ST. LOUIS -- Environmental groups have dropped a lawsuit that sought to reinstate solar energy rebates for customers of utility Ameren Missouri.

The Missouri Coalition for the Environment and Save Our Lawfully Authorized Rebates LLC filed earlier this month to dismiss the lawsuit against the Missouri Public Service Commission, the St. Louis Post-Dispatch reported.

The suit, filed last year in Cole County, sought to strike down a regulatory agreement capping the amount of customer rebates that can be issued by the state's largest utility companies.

But a recent Public Service Commission rule change on how the amount of rebates should be calculated prompted the groups to dismiss their lawsuit.

Paid for by the utilities, the rebates partially reimburse utility customers who install solar arrays on their property.

The lawsuit had focused on how to implement a 2008 voter-approved law that sets targets for renewable energy production by investor-owned utilities.

The law also requires them to pay rebates to customers who install solar energy panels on their properties.

The law required that renewable energy account for 5 percent of electricity in 2014, and 15 percent by 2021.

But it also said utilities couldn't raise electric rates by more than 1 percent to comply with the renewable-energy standards.

The law was amended in 2013 to allow utilities to stop solar rebates if power companies determined the 1 percent cap would be reached.

Ameren Missouri and Kansas City Power and Light Co. sought permission in 2013 to suspend the rebate programs because of customer demand.

As a result, the regulatory commission approved agreements capping Ameren Missouri's solar rebate payments at $91.9 million.

Separate agreements capped solar rebate payments at $36.5 million for one of KCP&L's service territories and $50 million for another of KCP&L's service regions.

The lawsuit challenged the calculation methods used to determine those limits, alleging they were based on "speculative and hypothetical expenditures" for future projects and significantly understated "the amount of solar rebates that should be paid."