The complexity of gregtech 6 is far greater than gt5u at this point but energy production specifically is the weakest point of gt6 by a mile. Your options include burning fossil fuels or producing absurd numbers of solar panels. If you go the fossil fuel path you’ll be using absurd amounts of coal or oil or both and you’ll need to sustain this probably through automated tree farms from other mods. The efficiency of fossil fuel systems is horrible if you want to actually store the energy you need to first convert HU -> Steam (100%) -> RU (through turbine 66.66% efficient) -> EU (68.75% efficient through electric dynamo). Of course whenever you need to use your stored up energy for many of the conventional machines that don’t require EU you will need to use an adapter between EU -> RU/KU/LU/MU/HU all of which have 50% loss. In total if you dont use the energy produced by the turbines immediately (which btw you wont be able to use for anything else than RU machines) and want to store it and convert it back at will this will have an efficiency of at most 25% not account for eventual loss that you will have in wires transporting the power. Alternative to fossil fuels is currently: solar panels. Solar panels are capped at 8EU/t (for refference the highest tier multi blocks can consume 4k GU/t and lowest tier machines consume 16GU/t) the efficiency of a solar panel system is extremely dependant on your ability to transform the voltage up immediately after leaving the solar panel as 1EU/cable loss is the lowest possible regardless of voltage/packet size. The disadvantage of solar panels is the infrastructure required to both produce them and harvest the power they produce but in my opinion its the most viable solution if you dont have infinite supply of fossil fuels otherwise go nuts i suppose. In terms of early game the way to power machines is materially expensive much more so than gt5, due to the nature of how machines in gt6 themselves automatically consume power if given the opportunity even when they have no possible work. This means that simply putting machines on a straight line and have one power supply connected to all of them it is highly reccomended to supply each machine individually even in early game. The general setup is Appropriate tier of burning box -> appropriate tier of steam boiler -> appropriate tier of appropriate adapter (steam -> RU/KU etc.) -> appropriate tier of machine. Don’t try to connect multiple adapters to the same steam supply even if you think the math works out it is highly unreliable and tricky to make work properly and you wont be able to control what uses power by any other means than simply switching pipe directions which could lead to problems of its own.
So in all if you want any other way of powering your machines in the current state of GT6 you will need to import mods that have reactors or whatever you fancy which produce redstone flux and then you can convert that RF to EU and so forth.
Disclaimer: haven’t personally tried to use RF to EU systems so I don’t know if they actually work but the Flux Motors ( RF -> RU ) have in-game recipes so I don’t see why they wouldn’t work and it certainly works the other way around through Flux Dynamos (EU -> RF).