I’m also very interested in this, and there have been other related requests in these forums elsewhere like Renewable Energy Usage too.
Of the links provided above by @zee, the Netactuate sustainability page no longer exists. Equinix currently shows 96% renewable energy across their DCs, which is great, but from what I understand Fly.io uses many providers, so not all regions and machines are run by Equinix.
Even if it’s difficult to provide exact numbers, it would be helpful to be able to provide information for specific regions if there are any specific cases where it is known. Scaleway for example list detailed metrics for all their regions on Environmental leadership | Scaleway, and when selecting a region in their console some are marked specifically as 100% renewable energy or not. OVHCloud also offer per-datacenter reports: https://www.ovhcloud.com/sites/default/files/external_files/kpis_per_dc-q1fy25.pdf
We’re investigating migrating to Fly.io at the moment, but 90%+ renewable energy in all production services we use is a strict minimum requirement, and being able to guarantee 100% would be very helpful. It sounds like Fly probably does fulfil that in some regions, but I can’t tell which! Even just a tiny bit of information here would be very helpful.