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solar sizing

Number of Cells in Series or Array Voltage. Which is more important?

I have reviewed manuals for several SmartSolar MPPT charge controllers. Section 3.3 "PV Configuration" lays out the guidelines for the solar array. It gives minimum, recommended and maximum number of individual solar cells in series, i.e. " Minimum number of cells in series: 72 (2x 12V panel in series or one 24V panel)".

Is the number of cells important or is this a generalization to get the user in the correct operating voltage range? That voltage range being Vbat+5 to 10-15% below the voltage limit.

For example, charging a 12v battery bank with a controller that has a recommended series cell count of 72. Using a single 24v panel, would it matter if the panel had 72 cells or 60 cells as long as the voltage is within the parameters?

I am using the Victron Energy MPPT Calculator Excel spreadsheet to determine voltage range vs temperature for individual panels.


coghst asked
childcarepro answered ·

2 Answers

MPPT 150/60 MC4 is wrong inside PVSYST database.

I have just enter here and I´m looking for a PVSYST file .OND from MPPT 150/60 MC4.. This file is wrong inside PVSYST database......this power is 1300W but we know that has 1720W. Who can send me the correct file?

marcos-rodrigues asked
Paul B commented ·

0 Answers

Does this graph indicate my solar array is not keeping up with usage?

Hi, I've attached a screenshot of my VRM dashboard for the past 30 days for my remote cabin off grid system. I've had to reset 100% SOC a few times once my LionEnergy battery bank (2 - 12V in series 105ah) batteries are showing 28V (for some reason the BMV never seems to show them as 100% charged...i have to rest them when they get to 100% 28V). Those resets are indicated by the peaks in battery SOC at 100% in image. I only leave on a refrigerator in the cabin when I'm not there and have it on a timer to turn off between 10PM-1AM and 2AM to 5AM. Does this graph indicate that the 3.16kW energy harvested per day isn't enough to keep up with the draw/load? I have a 1.46kW array (using victron MPPT and inverter/charger).


lo-g asked
billknny answered ·

3 Answers

ESS, shouldn't the solar array (20 x 360w) cover these loads?
  • Client has 20 x 360w (7200w) panels on the roof (roof, facing north). 5 strings of 4
  • 2 x MPII in parallel
  • SmartSolar MPPT 250|100.
  • ESS system not feeding in to grid. Set to about 70% state of charge for self consumption.

Why isn't the PV covering all the day loads?

A looks normal in this image, but the B section. The client is using high consumer (iron) during this time. Shouldn't the array handle this consumption?


And again here:


jond asked
jond commented ·

1 Answer

Is 233V 19A in each input (3pc MC4) ok? Smart Solar MPPT 250/100 48v!

I have 9,9kW panels. 36pc 275W Voc38,7V Isc9,17A.

That's all for Off-grid:

Quattro 10000 48

Smart Solar MPPT 250/100

BYD Premium LVL 30,8kWh


jonatanjensen asked
Vance Mitchell answered ·

2 Answers

4x 100w series into 100/15?

Hi. I have a SmartSolar mppt 100/15 powering a 12v house bank at my garden shed. I also monitor the system with a bmv712.
I currently have 4x 100w panels that on the ABSOLUTE BEST DAYS will output 20.5v each and usually about 5a up to 6.7 but average 4.5a. I once saw 8 amps for just a bit with 3x of the 100w in series but that was a a one time event. They regularly just put out about 4.5~5.6a total. I NEVER run them parallel (don't even have any splitter/joiners)!

We get a LOT of rain and when it's cold in the winter almost no sunlight at all (the panels won't even tirn on the MPPT).
I keep two of the 100w in series plugged in all the time and they put out 39~40v and about 5a give or take on sunny days for a few hours but when needed I add a 3rd into the series to bring the voltage up to 60v.

I would like to add the 4th 100w panel IN SERIES to bring the voltage up to 80v at 4.5~5.6a to run a much longer feed wire from the panels to the MPPT and house bank closer to my house which would be far more convenient than the garden shed where everything currently is at and requires frequent interaction and walking to charge thing daily.

It seems to do fine with the 3x 100w putting out the 60v/ 6a up to 8amp (but super rarely that high, again 99% of the time it is 5.6a or less).

I've used the solar calculator and I always get quoted that I need the FAR more expensive 100/30 at LEAST or even the 150/30 to safely have a 80v/5 to 8 amp setup! But I thought it was 100v and 15a?????

