Smartsolar: how often does it scan mppt

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techmuc asked Aug 7, '22

Smartsolar: how often does it scan mppt

Hi All,

I have two parallel strings with 4 panels in series connected to a smartsolar 150 35. The shadow situation is not always super simple therefore one question: how often does the mppt charger search for the perfect spot?

Test: I shadow one of the panels.

If I only have 1x4: Power immediately drops to zero, after around 10 seconds a value of little less than 3/4 is reached => good and as expected
2x4: power drops to the power of one string (4/8). The mppt scanner does not readjust in 2 min (not. Expected!). After manual restart (activate / deactivate) the power drops to around 6/8 - 7/8 (expected due to voltage drop on one string).

==> it seems as if the mppt scanner is not recognizing power drops in a 2 string environment immediately.

Is there sth I can do about it? Will the smartsolar do regular rescans and if yes in what time period?

Thanks

MPPT SmartSolar

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Answer 1 · 2022-08-07T11:51:48Z

JohnC answered · Aug 07, 2022 at 11:51 AM

It will scan every 10 minutes. In normal conditions during the main part of the day that's enough, and most people will rarely see a noticeable change in Vmp. I see changes early early morn and evening, when there's little W generated anyway. No direct sun then, and the sun behind cloud isn't the same as sun below the horizon.

You can actually watch it scan on the Connect Trends graphs. It takes a while, like 10 secs or so. What it's doing I've never seen published.. trade secret?

I won't scan when the batteryV setpoint is reached. By all means experiment with your panels, but these aren't practical conditions. It should rescan if you reboot it .

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techmuc commented · Aug 07, 2022 at 03:11 PM

@JohnC thanks a lot for your answer. With this in mind, does it make any sense do add two more panels on the left side facing west, so that I would have 5/5? The panels would have bypass diodes. As far as I understand your answer, the MPPT scan would happen every ten minutes. In the afternoon at around ~~3pm only those panels would be in the sun, but the MPPT scanner should adjust..

It does not have to be "worth it" (i.E. make a senseful return of invest), but the two additional panels should of course make the overall strings slightly better and not worse :-)

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JohnC ♦ techmuc commented · Aug 08, 2022 at 12:15 PM

@techmuc

If you added 2 more panels in a different direction, keep them in the same string.

I wouldn't like to predict what happens to the tracked Vmp as panels don't always do what's expected. It's likely downward in shade though. But if you're using 48V batteries the extra panel in each string may help keep things rolling at the 2 bad ends of the day.

When any part of a string is shaded the W will take a heavy hit, so don't rely on panel bypass diodes to do much.

All you can do is try it. The mppt will track the string outputs as a pair, and this usually means the Vmp will end up down closer to that of the shaded string. This is because there's not much W in the charge curve above the optimum Vmp of the poor string, it will drop sharply.

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techmuc JohnC ♦ commented · Aug 08, 2022 at 12:25 PM

Again thanks a lot @JohnC

Maybe a safer option would be to buy a hoymiles 350 and use ac coupling.. What do you think? That should work and the panels will 100% not affect the rest ++ I don't need to reach the 50V starting voltage of a mppt..

Ps: plan: buy the two panels, connect via mppt and see. If it does not work I will use a hoymiles.

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