Hi, I have an issue with newly installed solar panels (TR-665W - TRINA SOLAR 665W MONO SOLAR PANEL) on my roof.
I have split the panels up into 2 arrays at roughly the same angle (+- 20 degrees).

The more north array (array 2) casts a slight shadow on the second string but about 10 - 15% on the bottom of the panels as I installed in summer and forgot about the sun shift in winter.
Array 1 (the array with the shadow on) generates about only 50% of array 2 (the array with full sun)

I always assumed it was the shadow that caused the difference in power generation but this morning before the sun was up I checked the inverter and found that this difference was still present although the sun was not out yet (it was light but no direct sunlight yet).

Array 1 and array 2 both had the same voltage output (which indicates that all the panels in both arrays had the same amount of panels connected) at that point but array 1 was generating roughly half the amps of array 2 (even though there was no shadow yet)

I will move array 1's panels in time to get out of the shadow.

Anybody got any ideas as to why this would be?

Could be that the shaded set of panels still get less diffused light, as the "shadow" is probably still there, just not visible without direct sunlight...

You could take a light intensity reading using an old photography light meter if you have one, or just use an App on your smartphone. I'm quite happy with the free version of an App called: Photone. Take the readings on the same general area where the shadow is on both sets of panels, and check every panel as well - just a small (~10%) shade area on one panel can easily cut the total production of the string...