Comment by ZenoArrow

> "I mean, electrons are very very lightweight and tend to move quite slowly for typical currents. How much kinetic energy can they give?"

I only have a layman's understanding of this whole process, so I could be missing some important details, but I believe it's necessary to look at the atoms as a whole rather than just the electrons...

Consider, the electrons (from the outermost orbit of the nucleus) are travelling from atom to atom (the ease by which they can come and go determines how conductive the material is).

During this process, when an atom has more electrons than its stable state it is negatively charged, and when it has less electrons than its stable state it is positively charged. The greater the polarisation between the positively-charged atoms and the negatively-charged atoms, the more electrons can move through the material. I believe the potential difference between the poles is voltage, and the volume of electrons flowing at a given time is current, but I could be wrong on that.