Central Ohioans who have rooftop solar panels receive a credit on their electric bills for selling excess power back into the grid. After a ruling Wednesday by state utility regulators, that credit is likely to shrink.For an American Electric Power customer, the credit would be reduced by about 30 percent.The Public Utilities Commission of Ohio issued the 3-0 ruling in a case dealing with the rules for so-called “net metering,” a term that refers to the two-way flow of electricity for consumers who generate power through small-scale solar panels, wind turbines and the like.Right now, an AEP customer producing excess electricity receives a credit that is the equivalent of 5.86 cents per kilowatt hour sent back into the grid. For example, if a customer produces an excess of 100 kilowatt hours in a month, the current credit is $5.86. The amount rolls over and is applied to the next monthly bill.The PUCO ruling says that some parts of this credit no longer need to be applied. In the AEP example, this would reduce the amount of the credit by $1.81, or 31 percent percent, based on a review of AEP rates and confirmed by the company.