....Where I live solar is common and grid power is not especially cheap, so it become more sensible to mine during the daylight hours only and use just the solar power. Though it slows things down considerably, if your power costs are substantial it can make sense.

You would need more qualitative data to know for sure. For instance some countries have a high or even 100% green energy. Some individuals use solar power. Some might use off-peak which would otherwise go to waste. etc.