parallel solar array

Sulfur · September 2014

Is there a limit to how many solar panels can be wired in parallel? For example can 13 240 watt solar panels be wired in parallel, probably using 1 AWG to the charge controller, this is not my system being built so I don't know the charge controller being used, but lets assume it can handle these amps. Isc is 8.75Amps on these panels, Voc is 37.5. Nominal system voltage is 24VDC. I think he is planning to use a split bolt to connect the panels to the bigger wires going to the charge controller. This is an off grid system. Wire run from panels to charge controller is about 80'.

side question, 8 of the panels are facing about 15 degrees more west than the other 5 panels, plan is to wire these 13 in parallel, do these different orientations matter when wiring in parallel?

thanks for your help,

CDN_VT · September 2014

Re: parallel solar array

I would have the 5 panels on a KID & the rest of the 8 on a classic , if it's installed that way. Why not series 2 panels on the 8 panels & then use the kid for the five in parallel , but have the kid in follow me off the classic. Classic has the whizzbang ..
Just a thought
VT

vtmaps · September 2014

Re: parallel solar array

Sulfur wrote: »

Is there a limit to how many solar panels can be wired in parallel? For example can 13 240 watt solar panels be wired in parallel, probably using 1 AWG to the charge controller, this is not my system being built so I don't know the charge controller being used, but lets assume it can handle these amps. Isc is 8.75Amps on these panels, Voc is 37.5. Nominal system voltage is 24VDC. <snip> Wire run from panels to charge controller is about 80'.

No limit to how many panels in parallel... well actually there is a limit... the limit is what the charge controller can handle. And with a 24 volt system I don't know of a controller that can handle 3120 watts.

Also, putting all those panels in parallel means the Vmp is NOT high enough to charge a 24 volt battery. With 80 ft of cable you would need #0000 gauge to get below a 3% voltage drop.

The system as you described it will not work. You need two controllers and an even number of panels so they can be configured with a string length of two panels in series (Vmp about 60 volts).

Sulfur wrote: »

I think he is planning to use a split bolt to connect the panels to the bigger wires going to the charge controller.

Danger alert! he needs to use a combiner box and each parallel string that is combined in the box needs its own circuit breaker.

Sulfur wrote: »

side question, 8 of the panels are facing about 15 degrees more west than the other 5 panels, plan is to wire these 13 in parallel, do these different orientations matter when wiring in parallel?

No problem. But if he is going to use two controllers he can use one for each orientation.

--vtMaps

Sulfur · September 2014

Re: parallel solar array

Thanks for the comments.
I think the KID would be over loaded with 5 of these panels.
With these particular panels, what model charge controllers and in what configuration would work well? He could probably use 12 or 14 panels if even number is needed.

He thought these panels could be used in parallel to charge 24VDC battery bank but apparently the voltage is not quite high enough for that configuration? Would these panels in parallel charge the batteries but very inefficiently? He has a Xantrex inverter and was hoping to use Xantrex charge controller but their basic ones don't seem to handle voltage of 2 of these in series.

Voc=37.5
Vpm=29.3
Isc=8.75
Ipm=8.19

BB. · September 2014

Re: parallel solar array

Sulfur wrote: »

Voc=37.5
Vpm=29.3
Isc=8.75
Ipm=8.19

4 panels, 2 in series x 2 parallel strings would be nice for the Kid:

29.3v*8.19a= 240 Watt panels
4 * 240 watt panels * 0.77 panel+controller derating * 1/29 volts batt charging = 25.5 amps "nominal" max charging current

My other question is the use of 29.3 volt Vmp panels on a 24 volt battery bank... That is really a bit on the low voltage side--Vmp~35-40 volts (typical with PWM controller, minimum with MPPT controller) would be much better.

And, on average, 4 panels in series/parallel would probably generate more energy during the day than 5 of these panels in parallel at 29.3 Volt Vmp.

There are other options (such as a high voltage Midnite Classic controller) with 5 panels in series for ~150 Volt Vmp--But that is not going to save any money (Classic is going to be a more expensive controller) unless more panels were added (choose even numbers for 2 or 3 panels in series with a standard Classic 150 controller).

-Bill

Photowhit · September 2014

Re: parallel solar array

A Midnite Classic, would be a good bit over paneled with 12 of these, but in a functional range. Put one in the closet for a spare...

If he's looking for a cheap charge controller, he should be looking at different panels with a vmp in the 35volt range. It might be possible to move the batteries and charge controller near the panels and send the 120volt AC to the loads and save some wiring.

