FWIW, the peak demand in California typically occurs about 6PM, well after most PV installations fall off the grid (peak production from solar occurs at 12noon and solar output is largely gone after 3PM).
Peak demand varies depending on the time of year.
In the winter, peak is around 7-8pm.
In the summer, peak is around 3-4pm. Note that "solar noon" in the summer is actually around 1pm thanks to daylight savings, not 12pm.
Solar doesn't help at all with peak shaving in the winter, but it does help a lot in the summer. Peak grid demand is always in the summer due to air conditioning load.
This implies that grid tied PV solar without some sort of power storage is NOT an effective source of peak shaving.
Again, depends highly on the time of year and weather conditions. But yes, some grid storage would be very effective at eliminating more of the peak, but it wouldn't take much, just enough to shift a small portion of the generation a couple hours later.