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Panel layout help


stoic
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Hey guys, I'm sure you've heard enough from me already.

Can someone please make a suggestion on how i should lay out my solar panels.

I have:

 

Now, at first i thought i had it covered. I tried to go as high a voltage i can 6 panels in series, giving me about 180V and then string three of these series in parallel giving me about 27A and 180V, but then, @plonkster mentioned that those pylons need around 80A to charge. Now i am not sure if i need to give that from the solar array, or if the MPPT will manage my 27A, 180V and automatically deliver the 80 amps required to charge the pylons.

Can someone please comment and give some guidance?

Is it correct of me to try and get the voltage as high as possible? The cables i will be running will be no longer that 20m from the furthest panel to the MPPT. 

Lastly, based on my arrangement, or a better suggested arrangement, what thickness cable should i get?

I was at a solar store today, and they wanted to give me 6mm copper clad flex cable, i had my doubts as i believe copper clad has higher internal resistance, also, i am not sure if it will handle the current.

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The higher the voilts, the lower the voltage drop, the thinner the cable can be. 6mm2 wire is good on 20m. Voltage drop is negligible.

If you want to splurge on solar wire, you can go 10mm2 or even 16mm2 - but I'm not sure if you will see any real benefits at all.

Get the panel volts as high as you can keeping in mind the 250v max on the MPPT INPUT side from the panels. Try and reach 228v on the panel side ... others may add more advice's.

MPPT OUTPUT side to the batts: The MPPT handles the 27a (or whatever you set it at) max charging amps. You set that all in the ESS software.

EDIT: Once you start setting it all up, the questions will come fast and furious.

Edited by Guest
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43 minutes ago, stoic said:

Now i am not sure if i need to give that from the solar array, or if the MPPT will manage my 27A, 180V and automatically deliver the 80 amps required to charge the pylons.

The MPPT will take the Available power on the input side, and use it to output max 100Amps to your bats. In your case with 3 Pylontech's I believe it will be max 75 amps to your battery's.

43 minutes ago, stoic said:

Is it correct of me to try and get the voltage as high as possible?

Yes it has it benefits. 

43 minutes ago, stoic said:

or a better suggested arrangement, what thickness cable should i get?

What would the distance be between the Array and the combiner box. And then what would the distance be between Combiner box and MPPT? Do you think you will add more panels in the future and how many?

From there I will be able to comment on wire thickness. 

  

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22 minutes ago, Jaco de Jongh said:

What would the distance be between the Array and the combiner box. And then what would the distance be between Combiner box and MPPT? Do you think you will add more panels in the future and how many?

From there I will be able to comment on wire thickness. 

Combiner box to MPPT is at most 3m
Array to combiner box will be +/- 10m (that is from the furthest panel)

in future i would like to expand. but i will first increase my battery bank to about 12 kW before i do this.

image.png.61ef29114e49dbb3aaa8480b18c3a496.png

 

 

Edited by stoic
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now that i think about it... do i even need a combiner box, seeing though the MPPT can take three strings? can i not just connect my three strings directly to the MPPT?

sorry... it only has PV possitive and negative

Edited by stoic
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On 2018/12/17 at 7:15 PM, stoic said:

Is it correct of me to try and get the voltage as high as possible?

Yes within reason make sure you take temp compensation into account when calculating your max PV voltage.

On 2018/12/17 at 7:15 PM, stoic said:

Lastly, based on my arrangement, or a better suggested arrangement, what thickness cable should i get?

At 20m standard 4mm2 should be fine.

On 2018/12/17 at 7:15 PM, stoic said:

I was at a solar store today, and they wanted to give me 6mm copper clad flex cable, i had my doubts as i believe copper clad has higher internal resistance, also, i am not sure if it will handle the current.

They should know better double insulated PV wire.

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  • 3 weeks later...

So my panels are up and are connected to my Combiner Box and today i was a bit confused.

According to my specs, i should expect 31V @ 8.88A on a good day from each panel.

image.png.bbfc4cb3a7aa0ebc40cc89b4e6fa1330.png

I have 6 panels in serie, which means the voltage should be about 186V, however, during the day i am constantly sitting on around 215V it goes up or down by a 5-10 volts depending on cloud cover.

 

It is now 5:30PM with heavy cloud cover and I am now reading 192V from each string which is still more than what it is supposed to read at best conditions.

image.png.046e8ec436646876f9e14231932e3068.png

 

So i did read about the cloud edge effect, but there was no clouds when it was stable at around 215V. When ever a cloud did come over it would drop by a few volts.

I am just stumped that the voltage is so much higher than what the panel specifies.

 

... oh yes... and i ended up using 6mm wire.... max length of one of the strings is 6 meters.

Edited by stoic
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just to add.. the panels are fixed at 22 degrees, and facing true north.

My concern is, my CC is rated at 250V and i am worried that when i do get perfect conditions and some cloud edging that it might exceed the CC's limits

Edited by stoic
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4 minutes ago, Javi Martínez said:

You don´t have to worry. I suppose batteries were fully charged and there were no loads, or no heavy loads. In that case, the tracker of charger makes solar panel works closer to Vo than to Vmp. So, if Vo is 38.0 V, it is normal to have a voltage close to  6x38 V = 228 V.

yes... nothing connected yet, i am only getting my charge controller and inverters this week. 

Right now all panels are only connected to my combiner box.

And if you say its normal, then i suppose i did a good job and limiting voltage drop :)

Edited by stoic
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3 hours ago, stoic said:

Right now all panels are only connected to my combiner box.

In that case you should look at the Voc value instead of the Vmp.

38 * 6 = 228V.

So at 215V you are still a bit on the low side :-P

You have around 10% margin at the top here, so it seems perfectly fine to me.

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30 minutes ago, plonkster said:

In that case you should look at the Voc value instead of the Vmp.

38 * 6 = 228V.

So at 215V you are still a bit on the low side 😛

You have around 10% margin at the top here, so it seems perfectly fine to me.

What about the efficiency of Victron 250/100 working in PV side at 180-190 Vdc? Does it have a Buck or a Full Bridge?

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1 hour ago, Javi Martínez said:

What about the efficiency of Victron 250/100 working in PV side at 180-190 Vdc? Does it have a Buck or a Full Bridge?

Don't know the full details. I believe it is a synchronous buck converter, but it is interleaved (ie two sides switched out of phase). Efficiency is around 97% for most of the blue chargers.

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12 hours ago, plonkster said:

Don't know the full details. I believe it is a synchronous buck converter, but it is interleaved (ie two sides switched out of phase). Efficiency is around 97% for most of the blue chargers.

I suppose 97% is peak efficiency. Other brands have graphs, in which you can see efficiency VS power or PV voltage. I have never seen that in Victron, but maybe I havent searched enough.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

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2 hours ago, Javi Martínez said:

I suppose 97% is peak efficiency. Other brands have graphs, in which you can see efficiency VS power or PV voltage. I have never seen that in Victron, but maybe I havent searched enough.

I have never seen such a chart ever :-) I know in theory it exists, because a buck converter's efficiency does depend on the conversion ratio and all that... might make sense to test it some day :-)

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