Sulfur · September 2014

Re: parallel solar array

Could he use a XW-MPPT60-150 charge controller, wire the 8 panels with 2 parallel strings of 4 series panels and only use 4 of the 5 that are at different orientation and the put those 4 also in parallel with the other 2 groups of 4 panels?

So overall it would be 3 parallel strings of 4 series panels, with one of those groups of 4 at different orientation.

thanks for your advice,

Sulfur · September 2014

Re: parallel solar array

Would a panel rated at 37.5 Voc produce more than 37.5Voc in sunny cold weather? The arrangement I suggested in previous post has Voc right at the charge controllers limit, not sure if this would be a problem? I found out he has already ordered the XW-MPPT60-150 charge controller, so I am trying to see if this controller can work with the panels he also already has.

thanks,

Voc=37.5
Vpm=29.3
Isc=8.75
Ipm=8.19

Mountain Don · September 2014

Re: parallel solar array

Sulfur wrote: »

Would a panel rated at 37.5 Voc produce more than 37.5Voc in sunny cold weather?

It can; maybe only momentary, but it can.

Our panels in series have a total Voc = 108.3. The charge controller has recorded incoming voltages as high as 141 volts. It is rated to 150.

BB. · September 2014

Re: parallel solar array

Yes, Voc rises as temperatures fall below ~77F/25C.

Xantrex used to have a nice/easy to use string sizing tool... The last known location of that tool is down (this weekend?), and there is some huge design tool that Schneider is selling (?) which begins with a 100 MByte download and combined Zip RAR compressing/file types... Not trying to make it easy:

Schneider Electric Conext XW String Sizing Tool (dead or broken server for web design tool)
http://solar.schneider-electric.com/product/conext-designer/

In short, 4 panels in series is too much for this controller. 3 maximum--Especially if your installation in up north/cold region for a 140/150 VDC maximum input controller.

Use the Midnite sizing tool for the Classic 150--Their software appears to give "raw numbers" you can use to compare with the Schneider specifications...

http://www.solar-electric.com/inverters-controllers-accessories/chco/misoclchco.html

4 panels in series at -22F will give you (if I used their tool correctly):

VMP (Maximum Power Point Voltage) :
117.2
Volts

VOC (Open Circuit Voltage):
150
Volts

VMP @ -22 F°:
146.4
Volts

VOC @ -22 F°:
177.2
Volts

-Bill

Sulfur · September 2014

Re: parallel solar array

I agree, Voc can go higher in cold weather. He has 8 panels mounted and may have to change his plans for the other 4 panels, to make them all the same orientation. Would this controller work if he wires 4 parallel groups of 3 series panels? I think that may his best option, does this sound plausible?

thanks,

BB. · September 2014

Re: parallel solar array

3 series x 4 parallel strings--Add a combiner box + breaker/fuses per series string, and should be good to go (note, had to update to 240 Watt panels vs 220 default--Does not recaculate from Vmp*Imp inputted data) -Bill:

PV Array

Rated PV Array Power:
2880
Watts

Anticipated Array Power @ 104F:
2686
Watts

Rated PV Array Current:
32.76
Amps

Battery Charging Current @ 57.6 V:
50
Amps

VMP (Maximum Power Point Voltage) :
87.9
Volts

VOC (Open Circuit Voltage):
112.5
Volts

VMP @ -22 F°:
109.8
Volts

VOC @ -22 F°:
132.9
Volts

Charge Controller Selection

Classic150/Lite
Classic200/Lite
Classic250/Lite

Max Operating Voltage
150
200
250

Max Non operating VOC (HyperVOC) @ 48V Nominal Battery Voltage
198
248
298

Maximum Number Of Modules In Series
3
4
5

Max Number Of Modules In Series (Using HyperVOC)
4
5
6

Max Allowable Output Current Per Classic
Based On This Current Configuration
86
70
55

Max Allowable Wattage Per Classic
Based On This Current Configuration
5022
4080
3212

Present PV Array Wattage Of This Configuration
2880
2880
2880

Design Check

Max VOC
OK
OK
OK

Temperature The Classic Will
Enter HyperVOC
-104.8 F°
-347.8 F°
-589 F°

Array Power (Wattage)
OK
OK
OK

Classics Required
0.6
0.8
0.9

NOTE: MidNite Solar recommends a second controller be added after 1.2
WARNING: MidNite Solar makes no representation, warranty or assumption of liability regarding the use of the String Calculator. This tool uses data provided by other parties (such as PV module specs) and makes calculations based on assumptions which may or may not prove to be valid.

vtmaps · September 2014

Re: parallel solar array

BB. wrote: »

and makes calculations based on assumptions which may or may not prove to be valid.

