German video "Einfluss von Software auf den Ressourcenverbrauch (bub2018) — Jens Gröger" from the “Bits und Bäume 2018” conference. Also this talk (german) shows that the same work is sometimes done by various pieces of software with very different energy consumption.
dnf -y install pcp-zeroconf pcp-pmda-denki cd /usr/libexec/pcp/pmdas/denki ./Install pminfo -fF denki
pmda-denki is not focusing on saving power itself, more on measuring as the first step. For saving power: