That was a fair Impossible badge. After much frustration, consternation, and pure practice...and a little luck. Not the hardest Impossible, but definitely a fair one.
So, I had it. I'd made it through to the very end and was just listening to the end of the song. So I decided to see what the impossible badge was... and I lost. I hate that click thing :(
actually, nuclear is by far the most efficient, though thermal is good too. My recommendation is that you make a square of defenses, then plant the nuclear dump in the center. Since you only need one dump for numerous nuke plants, build a bunch of nuke plants and run everything off of energy (until defending, then switch vehicles to natural gas if you have it).
Dude! You just completed the Black Hole Escape Artist achievement in Fold and won the Black Hole Escape Artist badge and 60 points!
This game is phenomenally creative!!