I'm happy to report that I did not change my solar panel angle from 40 degrees (used for spring and fall) for summer and they still hit rated power in perfect solar conditions, and well over rated power during periods of "cloud edge effect".
We're only three weeks from the summer solstice, and from that point the angle starts getting better again.
I have arrived at the conclusion that it is a waste of time for me to adjust the angle of our panels four times a year, and down to 20 degrees for summer. Simply tilt them up to 70 degrees in late fall/early winter, and back down to 40 degrees in early spring, and they work fine. On any day with sunshine they make WAAAY more power than we can use in the long days. They're still putting out enough power to hold the bank in float at 7:00 in the evening most days. And if we got both wind and solar I just shut the turbines off and leave just one running because we can't use them. On cloudy days it don't make a bit of difference what angle the solar panels are at.
I can't say this is a "rule of thumb" for everybody, because some off-grid people might not have enough installed solar capacity. So a tracker or religious tilting of the panels to get more out of them might pay off. But we sized our system for winter-time power needs and this is the way it plays out.
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Chris