Oh, and if so, is there a point where no damage could be caused, say 10 shield generators?

Koda0

They don't stack (And it gets 80%)

I wouldn't consider it a complete loss, the enemy would still have to take out all 3 generators to take out your planet in good time. If you have them spread out in the gravity well OR in a massive defended cluster it could be tough for them. And this is especially important to consider in Entrenchment.

I've used 2 at a time but never three.

Without going into full detail I'll give you one example of why I would shield up over defenses. Decent players, and the Entrenchment AI, will often skirt defenses with siege and a small escort of antifighter frigates to take out multiple planets simultaneously. A shield (or shields) allows you to concentrate your defense into a single fortified unit that either forces them commit suicide with their siege/af fleet, bring in an attack force (which denies them aggressive options, particularly harassment strategies) or waste a lot of time trying to siege through the shields (which is not only wasteful, but gives me time to bring back just enough forces to take them out and they can be sent from pretty much anywhere because of the delay. This is turn is indirectly giving me a mobility advantage for my own aggressive and harassment strats).

I'd go into more depth but you get the idea.

Oh don't even get me started on the new strategies Entrenchment brings out...

Yeah don't even get me started on how excited I am for Entrenchment...watch it's the let down of the century...JK JK JK!!! I doubt it could be.

I'll save a puppy if that's the case

Cielos? They can put a debuff on hostile target that make them take 25% (I think) more damage from all sources for a while, and they throw around shield regen buffs on your ships - not a huge regen boost but it lasts a while and when mitigation gets high enough it helps.

I'll be back in a few hours, Annatar(Alex) class just ended

Koda0

PJI's only keep the enemy from jumping out of the system -- great to slow down raiders, but not really a way to defend the system itself.

That said, I usually use a mixture of hangers (half and half fighter/bomber), gauss cannons (if the enemy is stupid enough to come in and attack the hangars, the gauss can cause a fair bit of damage), and repair bays.  Shields / PJI's optional.

Alright, here's the final question I can pull of the top of my head since the game won't load:

I have version 1.05 right now, and I have two fleets.  One, my main fleet has 40 LRMs, 20 Cobalts, some 45 Percherons, 10 Kodiaks, 10 Gardas, and 15 Hoshikos and 15 Krosovs, no Cielos, yet, and 1 Sova carrier 2 Dunovs, 1 Akkan, 2 Kols and 2 Marzas. 

My 2nd fleet has 40LRMs, 25 Cobalts, no Percherons, 15 Kodiaks, 15 Gardas, 20 Hoshikos, 15 Krosovs and again, no Cielos.  As for Capital Ships, 2 Sova Carriers, 1 Dunov, 2 Akkans, 2 Kols and 1 Marza.

I'm currently destroying the last REAl threat to my empire, he's TEC has 8 planets (on a huge random map, he used to have 20-some but I took them) 2500 fleet supply, 1800 of it being used and attacking my first fleet in defense of an Ice world.  He also has planetary defenses, 2 Hangars, 2 PJIs, 2 repair bays, and my scout was destroyed B4 I could count all of his Gauss defense platforms, but I know he has 28 Percherons, 54 Hoshikos, 26 Kodiaks, 36 Cielos, 67 LRMs and 32 Cobalts, maybe 1 or 2 gardas and 1 Akkan, I destroyed most of them last battle(both Cap. ships and Garda's) . 

My question is, will my above fleet be able to destroy his without the loss of a Cap. ship or mass losses of Frigates, or should I attack with both fleets?

Thx,  Koda0

P.S. I make well over 100 creds per sec., and have 35-40 planets, so I can scuttle-rebuild ships if my fleets need changed.