The numbers you ran are for a 48 volt system. The OP is asking about a 24 volt system. Therefore the hypervoc numbers should be 24 volts lower and the number of classics needed is more than 0.6.

--vtMaps

BB. · September 2014

Re: parallel solar array

Thank you VtMaps--I was getting lost in the changes between a small array and everything on one array....

Here are the calculations based on 24 volt system:

The array is on the large size for a 24 volt @ 60 amp controller. Using typical design rules:

240 Watts * 12 panels * 0.77 panel+controller derating * 1/29 volts charging = 76.5 amps (typical) maximum charging current

An array designed for a 60 amp charge controller would be:

60 amps * 29 volts charging * 1/0.77 panel+controller derating = 2,260 watt "cost effective maximum array"
2,260 Watt array / 240 Watt panels = 9.4 panels

So, a 3x3 would be the maximum "cost effective" array I would suggest for the Schneider 60 amp MPPT charge controller

He can run a larger array--Won't break anything, but it will clip the output current to around 60 amps--Meaning that ~16.5 amps would be tossed away in the middle of the day...

Note the warnings and such are based on Midnite's product line, and do not have anything to do with the Schneider product line (and their missing/broken string calculator).

-Bill

PV Array

Rated PV Array Power:
2880
Watts

Anticipated Array Power @ 104F:
2686
Watts

Rated PV Array Current:
32.76
Amps

Battery Charging Current @ 28.8 V:
100
Amps

VMP (Maximum Power Point Voltage) :
87.9
Volts

VOC (Open Circuit Voltage):
112.5
Volts

VMP @ -22 F°:
109.8
Volts

VOC @ -22 F°:
132.9
Volts

Charge Controller Selection
Classic150/Lite
Classic200/Lite
Classic250/Lite

Max Operating Voltage
150
200
250

Max Non operating VOC (HyperVOC) @ 24V Nominal Battery Voltage
174
224
274

Maximum Number Of Modules In Series
3
4
5

Max Number Of Modules In Series (Using HyperVOC)
3
5
6

Max Allowable Output Current Per Classic
Based On This Current Configuration
94
74
62

Max Allowable Wattage Per Classic
Based On This Current Configuration
2700
2123
1779

Present PV Array Wattage Of This Configuration
2880
2880
2880

Design Check

Max VOC
OK
OK
OK

Temperature The Classic Will
Enter HyperVOC
-104.8 F°
-347.8 F°
-589 F°

Array Power (Wattage)
EXCESSIVE
EXCESSIVE
EXCESSIVE

Classics Required
1.1
1.4
1.7

Sulfur · September 2014

Re: parallel solar array

He has already bought a Xantrex XW-MPPT60-150 charge controller, so I am trying to see if this controller can work with the panels he also already has.
This charge controller is rated for 3500 watts, 60amp and 150Voc
here is a link to the manual on the charge controller https://ironedison.com/images/products/Xantrex/Xantrex%20W60%20Install%20and%20Operation%20Manual.pdf

I think he could run 4 parallel sets of 3 series panels, with this controller, is that right?

or probably could also run 6 parallel sets of 2 series panels, with this controller, is that right?

thanks,

Voc=37.5
Vpm=29.3
Isc=8.75
Ipm=8.19

BB. · September 2014

Re: parallel solar array

Short answer, yes it will work. Longer answer, it will not work as well as using two controllers for 12 panels.

The array is on the large size for a 24 volt @ 60 amp controller. Using typical design rules:

240 Watts * 12 panels * 0.77 panel+controller derating * 1/29 volts charging = 76.5 amps (typical) maximum charging current

An array designed for a 60 amp charge controller would be:

60 amps * 29 volts charging * 1/0.77 panel+controller derating = 2,260 watt "cost effective maximum array"
2,260 Watt array / 240 Watt panels = 9.4 panels

The recommended maximum array for a 60 amp charge controller on a 24 volt battery bank would be ~9 panels, or a 3sx3p array.

A 3sx4p array would work, but the controller will be spending much of the middle of the day outputting a maximum of 60 amps (reliably and safely) instead of the array's ability of ~76.5 amps.

-Bill

Sulfur · September 2014

Re: parallel solar array

Bill, your last reply was very helpful. I had not picked up on that constraint.

Due to some space and time constraint issues and the fact that 8 of the panels are already installed in 2 groups of 4. Can he wire these panels in 5Parallel groups of 2Series panels? total of 10 panels, 2 of which would be at different orientation?

