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mad-mike avatar image
mad-mike asked

Which MPPT option to use with 10 x 540 / 550W Panels ?

Hi Guys and Girls.I am new here so please be gentle with me!. My neighbour and I live in the Spanish Canary Islands and we are looking to self install 2 x identical systems (moving to off grid in time) on each of our houses, comprising either 10 x 550W Exiom panels or 10 x 540W Sharp panels. (I know there are other options but these are the 2 most easily obtainable here). Can anyone with real world experience advise me which choice to go with please? (Price is the same).

To wire them together (having done the Victron online MPPT course) Id planned to use 2 separate 150/45 Victron MPPT's and wire the 2 strings of 5 in an arrangement of 2 x 2 (4 panels) in parallel and then add the 5th in series to the 2 x 2. In my brain, this would give me 150V and 56 Amps. Correct? Specs are (Exiom STC, ISC 13.93 and VOC 49.97.) (Sharp STC, ISC 13.66 and VOC 50.34). A very well respected installer and supplier here has said they would not wire the system like that and would use one larger MPPT of a 150/100 specification and would wire 4 x 2 panels in parallel and the other 2 in series. This would give a single string of 150v and 112Amps if I am correct? Please put me right if not! My plan of 2 smaller MPPT's would give me 90 Amps of charging into a 48V 280A LiFePo4 16 cell module, would cope with using 6mm2 wire on the 2 separate strings and give me redundancy IF we ever had a breakdown on 1 MPPT. There suggestion would lack redundancy and need bigger than 6mm2 to cope with the larger Amperage? Agreed or not. I appreciate I could potentially throw 10 more amps at the battery but here its not really an issue.

(The cost of 2 x smaller or one larger MPPT are roughly the same)

I would appreciate any input on the choice of panels and more importantly, which MPPT option is considered better.


Yours in anticipation, Mike.

MPPT SmartSolar
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7 Answers
klim8skeptic avatar image
klim8skeptic answered ·

@Mad mike 2 strings of 5 in an arrangement of 2 x 2 (4 panels) in parallel and then add the 5th in series to the 2 x 2.

That is not going to work.

Post a link to your panels, and the record low temps for your location.

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mad-mike avatar image
mad-mike answered ·

Hi and thanks for taking the time to reply. Lowest temp here was 14C but this is generally middle of the night. Lowest daytime (winter no sun, 17-18C)


Links,

Sharp, https://secure.sharp.eu/cps/rde/xbcr/documents/documents/Marketing/Datasheet/2110_NUJD_540_HC-Mono_Datasheet_10Y_EN.pdf


Exiom

https://www.exiomsolution.com/productos-detalles/ex530-550mb-144hc182bf/


Can you please explain why you think this would not work?


Mike.

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seb71 avatar image seb71 commented ·
The 5th panel, because it is in series with that 2x2 series/parallel group of 4 panels, would limit the current of that entire arrangement (so each branch of that 2x2 group will have half the current). It will be like you have just 3 panels in series.
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seb71 avatar image
seb71 answered ·

Assuming identical PV panels:

You first make strings of panels in series (how many panels in a string depends on the string Voc and the maximum allowable voltage of the MPPT).

Because the panels are in series, voltage adds (string voltage = panel voltage x number of panels in a string), current remains the same (string current = panel current).


You can connect just one string to a MPPT or you could put two or more of those identical strings in parallel and connect that PV array to a MPPT (how many strings you can put in parallel, depends on the MPPT you chose).

Because strings are in parallel, voltage remains the same (array voltage = string voltage), current adds (array current = sum of currents from all your strings you put in parallel).

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So with an odd number of panels, all must be in series (a single string), but how many can be in a string is limited by the maximum voltage that MPPT can take (with your >50V panels and a 150V MPPT, that maximum limit is 2 panels in a string).

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mad-mike avatar image mad-mike commented ·

Hi Seb71.

Appreciate your reply.

To answer, "either 10 x 550W Exiom panels or 10 x 540W Sharp panels" so all panels the same.

To answer, (with your >50V panels and a 150V MPPT, that maximum limit is 2 panels in a string). Panels be it Sharp or Exiom are actually <50v each so 3 panels is allowable. (Qualified by my Victron supplier)

To reiterate, respected installer here and Victron supplier / distributor has stated a 150/100 MPPT with 4 sets of 2 panels in parallel and then 2 panels in series added to the end to create 4 x 2 panels 50v, 14 Amps each means 50v and 112A + No 9 panel added in series (now 100v and 112 amps) + no 10 panel added in series, now 150v 112 amps. (Using a 150/100 MPPT)


I don't see how this varies from my configuration of 2 strings, each with of 2 sets of 2 panels in parallel and 1 in series at the end (2 x 14A, 50v + 2x14A, 50v + 1 x 50v = 56A at 150V / string and MPPT, 150/45, all x 2, ending up with 112 Amps and 150v across 2 x 150/45 MPPT's.

I am yet to be persuaded y logic isn't sound. Sorry.

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seb71 avatar image seb71 mad-mike commented ·

To answer, (with your >50V panels and a 150V MPPT, that maximum limit is 2 panels in a string). Panels be it Sharp or Exiom are actually <50v each so 3 panels is allowable. (Qualified by my Victron supplier)

You listed VOC 49.97V for one model and VOC 50.34V for the other. Do not put 3 such panels in series on a 150V MPPT, no matter what that dealer said.


