Energy harvesting?? Only UN-intelligent civilizations fail to use nuclear sources for energy.
“Only UN-intelligent civilizations fail to use nuclear sources for energy.”
The max possible power output of all the fissile elements on Earth is pinprick compared to to energy the Sun puts out in a day. For any advanced civilization nuclear fission would have long been replaced.
Maybe they exhausted their planet’s crust off its sources of fissile material. Of course, they would develop fusion power while exhausting their fissile materials. Maybe they even cracked the code for low energy nuclear reactions.