What difficulty setting were you playing on? I'm surprised lighting would hit a building that early unless you were playing on Insane difficulty (or something harder than Normal).
Yes, it's painful when that happens as there's no good way to recover if you don't have backup, and we may add logic in the future to make lightning less likely to hit your only Geothermal if you only have one.
At the same time, this is, to be frank, part of the game. Your best bet is to make sure you cover your colony with Lightning Towers and acquire backup power sources as soon as possible.