An interesting tool from the article is ecograder.com which grades a website’s carbon emissions and provides recommendations to improve. There is also the Green Web Foundation’s directory of hosting providers powered by renewable energy.
This is the report for slrpnk.
I assume it can only reference known hosting services and their claimed green energy generation. For self-hosted servers like slrpnk.net, it wouldn’t know where the energy is coming from and can’t rate it.
That makes sense.
This is certainly it.