I will start with that i don't know if its correct category i didn't seen anything like 'questions about game' or something im sorry if its incorrect. Now question i don't know what to use to power MFE unit, for Batbox i used geothermal generator which is great for i think, for the 3rd tier unit MFSU of something like this i think the nuclear plant is good to power it, is there any middle way to power MFE between the geo generator and nuclear plant?
it doesn't really matter what you use to power a storage unit. you can power an mfsu with a single solar panel, it will just take a loooooong time to fill up(to be exact, the formula is Capacity/((EU/t)*20)= seconds iot takes to fill it up, or in this case 40000000EU/(1EU/t*20)=2000000 seconds, or 33333 minutes, or 555 hours, or about 23 days). If you want it reasonably quickly, I'd either use several weaker generators( an array of geothermals would work, for example), or a low-output nuclear reactor design(100-200 EU/t maybe?), i made a design in the reactor planner v3(just search "ic2 reactor planner") with the code 21p7ermw3qtczwaj2modfh5ziusy5xn2909518tc4iwfzqkcydv6onn5sil3v7y4v44b53qjj9hzytc which might work.