Not just power generation but also the calorific and opportunity cost of working on that (or indeed anything that does not immediately pay off in energy terms). Or else you die before your compiler is done ;)
If you have more than one survivor, you quickly need to learn to trade and cooperate to maximize your energy return, or else you all die, one by one.
This. Skill sharing among a small tribe is the most effective way to survive a catastrophe, and I am concerned modern societies are poorly conditioned to do it well.
Speaking from a North American perspective, kids are educated in how to succeed in a national/global economy, not how to build small communities and develop/share useful skills. TBH, the latter feels "obsolete" nowadays. Maybe that's a problem.
If you have more than one survivor, you quickly need to learn to trade and cooperate to maximize your energy return, or else you all die, one by one.