New Zealand's first super-sized grid-connected battery - built at a cost of $186 million - will help improve Northland's energy resilience in future power outages, Meridian Energy says.

The company said its Battery Energy Storage System (BESS) would also help smooth out power peaks and troughs, by storing energy when electricity is cheap and releasing it at times of peak demand, such as early mornings and evenings.

The battery park consisted of 80 shipping-container-sized batteries spread over a two-hectare site at Marsden Point, next the former oil refinery south of Whangārei.

Project director Alan de Lima said at full capacity the giant battery could supply 100 megawatts (MW) of power, enough for 60,000 homes or about half Northland's population, for two hours.

It had been connected to the grid since the beginning of the year and would start operating as soon as final tests had been signed off.

It was also stage one of Meridian's planned Ruakākā Energy Park.

Stage two would involve building a $227m 130MW solar farm, with 250,000 panels spread over 172ha of land next to the battery.

Work was due to start in August with power expected to start flowing in early 2027.