Question: How do Fusion Reactors work in this game?

I want to know how fusion reactors work in this game? Do you get any bonuses if you have a high energy tech level? Are they worth using until I can afford that next Solar Plant?

Early game they are a pretty poor choice. You need high energy levels (10+) to make them worth the consumption. Mixing levels between solar plants and fusion reactors is an even worse idea, as you'll consume more fields that way.

However, late game, when your deuterium synthesizer is a high level, your energy tech is a high level, and your fields are almost all used up, you may consider deconstructing your solar plant levels for fusion reactor levels. You'll gain more energy in fewer amount of fields (with the sacrifice of deuterium of course), but keep in mind that this is extremely expensive. Its a few million in metal and crystal for each level past level 15 or so I believe.

Right now I really don't have much of a choice..I need Fusion Generators to get the metal mine to the right level so I can build the Solar Plant. But right now I have plenty duet and fields. So I figure I can always decontruct if I really need to. Though I don't see much of a need untill I get the Nanite Foundry up and running, so right now Fusion Reactors are cheap and produce enough energy to suppliment my solar sats..I don't plan on keeping the Fusion Reactor permanite..just as a back-up so I can continue to build..once I get my plan actually rolling I have more colonies I will have less of a need for Fusion Reactors. But my plan is having my first colony to build fodder ships, cargo ships, and recyclers. My homeworld is going to build Crusiers and above, and my next colony will be for research. Then every colony after that will be farms. So its just a temporary solution to a temporary problem.

That's fine that you want to mix them for now, but I'd like to make just one thing clear to you, and you really need to listen to this.

You never, ever need to build up your mines so you can pay for something else. Especially at the lower levels, you are much better off simply waiting until your resources build up rather than spend 1/2 to 3/4 that same amount building up your mines. You are actually preventing yourself from getting that upgrade sooner with that method. Unless, of course, you are a miner. Then your mines should probably be your most expensive buildings.

I find it useful to have a mixture in early game as you don't really need much deterium. Later in the game when you need the deterium for high level research, ships and def you can simply deconstruct the synthesisers in favour of a solar plant level or more. By late game you will produce millions of resources an hours so its easier to build up your solar plant.

I personally use a solar plant for my metal and crystal mine, as each SP level is equal to the metal and crystal mine of the same level, and use solar satellites to cover the deuterium synthesizer...
I plan to build fusion reactors on my bigger planets only to cover the loss of these satellites if I was attacked, so I could keep outputting resources while I rebuilt them.
Although, in consideration, a SS only takes me 3 seconds to build anyway, so I might not bother at all, especially since I'll be pushing nanites past level 4