What becomes the single most important factor for sustained community survival during impact winter?

Sustained energy generation for heating and light, independent of solar energy.

While initial preparations like securing food and shelter are vital for regional impacts, surviving a civilization-threatening global impact, characterized by long-term darkness and freezing temperatures caused by the impact winter, places an unprecedented demand on infrastructure. In this protracted crisis, the ability to maintain a community pivots entirely on securing reliable, sustained energy generation capabilities. This energy must specifically power heating and light, functioning entirely independently of external globalized supply chains or the absent solar energy. Success depends on pre-existing expertise in resource management systems, such as closed-loop hydroponics, rather than just stockpiling consumables, as maintaining warmth and visibility over multiple years is the ultimate challenge.