I have 5kw of solar panels at home and am currently pulling in an average of 25KwH per day.  I get three times more money selling the power to the grid than using it to make bitcoins.  The sold power is tax free, refund from the power company comes automatically once every three months, there are no exchange fees to pay and I don't need to hand over my private info to some anonymous exchange in eastern Europe.

In other words, although I could mine for 'free' during the day, I would be losing a lot of money doing so.