What I want to know is why is my MPPT 100/15 is called a 100v 15a controller if it can suposedly only handle 40v and 8 amps going into my 12 bank? The moment I increase those figures or enter in a series of 4x 100w panels I get quoted the bigger MPPT controllers as necessary despite that at MAX the real world figures are 80v and at MOST ever 8amps and 99% of the time they are actually 90w panels. I could understand running two parallel strings could be iffy but in series, really, that 80v/8a is too much for a 100v/15a controller?

The current house bank is 12v and the max output my system ever does with 3x 100w panels is 240w so far (In 3 years). I don't see how the calculator can be correct in that I need a double-15amps charge controller.

I also considered that it might be 100v max INPUT and 15a MAX conversion OUT which would make more sense in that turning that 80v into my 14.6+v charge in ideal conditions would be maybe a 5.4 multiplier on the amps so my 4.5~5.6a would easily overload a 15a charge controller at x5.4 in an ideal no-conversion losses situation. I have adjusted the figires in the calculator but it still tells me to series 4x 90w panels @ my amps I need at least a 100/30!

So the amps-out on victron charge controllers is all the MPPT's can handle converting amps into then, not the max input? Is that really the case?

trinasgarden asked
trinasgarden commented ·

5 Answers

Spannung fällt beim Anschluss an den Solarregler

Hallo, kann mir hier vielleicht jemand helfen. Es geht um Solar. Unser neuer alter Wohnwagen hat Solar auf dem Dach. Jedoch wird die Batterie nicht geladen. Ich habe schon den Laderegler gewechselt gegen einen Victron 100/20 mit den selben Symptomen. Vom Solar aus gemessen kommen ca 18-20V an.Es befinden sich zwei Panel auf dem Dach. Ich habe noch nicht geschaut ob Parallel oder in Reihe, aber vielleicht kann man das anhand der Spannung evt erahnen? Sobald das Solar am Laderegler angeschlossen wird, fällt die Spannung auf ca. 12,5 v runter. Selbst wenn ich so ein Voltmeter die man einbauen kann anschließe fällt sofort die Spannung. Jemand vielleicht eine Idee woran das liegen kann? In Sachen Solar kenne ich mich noch nicht so gut aus. Dachte erst das der alte Regler defekt sei, aber leider besteht das Problem weiterhin.





defjam asked
tilo answered ·

4 Answers

4 x 320 Watt Panels (2 pairs in parallel and the pairs in series) 100/50 Controller

I currently have 2 - 320 watt panels in parallel with the Smart Solar 100/50. Looking for some peer review to see if I am correct. I want to add another 2 identical panels to my array. The only issue I see is exceeding the max wattage but the controller says it will reduce any wattage over 700 (and how likely are the panels to see max watts laying flat on a trailer). The panels would be approx. 20.28 isc and 80.2 voc. Both under the specs of this controller? My panels are the 320 watt on this document.

trent asked
billknny answered ·

2 Answers

3 solar panels, 2 in parallel, 1 in series?

Hi all

I want to permanently mount 3 solar panels on a caravan roof in a 12V system.

The 3 panels are identical, 100W, VOC 22.7V 5.5A and I have a SmartSolar MPPT 100/20.

I don't want to connect all 3 in series because of shading on the panels, with a caravan you can't exactly plan shading, shading is a given.

I also don't want to mount all 3 in parallel because of the 5V rule, I have a Lifepo4 battery which voltage stays above 13V for a very long time.

I can't get clarity on this, I read mentions which says yes it's fine and others which says it's a big no. Would I be able to connect the panels 2P + 1S or the other way around 2S + 1P?

I know 2S + 2P is good, but what about odd numbers?


bigboy529 asked
bigboy529 commented ·

3 Answers

How is "recommended number of cells in series for highest controller efficiency" (section 3.3 of smartsolar manual) determined?

I would like to understand the math or logic behind these recommendations. I understand that 'cells in series' is shorthand for operating voltage.

I assume that this calculation is a balance between maximizing voltage differential to optimize MPPT performance in less-ideal conditions, and minimizing voltage differential to optimize DC-DC conversion efficiency. Is this correct?

The recommendations only deal with 36 and 72 cell panels, I would like to understand the math/logic behind these recommendations so I can understand how it applies to 60 cell panels and 96 cell panels, etc.

For instance for a 24v battery, Victron recommends 144 cells in series. Would 120 cells or 96 cells be less ideal?

dzl asked
dzl answered ·

1 Answer

Small inverter used as ess system.

Hello, newbie here so please have patience

I've just acquired a used solar kit consisting of three 250w panels, a victron 12/1200/50 multiplus inverter, a victron mppt 100/30 and two large 6v rolls lead acid batteries for €300.

