COEUR d'ALENE - Avista Corp. no longer wants to be vulnerable to the whims of customer usage of electricity and natural gas - which is trending downward.

It wants to make sure it gets its money for standing ready at all times to make sure the lights come on when customers flip the switch, so the Spokane-based utility has asked Idaho's utilities regulator to approve a billing mechanism called a "fixed cost adjustment."

Avista, which serves 127,000 electric and 78,100 natural gas customers in Idaho, filed a request with the Idaho Public Utilities Commission this month for higher rates. It is seeking annual electric revenue increases of 5.2 percent, or $13.2 million, and 5.8 percent, or $3.2 million, for natural gas.

Rolled into that is the additional request for the fixed cost adjustment.

The mechanism is "designed to break the link between a utility's revenues and a consumer's energy usage," Avista said in a press announcement.

Such a mechanism could result in surcharges for customers.

AARP put out a report in 2012 titled "Increasing Use of Surcharges on Consumer Utility Bills."

"The proliferation of additional fees and surcharges generally shifts risks away from utility investors and onto consumers," the report said. "This report describes why consumers should be concerned about the shift toward utilities collecting more costs outside of the traditional rate structure."

The report said surcharges can also reduce incentives for utilities to control costs, and benefits them by assuring they can recover costs of operation.

Avista is trying to better recover its fixed costs - operating dams, turbines, and transmission and distribution systems.

"Generally, the investment community has been supportive of mechanisms like the proposed fixed cost adjustment because these types of mechanisms can provide utilities with a better opportunity to recover costs of providing service to customers," Jason Lang, Avista's manager of investor relations, said this week.

Depending on variables like weather, Avista might under-recover or over-recover costs.

"If we recover more we'll give it all back," said Pat Ehrbar, Avista's manager of rates and tariffs. "If we recover less, we can seek that back from customers through a surcharge."

Avista already has approval for this mechanism in Washington, except it's called "decoupling" in that state. It was effective there on Jan. 1.

There wouldn't be any charge or credit on customer bills, however. Avista would track the numbers for a year and seek a surcharge or provide a rebate. It would show up the following year in the form of a billing rate adjustment.

"Usage drives revenue and drives earnings today" in Idaho, Ehrbar said.

He said Avista wants to break that cycle.

"We've had this fundamental drop in use per customer in all our jurisdictions" in electric and gas service, Ehrbar said. "To the extent that we would have had one of these mechanisms, we would have had a better chance to earn our allowed rate of return set by the commission."

There have been a lot of years when Avista didn't reach its allowed return because of declining use by customers, he said.

Statistics show use per customer, for both residential electric and natural gas, declining the past nine years in Idaho.

"Among the chief reasons for this decline is increased energy efficiency," Ehrbar said.

Average monthly usage for Idaho residential users has slipped from 977 kilowatt-hours in 2006 to 929 last year. Average monthly usage of natural gas has dropped from 68 therms in 2006 to 61 last year.

Ben Otto, energy associate for the Boise-based Idaho Conservation League, said his group has watched Idaho Power use a fixed cost adjustment for seven years. Idaho Power serves 516,000 customers in southern Idaho and eastern Oregon.

"We've taken the stance that it's working," Otto said. "We'd like to see it expanded to other utilities."