ARIZONA settled only half the issues in a dispute between solar rooftop companies and Arizona Public Service, and then only temporarily.

The case is a test for what may end up a larger fight with utilities nationwide.

Arizona Public Service asked permission to charge customers who install rooftop solar systems to generate their own electricity $50 to $100 a month for the right to remain connected to the grid for backup power. It also complained that it is required to pay customers who sell it excess electricity from rooftop systems a retail rate for the electricity when the utility can buy the same power more cheaply from wholesale suppliers. It asked to be able to credit such customers at only the wholesale price.

The Arizona Corporation Commission in November by a 3-2 vote said APS can charge a monthly fee of 70¢ per kilowatt, which works out to roughly $4.90 a month for the average solar customer. The fee will be effective from January 1, 2014. Current solar customers and those who submit an application and a signed contract with a solar installer by December are not subject to the new charge.

The charge will remain in effect only until the next APS rate case, which the commission directed APS to file in 2015, at which time the commission will revisit the fee and also address the net metering issue.

APS estimates that solar installations are reducing load growth by about 0.5% a year. Only about 1.9% of APS customers have solar rooftop systems currently. About 80% of APS customers who add solar lease the systems. APS says the average homeowner saves about $70 a month by switching to solar.

Analysts are maintaining a “buy” rating on the APS parent company, Pinnacle West, because of disproportionate load growth expected over the next decade.