Yay math! For the record, "giant rocket thruster burning for millions of years" seemed like a pretty stupid solution to a pretty predictable problem. But I dug the geeky nerdy giant number-ness of it. Thus, your answer is awesome.

And while I'm right there with ya on the whole "death ray" aspect of it, and am not going to quibble about the orders of magnitude of doom projected, I do think there are some errors on your math.

So let's presume that 1368 W/m^2 falls on the earth. That's an "at noon" number for the sun directly overhead. However, when it's noon in New York it's sunset in London and sunrise in Alaska - total energy does not fall on the surface of the earth uniformly, but rather proportionally. Our actual number, then, is not 68e6/(AreaOfEarth/2) but 68e6/piRadiusOfEarth^2) = 1.75e14 W. Whack 12 digits off that and you've got 175 terawatts hitting the earth at any given time.

You get .13 terawatts. I get 175 terawatts. Actually, that is* four orders of magnitude. Do me a solid and double-check my math, wouldja? I gotta get back to work.