The Iowa Utilities Board has approved Alliant Energy’s one-time $110 million payment to end its purchase agreement with the Duane Arnold nuclear power plant in Palo in 2020. Members of the board said they are concerned about Alliant’s ability to find enough energy elsewhere, but the utility has said it plans to add wind energy and make other adjustments to make up for the power. Alliant’s shift away from Duane Arnold, which is expected to close eventually, will save customers $300 million beginning in 2020, dropping power bills by 2 to 3 percent. IUB staff said the board is required to make sure Alliant provides “safe and reasonably adequate service” and will monitor the transition.