Located about 40 miles northwest of Minneapolis, the Monticello plant will generate enough electricity to power nearly 500,000 homes.

The shutdown allowed workers to replace major equipment ad pumps to increase the plant’s generating capacity, as well as ensure continued safe and reliable operations.

The upgrade is anticipated to increase the plant’s electrical output by 12%.

Total cost of the power plant upgrade was over budget to $267m, while the company expects the final cost to be even higher.

Xcel Energy, which has 1.2 million electric customers in Minnesota, is urging users to pay for the cost overruns.

Earlier in 2013, Xcel Energy submitted a revised request with the Minnesota Public Utilities Commission, proposing a reduction on its increased electricity rates.