This is such a frustrating misconception. The annual peak is far more important than the daily peak for capacity planning. There are two capacity issues being

This is such a frustrating misconception. The annual peak is far more important than the daily peak for capacity planning. There are two capacity issues being confounded here: (1) Generation capacity. The idea here is that if solar doesn't generate during peak loads, then building solar will not displace power plant capacity. But solar does generate during peak loads, so building solar does reduce the number of natural gas plants you need. At higher levels of PV penetration this will be a concern, but we're not there yet. (2) Ramping capacity. The idea here is that solar generation is correlated and non-dispatchable, so dispatchable generation must be able to match the swings in solar output. Again, this will be a concern at higher penetrations, but right now the grid can handle it. Philipkglass's replies are excellent.