Minecraft wiki entry for Building_a_metropolis, associated text: Power Plant - A large factory-like building that can be a variety of types, used to create energy, possibly in the form of a redstone signal. You can also have "power lines" made of tripwire running from the plant.
Nuclear - Use gray blocks to simulate uranium. Add large exhaust towers with mass smoke generators inside. Remember to have it maintained and block all griefers. You can use command blocks to inflict the Wither status effect to anyone who comes too close to the reactors, to simulate the effects of radiation.
Hydro - Build a dam near a large reservoir.
Fire - Use large fires and use wood to fuel them. Furnaces work, too.
Mob - Put captured mobs in glass cages to use as a kind of fuel by either suffocating, physically killing them, or dropping gravel or anvils from above. Add fires where the drops will go so that they are a kind of fuel.
Solar - Use a lot of daylight sensors to create power.
Microwave- Same as solar, but place the daylight sensors on a space station that is beamed down with beacons.
Hydrobeams- Put a lot of guardians in a large glass tank and spawn squid with an admin using spawn eggs or a command block. Use the beams they create to kill the squid to power your city.
Wind- Build a lot of wind turbines in a relatively open area.