Thanks,

Photowhit · September 2014

Re: parallel solar array

Sulfur wrote: »

Due to some space and time constraint issues and the fact that 8 of the panels are already installed in 2 groups of 4. Can he wire these panels in 5Parallel groups of 2Series panels? total of 10 panels, 2 of which would be at different orientation?

Problem is your 80 feet away, if you can relocate the charge controller and batteries near the array, that would work out a bit better. With the lower voltage (4 strings of 2 panels) you have to run higher current(amperage) through the wires and will have higher loss in the lines or need larger wire.

Perhaps you've related the voltage to system wattage, While your statement "...This charge controller is rated for 3500 watts, 60amp and 150Voc" is true it has this rating for a 48 volt system. Charge controllers are limited by amperage/current. At 24 volts this would be rated for a 1750 watt array(3500/2). If you've been reading Bills replies, he is relating that panels typically only produce 77% of their panel rating so he has been using 2260 watts as the most cost effective array. 2260*.77=1740watts. Thought I might present this in hopes it might clean up any confusion.

Sulfur · September 2014

Re: parallel solar array

yes, I see what you and Bill are saying, that due to 24VDC battery bank, the 3500 watts can not be achieved. I am still curious if he can use 5p sets of 2s, seems like it would work, it is not ideal in my opinion but there are reasons that 3p 3s is difficult. I think #10AWG wire would be used for each string.

BB. · September 2014

Re: parallel solar array

Thanks to vtMaps--I missed the controller vs 24 volt limitation too.

Say:

5x Ipm 8.19amps = 40.95 amps Imp-array

Using a generic voltage drop calculator for 80' one way run of 10 awg wire: => 7.9 volt drop

2x Vpm 29.3 volts = 58.6 volts
7.9 volts / 58.6 volts = 0.135 = 13.5% voltage drop

That is a lot--We tend to recommend 1-3% voltage drop. Using the Voltage Drop Calculator, we can try a few values of AWG to find:

0.03 * 58.6 volts = 1.8 volts > 4 AWG = 2 volt drop
0.01 * 58.6 volts = 0.6 volts > 2/O AWG = 2 volt drop

If you use 5x set of 10 AWG wire, then you will get (Imp 8.19 amps at 80'): 1.6 volt drop

Lots of copper needed for lower voltage/high current transmission of power. 5x 10 AWG cables will give you just under 3% drop.

-Bill

Photowhit · September 2014

Re: parallel solar array

Sulfur wrote: »

yes, I see what you and Bill are saying, that due to 24VDC battery bank, the 3500 watts can not be achieved. I am still curious if he can use 5p sets of 2s, seems like it would work, it is not ideal in my opinion but there are reasons that 3p 3s is difficult. I think #10AWG wire would be used for each string.

....and combined at the soar panels into one string for the run to the charge controller 29.3 + 29.3 = 58.6volts current 8 amps x 5 for 40 amps carried 80 feet one direction will require 2agw for <2% loss and 4agw for less than 3% loss...

...but your array is considerably larger than your CC can use, so the losses are only at max current, so not as bad as I thought. You will still have the advantages at lower currents (over cast days) so not too bad.

Sulfur · September 2014

Re: parallel solar array

Considering using 10awg for each string, so voltage drop should not be bad. I don't really like the design but he has the wire on hand, so just checking plausibility of 5p 2s configuration to see if there would be any problems.

let me know if you have any concerns about that arrangement,

thanks,

BB. · September 2014

Re: parallel solar array

10 awg per string is OK ~ 1.6 volt drop or just under 3%. Will work fine.

-Bill

Photowhit · September 2014

Re: parallel solar array

Sulfur wrote: »

Considering using 10awg for each string, so voltage drop should not be bad. I don't really like the design but he has the wire on hand, so just checking plausibility of 5p 2s configuration to see if there would be any problems.

let me know if you have any concerns about that arrangement,

In my opinion it would be very odd to have 80 x 10 = 800 feet of 10 gauge use 2 wire on hand unless they worked on solar, I help others and am considering my first purchase of a 500ft spool, and only due to it being remains of a state contract job and very cheap.

I guess the inverter can direct wire/combine up to 6 strings, so maybe some cost savings there... Just be sure he uses the correct wiring for exposure to the sun...

CDN_VT · September 2014

Re: parallel solar array

80 foot run , times two wires +& - = 160 feet, then times 13 panels .. Thats a lot of wire & losses .
I have MC4 two into one connectors on my 12v Roof panels to supply my KID of 10 foot away.
Im still all parallel but just ganged up two panels , and only 10' run so 20 feet in total.

VT

parallel solar array

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