Hi. Hoping someone could provide me with some clarity. I have a client whom had a solar system installed very poorly and they asked my help to rectify the mistakes as the installer has disappeared. They have 9 panels in series, North facing, due to limited roof space. I measured the V coming from the panel and saw it was quite high. After pulling the spec sheet of the panel, I realized with the 9 panels in series they are slightly above the MPPT range, but below the Max PV input voltage. What happens in the case where the voltage is higher than the stated MPPT range, but lower than the Max PV input voltage?

Secondly, should I rectify this by splitting the string in a 5 and 4 and utilizing the 2nd MPPT or is there an alternative way to do this seeing that the 2 MPPT's will not have the same amount of panels?

7 minutes ago, Faze said:

What happens in the case where the voltage is higher than the stated MPPT range, but lower than the Max PV input voltage?

Some clouds moving away from the sun could see voltage spikes above spec which could result in some magic smoke.

Maybe post some of the specs so that some of the clever forum peoples can offer more accurate answers

Nice 

23 minutes ago, WannabeSolarSparky said:

Some clouds moving away from the sun could see voltage spikes above spec which could result in some magic smoke.

Maybe post some of the specs so that some of the clever forum peoples can offer more accurate answers

Inverter Luxpower SNA 5000 WPV

Max PV input Voltage (VOC) 480VDC

MPPT voltage range 120-385VDC

Canadian Solar 455W panels x 9 VOC 46.6V Isc 9.4A

So by my calculations, 9 in series could give a VDC of 420V, I measured quite late in the afternoon and got 397V

46 minutes ago, Faze said:

Inverter Luxpower SNA 5000 WPV

Max PV input Voltage (VOC) 480VDC

MPPT voltage range 120-385VDC

Canadian Solar 455W panels x 9 VOC 46.6V Isc 9.4A

So by my calculations, 9 in series could give a VDC of 420V, I measured quite late in the afternoon and got 397V

Nothing wrong with those 9 panels. During any condition they will never reach the MPPT 480V for Voc. Further even during cloud edge the Vmp of 385V I doubt will be reached. Even if it exceeds 385V to 397V to me will just reduce the efficiency of the MPPT by a few % for a short period. Bear in mind outside the peak production period as the current drops the voltage does rise. During peak power you should never see 397V.

Cloud egde does provide a lot more power due to amps increasing and not due to voltage increasing as stated.

Just how I see it but stand to be corrected.

1 hour ago, Scorp007 said:

Just how I see it but stand to be corrected.

You're right that at power production the voltage should be not too extreme, but why stress the system when sun is high and power consumption not at maximum smoke... I'd split the panels 5/4 and be happy in the knowledge that its well away from the voltages at peak that can cause the magic smoke to leak...

3 hours ago, Faze said:

What happens in the case where the voltage is higher than the stated MPPT range, but lower than the Max PV input voltage?

My understanding is that it still produces power, but it may not be able to hit the maximum power point. So you might be missing a little of the available solar power that way.

3 hours ago, Faze said:

or is there an alternative way to do this seeing that the 2 MPPT's will not have the same amount of panels?

There is no need for the MPPTs to have the same number of panels; the whole idea of a second MPPT is that it can independently find the maximum power point for two different arrays. The classic case is with some panels east and some west; even with the same number of panels, they will have very different maximum power points, so with two MPPT trackers, the maximum power point can be found for both arrays.

The only problem with a 4 and 5 panel split is if the string of 4 panels might be below the MPPT range in poor light conditions. But I imagine you'd nearly always get 30 V from those panels, so you'd nearly always meet the 120 V minimum requirement.

How are they configured? All into one MPPT? 
If so the max Wattage for the MPPT is exceeded and it will shut that MPPT down.
If I am not mistaken it's 3200W per MPPT. So the best would be to split it into a 4 panel and 5 panel series strings and feed both MPPTs. 

Edited August 29, 20224 yr by zsde

from my understanding you can exceed max wattage by up to 20\25% and its not a issue and would provide more production over a longer period of the day.

The unit will clip the wattage to the max value if its exceeded.

Voltage is the important/critical one not to exceed the units max limit as it will cause the magic smoke.

1 hour ago, zsde said:

How are they configured? All into one MPPT? 
If so the max Wattage for the MPPT is exceeded and it will shut that MPPT down.
If I am not mistaken it's 3200W per MPPT. So the best would be to split it into a 4 panel and 5 panel series strings and feed both MPPTs. 

Yes all on one MPPT, all 9 in series

 

Ok so according to the answers I've received, I can gather that being above the maximum MPPT range will mean the system is not as optimized as it could be, but it's not a massive train smash as long as the VDC is quite a bit below VOC?

7 hours ago, Kalahari Meerkat said:

You're right that at power production the voltage should be not too extreme, but why stress the system when sun is high and power consumption not at maximum smoke... I'd split the panels 5/4 and be happy in the knowledge that its well away from the voltages at peak that can cause the magic smoke to leak...

Perhaps this will explain the power vs voltage a lot better. When there is a burst of power right at cloud edge the voltage does not change. All we find is a high current suddenly flowing if the battery needs charge or load is connected.

This indicates at high sun there is no risk of voltage going too high even at cloud edge. There is thus no risk of leaking smoke. Based on the 9 panels I still feel the voltage should be very close or even below 385V being the top of the MPPT range. The volts will just be high when very cold and we agree the Voc will never be reached so the MPPT is save.

By the way the graph used is for a MPPT that can go to 550V and is actually idling at 150 - 200V. Time on graph is 07h30 to 18h00.

@zsdehas the best answer. I have only looked at the Voc and Vmp for 9 x 455W panels and not paying attention to the actual inverter used.

At the top is the voltage graph and below it the power. Not very clear but I wanted to show the Volts vs Power. The current follows the power graph.

Edited August 29, 20224 yr by Scorp007