Query on Comparisons

[npalani07]

For the first time, a Nuclear fusion experiment released more energy than was absorbed by the Hydrogen substance.

I could understand the meaning of the above sentence.
But, Please help me understand the dynamics of how this comparison works.
Especially, the phrase following "than" looks like a Passive-voice construction.
When is such construction appropriate?
Is there any limitations in using that in some sentence constructs?
If you know any other way to express the same meaning in the above sentence, do let me know.

And finally, Does GMAT test "Comparisons" this way?

[RonPurewal]

The whole sentence is fundamentally flawed, since experiments don't release energy.
The things involved in the experiment could conceivably release energy"”e.g., substance X released more energy than was absorbed by substance Y"”but this sentence doesn't do that.

There's nothing wrong with passive constructions.