It was used in a small off grid setup which I was thinking of using to power my garage and caravan as it's already setup for that task.

But I was also thinking of using it in our main house which has grid connection?

If I used it in this situation could I use it as an ess setup? Using the batteries for evening usage and grid as backup or in the event of needing extra power from the grid when required?

I've read that I'd need a gx monitoring system to use ess and read that a raspberry pi can be used for this task as I already have one.

I think I'd need a usb to mppt cable and a MK3 usb cable.

I believe I'd also need the MK3 cable to setup the inverter for grid/ess usage.

My questions are:

Is it worth using this as an ess system in the house, it's a small system but we are low consumers.

Is there any other items I need apart from the mentioned cables, is a battery monitor required?

Thank you in advance

Wayne asked
Wayne answered ·

3 Answers

Is there a way to limit Maximum PV voltage to controller?

I have a 100/20 Smart Solar controller and only 2ea 100w panels. I want it to operate at full capacity by adding panels. Due to conditions on my property I need a longish cable run from my panels to the controller. High current and long runs seem to be expensive due to the cable thickness required. I want to add enough panels, in series, to get close to 100v but am worried about damage to controller. How can I “over voltage” the panels and reduce that voltage at the controller. For example, I envision a voltage limiter of some type. Say feed 150v from panels in and get 100v max out to put into controller. Is such a thing possible? Also, why is the PV input voltage so low for the controllers? Sorry for my ignorance, and thanks for the explanation.


maxxmanic asked
wkirby answered ·

1 Answer

Solar upgrade

Looking for some portable solar advise. currently at 600 watts and 2 batterys.. I want to know what I need to purchase/do to get up to 1200 watts (or more if possible)

and also how many battery's can I go up to with this ? currently have 2 x 6 volt battery's connected in series .. so at 12 Vs atm .. if I add extra I can add them in parallel to stat at 12v ? Currently have 1 x Victron 12V 1200VA Pure Sine Wave Phoenix Inverter. 1 x Victron SmartSolar 75/15 MPPT Solar Charge Controller . 2 x 600 watt panels and 2 of these 6 volt/225 ah battery's..

dc1138 asked
dc1138 answered ·

6 Answers

Possible over ampage

I have a Caravan 23ft, running a 12 volt system, bought a Victron 100/30 controller yet to be fitted.

I am looking at replacing the 2x80=160 watt solar panels with, 2x200w =400 watt.

Coldest temperature is 26F or 2.6C the average will be 85F and 29C, Batteries 2 x 105 AMG=210 amps.

My calculations is a 320 watt panels will charge my Batteries based on 110.4 watts over 4hrs, there are more calculations.

Since the Panels are mounted flat on the roof they'll only reach full output with full sun and lowest temperature reached, so that's why I am thinking 400 watts over due to inefficiencies of roof mounting.

With perfect conditions the system would put out 32 amps.

The questions will the additional 2 amps harm the 100/30 Victron Blue Solar Controller.

jeffrey-fishlock asked
JohnC answered ·

1 Answer

Looking for suggestions - Best way to hook up 12, 100 Watt - 18v panels to my MPPT 150/85


I have an off-grid installation with 12 each of 18 VDC Solar PV panels producing 100Watts in direct sunlight (in the American Southwest, if that matters to you). My battery system is 4 each of 6 volt Duracell Ultra batteries which are wired series-parallel (producing 12VDC). I already own the MPPT 150/85 MCA, the feed wires are run, I have some 4-to-1 parallel cables which I was considering hooking 3 banks of 4 panels in parallel (there are 3 MCA input pairs on the unit)...

I believe that will produce 18-21V at about 22 amps per pair... which should be more than enough in theory to do what I need it to do if I understand my requirements correctly.

My question to you: Is there a more efficient way to charge these batteries with the current setup I have? I.E. - Should I do 6 banks of 2 panels in series (~36V), then parallel 2-to-1 down to the 3 inputs with 24V charging?

What is the best way to handle this considering my low wattage panels and the multitude of them?

(Panel Specs)

12 of the following panels -


Optimal power [Pmax]: 100W(±5%)

Working voltage [Vmp]: 18V

Working current [Imp]: 5.62A

Short circuit current [Isc]: 5.97A

Open circuit voltage [Voc]: 21.6V

Dimensions: 105 x 54 x 0.25 cm/41.3 x 21.3 x 0.09 inch

Net weight: 2.6kg/5.73 lbs.

