Hi Guys,

 

I've been reading up on many posts before and have studied the manuals from top-to-bottom ... but to-date I cannot find a "reasonable" answer as to the correct information I am seeking in terms of "PV Array / String Calculations" per MPPT Tracker [using multiple strings], etc.

 

I have the following setup:

 

2x Deye 8KW Hybrid Inverters ~ connected in parallel

24x 400W Mono Panels ~ strings are connected in series

 

Specifications for the Deye 8KW Hybrid Inverters:

Max. DC Input Power                     - 10400W
PV Input Voltage                            - 370V (100V~500V)
MPPT Range                                  - 125V ~ 425V
Start-up Voltage                            - 150V
PV Input Current                            - 22A + 22A
No. of MPPT Trackers                   - 2
No. of Strings Per MPPT Tracker - 2 + 2

 

Specifications for the 400W Mono Panels:

Maximum Power - Pmax (W)               - 400W
Positve Power Tolerance                     - 0 ~ +5W
Open Circuit Voltage - Voc (V)            - 49.76V
Short Circuit Current - Isc (A)              - 10.3A
Maximum Power Voltage - Vmpp (V)  - 41.19V
Maximum Power Current - Impp (A)    - 9.74A

 

Here is how I calculated the maximum PV Array Input Strings:

 

1. Deye 8KW Hybrid Inverter [PV Array Max - 10400W] / 400W Mono [PV Panel Max - 400W] = Max. 26 Panels ~ per Inverter

2. Max. 26 Panels / 2 (MPPT Trackers) = Max. 13 Panels [per MPPT]

3. [each MPPT Supports 2x Strings], therefore each string can theoretically be Max. 13 Panels [per MPPT] / 2 = 6.5 ~ Max. 6 Panels per String (rounded-down) [2x Strings per MPPT, 4x Strings per Inverter]

4. In order to balance the Strings - [i.e. 6x Panels per String] = Max. 12 Panels per MPPT ~ Max. 24 Panels per Inverter

 

Now let's verify the MPPT Range:

49.76V * 6 [volt increases in series connection] = 298.56V [theoretical V limit per String]

10.3A * 1 [amp does not increase in series connection] = 10.3A [theoretical A limit per String]

 

HERE is where I am stuck:

*each MPPT = 22A (max) or 500V (max) - if you will*

 

I *assume* that each string will be "combined" inside the internals of the Inverter itself, i.e. the Voltage will stay roughly the same [usually the lower of the two Strings], but the Amperage will double [since they will be connected in "Parallel"]?

 

Please can someone confirm for me whether the above logic is correct, are the Strings indeed "Paralleled" when each string is connected to A MPPT Tracker, or are they kept in "Series"?

 

The manual, online resources, searching countless hours, etc. ... nothing had produced any favorable results in terms of getting to the end-result of my *assumption*.

 

Edited August 17, 20214 yr by RabidBunny

you are correct in your calculations

13 minutes ago, Tariq said:

you are correct in your calculations

Thank you for confirming, but the question I am still unsure about is:

 

Are the "strings paralleled" when they are combined in the inputs for each MPPT [supporting 2x Strings], or are the "strings seriesed" [for the lack of a better word]?

They are paralleled inside the mppt 

17 hours ago, Tariq said:

They are paralleled inside the mppt 

Thank you! 😀

On 2021/08/17 at 3:13 PM, RabidBunny said:

Thank you for confirming, but the question I am still unsure about is:

 

Are the "strings paralleled" when they are combined in the inputs for each MPPT [supporting 2x Strings], or are the "strings seriesed" [for the lack of a better word]?

Is it really important. As long as you stick to the specs of 550V input per MPPT and not more than 22A per MPPT. Let the inverter take care of the rest 

Edited August 26, 20214 yr by Scorp007

6 hours ago, Scorp007 said:

Is it really important. As long as you stick to the specs of 550V input per MPPT and not more than 22A per MPPT. Let the inverter take care of the rest 

550V?

29 minutes ago, YellowTapemeasure said:

550V?

Sorry my mistake. Max is 500V so one can have up to 9 in series per string to give 448V per MPPT with a safety margin for cold clear days. I was thinking of another inverter that can handle 550V.

You can have 8 or 9 panels per string, you can oversize your array I believe. The 10400W max is the max the MPPTs are able to produce, not the max rated kWp of the array. Just don't exceed the voltage rating.

