Arizona Public Service recently filed a 15-year outlook on energy consumption for its customers, and one nonprofit would like to see the utility commit to using more renewable energy.

APS expects increased demand by 2031, when it hopes to shutter its coal-fired plants. The utility says it remains committed to producing clean power, but also wants to maintain reliability, especially during the summer months.

Alex Routhier of the nonprofit Western Resource Advocates said APS could save consumers more than $100 million by moving to renewable energy faster.

"We’re not asking them to sacrifice reliability for sustainability. We think those two things can work hand in hand and we can move forward in a way that’s both reliable and sustainable," Routhier said.

Jacob Tetlow with APS says the company will need a good mix of energy sources to meet that demand.

"Frankly, reliability really has to be first. If you can’t keep the lights on that’s fundamental. You also have to balance affordability, and you have to transition to clean or sustainable energy. And so we’re doing all three of those," he said.

But it will continue to reduce its carbon footprint.

"You know we’re over 51% clean energy today. We’re on track to be 65% clean by the end of the decade. So, we will shut down Four Corners Power Plant in 2031. It’s our plan," Tetlow said.

He says that changes in technology could give the company more flexibility in the future, allowing it to meet its clean energy goals sooner.