My friend made a machine that automatically farms cactuses and I was wondering if there is any combustable items that can be farmed without human intervention?
I discussed this in a chat before, the topic back then was keeping a furnace busy forever. My research results were that the only smeltable items that could be farmed fully automatically, meaning with no player even being on the server, were raw chicken and cobblestone.
And no fuel item was farmable fully automatically. That was in July, since then a few smeltable items and fuel items were added, but you still can't fully automatically farm a fuel item.
So what is the next best thing? Random ticks and mob spawning. They happen in a big radius around players, so you would just need one player being in the area, who does regular player stuff or sits at a different farm or whatever.
The fuel items that only depend on random ticks or mob spawning are:
- Coal (from wither skeletons)
(One funny alternative would be banners from pillager raids. But they require you to at least punch them yourself.)
As @Dan Bron implied in their comment, one other way that would work without having to go to the nether would be using a kelp farm. This one is simple and only requires a piston and observer. There are many possible layouts for kelp farms, but all you have to do is put the kelp into a smelter and make dried kelp, then once you have dried kelp you would craft dried kelp blocks to use as a combustable material. reference youtube video
The most common approach is to use the carpet duplicator - it's a bug exploitation but it's very efficient and easily keeps up with the demand, without problems.
The only other somewhat viable approach is sticks from the witch farm.
Blazes need to be killed by a player or tamed wolf to drop blaze rods. Wither skeletons are a little too rare spawns to make fully automatic coal farming viable (although if you do have an afk wither skeleton farm, you might add a full auto mode.)
Since 1.14 full auto bamboo farms become a viable source. Of course player presence within random tick range is required.