this sounds doable. i do something similar with syncthing. it depends on the internet connection speeds. see how it goes with wireguard. between two home NAT networks you might find something lile tailscale easier to set up. wouldnt recommend doing this when youre not able to drive over there and fix things occasionally. ethernet preferable for reliable connection over wifi at the remote end. if you secure the pi well and update it it should be fine. note that you probably need to trust the remote household with your data.

its annoying. i cope with the sleep then hibernate after 30min setting

most solar systems will not operate in a power cut.

edit: system detects no grid supply and shuts itself down. other systems with an off-grid mode exist, just theyre not the default and usually cheapest option a lot of people round here install.