The chairman of Maine’s Public Utilities Commission has stepped down, leaving empty a seat on the three-person commission at the center of the state’s divisive energy policy and utility rate issues.

Mark Vannoy resigned May 3, staying on after his six-year term ended in March to deliberate the New England Clean Energy Connect case.

The Portland Press Herald reports Vannoy’s term focused on Maine’s high electric rates and inadequate natural gas pipeline capacity, among other issues.

Renewable energy advocates criticized him for limiting financial incentives for residential solar power.

Gov. Janet Mills has yet to nominate a replacement. Her office said Tuesday she is currently reviewing candidates.

The position requires Senate confirmation.

There’s speculation on whether Mills will nominate a chair more favorable toward renewable energy and tougher on utilities.