Inland Power & Light Co., the Spokane-based electric cooperative, posted net margins of more than $5.8 million last year, up sharply from $3.6 million in 2010, but it says part of that gain was due to a one-time benefit.

"Bonneville (Power Administration) changed the way they bill us for power, which was advantageous," says CEO Kris Mikkelsen. Even without that benefit, though, she says, Inland Power still would have had a "very strong" year.

For the nonprofit co-op, net margins are the equivalent of a for-profit company's net income. It reported operating revenue for last year of $59.3 million, up 6 percent from $55.9 million in 2010. Meanwhile, its total cost of electric service in 2011 was $53.8 million, up 2 percent $52.7 million in the prior year.

Inland Power's total assets at the end of last year were $150.2 million, up 3 percent from $146.3 million a year earlier.

Mikkelsen says that a mild winter in terms of major snowstorms enabled the co-op to hold down costs related to power outages, but cold temperatures still increased the consumption of power on its system.

Looking ahead to the rest of 2012, she foresees slow, steady growth, and adds, "I think we should have another strong financial year."

Inland Power plans to implement a 6 percent rate increase in April to cover the cost of a wholesale power rate increase that the BPA enacted last October, she says. The co-op is what's called a "full requirements" customer of the BPA, meaning that the BPA, which markets the electricity generated by the Northwest's federal dams, provides all of the co-op's power requirements at cost-based rates.

Inland Power added just 210 new customers last year, boosting its overall membership to 38,660, and refunded $1.25 million in what are called capital credits to its members, which is the same amount it had refunded in three of the four prior years. Capital credits are sums returned to members in the form of checks out of any revenue surplus above what the cooperative needs to cover operating expenses and capital expenditures.

Mikkelsen informed Inland Power's board late last year that she plans to retire this spring. The board hired an executive search firm to help find her replacement, but hasn't released any information on how that search is progressing or when it expects to announce a successor.

"I'll do whatever it takes to make a smooth transition," Mikkelsen says. She says hasn't set a specific departure date and expects to remain with the co-op for a few more months.