They're part of the western grid, which helps some, but the sun is up broadly, so if Arizona has excess power, so do California, Nevada, and other Western state

They're part of the western grid, which helps some, but the sun is up broadly, so if Arizona has excess power, so do California, Nevada, and other Western states. Likewise, if they need power in the evenings, so do those other states as well so then additional generation is needed, or batteries that can be depleted in lieu of more expensive non-Solar generation.