much like mekanism. the ability to make/use/refine gasses, the kind that floats.. not the liquid kind.

I think 4 (5?) extra blocks, 4 items would be a good start

a gas canister - used to store the ingredients to make gasses

a gas tank - used to store gasses

a refiner - used to produce/refine gasses

a gas turbine generator - used to make power from gasses

pipe - to transfer gasses

and

helium
hydrogen
methane
cooling cell

as items

use gasses to generate power, each type of gas has different properties.
such as methane could have lots of bi-product.. idk maybe ashes

helium could burn slow, require energy to produce, but could also be used as a cooling method later in game via a cooling cell?

hydrogen could burn hot, so cooling the generator would make it more efficient and bring another challenge however would have the most energy output

Methane - (maybe from plant matter?) a canister for decomposition that requires water, plant matter and being in the sun.

Helium - I think tech reborn uses end stone, but since helium in the real world is from the decomposition of radio active material, maybe a tank that requires water, redstone dust and energy.
pros - higher energy output, can be used later to cool machines helium cons - you have to mine that redstone and already have energy to dump into the refiner.

Hydrogen - maybe something like using helium and lapis to make in a canister.

each gas starts by either decomposition in a gas canister or combination of ingredients in a gas canister.

from there it is transferred to a refiner which can then transfer to a tank or even to a generator.

possibilities can go further, as gasses can be used to make other materials or products.

Thank you for your suggestion! I'll start implementing more features when I'm 100% sure the mod is stable and working on 1.16.2