Demand for electricity has fallen, with a 5% fall in generation compared with the same quarter last year.
In the March quarter, there were 9,545 giga watt hours of generation, the lowest figure since June 2003.
Energy and Resources Minister Gerry Brownlee says the figure reflects the slow economy and reduced usage at the Tiwai Point aluminium smelter.
Mr Brownlee expects generation to pick up as the economy improves and the smelter comes back online.
He says one positive aspect is that 73% of the electricity generated and consumed in the past quarter came from renewable sources, the highest for a March quarter since 2005.