Good day All.

I am new to the group - My name is Vijen and I live in Centurion, Pretoria. I have had an Axpert 5kVA (4000W) system installed at my home for backup purposes for the last 2 years. I have 4 x 200AH gel batteries installed. The system has worked well but I would now like to add solar power to it.

Can someone please advise me what configuration I should go for if I use the 330W Canadian solar panels? My concern is both voltage and current. I was thinking of 9 panels in a 3 x 3 configuration. This would theoretically bring Voc to 136.8V and max current to 26.64A (8.,88A x 3). The open circuit voltage is below the theoretical 145V but I am not sure how close you should be to this. the current is obviously a big concern.

Any advise will be greatly appreciated. Please recommend other panels if you think they are better. 

Is it an Axpert MKS II model, or is it a 145 V max SCC model? As far as I know it can't be both. Check the large sticker on the side with the bar-code.

If it is 145 V max, then 3S is too much with 72 cell panels (I assume that 330 W panels would be 72 cell). If it's 450V max SCC, then you need at least 6S.

Hi Coulomb.

Thanks for the response. Apologies, the model is SOL-I-AX-5M. My manual seems to indicate MKS II but the sticker says otherwise. Max solar voltage (VOC) is 145VDC.

Does this mean that I should use 2 panels in series which will give max VOC of 91.2V and then use 3 of these in parallel to give combined max current of 26.64A? I would assume that realistic power generated from solar would be limited below 2kW in this configuration. Are there any other easily available panels you would recommend that would get me closer to the 3kW solar?
 

The sticker indicates rated current in solar charger mode is 60A. Does this refer to current charging battery or total current input from PV cells?

33 minutes ago, Vijen said:

Thanks for the response. Apologies, the model is SOL-I-AX-5M. My manual seems to indicate MKS II but the sticker says otherwise. Max solar voltage (VOC) is 145VDC.

It's not an MKS II. Perhaps they gave you the wrong manual.

Quote

Does this mean that I should use 2 panels in series which will give max VOC of 91.2V and then use 3 of these in parallel to give combined max current of 26.64A?

With 2S3P, that's only 6 panels. You should use either 2S4P (8 panels) or 2S5P (10 panels).  I have an inverter the same model as yours, and have 8 strings of 2S panels (only 200 W though). That's 3200 W nominal. I think you could get away with 3300 W nominal (2S5P). Or find some 300-320 W panels and run 3S5P to keep the nominal panel power closer to the 3000 W maximum output. It's not clear what the maximum allowed solar panel power is for these inverter-chargers.

The hassle with 2S is that it's more wiring than 3S. But 2S prevents the Solar Charge Controller from shutting down due to over-voltage, or possibly damaging itself.

Quote

I would assume that realistic power generated from solar would be limited below 2kW in this configuration.

Yes, because it's only 6 panels. That will always be 2/3 of the power of 9 panels.

Quote

Are there any other easily available panels you would recommend that would get me closer to the 3kW solar?

If you can find some 60 cell panels, then you can run 3S, saving some wiring, but then they'll likely be lower power (I think 275 W is the biggest 60 cell panel I've come across, from poor memory).

3S4P of 250 W panels (assuming that they are 60 cell) comes to a neat 3000 W nominal.
 

The sticker indicates rated current in solar charger mode is 60A. Does this refer to current charging battery or total current input from PV cells?

Thanks Coulomb - I  appreciate your feedback. I will try to source panels closer to 300W each, otherwise will take a chance with the 2S5P (10 panel) config on the 330W panels.

When you do multiple strings in parallel, is it  better to wire the PV panels to a connection panel directly below the PV installation and then run a pair of cables to the invertor for neatness and costs compared to running 10 wires to the invertor fro a 2S5P configuration?

On my last question (The sticker indicates rated current in solar charger mode is 60A. Does this refer to current charging battery or total current input from PV cells?) - what do you think. Does it mean that total current from PV panels is limited to 60A?

 

Artsolar 300W 60 cell panels; Voc is 39.7V.  Don't buy them online - email them for a quote - usually much cheaper.

Wiring: You should use a combiner box that includes fuses, an isolator and a surge arrester. So photos of an example below.

Where you mount the box depends on the distance to the MPPT. Short distance - mount the box close to the MPPT.  Longer distance, mount it close to the panels and combine the strings.  Run a thicker cable to the MPPT - it is carrying all the combined currents on the strings.

 

 

 

Thanks Ironman

Will drop them an email tomorrow.

From your combiner box it appears that you have 4 strings which are individually protected by fuses. Then you combine and protect with circuit breaker and surge protectors. Is this correct?

6 hours ago, Vijen said:

Does it mean that total current from PV panels is limited to 60A?

