Перевод - Португальский-Английский - A matriz do sistema de energia elétrica produzida...

This is neither bad enough to reject nor good enough to put to a vote until you take a close look at the English and make some corrections.

For instance:
The electric energy produced in Brazil predominantly comes from hydroelectric power plants.

Maybe "electricity" instead of "electric energy" would be better. And I would change the structure a bit just to sound more natural in English.

How about:

"The utmost of (the/all) electricity produced in Brazil comes from hydroelectric power plants." ?

I agree Lilly, I was having difficulty making the word "predominantly" fit properly in that sentence.

My edit has been made.

OK then..I'll set a poll to be sure we found the perfect way of saying that in English.
David, I hope you don't mind.

The utmost of all electricity produced in Brazil is totally not acceptable in English...it has to be changed or rejected Lilian. You must have missed the first part.

Pra mim a tradução está correta.

I think just "most" solves the problem, don't you, David?

A maior parte da energia eletrica produzida no Brasil é oriunda das usinas hidreletricas