After all, its a rational thing to do while I still have windmills and before they come with unknown intentions

That's the funniest sentence that I've read in a looooong time. But you're on a list now, ooli, you'll never be allowed into the Galactic Order. Bummer, dude.

Correction: You'd need 40 windmills to get their attention by blinking out a message like a star turning on and off. OH, and I forgot to mention above, you'll need to position your laser a long, long way from the planet, because it's too close to the star for us to see anything but the star if it's anywhere near the planets.

If "your friend" wanted to blind them, you'll need around, well, 400,000,000 windmills. How many do you have? How quickly does "your friend" need to exterminate said planet? "Your friend" could just cook them slowly with microwaves, and watch with enjoyment as their world grew hotter over several centuries (and you wouldn't even need to move far away from the star to do it).

What I'm trying to say is that global warming is obviously not man-made, and we're gonna be in an alien stew. They'll time their arrival with when the meal's done. See now THIS is science.