• Solar boiler and panel: will require replacing a component every now and then. Various tiers. Should use silver to give it more uses.
• Windmill: can only be placed once every 3x3 chunks or so otherwise efficiency will massively decrease.
• Watermill: same as windmill, only produces energy in rivers / oceans (a bit more in oceans).
• Geothermal: same as windmill, must be placed below a specific y level.

This sounds very neat, maybe have it so a geothermal thing needs like an input of coolant, some sort of drill head-like thing (Akin to quarries/rigs).

Just throwing out the idea: Perhaps the windmill, watermill and geothermal machines could be some kind of scaleable multiblock (similar to how you can build different sizes of the large tank)? Since they would be essentially free energy this would make them require more resources and space to make them more balanced

Perhaps larger passive energy generation, such as a solar reflector array, a hydroelectric dam, a wave generator, geothermal that requires fracked underground fluid transit or such?

Maybe the geothermal should require being placed in the Nether?
Then you have to ship batteries through portals or something. (But that would require #165, portable batteries)

I want to keep MI standalone, but I don't want teleporters or chunk loaders, so nothing should be forced to go in a different dimension.

Watermill should require a downwards flow (falling water) of at least 10 blocks

Another suggestion is the implementation of radioisotope thermoelectric generators. You'd need to eventually replace the RTG, but IRL they last for a long time. Could give some more uses to uranium and plutonium, and would fit nicely in a possible future nuclear update.

I'm not quite sure where RTGs fit in the mod. If you need temporary power, a diesel generator seems to be strictly better than an RTG unless you need a small amount of power over a very long period of time, and I don't think there's a use-case for that in the base mod.

As you can see from the initial comment in this issue, I dislike "spammable" passive generators. An RTG is definitely not appropriate. 😉

Fair enough!