Sucking energy from a powerplant

Others have pointed out that it would have made much more sense for Kronos to gather solar energy, but I see another problem in the film with respect to it sucking energy from a power plant. The total energy output of such a plant is its power output multiplied by the amount of time it operates. So if Kronos sits there for a couple of minutes, it only gets two minutes worth of energy. Not exactly an efficient use of time. So many power plants, so little time....