In order to really say something about sustainability not only the amount of renewable energy should be taken into account, but also how effective the energy is used (how much of the energy goes to IT processes, instead of cooling or other processes) and the way in which the energy is reused (in the form of heat).
Like described in article: https://eehpcwg.llnl.gov/documents/infra/06_energyreuseeffic...
And applied by cloud providers like Nerdalize who use their servers to heat homes: https://www.nerdalize.com/