Federation of American scientists (FAS) believe that the number is actually calculable:

"The quantity of radioactive material liberated by the burn- ing of coal is considerable, since on average it contains a few parts per million of uranium and thorium"

"Per gigawatt- year (GWe-yr) of electrical energy produced by coal, using the current mix of technology throughout the world, the population exposure is estimated to be about 0.8 lethal cancers per plant-year distributed over the affected population."

"Table 7.2 summarizes these data. With 400 GWe of coal-fired power plants in the world, this amounts to some 320 deaths per year; in the world at large, some plants have better filters and cause less harm, while others have little stack-gas cleanup and cause far more."

https://rlg.fas.org/mwmt-p233.pdf

That's about the number of people who died from Chernobyl, every year. From the radiation from coal power plants.