The electricity is "free" because the energy generation is highest at noon (sun is at its zenith), and the population is at the work (low demand for residential electricity). So there is an oversupply of energy at that point. Just like there is an under supply of (solar) electricity at night time when people are using lights, watching tv and eating dinner but the sun isn't shining.
Solar panels don't necessarily get the most power at noon, as it can depend on what angle they're at if they're static (eg on a roof). Ideally you would want it facing the sun in the afternoon (especially if you don't have batteries and are trying to cut into your AC bill) or morning as you'll get more direct sunlight. It would also depend on how far on the horizon the sun is, which will depend on latitude. So peak generation will depend on how much exposure you'll get.
IMO, this plays into how solar is used. An individual household would have different goals than a grid-level solar/battery project depending on how they consume electricity. A grid is going to optimize (ignoring any desire for extra capacity for days without sun) for the peak that tends to happen between 4-6 for most western grids.