Hi Stefanio,
As weird as it sounds, that’s exactly what they intend with energy yes 
Here’s an excerpt from RFC 7868:
5.5.4.2. Energy
Use of Energy-based Path Selection results in paths with the lowest
energy usage being selected in a loop-free and deterministic manner.
The amount of energy used is accumulative and has results in a higher
aggregate metric than those having lower energy.Presently, EIGRP does not report energy usage, and as such the
default value will be zero (0).
On the Cisco site, you can find this:
likewise energy would be expressed in power per kilobytes per second of usage
So the idea is to select an interface, based on how much power it consumes.
You can find the wide metrics formula (that includes K6) here:
Hope this helps!
Rene