The country's largest listed power company, Contact Energy, says prices have risen to over $79 a megawatt hour - more than double that of the same period a year ago.
The company notes North Island storage levels are only a third of the mean for the time of year, reflecting the dry autumn, though South Island storage is 139% of the mean.
Total generation declined 6% to 756 gigawatt hours.
Contact had 476,500 customers in April, as decrease of 0.4%.