To reiterate, respected installer here and Victron supplier / distributor has stated a 150/100 MPPT with 4 sets of 2 panels in parallel and then 2 panels in series added to the end

Do not do this.


I am yet to be persuaded y logic isn't sound.

Tell this to that Kirchhoff guy.

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mad-mike avatar image mad-mike seb71 commented ·
seb71.


My apologies, you are correct. I was looking at the Exiom panels, forgot about the Sharp. Yes you are correct. Having re-read the suppliers suggestion, he is advocating 5 x 2 panels in parallel, so 100V and 140Amps. That seems a reasonable solution i guess.
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seb71 avatar image seb71 mad-mike commented ·

I was looking at the Exiom panels, forgot about the Sharp.

Even for the panels with VOC 49.97V it is not safe to connect 3 in series for an 150V MPPT.


Having re-read the suppliers suggestion, he is advocating 5 x 2 panels in parallel, so 100V and 140Amps.

Voltage is correct, but amperage is not correct.

If you have strings of 2 panels in series, the current for each string will be the panel current (same current pases through both panels from that string of panels in series).

If then you put 5 such strings in parallel, for the entire PV array you will have 5 times the current of a string (not 10 times as you wrote).

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mad-mike avatar image mad-mike seb71 commented ·
Yep, I get that. Think I was having a senior moment. I confirmed with the supplier and he put me right as well. 100V, 70 amps. Will use the Tr MPPT as suggested to allow for their recommended thickness of cable. Appreciate the time people have taken to help out, thank you.
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nesswill avatar image
nesswill answered ·

I have A SmartSolar MPPT 450/100 with x6 550w in series on each tracker very similar panels to the 550w you are looking at.

Probably a bit over kill you what you need but does leave room for expansion should you choose to at some point.

I have found these MPPT,s to be very good in all weather conditions. Especially good in cloudy conditions. My real world finding.

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mad-mike avatar image mad-mike commented ·
Hi nesswil.

Appreciate your reply.

I am happy that the Victron MPPT's are the best in the business. My question on choice was related to the Exiom v Sharp panel choice.

A 450/100 is massive overkill I think, but as you say, plenty of headroom to expand in the future.

Best regards, Mike


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klim8skeptic avatar image
klim8skeptic answered ·

@Mad mike As previously mentioned there is a limit of 2 series panels for a 150v mppt. At 10c the panel Voc goes up to 52v.

If you are keen to put all 10 panels on a 150-100 mppt the only option is to string them up as 2 series x 5 parallel.

This will require series fusing on each string, both pos and neg cables. Failure to have proper fusing in place can result in a fire should a fault occur in 1 string.

Note the 150-100 has a "Max. PV short circuit current" of 70a. 5 parallel Sharp panels has a Isc of 68.3a, within the mppt's limit.

5 parrallel Exiom have a Isc of 75.75a, above the mppt's Max PV short circuit current limit.

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mad-mike avatar image mad-mike commented ·
Hi klim8skeptic.


That's great info thank you. I wasn't aware that the 150/100 had a max current limit of 70Amps! I guess 5 x 2 parallel and the Sharp Panels is going to have to be the way to go. Can you tell me what CS of wire is required to carry that amperage please? Will the standard 6mm2 be enough? Will anything bigger fit the MC4 connectors?

Thanks for your input

Mike

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mad-mike avatar image mad-mike commented ·
Hi klim8skeptic. You were right on the Sharp panels, 68.3A but the Exiom 550w are 5 x 13.93A, so 69.65A. Tight but still in! Not sure where the 75.75A came from?
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seb71 avatar image seb71 commented ·

If you are keen to put all 10 panels on a 150-100 mppt the only option is to string them up as 2 series x 5 parallel.

Correction: two such panels in series would be too much for an 100V MPPT (same issue as 3 such panels in series for an 150V MPPT).

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I would avoid that may strings in parallel on a single MPPT.

Better use two (or more) smaller MPPTs instead. True that multiple MPPTs would work best with a GX device included in the system, but I would also get a GX device anyway, even for a system with a single MPPT (unless that system is very small, which is not the case here).

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Michelle Konzack avatar image
Michelle Konzack answered ·

Since you gave a 48V system use a SmartSolar MPPT 250/100 and make eight Solarpanels in 4S 2P and for the other two use a SmartSolar MPPT 150/35


But better would be, if you use three SmartSolar MPPT 250/70-Tr VE.Can because then you can have on two 4 modules in series and on the third 2 modules and can still upgrade to 4 modules.


VE.Can because they synchronise to each other and are more suitable for larger systems

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mad-mike avatar image mad-mike commented ·
Hi Michelle. Thank you for the input. If I had that sort of money I think I'd just sit back on the beach here and let someone else do the whole thing for me! . I'm only doing this myself so that I can save some money, so I'm using good products but at the tightest budget I can.
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mad-mike avatar image
mad-mike answered ·

Hi Seb71.


150/100 MPPT not 100/100 so all ok. Yes, going to put a GX in to keep an eye on things and report back to the cloud. Thanks again.

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