I have a kelp farm that produced a hefty surplus of dried kelp under 1.15 (creating more dried kelp blocks than it consumed in fuel), and under 1.16 it just breaks even. Anyone else having this issue? I can't tell whether it's taking more fuel to cook each kelp leaf down, or if dried kelp blocks don't last as long as smoker fuel.
For me a dried kelp block smelts 20 kelp in 1.16.1 (in either a furnace or smoker) just like the Wiki says it should.
That would give a surplus of 11 dried kelp for every 20 kelp you start with.
So I'd suspect your farm is broken in some other way, allowing kelp or kelp blocks to build up and despawn somewhere.
Are you in single player or on a server?
I was on a server once where they had a plugin that doubled the number of smeltings in a smelter/furnace but I had to stop using lava as a fuel because the furnaces just stopped, wasting the lava, when the chunk was unloaded.
I'd suggest temporarily breaking the supply line between the farm and smokers so you can feed in a stack or two of kelp at a time and see exactly what it does with it.
I'm no redstone expert but if you upload a world download I'd be willing to mess around and see if I can find something, two eyes are better than one.
Kelp grows, gets clipped by the pistons when 3 high, and flows into a pair of smokers all at a steady clip (it's a pair of smokers because my farm is slightly wider than the model, and the kelp WAS backing up with a single smoker when I built it under 1.15). Kelp does not now, nor did it ever, grow fast enough to keep the hopper full before feeding it to a pair of smokers. I will try delaying the feed, changing to a single smoker, and swapping the smokers out for furnaces to let it build up (I could also dump a huge amount of kelp in there to basically prime it). Expanding would be a little bit of a pain, but who doesn't like yet another build?
It's a multiplayer server and the world file is many gigabytes, but I'll see what I can do.
Reminder: it worked fine in 1.15, and I haven't made any design changes since then.