Tucson Electric Power Co. has filed a petition with the Arizona Corporation Commission seeking higher rates that could increase customers’ bills by an average $13 a month, officials say.

The 15 percent rate increase is needed to cover rising cost and system investments, said Joseph Barrios, a TEP spokesman. Between 2007 and 2011 TEP spent more than $1 billion maintaining the system that serves more than 400,000 customers in the Tucson area, he said.

“That money went to projects that strengthened our power plants, it went to improvements to our distribution centers, it went to environmental projects that reduced emissions, and it also went to our solar energy projects,” Barrios said.

TEP’s request will be reviewed by the ACC, a five-member panel of elected officials that sets utility rates and oversees other aspects of the company’s operations, according to TEP.

If approved, this would be TEP’s first rate increase since 2008. It would take effect as early as August 2013.