Working Temperature-40~+85

whitewhale asked
whitewhale answered ·

4 Answers

Smartsolar VE Direct vs VE CAN

Hi. Just wondering whether or not there is any difference in terms of functionality and remote control between Smartsolar VE Direct and VE Can products. Is there anyone that have some experience with both that can explain?

Thanks in advance for your help

Jesus Mazo asked
Guy Stewart (Victron Community Manager) answered ·

1 Answer

MTTP 100/30 terminals wire size

What is the maximum wire size that the solar and battery terminals can accommodate on a smart MTTP 100/30 charge controller? I didn’t see this mentioned in the manual or wiring schematic PDF.

hhaley asked
Justin Cook - Bay Marine Supply USA answered ·

1 Answer

How many panels can be connected to a 100/20 MPPT in 12V?

How many 100w solar panels can I hook up to a 100/20 MPPT SCC for 12v system?

Kristina Elaine asked
wkirby answered ·

1 Answer

Solar Power Supply Parameters - a practical solution?

I'd like to hear from community members their experience of solar power supplies. Given the below power requirement, how would one determine the optimum solar configuration that would "reasonably" guarantee power 24/7 all year round?

Of course, it will be location dependent to allow for latitude and inclement weather days. Let's say in this case it's Sydney, Australia. I'd be very interested to hear both calculated and rule-of-thumb answers.

Nominal Voltage: 12-volt
Load: 3-amps constant
Battery Amp-Hours: ?
Solar Watts: ?

Gary Pacey asked
ejrossouw answered ·

5 Answers

Panasonic HIT panels /MPPT controller

I have 3 Panasonic 325w HIT PV panels I am installing on our sail boat. It says on them that the open circuit Voltage VOC is 70.9

ISC 5.94A

Imp 5.50A

VMP 59.2

Question is can I run the panels in parallel in to a single Victron 150/100 MPPTcontroller or do I have to go to the 250 model.

Any help appreciated!

seraphina asked
seraphina commented ·

1 Answer

How much PV can I attach to a Victron 100/20

A Solar power question. I have a Victron 100/20. Manual states Nominal PV 290W, Max PV current 20A and Max voltage 100v.

I have 2 house panels which are 275w, 8.71A and 31.6V. Would it be better to connect in parallel giving me 63.2V/8Amp or Serial to get 31.6V and 17.42Amp

Also either way i will get 550w will this be an issue with Nominal PV being 290W on the 100/20?

cstylianou asked
Guy Stewart (Victron Community Manager) edited ·

1 Answer

Smart battery sense continuously disconnecting.

I have noticed recently, and to the best of my knowledge this is a recent issue, that the smart battery sense seems to be dropping out and losing connection every 10-30 seconds. It will connect and the wattage will spike to near PV capacity, then normalize. Then upon disconnecting the wattage will drop to near zero. This can't be good for things. I have tried resetting the smart solar MPPT 100/20, disconnecting and reconnecting from the network, even creating a new network. All to no avail. I am starting to wonder if I have a faulty battery sensor.


Jason Beug asked
Jason Beug answered ·

1 Answer

Solar Controllers 250/100 Parallel


Building a Solar System Consisting of

24 Panels 6 x 96v strings Southern Australia North & West Facing

2x 250/100 solar controllers

BMV 702

Multiplus 5000/240

CCGX,I have? or go VenusGX OctoGX for VE connections

My Question is how to parallel them correctly (presuming both Battery direct connection ? ) and provide ccgx connection of VE Direct including a BMV

& max length of VE Direct cables for fault free operation

wolfbarnsolar asked
wolfbarnsolar answered ·

3 Answers

Solar panel configuration with bluesolar mppt 150/ 85

Hi everybody

I'm in the process of putting together my first solar system. I have a victron quattro 48 10000 along with bluesolar mppt 150/85. I also have the bmv-700 and the colour control.

I have a bank of 8 12 volt 180ah AGM batteries wired as two parallel banks of 4 in series, giving a resultant 48 volt 360ah. I also have a generator set on board which currently provides mains power when the batteries become discharged.

I have purchased 9x panasonic hit 245w solar panels. These operate at a maximum of 44.3 volts. I can either use eight panels wired as series pairs. Or I can run the full 9 panels with 3 paralleled banks of 3 series wired panels.

My resultant voltages would be 132.9v with the 9 panels or 88.6v with 8. I have read in the manual for the blue solar mppt that the PV voltage must not exceed 150 volts under any circumstances and that is in the coldest of conditions. Further to this in the cable selection chart it is said that maximum efficiency is it twice the battery bank voltage.

