Transpower admits it messed up numbers after mistakenly pulling power from too many homes

Transpower has admitted it messed up the numbers when calculating where power needed to be cut on Monday night after it mistakenly pulled the plug on too many homes.

Thousands of Kiwi households were left freezing and fuming on Monday night after a series of surprise outages, some of which may have been avoidable.

"We made an error," Transpower CEO Alison Andrew says.

Transpower operates the national power grid, and It miscalculated how much power needed to be reduced by certain customers in certain areas. For example, Tiwai Point Smelter was mistakenly told to cut consumption by a massive 993 megawatts. 

"We got that wrong and we own that mistake. That meant that some market participants were asked to reduce more demand than others," Andrew says.

Lines company WEL Networks, which sends power to thousands of Hamilton homes, says Transpower ordered it to pull the plug on almost 18,000 homes on Monday night - but that was too many.

Internal experts within Transpower told Newshub on Wednesday that it's investigating the calculation errors. 

But it's not the only mistake it made. Newshub can reveal that power company Mercury offered Transpower an extra 12 megawatts of power on Monday, but it ignored the request.

When asked whether Transpower is incompetent, Andrew says that generation isn't within the company's control.

Transpower is pinning the blame for the blackouts back on power generators, saying if there was enough power in the system, this would have never happened. 

But power companies Mercury, Meridian, and Contact have all sent letters to Energy Minister Megan Woods saying they were making as much power as they could on Monday. 

"All of Mercury's equipment that it could possibly generate with was fully operating at the time," says Mercury chief executive Vince Hawksworth.

Genesis Energy boss Marc England told Newshub on Tuesday he didn't get enough warning to ramp up an extra unit at the Huntly power station. But on Wednesday he was hauled in front of the Energy Minister for a please explain.

"Oh look, I'm unhappy with the way she's pointed us out," England says.

The generators want the finger to stop being pointed at them and instead at a solution. 

"Monday night shouldn't be a repeatable thing," Hawksworth says.