2 points to consider here, first the damage to the grid in terms of lost power, second the environmental damage. For nuclear both are quite severe, but blowing

2 points to consider here, first the damage to the grid in terms of lost power, second the environmental damage. For nuclear both are quite severe, but blowing up a dam could be devastating in both points too, think of the flooding etc.. Blowing up single wind turbines is ineffective in both terms, and damaging a coal/oil plant only in regards to the first point(Well, there will be environmental damage too, but not on the scale a terrorist desires..) Solar seems to be the safest with that in in mind.