Federal grid watchdogs are raising alarm bells over a solar panel design flaw that could result in power outages nationwide if not addressed, based on the results of a near year-long investigation into a major outage last summer in California.

The North American Electric Reliability Corporation on Thursday issued the results of the investigation on an August 16, 2016, outage that occurred in southern California as a result of a wildfire that caused a large chunk of solar rooftops to trip and stop delivering electricity at a critical time.