Yes there are.
As was mentioned , you can rearrange you Heros Invader skills,and have several sets to suit whatever you are doing at the time, however you will need to be able to switch sets and you probably havent the means or gold to do this presently.
As you research Knowledge you will find out that the basic level of 1000 can/will be increased.
There are several bonuses which help with energy, but you either have to win those or buy them. Like energy restore speed up, and increased Hero attack.
There are also Town skins and the Guardsaman gear helps with attacking invaders.
There are days when the amount of energy per attack is reduced by10% which helps.
The things you can get for free are the emerald and peridot gems. the emerald restores the energy and the peridot gives extra capacity.
Of course the other way is to get energy packs, but they dont last long and cost real money.