Their research indicates that a minority of mining is done using renewable resources:
> The survey findings estimate that on average 39% of proof-of-work mining is powered by renewable energy, primarily hydroelectric energy.
It also specifically addresses this popular claim of mining being powered mostly by renewables:
> China’s oversupply of hydroelectric energy during the rainy season has often been used as evidence in claims that a vast majority of mining is powered by environment-friendly power sources. While it is true that the Chinese government’s strategy to ensure energy self-sufficiency has led to the development of massive hydropower capacity, the same strategy has driven public investments in the construction of large-scale coal mines. Like hydroelectric power plants, these coal power plants often generate surpluses. It should not come as a surprise then that a significant share of hashers in the region equally report using both hydropower and coal energy to power their operations.