Technically not completely powered by solar power, since they decided to include remote analytics[1] served by a cdn which is probably hosted in one of those data centers they mention. :)
(If we want to get really pedantic, the solar panels and battery need a few years to pay back their own CO2 debt for when they were produced. This server might need to run 3 years before it’s carbon negative. Maybe even longer because not all of the captured energy can be stored in the battery.)