Not everyone mine with coal. «A signifcant concentration [of Bitcoin mines] can be observed in the Sichuan province, where miners have struck deals with local hydroelectric power statons to access cheap electricity» p. 94 of https://www.jbs.cam.ac.uk/fileadmin/user_upload/research/cen...
I think solar would have to become cheaper before this becomes viable.
Luckily trends show that this will happen soon, but other challenges posed in Africa is political stability (e.g. government decides BitCoin mining is illegal or imposes unreasonable taxes due to lack of understanding), lack of competency, and other types of infrastructure.
The only countries I can see that are suitable are South Africa and Namibia.
Does it matter, really? If Bitcoin mining wasn't run on chinese hydro power, some other industry could use that power but now instead uses a more polluting option.