Hello,
I was looking inside the fuel recipe since I'm about to finally launch myself in the chimical era and was surprised to see that building fuel via solid fuel is actually more expensive than building fuel directly from light oil. In both case, if you have your solid fuel via light oil, it's 60 light oil for 10 fuels but you have to ass an other 50 hydrogen when you produce fuel via solid fuel. Is it intended ? Is there something I miss ?

Honestly, I never understood it either. There doesn't appear to be any practical use for solid fuel when wood can easily carry you all the way to electric furnaces and biofuel tier, so you're never incentivized to make it in the first place. I suppose you do have a bunch of Hydrogen left over from making Chlorine, but again, voiding hundreds of thousands of excess fluid is as easily as deconstructing a couple of large storage tanks. The hassle of coupling your stone/sand processing area to all your petrochem stuff through this one link just doesn't seem to be worth the hassle.

The wood was nerferd for this topic in fact, be able to produce wood make it too worth, in fact for use wood as combustible require a lot of resources. The requirement of Hydrogen in the Fuel from Solid Fuel is a nerf to the Solid Fuel and an incentive to use Hydrogen.

To be honest, I'm not sure it's an incentive to use hydrogen. it' just better, for someone wanting to transiting from solid fuel to fuel, to just replace those chemical plant (or whatever the name). It's purely a waste of hydrogen to make fuel via solid fuel, and it's produce more pollution (one more line). Better add/Delete huge tank, indeed.
I have to admit I have no clue how it is difficult to balance a huge mod like Krastorio 2, and you make a really good job since it's the only point that bother me (some items also are quite scarce in description, but it's nothing). So it's only a 2 cents viewpoints from myself (I just add a modded recipe to use my excess of hydrogen so I'm fine anyway).
Thanks for your good job :)

Oh u don't know, trust me, balance a huge mod is a pain, ahahah :)
Anyway, yeah we can say that hydrogen in this case isn't very useful or necessay, this design can be improved but we prefer do not do a lot of modification where they are not necessary, now there are many open game with our mod and deep modification can make them difficult to reorganize. Hydrogen isn't an issue, also isn't so difficult.

Our idea was, pay a conversion cost if the light oil was already modified for a purpose, and hydrogen was an ingredient easy to produce and available in big quantities.

As for the use for solid fuel (or non-use, as stated) I used solid fuel in my furnaces until late game.. Much more energy than coal/coke per unit. The conversion coal > coke > oil > solid fuel worked really well.. Didn't run the math on how efficient it was, but worked good enough for me..

Sure, but why not just use wood? The energy requirements of smelting never outpace the energy density of wood, which is free and generates negative pollution to produce. Sure, greenhouses have a huge footprint, but it's an investment that will pay off for the rest of the game.

Early game, they generate wood that feeds your steam/smelters.
Mid-game, they generate wood that feeds your biomethanol plants and more smelters.
Late-game, as you transition to nuclear energy and electric smelting, they feed into coke production for liquefaction.
End-game, they get juiced up with fertilizer and run directly into matter.

Bumping, as I encountered this last night and it felt very wrong. I was setting up to mass produce fuel, saw the recipe using Hydrogen and thought "perfect, a logical way to utilize this excess Hydrogen I have stored up", starting setting up to mass produce Solid Fuel to combine with the Hydrogen... then realized I'm doing an extra step for literally no value, because you're spending the same amount of Light Oil whether you use it directly or convert to Solid Fuel and them into Fuel by combining with Hydrogen.

The difference doesn't need to be drastic, but I definitely feel there should be some change here. The most obvious and easiest tweak is to simply improve the return with the Solid Fuel + Hydrogen recipe compared to the Light Oil recipe, either by improving the ratio for SF+H or making the LO ratio worse. (E.g., the SF+H recipe could produce 12 Fuel instead of 10, or the LO recipe might only produce 8 Fuel, or it could cost 75 LO instead of 60.)

Another idea would be to have the recipes available at different Tech Tiers or something along those lines, tho I haven't looked carefully enough at the Tech Tree to know how much sense this makes in practice.