Having a combination of:
1) Sunny Day triggering Solar Power (50% Sp. Atk increase)
2) Electric Terrain (50% increase electric moves)
3) Charge (increase double damage of electric moves; with Sp. Def by one stage)
makes this an extremely good method.
But, only maxed power could be dealt when the Sp. Atk is at the +6 stage - it's highest.
Otherwise, you can use these other ways to help increase:
Having a heliolisk with this tactic is very well. But, you need to consider the other variables. Heliolisk doesn't mave much defenses; and you will only use thunderbolt on your 3rd turn. This makes it very easy to faint this Pokemon - but I wish the best of luck for it to work.
Also, you haven't considered an item to be held yet.
The two items to choose from are: Electric Gem (electric moves increase 30%; consumed once) or Zap Plate (electric moves increase 20%; used multiple times).
This will definitely increase thunderbolt much more making it maxed attack. Though it will make much more sense to keep a Zap Plate to use forever; unless there is another easier way to spawn plenty of the gems.
Furthermore, you can give your heliolisk a max Sp. Atk EV spread, or feed it lots of Calcium. Look at all the possibilities to actually make thunderbolt to it's MAX power.
Hope I helped! :)