Article on Death Star Firepower:
The article works out how much energy had to be in the beam that blew up Alderaan. Long story short, something in the range of 10^32 joules is necessary to blow apart a planet. A joule is one watt-second, so considering that the beam struck Alderaan for about one second in Episode IV, that means the Death Star superlaser had a an output of 10^32 watts.
The National Ignition Facility–which is using the world’s largest laser array to try and create a microsoecond of fusion–informs us that the entire United States has an electrical generating capacity of about 5 x 10^11 watts. Back-of-the-napkin math: It would take 10^21 United States-worth of generators–as in a billion trillion Americas–to generate the same amount of energy that the Death Star superlaser released in one second.
If anyone can find a way to solve the energy crisis it's Darth Sidious.