I am therefore trying to weigh up the advantages and disadvantages of running a 9 panel system or an 8 panel system as with 9 panels I'm approaching the maximum voltage but gain an extra 245w of power.

I would really appreciate the opinion of somebody more experienced than myself in setting up such a system.

Kind regards, Ivor

ivorandrews asked
klim8skeptic edited ·

1 Answer

3 panels in series vs 4 panels in series (SmartSolar 150/70)

I am preparing to finally install my solar panels on the roof of my van conversion. My battery is 24 volt. I have nine (9) 12 volt, 100 watt renogy mono panels and was planning to have a 3s/3p configuration However, I was reading through the manual of my smartsolar 150/70 and noticed that it states that while 3 in series will work, the highest recommendation is for 4 in series.

Is the efficiency with 4 in series so much better that it would be worth going with an 8 panel (2s2p) config and ditching one of my panels, instead of my originally planned 3s3p?

In other words, would I stand to get more from an 8 panel system than a 9 panel system?

Stephen Otto asked
JohnC answered ·

1 Answer

Solar Controller options?


We are currently looking to install a large solar array to our catamaran and would like to know the most suitable Victron Solar Controller options for our application.

The array is to consist of 10 panels in total. 6x300w panels and 4x270w panels whis are to the specifications shown below..

The thought process is to break the panels into 5 pairs connected in series (3x600w & 2x540w) which will then run to the solar chargers (potentially 5 separate MPPT's), which will intern charge a large 12v lithium battery bank.
Can anyone provide information on the most suitable Charge controllers to achieve this, or if the is a better alternative to running 5 controllers. (I do not which to connect any more than 2 panels in series, to maintain optimum output protection against potential shading of panels)

Any thoughts would be much appreciated. Thanks in advance.


sidaniels asked
adev edited ·

2 Answers

spotty drops in solar generation


I just upgraded my solar configuration:

  • used to have a single string of a series of 10 panels
  • Moved to two strings one with roughly 600w and the second with about the same

Since then the production graph shows this strange curve that I never experienced before - looks like every now and then there is a negative spike of about the half (although timing and amount seems not have a connection):




Anybody have any idea of what it could be? could it be that the isolator diodes used between the two strings are not properly working?


stepir asked
stepir answered ·

2 Answers

Solar PV OFF GRID system powering 1 ton air conditioners and other electrical loads

Dear Experts,

This is an enquiry from a construction company in Al Ain, UAE who requires a solar PV powered port-a-cabin. I have also attached our system sizing report, Trina solar panel ( 400 Wp) , Midea 1 ton AC and battery datasheet for your kind consideration.

This port-a-cabin is going to be operated at a construction site.The load chart is finalized as per the client’s requirement. All the mentioned load will be working from 6 am to 6 pm continuously 24x7 for 6 days / week. Night time consumption i.e. from 6 pm – 6 am is 0 excluding modem.

Client is worried about the two 1 Ton air conditioners working together with the other loads as mentioned in our case study report at a temperature of 45 to 55 degree Celsius. They are looking for some similar project reference or technical assurance from the inverter manufacturers that their inverter and other related components will be sufficient enough to operate these loads at the afore mentioned temperature conditions.

As per our calculation , battery requirement is in the range of 24 – 28 pcs of 12 V,200 Ah LEAD ACID. In this situation BMS is mandatory to make sure that all the batteries are charging and discharging equally .

We have tried our level best to convince our client by saying that even though your system is working during day time , battery bank should be optimized. Client is having a thought that they can reduce the no.of battery to 12 or 16 pcs. They don’t have a generator or grid as back up.

What is your opinion in this case ?

Please cross check and verify whether our study is correct or not , if not then please suggest us a better solution from your side so as to make it more economical and practical.


Eng.Prabi Prasad

Alain Solar

prabi-prasad asked
prabi-prasad commented ·

1 Answer

MPPT Sizing calculator

I am using the mppt sizing calculator and have some questions about the results. Here are my inputs using a custom module:

Wp: 305

1 series 3 parallel

Voc: 45.6

Isc: 9.05

Vmpp: 37.4

Impp: 8.16

System voltage 12.

With these inputs in recommends the BlueSolar MPPT 150/60 Tr but not the SmartSolar Mppt 150/60 Tr. As near as I can tell they have the same specs. Is there a limiting factor?

Also, given the input, what would the outputted amps be from the charge controller given the best case scenario? I am not sure how to calculate the conversion.

dlong20 asked
Mark answered ·

4 Answers

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