Optimal string arrangement

[Scubadude]

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! 

[Scubadude]

* Suppose I should have added the panels are Canadian CS3W-455MS 455W.

Edited November 25, 2021 by Scubadude

[P1000]

2 panels on a string will not work. 5 is also a bit low. Your inverter has 2 MPPTs, so put 7 panels on each.

[Scubadude]

Thanks @P1000

 

[Gerrie]

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.

[P1000]

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 November 25, 2021 by P1000

[Robbo]

17 minutes ago, Gerrie said:

8KW installation with 20 panels

I have the same and went with 8 panels on 1 mppt and 2x6 on the other. As @P1000says, the higher the voltage the better

[TimCam]

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! 

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.

 

[Scubadude]

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.    

[TimCam]

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.

[system32]

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 November 26, 2021 by system32

[TimCam]

Any feedback on your new install, or is the weather this time of year, putting the breaks on?

[Scubadude]

I started a new thread of the actual install. https://powerforum.co.za/topic/10821-my-8kw-deye-canadian-solar-shoto-hybrid-solar-installation/

[Goedman]

I have an Axpert (Mecer) 5000W inverter running on two batteries as a back-up for loadshedding.

Now I got 10 Canadian 420 W panels and want to space them at 90 degrees (four panels to catch the morning sun and six panels for the midday sun).

If all the strings go to one connector box and then to the inverter how will they effect each other. Will the morning panels be pulled down by the other six that are still in the shadows? Similarly late afternoon will the morning panels moving into the shadows, have a negative effect on the six midday panels?

How serious is this effect and what can be done to mitigate the problem?

[Yellow Measure]

3 hours ago, Goedman said:

I have an Axpert (Mecer) 5000W inverter running on two batteries as a back-up for loadshedding.

Now I got 10 Canadian 420 W panels and want to space them at 90 degrees (four panels to catch the morning sun and six panels for the midday sun).

If all the strings go to one connector box and then to the inverter how will they effect each other. Will the morning panels be pulled down by the other six that are still in the shadows? Similarly late afternoon will the morning panels moving into the shadows, have a negative effect on the six midday panels?

How serious is this effect and what can be done to mitigate the problem?

Yes, it will affect the production. You can use multiple MPPTs for each array. Alternatively, use optimisers for the panels that are shaded (but it is equally expensive to installing additional panels).

[Gerrie]

On 2021/11/25 at 3:24 PM, P1000 said:

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.

I am ready to connect the 20 x 450W panels to the 8KW Sunsync but am still in two minds on what to do. I would like a perfectly balanced system by connecting 2 x 5panels to one MPPT and again 2 x 5panels to the other MPPT. I know the voltage will only be 243.5V.

But than the other good option not as balanced though is 1 x 8 panels on one MPPT and 2 x 6panels in other MPPT, which mean one MPPT has 3600W @ 389.6V and other has 5400W @ 291.6V The panels face true North at about 25degrees with no shade. 

Will the second option really make much difference?

[Tariq]

@Gerrie, attached is my pv voltages, the blue graph is six JaSolar 540 watt panels, the total Voc is 300 volts, seems to work fine around 250-260 volts.

[Gerrie]

17 minutes ago, Tariq said:

the blue graph is six JaSolar 540 watt panels, the total Voc is 300 volts, seems to work fine around 250-260 volts.

Thanks for sharing Tariq, the blue voltage looks quite stable with nothing out of the ordinary. Does the green graph have more panels as voltage looks a bit higher, green seems a bit up and down early morning and late afternoon is that normal?

[Tariq]

8 hours ago, Gerrie said:

Thanks for sharing Tariq, the blue voltage looks quite stable with nothing out of the ordinary. Does the green graph have more panels as voltage looks a bit higher, green seems a bit up and down early morning and late afternoon is that normal?

The green graph is nine Canadian Solar 355 watt panel ( had those originally with a Victron ), that is why it is a higher voltage string and the orientation is NE versus NW for the JaSolar panels

[Gerrie]

On 2022/01/12 at 8:16 PM, Tariq said:

@Gerrie, attached is my pv voltages, the blue graph is six JaSolar 540 watt panels, the total Voc is 300 volts, seems to work fine around 250-260 volts.

Hi Tariq, Just a bit of feedback I did connect the 20 x 450W panels in 2P x 5panels on each string the voltage measured is about 220V spot-on at each string. It is balanced quite equal between the two MPPT’s and looks like it will be fine. I will monitor it over the next few days to see how it performs but it looked impressive today even with very cloudy weather.

[Tariq]

@Gerrie, good to hear that even 220 volts on the Sunsynk mppt is working fine, yes, do keep us informed, I do think that it doesn't "much" of a difference if you are running mppt voltages closer to the high end of the voltage range

[Scubadude]

OK, so the installer basically arranged the strings as two rows.  The problems is the one palm shades the edge of both strings in the morning and the other shades the other end of both strings in the afternoon.  This makes for a very nawrrow operating window during our shorter winter days.  So I want to re-arrange the strings to split the array East/West rather than North/South.  

Two questions:

1. Do you think this will improve winter yield?

2. Who could I get to do this little job for me - my installer seems to have gone awol and most installers dont want to pick up small maintenance jobs. 

Edited May 12, 2022 by Scubadude

[Buyeye]

You could sell the palm trees or move them but that might cost more. They incredibly easy to move to people with the right tools.

They have very small shallow roots.