Even if you have free electricity ROI is hard to reach if you spend money for miners
In 4 years with free electricity, one still may not make their money back? I'm personally not a miner, and I understand it's too late in the game for the general population to get involved... but that sounds ridiculous. With free electricity, OP still shouldn't expect to turn a profit?
It is actually possible to not reach ROI even with free electricity.
I'm fairly certain any method used 4 years ago couldn't even get a single share in a pool or solve a block alone right now.
However, unless you buy a really outdated miner or difficulty goes up incredibly fast, people should be able to ROI in about 6 months (very rough estimate).