Power company Mercury will spend another $208 million building the country's largest wind farm near Palmerston North.
It had resource consent to build up to 60 turbines on the site in Turitea, but initially agreed to erect only 33 in March, at a cost of $256m.
However, it will now add the remaining 27 turbines.
"Being able to complete the Turitea wind farm at its full scale contributes further to New Zealand's sustainable, low emissions future by making more renewable, Kiwi-made electricity available for homes, businesses and vehicles throughout the country," Mercury chief executive Fraser Whineray said in a statement.
"The combination of long-term electricity demand projections, synergies from already committed transmission infrastructure, construction and operations on site, and co-benefits with the Waikato hydro system mean completion of the Turitea wind farm makes sense."
The completed wind farm would produce as much as 840 gigawatt hours of electricity a year.
Mr Whineray said the Zero Carbon Act meant there would be a need for significant amounts of renewable electricity.
"Renewable energy projects are about the very long term, and we believe the case is compelling for the completion of this leading North Island wind farm site, situated close to the national grid, supporting New Zealand demand into the future."