wireing pv array ??'s

shockman · March 2013

I have 3 240w 24V panels (new) and 2 125W 12V panels to make an array. So how do I wire them, series parrallel etc. I realize the 2 12Vers will go together but not sure how to put them all together and should I need a combiner box and what breakers???? do tell pls. Will order what I need once I know. 12V system with classic 150 controller
Marc

Cariboocoot · March 2013

Re: wireing pv array ??'s

Okay, what we need to known here are the actual Vmp and Imp of the two panel types. '24 Volt' and '12 Volt' are rather generic descriptions that cover a variety of Vmp/Imp combinations which happen to factor out to the rated Voltage.

For instance the 240 Watt panels may have a Vmp of 30 and the 125 Watt panels probably have a Vmp of 17.5. This would make the two basically incompatible for a single array as there is no combination which adds up: 2X 17.5 = 35, not 30, so there would be power loss over-all (although you may deem this acceptable).

If the Imp of the two types is close enough then they can be put together as two strings of one each. But if it's not then the current will be limited to the lowest number and again you get some power loss (which again you may find acceptable or not).

Probable specs: 240 Watt 30 Vmp 8 Imp, 125 watt 17.5 Vmp 7 Imp.
Those don't add up to any winning combinations.

shockman · March 2013

Re: wireing pv array ??'s

Cariboocoot wrote: »

Okay, what we need to known here are the actual Vmp and Imp of the two panel types. '24 Volt' and '12 Volt' are rather generic descriptions that cover a variety of Vmp/Imp combinations which happen to factor out to the rated Voltage.

For instance the 240 Watt panels may have a Vmp of 30 and the 125 Watt panels probably have a Vmp of 17.5. This would make the two basically incompatible for a single array as there is no combination which adds up: 2X 17.5 = 35, not 30, so there would be power loss over-all (although you may deem this acceptable).

If the Imp of the two types is close enough then they can be put together as two strings of one each. But if it's not then the current will be limited to the lowest number and again you get some power loss (which again you may find acceptable or not).

Probable specs: 240 Watt 30 Vmp 8 Imp, 125 watt 17.5 Vmp 7 Imp.
Those don't add up to any winning combinations.

You are very close on 12V vmp (17.39) the 24V panel says Open circuit V 36.9 and max pwr 29.8 ??? if this is what your pedicting should the 12V ones not be used in the array?????

shockman · March 2013

Re: wireing pv array ??'s

Okay thinking about this would the result only be that the 2 12V panels would be drawn down to 30V ?? still better than nothing?? or would they draw down the 24Vers????

Cariboocoot · March 2013

Re: wireing pv array ??'s

Maximum power Voltage would be the Vmp: 29.8

From that we can judge the Imp of each: 125 Watts / 17.39 Volts = ~7.2 Imp, 240 Watts / 29.8 Volts = ~8.0 Imp.

So options:
1). Get a separate, inexpensive PWM controller for the 125 Watt panels: http://www.solar-electric.com/ss-20l.html Total Watts: 730
2). Use one of each in a string for Vmp 47.19 @ Imp 7.2 (340 Watts from a possible 365) on the MidNite. Total Watts: 680
3). Put the two 125 Watts in series and parallel them to the 240 Watts allowing the Vmp to be pulled down to 29.8 and reducing the panel output to approximately 214 Watts instead of 250 for the two smaller panels. Total Watts: 694

Please note those are approximations to show the relative effectiveness of the various configurations, not absolute values of performance.

Is the extra 36 Watts of #1 worth the $80+ for a charge controller? Your call.

inetdog · March 2013

Re: wireing pv array ??'s

shockman wrote: »

Okay thinking about this would the result only be that the 2 12V panels would be drawn down to 30V ?? still better than nothing?? or would they draw down the 24Vers????

If you put the two 12 volt panels in series, you will have a Vmp for the string of 35 volts. By running that string in parallel with the 24 volt panels, you will get a nominal 210 watts from the pair instead of the potential nominal 250 watts. That is still a lot better than not using them at all.
Since the Voc of the 24 volt panels is slightly higher than the Vmp of the string, a good MPPT controller (which the Classic definitely is!) should be able to find the true maximum power point of 30 volts, but it will be easy enough to test that when you turn the system on. If you do not get any current out of the 24 volt panels, just disconnect the string of 12 volt panels or put one or two forward-biased diodes in series with that string to pull the Vmp seen by the CC down a bit.

shockman · March 2013

Re: wireing pv array ??'s

Cariboocoot wrote: »

Maximum power Voltage would be the Vmp: 29.8

From that we can judge the Imp of each: 125 Watts / 17.39 Volts = ~7.2 Imp, 240 Watts / 29.8 Volts = ~8.0 Imp.

