Twelfth power energy was the measurement given by passive sensor scans on the USS Enterprise, regarding the power output of the V'ger energy cloud when scanned by Spock.
According to Commander Decker, "thousands of starships couldn't generate that much..." Spock further elaborated that V'ger was "generating a force field greater than the radiation of Earth's sun." (Earth's sun radiates 384.6 Yottawatts) (Star Trek: The Motion Picture)
In a possibly related nomenclature, the collapse of the Amargosa star was stated as generating a "...level-12 shockwave." (Star Trek Generations).