North Carolinians' spending on renewable energy doubled last year and has grown 25-fold just in the past five years, according to state tax data. Whether you approve of green energy or not, that's a remarkable transformation for a state in which solar panels were virtually unknown until recent years.

N.C. Department of Revenue data show that interest in renewable upgrades blasted off after the state legislature passed an energy law in 2007. The law requires electric utilities to buy output from solar panels, wind turbines and other private renewable generators.

The revenue data tracks state tax credits claimed every year on renewable investments. The state's 35 percent tax credit is considered one of the most generous in in the nation. Combined with a 30 percent federal tax credit, it reduces the cost of renewable project by more than half.

In 2011, North Carolina residents and businesses claimed $11.3 million in tax credits for renewable property. Such projects typically include solar photovoltaic, solar thermal, geothermal and wind turbines.

The 2011 credits doubled the previous year's, which came to $5.3 million. The 2010 credits again doubled from the year before, or $2.7 million in 2009.

A nearly completed review of backlogged tax returns shows that seven thousand people who did not know they had overpaid their taxes are due refunds that add up to $2.3 million, the Revenue Department's new secretary told lawmakers today.

Secretary David Hoyle, a former state senator from Gaston County, told them that the department has cleared the backlog of flagged items from individual tax returns. He told them they will need to pass legislation next year in order for the department to return the money.

State tax authorities are offering a compromise to online retailers that don't charge charge the state sales tax to their North Carolina customers.

The N.C. Department of Revenue said this morning it will forgive all back sales taxes and penalties to businesses that sign an agreement by Aug. 31 to start charging customers the sales tax.

"We are going to be asking quite a number of them to participate in the program," said revenue Secretary Kenneth Lay. "We have positive indications that several will sign up."