One day when I have some extra bucks I'd try to get a home server running, but the idea of having something eating grid electricity 24/7 doesn't seem to play along well with this 3rd world budget. Are there some foolproof and not so costly off-grid/solar setups to look at (like a Raspberry-based thingy or similar)?
Your fridge and other home appliances likely use much more power than whatever a small server would. The mini PC in the article is very power efficient. You likely won't notice it in your power bill, regardless of your budget. You could go with a solar-powered setup if you prefer, but IMO for this type of use case it would be overengineering.
Mac Mini (M1 and later) under Asahi Linux just uses 5 W for a normal workload. If you push it to 100% of CPU it reaches 20 W. That’s very little.