If you are running the machine anyway to do other tasks like backing up and running Jellyfish then it might be worth it.

How did you get to 150kg of CO2 per user? I'm going to assume you mean each person has one instance rather than sharing an instance like a family would. So thats 375Kwh per year, which works out as drawing 42W. That seems rather high to me.

I'm hoping to try and run this on my Pi4 which idles at under 1W. You could run on a Macbook M1 which only under heavy load conumes 42W, but I doubt this is going to need consistent heavy load: https://www.anandtech.com/show/17024/apple-m1-max-performanc...