Dark Energy is an explanation for why the expansion speed of the universe increases.
Except that it doesn't increase, measuring distance and speed by red shift is accurate only at relatively close distances. It's absurd to postulate that galaxies are moving away from each other faster than the speed of light. All the scientists belly ache about nothing being able to move faster than light, but oh yeah, if it makes their model of the universe work, then its OK. Our solar system rotates around a gravitational center, which rotates around another gravitational center, and so on which rotates around the center of the galaxy, which rotates around another gravitational center, and so on. There is so much contrary motion that is mistaken for expansion due to errors of the red shift hypothesis.
It is impossible to enjoy idling thoroughly unless one has plenty of work to do. -- Jerome Klapka Jerome