Energy is everything. Without it, no system can function. There is more to energy than many of us consider (i.e. fossil fuels and electricity). Solar panels/windmills and batteries are one way to store energy, but are by no means the only way. Catching rainwater at a high point is a store of gravitational energy. Catching sunlight with plants to build biomass is a store of chemical energy, as is diverting food waste and composting it into organic rich soil. When a system is charged with energy, it can be more productive.