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Optimal string arrangement


Scubadude
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Hi all,

I'm getting an 8kW Sunsynk system installed today.  The attached pic shows my roof looking true north. Roof has 7° slope to the north - not much but enough to not warrant lifting the panels. The pool heater is going. There are 3 tall palm trees - two to the left and one to the right.  

The question I have I about how to group the panels in strings. Obviously the left (as we look) will catch more morning sun, and the right more afternoon sun as the palm shade moves over the array.  There is also the parrapit that will cast afternoon shade over panel 9.  My thinkning is to group  it as follows:

- String 1: 1 & 2

- String 2: 8 & 14

- String 3: 3, 4, 9, 10, 11

- String 4: 5, 6, 7, 12, 13

... and then put strings 1&4 on one MPPT and 2&3 on the other. Sort of one morning and one afternoon string totalling 7 panels per MPPT.

Is this a workable solution to balance the workload between the MPPTs? Are there other considerations I need to bear in mind?

Thanks! 

SolarLayout.JPG

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4 hours ago, P1000 said:

5 is also a bit low.

Do you think there is a problem with only 5 x panels on a string. I am also planning a 8KW installation with 20 panels (VOC = 48.7V /450W/10.92A) It will be 5 x panels per string (389.6V)and the 8KW has 4MPPT’s so I was hoping to use all 4 x MPPT’s. Would this be ok or am I not seeing something.

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10 minutes ago, Gerrie said:

Do you think there is a problem with only 5 x panels on a string. I am also planning a 8KW installation with 20 panels (VOC = 48.7V /450W/10.92A) It will be 5 x panels per string (389.6V)and the 8KW has 4MPPT’s so I was hoping to use all 4 x MPPT’s. Would this be ok or am I not seeing something.

It has 2 MPPTs (with 2 ports each, but they are just joined together). 5x48.7V=243.5V. Your NOCT voltage will be quite a bit lower. Ideally, you want to be in the upper range of the MPPT voltage, so that you can maximize power on cloudy days/early in the morning/late evening.

You can most likely just do 10 panels per MPPT in series.

Edited by P1000
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8 hours ago, Scubadude said:

Hi all,

I'm getting an 8kW Sunsynk system installed today.  The attached pic shows my roof looking true north. Roof has 7° slope to the north - not much but enough to not warrant lifting the panels. The pool heater is going. There are 3 tall palm trees - two to the left and one to the right.  

The question I have I about how to group the panels in strings. Obviously the left (as we look) will catch more morning sun, and the right more afternoon sun as the palm shade moves over the array.  There is also the parrapit that will cast afternoon shade over panel 9.  My thinkning is to group  it as follows:

- String 1: 1 & 2

- String 2: 8 & 14

- String 3: 3, 4, 9, 10, 11

- String 4: 5, 6, 7, 12, 13

... and then put strings 1&4 on one MPPT and 2&3 on the other. Sort of one morning and one afternoon string totalling 7 panels per MPPT.

Is this a workable solution to balance the workload between the MPPTs? Are there other considerations I need to bear in mind?

Thanks! 

SolarLayout.JPG

I'm going to be devils advocate, and suggest sacrificing the old palm trees for now, and try and fit 18 panels on the roof.

Split them into two strings of nine each.

To make up for the loss of the trees, get new small palms from the nursery and plant them on the other side of the yard, far from the panels.

Many people have to make such choices, that are not always pleasant but sometimes necessary. 🤔

 

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The effect of the trees remains to be seen ... I dont think it is that severe.  I added two panels more than needed to somewhat offset the shading effect.  For now I'll keep the trees where they are and keep them trimmed.

I dont follow your logic to max out on panels without knowing my usage and storage - 18 would be way too much.  If I wanted to burn more cash I'd go for a 3rd 5.1kWh battery instead of generating more unused electricity. Also clearly you never had the misfortune of experiencing the total lack of compatibility between palm trees and pool cleaners.    

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I've had to remove one palm tree completely, trim two yellow woods, and trim avo trees, so I do understand. 👍

On bad weather days, you will appreciate more panels just to get through the day without using Eskom.

Burning cash on batteries is never a waste, especially if you intend going off grid.

I too have a SunSynk 8.8 kW machine, and am extremely satisfied with it, and wish you well with your install.

I am currently expanding the panel arrays over time, and aim to reach a total of +- 13 kW of panels.

When you have your system installed, we always enjoy a couple of pictures and comments about the process. 😀

3 hours ago, Scubadude said:

Also clearly you never had the misfortune of experiencing the total lack of compatibility between palm trees and pool cleaners. 

Yip, Kreepy will try and eat anything, and then choke. 😂

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I found the following to be quite good:
Case Study 3: 8kW Hybrid Inverter with 400W Panels
https://solaradvice.co.za/how-to-size-a-pv-array

Be sure to keep the PV string Volts between 125V.dc and 425V.dc, closer to the upper limit.

2 panels in series is too low a voltage.

See Keith Gough comments at 38m18s on the training video wrt to voltage:

 

Edited by system32
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