Get a transport chopper and fly to the right side of the oppositions base you can hide behind one of the buildings without getting hit by the obelisk/guard tower. Once you get there you can fly behind the power plant. You may be hit once by the tower but it won't destroy you're chopper. Land behind the power plant and run in to destroy it, with C4 or an Ion/Nuclear beacon.

Then just defend yourself till its blown and you can escape in you're chopper. You can also fly behind the power plant and keep going and blow up the building next door instead.