The pirates start with a full defense compliment of 19 turrets and usually 1.5-3 dozen ships.

But after every raid the surviving pirate ships add themselves to the defense force. In large games its totally possible for the pirate base to have several hundred ships, including 30-80 ships worth of their version of the Kodiak heavy cruiser.

With that many ships even large fleets can be torn to ribbons. You'll want to look for abilities that target multiple ships(combining the Advent capital ship techs of Malice and Cleansing Brilliance for example, assuming a level 6 Radiance capital). Or you can try to outnumber them with gigantic swarms of your own LRM frigates, but you'll incur many losses as ships die by the seconds due to heavy focus firing on the part of the pirates.

Or just be TEC and blow them to hades with two shots from your MegaCannon.

It seems to only damage the planet. I had my ships right next to the planet I was attacking and I lost nothing.

I was just finishing up a game and I managed to get two of those things built. After the second one fired, I got the victory screen. Pretty powerful (and expensive) stuff.

For the Novalith cannon, scout his planets for locations with 3,000hp or less. The TEC scouts get sensor probe, giving you a view of most enemy locations. Or if you can build several cannons, put them together in a Ctrl-group and fire on his home planet. Goodbye 10credits/sec of income. Every time the opponent rebuilds the planet they have to leave it in a weakened state, or spend 1,000's in credits and 100's of resources to get it back to its previous state. Killing a colony every 5 minutes quickly widens the economic gap that the TEC enjoy.

Example: You see a planet you want to attack, you press '0' to select the ctrl-group, you press 'Q' to activate them, then click on the target. Its as simple as that.