Nope, the max PV current is normally in the region of 18Amps, this rating is for Max Charging Current (Battery Charging)

10 hours ago, Vijen said:

When you do multiple strings in parallel, is it  better to wire the PV panels to a connection panel directly below the PV installation and then run a pair of cables to the invertor for neatness and costs compared to running 10 wires to the inverter fro a 2S5P configuration?

This has been well answered already. I'll just add that there is a compromise: join pairs of strings on the roof (with fuses on each pair into an MC4 Y adapter), and bring down just those pairs to either the combiner box or directly to the Solar Charge Controller. For 5S, you could join 2 pairs and bring the third string down on its own.

10 hours ago, Vijen said:

On my last question (The sticker indicates rated current in solar charger mode is 60A. Does this refer to current charging battery or total current input from PV cells?) - what do you think. Does it mean that total current from PV panels is limited to 60A?

As Jaco mentioned, the 60 A is on the battery side. With higher voltage strings (for a 450 V max SCC), this comes to around 18 A (225 V x 18 A = 4050 W), and indeed these models actually state an 18 A maximum PV current in their specifications. But for 145 V max SCCs (really 130 V for maximum power), the current can be a lot higher, e.g. 8.9 A x 5 strings = 44.5 A, which will become some 60 A on the battery side through the magic of buck converters. So for 5S, you'll need more than the 32 A breaker pictured. Lightning protection seems to be more important in South Africa than elsewhere, so don't leave it out.

You should also consider the option to get a stand alone MPPT that can handle the panel configuration that suits you best, rather than be subject to the limitations of the inverter.

Thank you for the replies gents. It has been very informative. 

5 hours ago, DeepBass9 said:

You should also consider the option to get a stand alone MPPT that can handle the panel configuration that suits you best, rather than be subject to the limitations of the inverter.

With another MPPT you could have 2 arrays with with one favouring the morning sun for instance on your inverter, and one doing the heavy lifting on its own MPPT.

Morning Vijen,

 got the same setup as you got and this is how I did my panel configuration, 

 

3 Panels combined in series: Pmax = 3 x 325 watts = 975 watts Voc=137.4v Isc=9.15A Use a 12A fuse	3 Panels combined in parallel: Pmax = 3 x 325 watts = 975 watts Voc=45.8v Isc=27.45A Use a 32A fuse
2 x Series combined in parallel: Pmax = 2(3 x 325) watts = 1950 watts Voc= 137.4v Isc= 18.3A Use a 32A fuse	2 x Parallel combined in series: Pmax = 2(3x 325) watts = 1950 watts Voc= 91.6v Isc= 27.45A Use a 32A fuse per string and a 63A  close to the inverter

With this setup I can add another 6 panels in parallel to my inverter thus would run with 3900 watts, with a combiner box closest to the panels on the roof.

Do Our learned friends agree with this setup?

5 hours ago, Samsed said:

Do Our learned friends agree with this setup?

Usually you would series pairs of panels first, then fuses and combiners. That saves you 6 fuses and two combiners (half what you have depicted). I assume that those are meant to be fuses before the combiners. I think that you'll get better shading performance this way too.

5 hours ago, Samsed said:

With this setup I can add another 6 panels in parallel to my inverter thus would run with 3900 watts, with a combiner box closest to the panels on the roof.

Yes, though you might want to run both sets of 6 panels down to a combiner box with Noark or similar breaker/isolators, so you can isolate a set to check that each is performing properly.

16 hours ago, Coulomb said:

Usually you would series pairs of panels first, then fuses and combiners. That saves you 6 fuses and two combiners (half what you have depicted). I assume that those are meant to be fuses before the combiners. I think that you'll get better shading performance this way too.

Yes, though you might want to run both sets of 6 panels down to a combiner box with Noark or similar breaker/isolators, so you can isolate a set to check that each is performing properly.

Hi Coulomb, I had to keep the Volts down and upped the Amps so that I could add more panels, 

I placed 3 panels in parallel (lowering Volts) and then series the 2 sets (higher Amps) with a ultra fast fuses between the 2 sets, I wanted to buy the inline fuses but could not get them in time so I opted for a normal fuse/holder.

The pictures are the combiner box closest to the panels on the side of my roof, with cable going down to my Inverter where I also got a bigger fuse/holder installed to handle the Amps before connecting to the Inverter.

Hi

 

Also new got same inverter running a couple of months now no problems.

My plan was to use 415W Canadian solar panels 3S3P.

On factory testing STC data sheet works out to 144.6V @ 32.1A = 4641W  Too much

On Running testing NMOT data sheet works out to 136.2V @ 25.68A = 3497.62W 

Question is which 1 should I use ?

 

Thanks