ve been doing this for decades," Mr Parker said.
Once again Otago was being asked to bear the local environmental damage, but there could be offsets, including protection for the Upper Taieri scroll plain, he said.
Mr Parker and Mr Shaw were guests of the environment branch of the Dunedin Labour Party at the University of Otago yesterday.
They addressed the Climate Change Commission’s forthcoming advice to Government to be used to make national emissions budgets at the end of the year.
The consultation this year attracted more than 10,000 submissions.
The draft advice included planting permanent native forests, ending imports of petrol and diesel-fuelled cars to shift the country into electric vehicles, and a major uptake of wind and solar energy.
The Government last year announced $30 million for a business case to investigate the proposal to build the scheme at Lake Onslow.
It was advertised as a means to achieve a fully renewable electricity system, and to solve the problem of dry hydrological years.
Because the country lacked adequate hydro storage, one out of every 10 years was dry enough that it had to rely on fossil-fuel derived energy from Huntly.
This year would be one of them.
There was not enough rain falling into the country’s largest storage lake, Lake Pukaki, Mr Parker said.
"It’s sad to say, but this year we are going to burn more coal in New Zealand than we have for a few years because we are short of fuel - water - in our hydro system."
Wind and solar farms between them were the cheapest sources of new power generation, but were intermittent.
When the wind did not blow, or the sun did not shine, there needed to be stored energy.
The proposal was to "overbuild" wind and solar, and when the water was available, to pump it out of the Clutha into a big dam on Lake Onslow, which could cover either a dry year or intermittent periods when wind and solar were not producing. Lake Onslow would be able to store twice the amount of water as Lake Pukaki.
Mr Shaw said key decisions were expected to be made before the end of the year.
New Zealand’s first emissions reduction plan was required under law to be tabled in Parliament by December 15, he said.