But National education spokesperson Erica Stanford says Hipkins is making "one of the lamest excuses [she's] ever heard", and the spend is "completely reckless".
The Ministry of Education told ZB it had "reminded contractors to ensure lights are turned off when they leave for the day".
During May, the ministry announced staff would have to leave Mātauranga House on Bowen St, after an engineering report rated it 25 per cent of the New Building Standard (NBS), due to its concrete floors.
It was too early to know how long remediation work would take, or even if staff would be able to return to the same building.
In 2015, a year before the ministry moved in, the building was regarded as "low risk".
Responding to written questions by National, Hipkins said "electricity costs for Mātauranga House for the months of June, July and August total $21,502".
"The Ministry is continuing to honour the lease whilst further engineering evaluations are taking place and the dispute resolution process is worked through."
Ministry of Education infrastructure and digital group manager Rob Campbell has confirmed "lights are on and lifts are working".
"Contractors are dismantling furniture and IT equipment ahead of our planned move to new premises," he said.
He revealed the move is set to be "largely completed by 10 October", with the power bill expected to drop after that.
"Emergency lighting will remain on permanently in areas such as stairwells and to create a secure area outside the building, and we've asked an electrician to check that we are using power efficiently in these areas," he said.
In an interview with Newstalk ZB, Hipkins accepted the process of moving "has taken some time".
"It's been done with relatively reduced numbers of people due to safety reasons.
"Those big buildings do require a lot of juice to keep them going."
Photos and timestamps seen by Newstalk ZB show lights burning hot in Mātauranga House, from reception area to office spaces, as early as 5.08am.
But Hipkins dismissed any concerns power was still flowing, even when contractors weren't on site.
"To be honest, I'm not keeping a time sheet of who is going in and out."
National's Erica Stanford has hit back, saying "Chris Hipkins likes to be flippant about these things... [but] it's a slap in the face for New Zealanders who saved power over winter.
"He can literally see the Ministry of Education building from his office [Beehive], I would suggest... he knows the lights are on and he's done absolutely nothing about it.
"This is a sign of a Government that is out of touch, and has a general disdain for taxpayers' money".
