Im designing a 4x sci fi game about war and colonizing planets. Energy generation is an important part so power plants are important! I'd like some input on how this could play out.

Early tech:
Nuclear fission plants. Not so efficient but can be built everywhere.
Solar arrays. Efficiency depends on planet type (clouds etc), distance to star and (possibly) star type.

Later tech: 
Fusion plant. Pretty efficient. What can be limiting here? Maybe require lots of research? 
Geothermal plants. Needs geothermal deposit (more common on some planets such as "vulcanic" and such).

What else? Something more fictional like gravity wave plant? Antimatter plant? "Fictional gas" - extraction? How would they compare to other types of plants? Pros & cons.
Also good if it is connected to a deposit or node, that can be found on some planets more than others (such as thermal deposits for vulcanic planets).

Non-planet generation:
In Stellaris you can build orbital station around gas planets that generate energy. Can this be developed more? Can you extract energy from gas clouds, plasma storms etc?

Thank you for your feedback!

Find meaningful power plant varieties, don't put them in the game only for "realism". Given the obvious baseline of "whatever power plant type is appropriate for a planet and its resources", making the player decide what power plant to build, or even explicitly giving details of what the actual power plant types are, should bring some value to the game:

• There could be important "side effects" beyond energy. For example, a fission power plant can produce weapon-grade plutonium in addition to energy, which matters a lot if nukes are an important weapon, geothermal plants can make cold planets habitable, and exotic ultra-tech power plants could be high performance but easy to blow up.
• There can be ties to the story and world settings. For example there could be a choice between mundane power plants and advanced alien technology-based power plants that perform much better, can be obtained as a favor from a certain faction, and can be remotely disabled by the aliens in case you cease to be their friend.
• There can be a thematic relevance; for example, fission and fusion power plants, with their opportunity for radiation and accidents, are appropriate (excluding other less dangerous types) if the game is about mitigation of widespread radiation and contamination from nuclear weapons, radioactive materials, space phenomena etc.