This website made me reconsider if 99.9999% SLA and always online is really that important for lots of websites. I used to self-host my own server in my own apartment, but gave up on that after my internet provider had their first major outage that lasted almost a week. Also I didn’t want to worry about the fire hazard, or the server going down when I was traveling etc.
But a solar powered server seems interesting, if the batteries could be made fire safe.
You’re better off with the LiFePO4 batteries even if you don’t care about weight. A lead acid battery will wear out quickly when you cycle it daily. Lithium also has a higher charging efficiency, so you get more usable power from the solar panel.
Lithium-iron is about 2x more expensive, there might be different availability and energy use during manufacture is probably higher