MONTGOMERY, (AP) — Homeowners and an environmental group are asking federal regulators to step in over Alabama Power’s fees on home solar panels, fees they argue purposely discourages the use of solar in the sun-rich state.

The petition filed with the Federal Energy Regulatory Commission asserts that the Alabama Public Service Commission violated federal law when it upheld the fees. It asks the commission to initiate an enforcement action against the PSC and direct the state agency to order Alabama Power to sell electricity to solar customers at nondiscriminatory rates.

“By imposing one of the highest fees on solar customers of any regulated utility nationwide, Alabama Power’s unjustified solar charges are severely curtailing renewable energy development in our state, and other states are leaving Alabama behind because of it,” Keith Johnston, director of Southern Environmental Law Center’s Alabama office.

“We are asking FERC to exercise its authority to enforce federal protections for solar customers in Alabama Power’s service territory.”

The action comes after the Alabama Public Service Commission last year upheld the fees and approved an increase.

Alabama Power charges a $5.41-per-kilowatt fee, based on the capacity of the home system, on people who use solar panels, or other means, to generate part of their own electricity. That amounts to a $27 monthly fee on a typical 5-kilowatt system. The average solar panel setup for a home costs about $10,000, according to the Environmental Law Center. The fees add another $9,000 or so over the 30-year-lifespan of a system, dramatically increasing a homeowner’s cost and reducing any financial benefit they see from solar.

Alabama Power has maintained the fee is needed to maintain the infrastructure that will provide backup power to customers when the solar panels don’t provide enough energy.

“Alabama Power is focused on providing customers with safe, reliable, cost-effective energy. This issue was fully examined by the Alabama Public Service Commission, which included a lengthy public hearing, with the plaintiffs choosing not to pursue the case further in state court,” Alabama Power spokeswoman Alyson Tucker wrote in an email.

“Customers with on-site generation who want backup service from the grid should pay the cost for that service. If not, other customers unfairly pay the costs for those individuals and businesses,” Tucker said.

Experts for environmental groups said the charge eliminates much of the savings that customers expect to realize for their investments in installing solar panels.

Teresa Thorne, who had a four-kilowatt system installed on her roof in Blount County, Alabama, told The Associated Press last year that the fees, “cuts my savings in half.”

“Alabama Power’s monthly fee makes it extremely difficult for people like me who want to install solar to lower their monthly bills and generate clean energy,” Thorne said in a statement released by the Southern Environmental Law Center.