I have an older installation consisting of 2 independent but identical arrays installed in 2008. The problem: one of the arrays produces 3x less the power than the other (say ~5KWh vs 15KWh per day). I am new to solar so I need some "ropes" (or perhaps "cables" ).

The arrays:
- consist of 14 SPR-210 panels and dedicated SPR-3300 inverter in each.
- have no shade and are mounted on the same rack (same angle and direction).
- the inverters report 160-180V on bad array and 260-280V on the other array.
- the inverters do not go online with lower voltage than ~170V (or there about) so I assume when it is in off-line state the reported voltage is a "no load" voltage of the array.
- on bad array the voltage is usually <180V (the reported amps in off-line are 0.2A vs in on-line when in strong sunshine it could go up to 4A but still with low voltage).
- when eventually both arrays go on-line (with more sunshine) the amps are also lower on bad array (afair about 4A vs 7A)

I think:
1) hence the panels are rated at ~40V and hence 7x40V=280V, each array is made up of 2 strings of 7 panels each
2) the bad array low voltage in both the load and no-load state suggests that there is no high resistance in connections
3) the bad array low voltage in no-load state suggests that at least 3 panels (280V-160V=120V=3x40V) in each of its strings would have to be off line (bypassed) for the voltage to be so low?
4) per 3 above I'd have to have 6 panels down (3 in each string) but this is not very likely so I suspect one of the strings is completely off-line while the other is limping with just 4 active panels?

Any comments or suggestions about how to diagnose this problem (and not get electrocuted )?