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Hello everyone,
I have 11 panels and an RS450 with 2 MPPTs. I originally thought I would connect one string of 6 panels and one of string of 5. Easy.
Due to a chimney there will be the possibiity of shade on 2 of the panels and I have learnt that one panel shaded will bring down the entire string so should I connect the 9 'safe' panels to one MPPT and the 2 'shady' panels to the other MPPT or would this imbalance cause problems?
There are two separate trackers, so uneven strings are not a problem.
However, there are a minimum number of panels for a single string. I don't know the parameters of your panels, but a ballpark Voc of 40V would mean that two panels in a string would be 80V. This is the absolute minimum operating Voltage for a tracker. Then the startup Voltage needs to be at least 120V, so a minimum of three panels in series would be required. Given that 120V is pretty close to the Voc of three panels, that string might not start until later in the day than the longer string.
If the Voc of your panels is actually higher than 40V then you might get away with a string of three, otherwise a minimum string of 4 panels.
Shade will not necessarily bring down the entire string. Panels generally have two or more strings connected in parallel. Each string has isolation and reverse polarity protection diodes. So if the cells in one string are shaded but the other string is in full sun that panel will drop back to the current of the unshaded strings. Because panels are series connected, the result may be that the entire string is reduced to the current of the unshaded strings in one panel. It also may be that the other panels will overpower the panel with the shaded string and that panel will be taken out of circuit by its reverse protection diodes. So in panels with two internal strings and a series of say 5 panels in series the power may drop to between 4/5 or 1/2 the output you'd get under full sun (no shade).
Running some experiments may help you understand what effect shade has on your array. It can't always be predicted.
Ah yes, the minimum start up voltage. My panels are around 40Voc and they are "half and half" split.
Someone had suggested to me to completely remove the one panel that would definitely be in shade after 5pm.
