Tucson Electric Power is planning to cut its coal generation capacity by one-third over the next 15 years, while expanding its reliance on natural gas and renewables.

The company outlined its objectives in its Integrated Resource Plan, submitted to the Arizona Corporation Commission at the beginning of the month.

Company spokesperson Joseph Barrios said the plan outlines TEP’s diversification strategy.

“What the integrated resource plan does is it provides a map....a long-term map that shows how we plan to meet the energy needs of our customers over the next 15 years," Barrios said.

The report said coal will still contribute the largest portion of the company’s energy mix. By 2028, TEP projects that just over 40 percent of its electricity will come from coal, just over a third from natural gas, and about 20 percent from renewable energy and energy-efficiency programs.

To replace some of the lost capacity from existing coal-fired resources, TEP and UniSource Energy Services are planning a joint purchase of a unit at the natural gas-fired Gila River Power Station in Gila Bend. Barrios said the sale will be completed by the end of the year.

TEP expects to add more than 50,000 customers over the next decade. Peak demand is projected to grow annually by about 1 to 1.5 percent.