Benton PUD electricity rates will increase 2.9 percent starting in October, the agency announced Tuesday.
The average residential customer will pay $3 more a month, with the average bill increasing from $116 to $119.
The last rate increase was nearly 2 percent two years ago, following a 4.9 percent increase in 2016 and a 3.9 percent increase in 2015.
The public utility district says its average monthly bill remains below the median monthly residential bill of $127 for comparable Northwest utilities.
The almost 3 percent increase set by the Benton PUD applies to all parts of the bill, including the cost of providing service and the kilowatt-hour rate.
Rising power costs are behind the rate increase, according to the PUD.
It spends 60 percent of its budget buying power to distribute to 50,000 customers in Kennewick, Finley, Benton City, Prosser and some other outlying areas.
On Oct. 1, the PUD will have to start paying more for much of the electricity it buys because of a rate increase for the wholesale power from Bonneville Power Administration.
Less low-cost hydro-generated electricity is coming from Columbia and Snake dams, because of trends toward lower water flows in the summer and a federal court order to spill more water over the dams rather than use it for hydropower to help juvenile fish migration.
Benton PUD has to buy higher-priced power during the peak summer air conditioning months, as less hydropower is available.
The Energy Independence Act also increased requirements for the Benton PUD this year. It now must supply 15 percent of its energy from wind and solar sources at a higher cost, up from 9 percent last year.
The act was the result of voters approving Initiative 937 for larger electric utilities in the state of Washington to increase the use of certain renewables.
Hydropower is excluded as an approved renewable power source under the act.