A Meridian Energy witness was scrutinised for not considering Central Otago's harsh winter, which could shut down wind turbines in times of high demand.

The Environment Court hearing into the $2 billion Project Hayes windfarm continued yesterday with wind energy consultant Graham White appearing for Meridian.

He said in freezing humid condition wind turbines could ice up and no longer operate.

"They do lose some time but not much power," he said.

The problem has been dealt with effectively in Canadian wind farms for years but he admitted he had not visited the Project Hayes site during winter.

On cross-examination from Central Otago District Council lawyer Graeme Todd, Mr White said he was not aware how many days a year the Project Hayes turbine could be inoperable because of ice.

Upland Landscape Protection Society litigation co-ordinator Ewan Carr asked whether Mr White had considered the number of still days during winter, when the demand for power was highest but the turbines would be generating little if any power.

But Mr White said it was not an issue and the Project Hayes site remained the best site in New Zealand for a wind farm.

All practical "Class 1" sites, which were more wind exposed and therefore produced more energy, had been taken.

The Project Hayes site was the best "Class 2" site in the country, he said. "(It) may in fact exceed the productivity of some lower end Class 1 sites ... as a Class 2 site Project Hayes is exceptional."

It had a good road and power grid access and had few neighbouring residential locations, he said.

Also appearing for Meridian yesterday, Orion New Zealand chief executive Roger Sutton said Project Hayes was needed to protect against recent volatility in power prices. "More energy is required to satisfy growth. Energy efficiency and conservation efforts are simply not enough to stave off demand."