Solar powered battery banks which keep a few things up and running in my office (glass sliding doors, so I get plenty of light. Also use them to charge my phone and such.
My bike, which I used to ride to the bus to get into work until I went full remote. Has a small solar kit for my lights to stay charged on long rides. It's been a bit due to some joint issues, getting back into it now, but used to do centuries every weekend. Didn't need to it charge to full, whatever trickle worked just to extend it past the 4 or so hours it would do from full, then charge on the battery banks.
Gardening and associated sensors. Working on moving those over to lorawan, right now the updates are a bit spotty even at once every 4 hours updating due to distance.
I've got a bunch of stuff that's running on lightweight chips, like esp8266's and ESP32s, to do things like Bluetooth beaconing, lights (wled), etc.
It'll be a bit, but we are going to need to move to something with a bit more space, so other plans (solar + battery for the whole home, indirect solar water heating, etc) will be on hold for a bit.