Apple - "powerd" process uses a lot of CPU

sudo kill -HUP $(pgrep powerd)

(I don't have an answer for 'why')

Have you tried to stop powerd by Activity Monitor? This solved the CPU consumption for me.

But after stopping powerd I got strange effect in Activity Monitor - it was like Update Frequency was changed from Often (2 sec) to Nonstop (0 sec), i.e. continuous without any delay. So I had to quit Activity Monitor too.

After these operations and restart of Activity Monitor all works fine.

On my computer, it was Activity Monitor which caused the powerd process to use a lot of cpu (20-30%, sometimes 50%, resetting the SMC didn't help). Quitting Activity Monitor "solved" the problem. Checked in the Terminal by running top.