1. Grow sugar (sweet potato is probably the most efficient, but your environment may dictate otherwise)
2. Ferment
3. Distill
4. Burn in a generator for electricity, or for heating/cooking, etc.
Discussion
This is a brilliant idea thank you
Sugar very energy dense
Conversion kits and books to help can be found here. I recommend a reflux still and zeolite.
Geothermal.
Distillation like Troy mentioned but gather day-old doughnuts, pastries and fruit from stores that would otherwise throw them out.
You're still relying on the industrialized supply chain when sourcing that way. It certainly wouldn't hurt to have external sources in addition, but they can be "shut off" compared to growing your own sugars.