A couple of tricks I've used for cooking beans using very little fuel:

Solar Cooker - Soak the beans overnight. I had a gas cooker so I would bring the beans to a boil then shut off the gas. Then I'd put the beans into the solar cooker. This gets the beans up to temperature very quickly so they can cook for a long time in the solar cooker, whereas it would take a while to heat up if you put them in cold.

Thermos - This is the "fireless cooker" method. Soak the beans overnight. I'd bring them to a boil like before, then pour them into a large thermos. I made sure to fill the thermos all the way with water. I'd let it sit for about 8 hours or so. This didn't work as well as the solar cooker, but it's an option if there's no sun.