While we might talk about a "burst" of energy, or a "wave" of energy, these are more descriptive terms rather than true collective nouns.
The reason there isn't a specific collective noun for energy is likely due to its abstract nature. Energy is a concept, not a physical object.
If you're looking for a way to describe a large amount of energy, you could use phrases like:
* A reservoir of energy
* A surge of energy
* A wealth of energy
* An abundance of energy
Ultimately, the best way to describe a collection of energy will depend on the specific context.