Side question first: What is the Latin phrase used for impossible inventions etc. It's something like arca dei but meaning something more like god in a box?.
SF free energy idea
This is human created tech. No ET science needed.
Dark Energy Abatement Matrix โ DEAM (Ratz โ Black Energy would make a better acronym)
Premises:
~Dark Energy is abundant in our real universe
~String Theory predicts ten or eleven dimensions which (for this idea) some of which exist in dark energy deficient universes
~Stranger than normal quantum states can open a window into one of these universes
~These states can be achieved and controlled using properly tuned and polarized x-rays
Scientist or team of scientists with serious expertise in string theory and strange quantum stuff conclude that premise 4 just might be possible.
A nanosecond burst of high-energy x-rays 'breaks through' the barrier to that other universe. Smaller amounts of x-ray keep the barrier open based on the amount of x-ray. The dark energy leaving our universe leaves behind serious thermal energy. Some kind of x-ray reflector setup limits the size of and contains the Abatement Matrix. This replaces fossil fuels and nuclear for electric power generation. Heat transfer for power stations likely uses liquid sodium filled pipes.
It is naturally safe. Stop emitting those x-rays and the Abatement Matrix collapses.
Other than the chemistry issue of liquid sodium and water in proximity (and the thermodynamic need for cooling water) power plants become much safer. Automobiles? Bring back the Stanly Steamer? Home heating is almost a no brainer.
Of course, the Lovecraftian Evil monsters living in that other universe might not like our dark energy showing up in their universe...
[Never think] that man is either the oldest or the last of earth's masters, or that the common bulk of life and substances walks alone. The Old Ones were, the Old Ones are, and the Old Ones shall be. Not in the spaces we know, but between them, They walk serene and primal, undimensioned and to us unseen. โฆ Man rules now where They ruled once; They shall soon rule where man rules now. After summer is winter, and after winter summer. They wait patient and potent, for here shall They reign again."
Quote from The Necronomicon is from "The Dunwich Horror" by (you guessed it) H. P. Lovecraft