In the good old days a decade or so ago where the full fat Pi board was always 35 dollars and the zero was just 5, they were so cheap as to be practically disposable. I have an insane number of Pi 3/4 and Zero/ZeroW boards in projects and drawers around the house, but this has massively tapered off as prices have gone up. At one point I had an 8 pi 3 cluster to learn kubernetes/container orchestration techniques on - completely unnecessary, but building the little rack was 85% of the fun. That cluster ran my home stack for years (DNS, home automation, network admin UI etc).

I've since got a lot more interested in the microcontroller community - so many Pi projects should really be microcontroller projects - the esp32 especially scratches the itch for cheap things to hack on, and you can get them for like 6-7 bucks each with wifi.

I assembled a solar server with those parts laying around last year:

- Victron Monocrystalline Panel 90W 12V

- Victron Gel Battery 12V 60Ah

- Victron MPPT Charge Controller 75V 15A

- Raspberry Pi Zero W

- Witty Pi 5

- Sixfab 4G/LTE Base HAT

- Quectel EC25 Mini PCle 4G/LTE Module

Almost 100% uptime except for a few days after a bad winter storm, pretty neat!