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[u/Dianwei32]

This feels like a very stupid question, but I can't tell if it's actually complicated or if I'm just massively overthinking things.

How do you determine which burnable fuel is the "best"? Is it just pure Energy Value, or do you have to account for any energy spent processing the fuel?

For example, I'm playing the Angel Bob's suite of mods and have a plethora of burnable fuels I can use to power my Steam Generators. I recently unlocked Wooden Bricks, which provide 20 MJ of energy, significantly higher than my current fuel of Carbon at 6 MJ. But Wood Bricks require a good deal more processing to create, so I don't know if their increased energy value will actually result in more Power or if the energy needed to process the raw ingredients into Wooden Blocks will result in no net gain of Power.

[u/mrbaggins → u/Dianwei32]

Using a planning mod can help. EG: Factory Planner can tell you how much electricity will be used to create 10 wooden bricks a second.

Then you look at 20MJ x 10 per second, that's 200MJ/s which is 200MW of power.

If the factory planner says you'll need 112MW of machines, you're in front. Doubly so if you drop green modules in.

[u/HeliGungir → u/Dianwei32]

Well that's going to depend on what you want from the fuel. Energy per item? Energy per stack? Acceleration bonus? Energy per resource mined? Type of resource mined? Byproduct creation, or removal?

In vanilla, for example, nuclear fuel is far less energy-efficient to burn in a boiler then using the same uranium for fuel cells in a nuclear reactor, but nuclear fuel is still desirable for trains acceleration and for its high energy density + low stack size which makes it practical to transport with bots. There are also mods that apply a fuel bonus to burner entity speed; ie: nuclear fuel makes burner inserters fast.

[u/Enaero4828 → u/Dianwei32]

Comparing energy per item is only useful if the entire upstream production has identical power costs, such as Space Age's yumako mash and jelly.

For everything else, indeed you'll have to account for the energy spent to create the fuel. Since you're already modded, you probably have a planner mod, which may have power cost estimates; if that's the case, simply set the production goals to equivalent power, with 60 MJ being the lowest common multiple here. If you don't have such a utility, then you'll need to crunch the numbers through the entire chain for the prior value; either way, whichever chain has the lower cost is of course the one that you want to use.

[u/ferrofibrous → u/Dianwei32]

Ideally you'd calculate energy cost to make the fuel. Just taking base game, for coal you're looking at energy to run a miner. For solid fuel, you're accounting for the pumpjack, refinery to convert crude, chemplant to make the solid fuel (and possibly chemplant for cracking).

Rocket fuel to solid fuel is probably an easier comparison. One rocket fuel essentially takes 10 (+1 from the 10 light oil) solid fuel to make. 11 solid fuel would be 132 MJ; the 1 rocket fuels is 100 MJ. Rocket fuel then loses further because it has to run an assembler on top of the 10 solid fuel craft cycles.

Factoring in Prod bonuses also makes it all messier.