Voltar has a weak early game and a very powerful late game. Play defensively and focus on farming Solar with your Healing Wave at the start.
Voltar needs to have companions to be effective. He needs something that can attack because he can't attack without his Drones. The best way to use Voltar is to follow a group of droids, or follow other Awesomenauts and support them.
Voltar may be able to take down a turret if left alone with just droids and drones while the rest of his team is distracting the emeny. Dark Matter Shots makes this tactic even more effective as the enemy droids are incapacitated by blind.