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2 strings and one mppt


Rick C
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Hello again. 
As I wrote in a previous entry, I have a Voltonic tri (3 mppts). I have 3s2p facing east 3s1p facing north and 3s4p facing west. As you can see, all in trios.
I have noticed that the inverter can’t handle well the three mppts working together. Sometimes (more often last days) the north array (mppt nr 3) disconnects and goes to 0, and don’t connect until the day after in the morning.
The thing is: Can I connect the north facing array in pararell to the east facing array (3s2p + 3s1p = 3s3p)??

the North one gets some shadows in the morning... Can it affect the performance of east facing, even though they are connected in paralell?

thanks again.

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8 hours ago, Rick C said:

Can I connect the north facing array in parallel to the east facing array (3s2p + 3s1p = 3s3p)??

Sure, as long as the total power isn't too high for that SCC (Solar Charge Controller).

8 hours ago, Rick C said:

the North one gets some shadows in the morning... Can it affect the performance of east facing, even though they are connected in paralell?

Yes, it can, because then the voltage of the shaded panels will drag the others away from their maximum power point. That's mitigated a little by the fact that shaded panels are cooler, and therefore have higher voltage. But it's still recommended to run them on separate MPPTs, if possible. And you have 3 MPPTs, so that's ideal.

But you have a total of some 21 panels; are all these into one trio inverter? Panels range in power from around 200 W to around 400 W, so that would be some 4.2 - 8.4 kW nominal. The latter is way more than the inverter can probably handle. Each SCC will limit itself to some 3 kW of charging, but with your high panel voltage (unavoidable because they're 60-cell), it may be that the inverter is shutting down from overheating. One of the SCCs may be getting hotter than the others; I have no idea how they pack the three SCCs into one box in the triple-MPPT models, and how well all those heatsinks are served by the fans. It might be that they just can't handle the total heat load.

Can you monitor the peak temperature of the inverter? Some monitoring software should be able to show the temperature of the hottest component (out of 3 SCCs, two inverter heatsinks, and the transformer). If it's above 60°C, that is likely the problem.

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13 hours ago, Coulomb said:

But you have a total of some 21 panels; are all these into one trio inverter? Panels range in power from around 200 W to around 400 W, so that would be some 4.2 - 8.4 kW nominal. The latter is way more than the inverter can probably handle. Each SCC will limit itself to some 3 kW of charging, but with your high panel voltage (unavoidable because they're 60-cell), it may be that the inverter is shutting down from overheating. One of the SCCs may be getting hotter than the others; I have no idea how they pack the three SCCs into one box in the triple-MPPT models, and how well all those heatsinks are served by the fans. It might be that they just can't handle the total heat load.

Actually, nominal sum of the arrays power is 5.8 kw, but because of the different facing of them, the (planned) distribution is ideal to my needs and using of energy. The west array sometimes reaches 3.2 KW @3 pm (almost 40A), but the little north facing array (3s1p, mppt nr 3) begins to fail in the morning, when the amperage and heat are not quite high. 

I think it was a mistake to buy this inverter, (I bought it 2 years ago, having in mind to increase the panels in the future). But, I'm in this boat , so I have to sail as best as possible.

I´m thinking in  Growatt Hybrid SPH for the next years, The only thing that makes me feel in doubt is the limited amperage of the 2 mppts (just 12A). That forces to put the panels all in series, with the risk of affecting all the production because of little shadows.

Thanks again for the help.

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