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MPPT limits and PV arrays


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Wanting to take my inverter setup to the next level by adding solar and am confused about how to calculate what I can do with what my new MPPT offers. 

I have a 5KVA system with 2 x 3.5KWh Lith batteries. I recently bought a 250/100 MPPT and 12 x 450w Canadian solar panels.

I was told that I could put 3 Strings of 4 x Panels onto the MPPT but not 4 strings?

When I downloaded the Victron excel sheet and added the specs for the 450 Canadians (41v and 10 A) it said it was acceptable to have 3 or 4 strings of 4 x panels.

So I was wondering if the limitation was an the VOLTS or Amps of the MPPT, but am not sure where the calc is finding 100 Amps out of 3 or 4 strings

Or maybe something else I have missed ?

Any guidance would be appreciated 1491364602_4x4PVArray.thumb.JPG.7f4af1fe8e687d6ecaccbf634a5e6609.JPG1172173857_3x4PVArray.thumb.JPG.e690dc23f9e85c96121516596f11659b.JPG

I included 2 screen shots from the Victron calculator with 3 string x 4 PV and 4 string x 4 PV options

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You can oversize your array (up to a certain point*) but the max the MPPT can push is 100A and the battery float voltage is about 53V so it can only supply 5300W. 12x450W panels are already 5400W. 16 panels are 7200W which is maybe a bit over-specced unless they are not optimally placed?

*The max PV short circuit current for the 250/100 MPPT is 70A. I'm estimating an Isc of about 11A per string so you could do up to 6 strings if you wanted. Just check your panels' Isc: floor(70/Isc) = max number of strings.

Edited by gooseberry
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Thank you for your reply, so would any PV over the 5300 watts be wasted and not worth while, or would it do some damage to the system ?

I understand that I can just buy another mppt to extend the watts, but was wondering what the optimal config would be, as the mppt's are quite pricy.

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9 hours ago, TerryFos said:

Thank you for your reply, so would any PV over the 5300 watts be wasted and not worth while, or would it do some damage to the system ?

I understand that I can just buy another mppt to extend the watts, but was wondering what the optimal config would be, as the mppt's are quite pricy.

It won't damage the system and it will not be totally wasted as it will get you closer to 5300W in the morning and late afternoon.

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Hi All

Need some help with an issue. I have a MUST 5kw Hybrid Inverter (this is probably a Voltronic white labelled inverter) and its MPPT range is 64-130V, 9 x 375kw Fivestar solar panels connected with 3 strings (so 3 x 3), and 4 x 200ah Gel batteries. I noticed earlier this year (as i can monitor the system remotely via a wifi card setup) that randomly, the PV voltage spikes to between 125 and 131 volts. When this happens, the charge power from the PV drops to 150w odd and the charger current to 3A. This can happen randomly during the day and can sometimes stay at these levels for up to an hour or so and hence the load is not being fulfilled by the solar even though there is plenty of sunlight. Does anyone know how to resolve this issue? I understand the PV is going to the top of the MPPT range but how do i prevent it from doing this. It seems much worse now ie its happening more often than it was earlier in the year. 

Do i need to reconfigure the setup of my panels to a different combination to reduce the PV voltage etc or what do i do to maximise production without the voltage spiking and effectively killing the charge power? i am not super technical so would appreciate a layman response on this.

Screenshot 2021-08-11 234311.png

Screenshot 2021-08-11 234411.png

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