I wouldn't be worried about off-grid systems personally. That seems like a fair way to reduce the negative side effects. But, to answer your question, even if

I wouldn't be worried about off-grid systems personally. That seems like a fair way to reduce the negative side effects. But, to answer your question, even if 100% of mining were off-grid: 1) Setting up and maintaining a cryptocurrency mining operation still takes up tons of resources, resulting in scarcity and higher prices (see, e.g.: many gamers can't buy GPUs right now) 2) This is likely minor, but the land taken up by your cryptocurrency mining operation could be put to more productive use, even if unmaintained (acting as a carbon sink). 3) Even an off-grid solar operation has many environmental impacts, including all of the on-grid energy that went into making that equipment, all of the pollution caused by manufacture, and all of the use of society's infrastructure that the manufacturing tied up.