24 x 400W panels gives 9600W. For Gauteng it means about 8000W in summer in line with the inverter used. Based on irradiation of 800W/sq m. 

 

On 2021/08/26 at 10:31 PM, Scorp007 said:

Sorry my mistake. Max is 500V so one can have up to 9 in series per string to give 448V per MPPT with a safety margin for cold clear days. I was thinking of another inverter that can handle 550V.

The voltage ratings won't be exceeded (6x Panels per String and 2x Strings per MPPT), since the PV Array is paralleled, the amp ratings doubled when I connected the second PV String (per MPPT).

 

Voltage ratings stayed within the MPPT min and max range ~ taking the lower of the two into account, which is correct.

 

On sunny days I tend to average around 79.86% of the PV Array capacity.

 

PS: be aware with 9 x Panels per String, exceeding the optimal MPPT range - 125V ~ 425V ~ may negatively affect performance.

Edited September 1, 20214 yr by RabidBunny

Everyonne should keep in mind that inverters, (most ) are ddesigned with ,2500Wp pv's in mind.

Canadians Pv's has a ratio of pv voc x 1.14 at -10degrees C, so its pretty easy to blow your mppt witth voltage on a cold Clear winters morning!!

 

 

 

perhaps an easier/cheaper setup could have been 18x 535w, 9 in series per mppt.

pv v max would be 450v, under load closer to 380v-400v

pv i max would never be exceeded, but around 13A per mppt.

24x 400w = 9600w

18x 535w = 9630w

could've gotten away with 1x inverter as well depending on peak load requirements.

 

Edited December 4, 20214 yr by Nitrious

9x 535 will push you over the voltage limit and damage the mppt 9x49x1.14 = smoke.

While 8x49x1.14 will just make it on the voc of the inverter. The 1.14 is for morning cold start.

Run 5pv x4 string 25A hard clamp fuses  maybe midis and 6mm² wirr and holders.

Generally the unit will take between 110%-130% of current as with victron mppts 

 

 

On 2021/12/04 at 6:19 AM, Nitrious said:

perhaps an easier/cheaper setup could have been 18x 535w, 9 in series per mppt.

pv v max would be 450v, under load closer to 380v-400v

pv i max would never be exceeded, but around 13A per mppt.

24x 400w = 9600w

18x 535w = 9630w

could've gotten away with 1x inverter as well depending on peak load requirements.

 

The price I paid for the 24x 410W panels worked out cheaper than 18x 535W panels would have cost me ~ I have since expanded my PV Array.

No, I would not have been able to get away with only 1 x inverter.

My daily consumption peak exceeds 8kW ~ tends to peak between 10.5kW and 12kW.

My goal is to be {eksdom} independent; therefor I can't rely on additional AC throughput, since AC is not available.

I also could not cope with 1 x inverter + PV Array configuration, pushing enough charge for the battery bank.

@RabidBunny

Would you mind sharing your wiring diagram 

 

@RabidBunny do you know if the voltage limit on the Deye 8KW inverter of 425V is per MPPT or per string into the MPPT? As far as I understand each MPPT can take two strings of panels, does it combine this and then have a limit of 425V per string or total?

My system is a Deye 8KW with 10 panels of 455W which have a voltage of +-49V per panel all connected in series. So total voltage of +-490V, which come into a single MPPT via the + and - cables from the panels. So am I exceeding the MPPT tolerance? My max output is 3.6KW that I have seen. Which is far too little.

This was all done by an installer, I am not getting the desired output from my panels and thus I am now checking everything myself.

Thanks!

Edited June 1, 20224 yr by Maverick

4 hours ago, Maverick said:

@RabidBunny do you know if the voltage limit on the Deye 8KW inverter of 425V is per MPPT or per string into the MPPT? As far as I understand each MPPT can take two strings of panels, does it combine this and then have a limit of 425V per string or total?

My system is a Deye 8KW with 10 panels of 455W which have a voltage of +-49V per panel all connected in series. So total voltage of +-490V, which come into a single MPPT via the + and - cables from the panels. So am I exceeding the MPPT tolerance? My max output is 3.6KW that I have seen. Which is far too little.

This was all done by an installer, I am not getting the desired output from my panels and thus I am now checking everything myself.

Thanks!

Per MPPT

4 hours ago, Maverick said:

My system is a Deye 8KW with 10 panels of 455W which have a voltage of +-49V per panel all connected in series. So total voltage of +-490V, which come into a single MPPT via the + and - cables from the panels. So am I exceeding the MPPT tolerance? My max output is 3.6KW that I have seen. Which is far too little.

