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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
COghst 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

What happens if you add more solar wattage than the max Nominal PV Power?


My victron mppt 100/50 in 12V mode says Nominal max is 700W, but down the bottom it says "If more PV power is connected, the controller will limit input power. "

What happens If I hook up 900Watts of solar to controller? & This is the full 900watts noon summertime.

Does it simple take in 700W & the rest is wasted/left? Will doing this damage the controller?


Jman asked
Boekel commented ·

2 Answers

Optimal connections and correct MPPT for mix of panels?

I have an existing panel and am planning to add two panels and a new MPPT. Not sure how to connect them and what MPPT to use for most efficiency.

All three panels will be fitted on the deck of my sailing boat and will get partially shaded (no way to avoid this. Two of the panels will be fitted under the boom, one on the deck under the boom and the other on the spray hood. The third will be fitted in front of the mast and will get partially shaded from the sails.

- How should I connect these panels (serial of parallel)?

- What is the best suited MPPT for these panels (depending on if they are serial or parallel connected?

- Would it be better to replace the existing 55W solar panel with two new 18W solar panels?

New solar panel on spray hood (Sunbeam Tough T70F):
Pmax: 70 W
Voc: 22.1 V
Isc: 4.26 A
Vmp: 17.6 V
Imp: 3.98 A

New solar panel in front of mast (Sunbeam Tough+ TP56F2):
P max: 56 W
Voc: 23.6 V
Isc: 3.3 A
Vmp: 17.6 V
Imp: 3.18 A

Existing solar panel under boom (M-Series 55W S220P43):
Rated output (Pmpp) Wp: 55 W
Short-circuit current (Isc): 2.54 A
Open-circuit voltage (Uoc): 27.13 V
Voltage (Umpp): 22.88 V
Current (Impp) 2.40 A
System voltage: 24 V
Reverse current carrying capacity IR: 12 A

Optional 2 new 18W panels instead of existing 55W panel (Sunbeam Tough 18w L):
Pmax: 18 W
Voc: 23.7 V
Isc: 0.99 A
Vmp: 19.4 V
Imp: 0.92 A

Sunbeam and Solara are using a bit different terminology for the data, hope this is ok.

Djingis asked
JohnC answered ·

1 Answer

Size Photovoltaic system OFF-Grid
Hi, I wanted to size a photovoltaic system, for use from June to September, all day, with loads: Refrigerator class AA 24H / 24H, LED TV 20 "6h / day, PHON 2000W 1h / day, smartphone recharge 4h / day , electric pump 500VA 5h / day, LED Light 300W 7h / day 
Everything works at 220V AC, I need to size: How many photovoltaic modules are needed, Which charge controller, which inveter, how many batteries?

elektro asked
Guy Stewart (Victron Community Manager) answered ·

1 Answer

Solar controller not putting out full power
  • Hello I have attached a 100/50 controller to a 600ah 12v lifepo4 battery bank. And am charging that with 1000w at 40 v.

I put a clamp meter on the the cables and I know the batteries are a bit low yet it is still only putting in 15 amps. I have also a 24v set of 300ah these are doing a bit better but I still don't believe that I'm getting everything out of my panels and in to the batteries.

Any ideas please

Roger asked
Roger answered ·

4 Answers

PVsyst Simulation

Hi All,

Have any tried simulating the energy yield of the system using the PV system with Multiplus, Bluesolar charger on the pvsyst ?

Earl asked
Peter Polz edited ·

1 Answer

Best mppt for my array

Hi, I have a few panels, of different sides. Which mppt should I use?

mvader (Victron Energy) asked
mvader (Victron Energy) commented ·

2 Answers

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