California is the leader in solar capacity by a mile, with roughly five times North Carolina’s solar capacity. But requiring rooftop solar panels on new housing could add another 13,160 megawatts to those Tar Heel numbers, Environment North Carolina asserts in the report.

That could lead to the 9 percent drop in the state’s power-related carbon emissions over the next 25 years, the nation’s largest percentage reduction in greenhouse-gas emissions linked to residential solar arrays, according to the report prepared by researchers for Environment North Carolina’s parent group headquartered in Colorado.

But the cost factor could be an obstacle. California’s new standards are expected to add about $9,500 to the cost of a new house, although the report says rooftop solar then would go on to save the average homeowner about $19,000 in energy and maintenance costs over the next 30 years.

The builders association’s Carpenter considers those numbers misleadingly optimistic. He said that on average, North Carolina residents stay in their houses 10 years before moving on, suggesting that many buyers would not reap the financial benefits described in the report.