I've spoken to mythic beasts, the hosting company I use for mastodon.radio.
They were excellent (as usual) and helped me identify the data centre the vps lives in.
They also pointed me to the data centre's "clean energy" page:
mastodon.radio is (probably) powered by renewable energy from the UK national grid.
The social network of the future: No ads, no corporate surveillance, ethical design, and decentralization! Own your data with Mastodon!