I believe it was either a major failure of a key gas, coal or hydroelectric plant, or it was an overload possibly from wind or solar interruption or a simple increase in demand. I don't think it was an EMP or CME, as this wouldn't have caused a sag in the frequency leading up to failure. In regard to green energy, I believe it is highly unlikely this to be the cause unless their grid is grossly mismanaged and lacking basic safety equipment. The fact that they are able to bring power back to some areas and not others indicates the underlying problem is either a loss of baseload generation, a failure or lack of over generation loads, or a failure of a key distribution station.