I live in CZ 4a. I will be building a house with an unvented attic, insulated with ccsf on the roof sheathing. I will also have asphalt shingles with tar paper as an underlayment. I also will be getting solar panels installed on my roof. My question is, will I have any issues with exterior drying on the shingles that are under the shingles since they will be covered from the sun?
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guessing you are worried about shingles under the solar panels. (not under the shingles)
It is true that you will have slower drying of the covered shingles, but the solar panels will protect them from direct UV light, decrease solar heat gain on the shingles, and reduce impact from rain, hail, and stuff that falls from above (like tree stuff and other blown objects)
Since solar panels will be up there for 25+ years, you should consider a roof that will last at least that long. Removing the solar panel installation to replace an asphalt shingle roof is an expensive extra to your roofing costs.
A standing seam metal roof may be a better option, particularly if combined with a rack system that clips directly to the standing seams, avoiding any penetrations through the roof deck. It will be more initial expense, but probably less life time cost.
I've had solar panels on my asphalt shingles for 10 years. CZ 4 - Oregon / Maritime climate (wet). No problems, they dry out fine - you'll get a lot of air flow if they are mounted on the standard rack system. The shingles haven't shown any aging at all. I put moss-out above the panels twice a year, and the rain carries it down.