Jun. 30—The amount the average Avista residential customer in Washington pays for electricity will increase Saturday by about $2.84 a month, according to the Spokane-based utility.

Avista previously had sought approval of the rate increase by the Washington Utilities and Transportation Commission to have ratepayers pay for "deferred power supply costs" as part of the company's Energy Recovery Mechanism.

The "mechanism" is used to track the differences between what it costs Avista to generate and purchase electric power and the cost it charges ratepayers in their monthly bills, according to Avista spokeswoman Lena Funston.

When the balance of the mechanism falls below $30 million, Avista increases rates that users pay. When the balance of the mechanism exceeds $30 million, the rates can be lowered in the form of rebates.

"With the ERM, customers can see their bills increase or decrease as a result of the adjustment," Funston wrote. "In this instance, costs are being recovered from customers."

The rate increase that kicks in Saturday reflects an overall 9.8% increase to Washington residents' monthly electricity bills since Jan. 1, 2020. At that time, the average monthly bill, based 932 kilowatts of usage, was $83.48, according to Avista.

After the most recent rate increase, the average bill will be $91.66, an increase of $8.18 a month in just over three years.

"By way of background, in 2022, the Company experienced an increase in customer usage related to above-normal high temperatures in the summer months and below-normal cold temperatures in the winter months of November and December," Funston wrote.

Those extremes and usage increases "across the region led to higher wholesale electric and natural gas commodity costs that were well above the prices currently embedded in customer rates," she wrote.

The resulting deferral balance of the Energy Recovery Mechanism "was greater than $30 million, thus triggering this rate adjustment filing," Funston wrote.

Under another rate increase approved by state regulators in December, Avista electric and natural gas rate also will increase on Dec. 21, 2023.

Avista officials last year said those increases had been sought in January 2022 and the UTC took 11 months to finally approve them.

The commission eventually approved Avista's request despite expert testimony from Attorney General Bob Ferguson's Public Counsel Unit in the summer of 2022 that the request was "not fair" for customers.

"Washington families are struggling right now," Ferguson said in a statement at the time. "They do not need utility bills any higher than is absolutely necessary."