In April Unison introduced a controversial new lines charge to ensure solar customers contributed fairly to the network they used at peak-demand times.
Mr Atkinson said it sought to ensure customers without solar were not disadvantaged by having to subsidise customers with solar. From April 1, the company also made available a time-of-use price structure, which provides significant rewards for customers willing to actively manage their demands and reduce pressure on the network at peak times.
Mr Atkinson has served on the board for nearly two decades, chairing it for the last eight years.
"The business has come a long way since my first board meeting in June 1998. Back then, a key item on the agenda was Unison's float at the Hastings Blossom Festival," he said.
"The challenges and opportunities facing Unison today are substantial and more complex, though perhaps no less controversial."
Power Consumers' Trust chairman John Newland said Trustees were pleased with another "solid" financial result.
"While network performance was down, we appreciate the vagaries of the weather and believe Unison's response to the August snow storm was exceptional in very difficult conditions," he said.
Unison Group chief executive Ken Sutherland thanked Mr Atkinson for his dedication.
"Kevin's drive and passion for the Unison Group and its people has resulted in solid and sustained growth during his term as chair," he said.
"His financial directorship and strong commercial acumen has ensured the business consistently delivered on key targets. His contribution to the direction of Unison will be missed but means we are well placed for the future."
Both Mr Atkinson and Mr Sutherland extended thanks to John Newland and Trustee Arch Buntain, who have served the maximum consecutive term of nine years and are not eligible for re-election.
Nominations for the Trust election close this week.