You will out put more damage(DPS) if you use all the same energy type: plasma, polaron or antiproton, not a mix. See the tool tip -10 power when firing other energy types. Or something like that..
Err, no. It's -10 Weapon Energy power for each weapon fired beyond the first. And that's just for the weapons that give -10 energy. Turrets do -8, Dual Heavy Cannons do -12, and I think everything else that's an energy weapon does -10. Here's a short explanation.
I have 5 beam arrays and 100 Weapon power. 1 beam array is firing, it's firing at 100 weapon power. (Power drain as I said only kicks in after the first weapon fired, so that weapon is free). 2 beam arrays firing, firing at 90 Weapon power. 3 fire at 80 weapon power. 4 fire at 70 weapon power. 5 fire at 60 weapon power. Now because not all weapons fire at exactly the same time and weapon cycle on and off and energy is almost always returning back to it's normal set value (100 in this case), this is not exactly true. But it's close enough to understand the concept.
Again, let's say I am firing 3 Dual Heavy Cannons at 100 Weapon power. 1 fires at 100 weapon power, 2 fire at 88 weapon power, and 3 fire at 76 weapon power. Make sense? This doesn't matter which energy type you're using. You can have a 6 Turret ship with one of each of the six energy types, it still will have the same energy drain as if it was 6 phaser turrets.
However from an economy of skill points and console bonuses, it is usually advisable to stick to one energy type to increase DPS.
Sticking to one energy type, disruptors, for example would let you run disruptor coil tactical consoles to benefit all of your energy weapons. When spending your skill points, having only one energy type will take fewer skill points than having to buff multiple.