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karel avatar image
karel asked

Smart Solar MPPT 150/70 with PV array's facing different direction

I have a Smart Solar 150/70 with 4 strings of 3 (series) PV panels connected in parallel. Had 3 strings on for a year and then added the 4th string. Due mainly to roof constraints string 4 is now facing west while strings 1-3 faces North. Except for maybe some inefficiencies on the MPPT's part during peak hrs, I cannot see any other problems with this configuration. All strings are properly isolated with DC CB's and fuses on each string. I do get longer hrs of yield from the MPPT but was informed that this configuration is not ok, i.e. facing north and west strings on 1 MPPT. Can anyone explain to me why this would be a problem apart from maybe not being an optimal MPPT yield configuration. Max PV panel Watts is 4455W but input measured never exceeded 2950W.

The rest of the system comprises a Multiplus II 48/3000/35, Venus GX and Pylontech 2000 with DVCC enabled and ESS operational.

MPPT Controllers
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chrisawp avatar image chrisawp commented ·

@Guy Stewart (Victron Community Manager) - Not much available on the topic of mixing orientations on a single MPPT, your input will be appreciated?


Is it actually possible to have east/west facing panels on the same (single) Victron MPPT? The important reason for this question is purely based on cost. If a single MPPT can be used for a east/west roof then it would be the ideal configuration based on COST.

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ess-and-solar-solutions avatar image ess-and-solar-solutions chrisawp commented ·

@ChrisAWP If you think high level about it, it is to a degree no different to shading effects. This can be countered with measures such as connecting panels/strings in parallel or indeed multiple charge controllers. In an ideal world however, best practice will be to have multiple mppts and Jinko MX panels even offer 3 integrated optimizer modules per panel these days.

I am also at odds with the expert answer since there are many installations with one large controller and multiple parallel string. Were one to be covered by e.g. snow, leaves or even fail, a similar situation could arise, yet they continue to make even larger controllers? Have you ever watched one slow drifting cloud slowly creeping across one section of an installation and the impacts ;)

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Phil Gavin avatar image
Phil Gavin answered ·

Caveat: All strings are equal and each individual string's panels are the same direction and slope.

I respectfully have to disagree with @WKirby, a string attains full voltage with very little light and will also not pass reverse current until the voltage across it is higher than its Voc. The same Voc that the other strings have, so by definition a voltage that cannot be attained.

I deliberately mix strings of different slopes and directions to minimise the noon peak but have my MPPT's working a long day. I can get far more panels/MPPT and subsequently far more kWh/day/MPPT. None of my MPPT's clip at noon, but I get them as close as possible to it and try and keep them at a higher current for as long as possible.

MPPT's are not cheap and to have them sized for short midday peak capacity while idling for the remainder of the day is under-utilizing them.

I thoroughly recommend doing it.

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snoobler avatar image snoobler commented ·

I agree with Phil Gavin vigorously with same caveats. Example: Northern Latitude, SE and SW facing arrays with equal series Voc in parallel with each other will have no appreciable negative impact.


Stated in a different way, even shaded panels will have a Voc above the Vmp of the parallel array will not impact the unshaded panel performance.


It's essentially no different than a 3S4P array with ONE string shaded. The shaded string will have dramatically reduced performance, but the other 3 strings will be unaffected.



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wkirby answered ·

This can cause a big problem. You can have the three north strings backfeeding the west string with more power than it is rated for.
If you enter float around mid day with the north strings making 3KW and the MPPT backs off because the battery is full and the grid has failed, then the west string will have a lower Voltage then the north strings. This could cause up to 3KW to backfeed a 1KW array.
Although you have got fuses and circuit breakers, you don't want to have to rely on them. It is not good to design a system where you can foresee over current situations. Protection devices are for the unforeseen situations.

A separate controller for your west array would be the best option. You'd probably see more yield too.

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carel-landman avatar image carel-landman commented ·
Hi there!


Do you perhaps have any literature on this topic?

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daba avatar image daba commented ·

in my opinion the mppt will allways drive the string with the higher power on optimum, so the mmp voltage will be definded by this string. the smaller string will than have no mpp. nothing else, dont think any backfeeding will occur.


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