For self-consumption, east-west is usually better. But if you can export north-facing will give you much more kWh.
I have a Fronius Primo PV inverter with two MPPTs. The graph below is for the most recent cloudless day (early August):
The dark blue graph is a 3280Wp array facing north. The light blue graph is a 1630Wp array facing west.
The west array is almost exactly half the size of the north array, so if you double its output you would be comparing apples to apples.
The west array only starts contributing significantly after 10am, and the per-panel yield peaks at about 20% less than the north facing panels. The upside is that in the two hours before sunset the per-panel yield of the west facing panels is almost double that of north facing panels.
In summer months the west facing panels compare even better (early January):
This is exactly what you want especially if you need that bit of extra sun to get batteries toped up before dark. when Iām done I will have more facing west than north
Yes that is what you will see.
As soon as the first light hits your PV panels they will jump up to their working voltage (blue line), but only when the angle of the sun is better will your current start ramping up (yellow line).
The MPPT wil try and āpullā as much current from the panels as it can without the voltage dropping to low below where the panels want to be. This is the Max Point Point.
When you have one west string and one east string and the PV panels are the same, the working voltage will also be the same. The amount of current that the west string will produce in the morning will be very low, so the tracker will track for the east string swopping in the afternoon.
I would not recommend this for strings that do not use matching PV panels.
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I read about using the same MPPT for west and east panels and the consequence of doing so. Now I canāt find itā¦
How does this affect the performance of a MPPT?
I followed an alternative path to this. My panels point north but I change the angle to get a different yield. See my last post here: My skewed yield
Groetnis
See around post 12. It has al the details.
I like that idea, but it is something different to what we are talking about here. You get more out of the same panel direction. I do agree that it makes much more sence to optimise your panels for winter time.
The east west setup can add too your productive time during the day and moving your peak point from one high peak mid day to 2 lower peaks before and after mid day.
Perfectly aware of east/west vs north. This is just an alternate idea I do not see frequently mentioned and not wanting to hijack thisā¦
Groetnis
It would be interesting to know what the loss wasā¦
Perhaps you need a DC contactor to kick in when power of the one bank exceeds the power of the other. Hmmmā¦
(But you are then disconnecting power that could add to the mix)
Iāve had difficulty finding MPPTs that arenāt charge controllersā¦
Can you explain this in more detail. I thought MPPT = Charge Controller?
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MPPT only means Maximum Power Point Tracking. That is useful in many instances.
We know it from (solar) charge controllers. The older tech was PWM (pulse width modulation), and before that we wired the panel directly to the battery and called it a day.
Not sure what @Richard_Mackayās plan is, but an MPPT can be useful outside a charger.
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Well one easy example would be in a PV-inverter. Then the MPPT tracks the max power level, but there is no battery charging on the other end. It all just goes into the grid (ignoring cases where a limiter is employed).
Also to be noted, there are cheaper versions of this that is sometimes called MPPC, maximum power point control. All that means is there is no automatic tracking of the power point, so no microcontroller needed, much simpler analogue timing can be used. You manually set the mark/space ratio, and in some cases, eg a temporary/camping setup, a static value on a sunny day may work just fine.
I donāt know exactly what @PaBz0r setup is but I presume the PV panels are connected to his PV inverter that has limited number of PV inputs. So to maximise his efficiency heās established that his east and west array do better when they have separate MPPTs.
These MPPTs will probably not reduce the DC output voltage to one of the standard battery voltages, referred to as charge controllers (12, 24 & 48V) but will simply drive an output voltage and current that produces the maximum power whatever that is (but lower than the max voltage the MPPT can handle)
Indeed. Where a charge controller (solar charger) kind of MPPT is a buck converter, because it goes down, PV-inverters will likely use a boost-converter (or buck-boost) because it needs to go UP (to around 400V) to do its job. You can do MPP-tracking with both buck and boost converters.
There are even cheap boost converter MPPTs available. Google for āMing He MPT-7210Aā 
Itās a 24V-and-up charger, working from a lower PV voltage.
I think it is more of the gain of the shaded panels, which will also be producing something, but masked by the string that is in the sun (from the POV of the MPPT).
If you search for MPPT in Gumtree you get zillions of hits for inverters and if not they are offering a charge controllerā¦ 
Seeing how this thread got revived Iāll just ask it here:
Is it possible to do East, North and West strings on the same MPPT?
Iāve got a roof space challenge and can do 2-3 panels on my East and North roofs with more space on the West roof. As I donāt really need a lot of PV to cover the loads and charge the batteries Iām thinking about starting with matched strings on the 3x roofs going to the same MPPT.
If in future more PV is needed then I can add more panels West and put all of West on the same MPPT, but I donāt really think thatāll be needed hence the ask if 3x directions of matched strings on the same MPPT makes sense?
You should be able to add a north string as well. Will work the same as just having a east/west.
Yeah that was the idea, but also later realised the installer messed around with the max amps on the MPPT which also had an impact, so the actual āimprovementā I couldnāt determine.
I use a taxi approach to optimize my MPPTās capacity.
I guess at the maximum number of strings and I normally find out there is room for one more.
Pairing strings from different pitches and directions can really allow for crazy amounts of panels on the same MPPT.
I recently reconfigured all my panels. I have 85-ish panels so I could reconfigure and measure as I did it.
I managed to double the theoretical maximum and still have a little headroom.