North Dakota's Public Service Commission, which has been investigating Otter Tail's handling of the short-term price spike, voted to end its probe with the conclusion that the utility should not be blamed for the problems.
"The commission realizes the hardships that this posed to Otter Tail customers," said Susan Wefald, the commission's president.
"However, we also recognize that sometimes these things happen."
Otter Tail, based in Fergus Falls, Minn., has about 57,000 North Dakota electric ratepayers. It serves the cities of Wahpeton, Jamestown, Devils Lake and a number of smaller communities.
One of Otter Tail's primary suppliers of electricity, the Big Stone power station near Milbank in northeastern South Dakota, was shut down for two months late last year for maintenance.
Otter Tail had planned for the shutdown and arranged to buy replacement power in advance, commissioners said. But problems developed with the company that had been hired to do repairs, and the job was more extensive than the utility expected.
Otter Tail then had to buy more replacement power at costly rates, said Wefald and Commissioner Tony Clark. Those increased expenses were passed along to customers through their monthly bills from January through May, prompting a flood of ratepayer complaints.
Wefald and Clark said that although the higher bills hit customers' wallets, Otter Tail acted correctly in pressing ahead with repairs instead of deciding to limp through last winter and hope the maintenance could be done in the spring.
Delaying the repair work could have forced a longer plant shutdown, which would have meant buying even more expensive replacement electricity, the commissioners said.
"It was really making the best of a bad situation," Clark said. "It's not a conspiracy, it's not any sort of malfeasance or incompetence on the part of the utility. It's just bad luck."