I'm hosting al my services on an old Android mobile with termux. Power consumption is ridiculous, not 100% sustainable but it is very low power. You could add solar panels and you're done.
In terms of performance, mainly for family use, I've never had an issue once I plugged it to an ethernet port.
No Docker unfortunately, it would require either to recompile the mobile Kernel or use QEMU and I believe it would have a big impact on the performances.
Basically this time the approach was: what can I do with an old mobile without rooting or anything.
Hardware:
Samsung S20
USB3 to Ethernet & charger port
128GB SD card
Sofrware:
Termux (android app)
SSH (OpenSSH in Termux)
Rclone (in Termux)
Sonarr, Radarr, Lidarr, Prowlarr (in proot-distro)
Transmission (in proot-distro)
Kavitha (in proot-distro)
Podgrab (in proot-distro)
Ombi (in proot-distro)
ntfy (in proot-distro)
Filebrowser (in proot-distro)
Vaultwarden (in proot-distro)
Homer with lighttpd (in proot-distro)
Since I wasn't able to install .NET Runtime in Termux directly, I used the proot-distro (Ubuntu) and inside I've installed all the services.
Services are started manually every time I restart the proot-distro (unfortunately I'm getting an error when installing Termux:Boot), it's a simple script so I'm not dying over it.
To keep the proot-distro alive I launch is with the screen command so I'm ensuring persistence even when the terminal is closed.
It's not a clean solution like docker etc. but I'm consuming 5 or 10Wh of energy every day which is close to nothing and probably sustainable with a solar panel.
Every once in a while (basically when the SD is almost full) I transfer the files with rclone to an external drive where I consolidate the files.
Oh extra tip, with rclone you can create a DLNA server so you can serve the files you have download immediately (tested with VNC and Kodi)
The phone/server has still room (CPU & RAM) to go and possibly I could install HomeAssistant without any issue. Also I could add Joplin and Floccus using webdav for storage as I had in my previous server but I don't miss them.
Any other questions, doubts, scripts, feel free to ask!