Post a link to the panel's actual specs? It certainly sounds like you may be getting a little close to the the 500V limit. 

Reasons for getting less may be because of suboptimal azimuth and tilt. How are they installed? Also, what is your location?

5 hours ago, Maverick said:

@RabidBunny do you know if the voltage limit on the Deye 8KW inverter of 425V is per MPPT or per string into the MPPT? As far as I understand each MPPT can take two strings of panels, does it combine this and then have a limit of 425V per string or total?

My system is a Deye 8KW with 10 panels of 455W which have a voltage of +-49V per panel all connected in series. So total voltage of +-490V, which come into a single MPPT via the + and - cables from the panels. So am I exceeding the MPPT tolerance? My max output is 3.6KW that I have seen. Which is far too little.

This was all done by an installer, I am not getting the desired output from my panels and thus I am now checking everything myself.

Thanks!

With 10 of those panels is a bit much for one series string , you are going to be operating right at the limit of the MPPT voltage wise especially in the cold winter. I would split them into 2 series strings of 5 panels. I have seen 380 volts with my 8 455w panels on a sting ,voltage went up quite a bit with the cold temps lately.

9 hours ago, Maverick said:

@RabidBunny do you know if the voltage limit on the Deye 8KW inverter of 425V is per MPPT or per string into the MPPT? As far as I understand each MPPT can take two strings of panels, does it combine this and then have a limit of 425V per string or total?

My system is a Deye 8KW with 10 panels of 455W which have a voltage of +-49V per panel all connected in series. So total voltage of +-490V, which come into a single MPPT via the + and - cables from the panels. So am I exceeding the MPPT tolerance? My max output is 3.6KW that I have seen. Which is far too little.

This was all done by an installer, I am not getting the desired output from my panels and thus I am now checking everything myself.

Thanks!

The sweet spot per MPPT is up to 425V. It can accept up to a max of 500V. Above 425V you might just loose a few % in efficiency. Not 10% or more.

This time of the year 3.6kw peak is normal from a 4.55kw array.

Thanks gents, I have asked the installer to come back and split them into two strings of 5 panels and see what the results are then. Max voltage thus far is 480V and that makes me a bit uncomfortable. I know the optimal operating voltage for the MPPT is 370V but is there any loss below this for the 125V minimum to the 370V optimal value? Or will that work fine?

Location is Centurion in Gauteng and panels are north facing, all 10 of them. Peak operating output on them is between 9am and 3pm, after that they start producing much less. But max I have seen on the array is 3.6KW which is far less than I had hoped. 

What I can see is that when the PV array voltage goes over 425V I then start dropping off from the 3.6KW down so sub 3KW output, scratching my head a bit at it all.

Edited June 2, 20224 yr by Maverick

22 minutes ago, Maverick said:

What I can see is that when the PV array voltage goes over 425V I then start dropping off from the 3.6KW down so sub 3KW output, scratching my head a bit at it all.

Thats because 425V is the absolute maximum that the MPPT can produce power at and with 10 panels in series you will certainly at times be above that meaning the inverter will have to try bring the voltage down meaning you lose some power. At least thats my theory haha. I would say 9 of those panels is absolute max on a string to not push the MPPT to its limits. 

Got up to 407V this early winter morning on my one string of 8 x 460W Jinko panels...

8 hours ago, Maverick said:

Thanks gents, I have asked the installer to come back and split them into two strings of 5 panels and see what the results are then. Max voltage thus far is 480V and that makes me a bit uncomfortable. I know the optimal operating voltage for the MPPT is 370V but is there any loss below this for the 125V minimum to the 370V optimal value? Or will that work fine?

Location is Centurion in Gauteng and panels are north facing, all 10 of them. Peak operating output on them is between 9am and 3pm, after that they start producing much less. But max I have seen on the array is 3.6KW which is far less than I had hoped. 

What I can see is that when the PV array voltage goes over 425V I then start dropping off from the 3.6KW down so sub 3KW output, scratching my head a bit at it all.

I'm also in Cent with North facing panels. Your 3.6kw is a touch more than mine and pretty spot on for May. 31 May was a stand out day for the last few weeks. About a 10% higher peak and also a bit higher daily yield.

So nothing wrong with getting close to the 500V max but you never want to get 500V so a good call to split the 10 series.