Clean energy sources are the cheapest [0], and they get cheaper with every new investment and innovation. The competition in Bitcoin mining is global, which means that it becomes unprofitable for everyone to use fossil fuels when profit margins fall enough. This isn't true yet, and it's profitable to use fossil fuels in certain regions.

Usually the cheapest sources are also far away from people, because any local demand will increase energy price. However, when renewables near people have overcapacity, Bitcoin miners can serve as a buyer of last resort. This way, investments in renewables become more profitable.

[0] https://www.weforum.org/agenda/2021/07/renewables-cheapest-e...