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Should I use the second MPPT after Growatt to Sunsynk upgrade?


Mark R
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Dear All

Would value your advice.

Have upgraded from a Growatt to a Sunsynk 5kW Hybrid and all going well. Have two strings- the first, 6 x 360W panels in series facing North, and the second, 3x360W in series, facing west in Claremont, Cape Town. After installation of the Sunsynk, the second MPPT still remains unused. My production graph is attached. My roof pitch is approximately 22 degrees (and 16 deg Azimuth).

On a sunny day like today, the total production from 3.2kW of panel was 9kWh. Peak production was at about 2kWh.

Question- would I gain that much more out of my panels were I to connect the West facing panels to the second MPPT? 

Screenshot_20210606_214622_com.igen.xiaomaizhidian.jpg

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1 hour ago, Mark R said:

Dear All

Would value your advice.

Have upgraded from a Growatt to a Sunsynk 5kW Hybrid and all going well. Have two strings- the first, 6 x 360W panels in series facing North, and the second, 3x360W in series, facing west in Claremont, Cape Town. After installation of the Sunsynk, the second MPPT still remains unused. My production graph is attached. My roof pitch is approximately 22 degrees (and 16 deg Azimuth).

On a sunny day like today, the total production from 3.2kW of panel was 9kWh. Peak production was at about 2kWh.

Question- would I gain that much more out of my panels were I to connect the West facing panels to the second MPPT? 

Screenshot_20210606_214622_com.igen.xiaomaizhidian.jpg

You would see better production having differently orientated strings on separate MPPTs. 

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Thank you for both replies.

Don't completely understand the physics, but will take a stab at reasonable questions

1. Currently, isn't the West facing string of 3 panels in series being subjected to the minimum start voltage that the North facing panels are being subjected to by the MPPT by virtue of the two strings in parallel? 

If that is the case, is there anything to lose? 

2. If the above is not the case, will adding them to a separate MPPT circuit result in a shorter more intense production day, rather than a more prolonged one (with the others), albeit in a less productive day in total? 

I am wary of more hardware (ie panels)- this is a rabbit hole whose bottom is proving illusory.

Thanks again

Mark 

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Hi I'm not sure if you have a space issue on the roof but it seems connecting them in series with 9 or maybe 8 and keeping the one until you have another 7? Wouldn't that improve your peak production?

There doesn't seem to be much that can be done about the rest until you get more panels.

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Thanks for asking Tariq (and apologies to @Brani) - have confirmed with installer - all panels in a single series. (3 facing west, 6 North)

Which makes me wonder about the shade effect of no sun.

The installer joined the two strings into a single string because of the Sunsynk's greater voltage requirements. 

Have looked through my records and noted that the Growatt's best efforts at this time of the year were also just above 2kWh.

Mark 

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i have panels facing NE and NW, so 90 degrees apart one ONE mppt on a Victron, then switched to a Sunsynk and put one string on each mppt, the difference in gain was about 10 percent, yes, shading does have an effect of killing some of the production also

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Chatted to installer who said that 3x360 panels runs the risk of not sustainably managing the start voltage and being 'kicked off' frequently. 

Would two more panels with a westerly orientation manage to avoid this? (I see start up voltage is 150V- are voltages for panels in series simply added together?)  

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i "think" you will be ok, but three is better, or at least install the railing for more than two panels, this way all that needs to be done in the future is to add the panels. I have six 355 watt panels on each mppt, trying to add three panels on each side, for a total of 18 panels, unfortunately the 400 watt plus panels were too expensive last year, so bought the 355 watt panels instead

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29 minutes ago, Mark R said:

Chatted to installer who said that 3x360 panels runs the risk of not sustainably managing the start voltage and being 'kicked off' frequently. 

Sounds right

30 minutes ago, Mark R said:

Would two more panels with a westerly orientation manage to avoid this? (I see start up voltage is 150V- are voltages for panels in series simply added together?)  

The more the better 😉 You probably should be able to put up to 9 of your panels in series. And yes, when in series, the voltages are added

With 3 panels, each panel would need to produce around 50V to get the MPPT started - which is probably even higher than the specs of your panels. With 5 panels, that voltage would be around 30V - and much better achievable for your panels.

The more panels you add, the lower the required voltage from each panel to get the MPPT started - which means the earlier your PV production starts in the day and the longer in the eve you still get production

And yes, if your strings are facing different directions, put them onto separate MPPT. You will get more yield out of them. But it also means having to pull another set of cables from your panels to the inverter, another set of surge protectors and isolators, etc.

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Yes- primarily for two reasons. I installed solar to mitigate my carbon footprint, intending to use as little grid as possible.

The inverter was incompatible with two US3000 Pylontech batteries - was only ever able to charge to a maximum of 32A. This led to prolonged charging times at the end of a battery cycle (which was mostly daily for half the year) during which time the inverter operated in line mode (with the panels only available for charging) until the SOC got to 60%, which was around midday. Plenty of morning grid use as a result.

This despite an initially intact BMS-inverter connection.

Had the firmware upgraded from China in about September, after which I completely lost the connection to the BMS and ran the system on voltages with worse efficiences. 

Learned a lot about solar generation during the year I had the system, and the sunsynk hits the spot. Except it is a hungrier voltage machine, so have come to the conclusion that I need to create a second string for the second MPPT which will need two more panels. Will have a go myself. 

Image attached describes the behaviour.

 

image (1).png

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On 2021/06/06 at 9:58 PM, Mark R said:

Dear All

Would value your advice.

Have upgraded from a Growatt to a Sunsynk 5kW Hybrid and all going well. Have two strings- the first, 6 x 360W panels in series facing North, and the second, 3x360W in series, facing west in Claremont, Cape Town. After installation of the Sunsynk, the second MPPT still remains unused. My production graph is attached. My roof pitch is approximately 22 degrees (and 16 deg Azimuth).

On a sunny day like today, the total production from 3.2kW of panel was 9kWh. Peak production was at about 2kWh.

Question- would I gain that much more out of my panels were I to connect the West facing panels to the second MPPT? 

Screenshot_20210606_214622_com.igen.xiaomaizhidian.jpg

Your Configuration on your strings are wrong 3 x 360 watt panels will have no meaningful production because of the low VOC so I would move 3 panels to the north roof and add another string of 6 or 8 panels facing east or west you can also add a third string using a small grid tie inverter on the Aux port of the sunsynk Facing west of around 2.5KW. 

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