So options:
1). Get a separate, inexpensive PWM controller for the 125 Watt panels: http://www.solar-electric.com/ss-20l.html Total Watts: 730
2). Use one of each in a string for Vmp 47.19 @ Imp 7.2 (340 Watts from a possible 365) on the MidNite. Total Watts: 680
3). Put the two 125 Watts in series and parallel them to the 240 Watts allowing the Vmp to be pulled down to 29.8 and reducing the panel output to approximately 214 Watts instead of 250 for the two smaller panels. Total Watts: 694

Please note those are approximations to show the relative effectiveness of the various configurations, not absolute values of performance.

Is the extra 36 Watts of #1 worth the $80+ for a charge controller? Your call.

Okay getting it slowly :>) but you missed the fact I will have 3 new panels and maybe wanting to add more later. So looks like option 3 would be the way to go???? I do have a pmw controller but have other plans for it. And at present 4 strings of 2 panels with no fuses or breakers other than on main supply line to controller. I'm reading on here that might not be right?

Cariboocoot · March 2013

Re: wireing pv array ??'s

shockman wrote: »

Okay getting it slowly :>) but you missed the fact I will have 3 new panels and maybe wanting to add more later. So looks like option 3 would be the way to go???? I do have a pmw controller but have other plans for it. And at present 4 strings of 2 panels with no fuses or breakers other than on main supply line to controller. I'm reading on here that might not be right?

If you're planning on adding more of the 240's you may not want to bother with the 125's at all.

Yes, if you have more than two panels in parallel you want circuit protection on each just in case one of them should short. That way the others can't 'feed' it more than its Isc rating (maximum current it's designed to handle).

Again if you're considering expansion wire for it now. It's not good if you go to add another 16 Amps of current and have to take the wiring out because it's too small to handle it!

shockman · March 2013

Re: wireing pv array ??'s

Okay so I will have the 2 12v panels in series, and 3 maybe 4 24v panels in parrallel, so I have + & - from both sets. If I get a combiner box which can hold 6 breakers and has + & - bussbars, how do I run wires in box and what size breakers?? and how many will I need
Okay just had a good read on MC4 connecters!! that sheds a little light on my problem, damn I cut those off my 12V panels, still not sure where the circuit protection belongs, Just between the 2 strings, or do I need something between the individual panels??

Cariboocoot · March 2013

Re: wireing pv array ??'s

You need one breaker per string (which is one or more panels in series). The size depends on the recommended series fuse rating of the panels. This is typically the nearest size up from the Isc rating. The 240 Watt panels @ 30 Vmp will probably have an Isc around 8.5 and probably recommended series fuse rating of 15 Amps whereas the 125 Watt panels @ Vmp 17.5 probably have an Isc around 7.5 and probably a recommended series fuse rating of 10 Amps. Two in series does not change this as the current remains the same.

It is important to understand that the breaker or fuse is there to protect the panel string it is connected to should it short and become a load rather than a source.

MidNite makes these great pre-wired units which really simplify installation: http://www.solar-electric.com/prpvcobo.html

shockman · March 2013

Re: wireing pv array ??'s

Cariboocoot wrote: »

You need one breaker per string (which is one or more panels in series). The size depends on the recommended series fuse rating of the panels. This is typically the nearest size up from the Isc rating. The 240 Watt panels @ 30 Vmp will probably have an Isc around 8.5 and probably recommended series fuse rating of 15 Amps whereas the 125 Watt panels @ Vmp 17.5 probably have an Isc around 7.5 and probably a recommended series fuse rating of 10 Amps. Two in series does not change this as the current remains the same.

It is important to understand that the breaker or fuse is there to protect the panel string it is connected to should it short and become a load rather than a source.

MidNite makes these great pre-wired units which really simplify installation: http://www.solar-electric.com/prpvcobo.html

Okay so if I understand this correctly I need a 10A and 15A breaker in the box and should be good to go?? 24V string on 15A breaker and 12V string on 10A breaker!

Cariboocoot · March 2013

Re: wireing pv array ??'s

Not quite.
You have three of the 240 Watt panels, right? And you have one string made up of two 120 Watt panels in series, right?
So you would parallel the 240's with the string of 120's, and there would be a 15 Amp breaker on each 240 Watt panel and one 10 Amp breaker on the string of 120's.

Does that make sense?

shockman · March 2013

Re: wireing pv array ??'s

Okay got that! but will go back to your link to the store and find a bigger box than 4 in case I want to add another panel. I am also thinking nightmare to get box close enough to reach with all wires without needing a bunch of MC4 extensions and connecters

Cariboocoot · March 2013

Re: wireing pv array ??'s

Yes; the bigger the array the further away some of the wires must be! This is another reason why larger arrays work better on MPPT: higher Voltage strings, fewer connections. To be picky the length of wire from the panel to the combiner counts against Voltage too. Usually it's too small to matter, but there's always a chance.

shockman · March 2013

Re: wireing pv array ??'s

Cariboocoot wrote: »

Yes; the bigger the array the further away some of the wires must be! This is another reason why larger arrays work better on MPPT: higher Voltage strings, fewer connections. To be picky the length of wire from the panel to the combiner counts against Voltage too. Usually it's too small to matter, but there's always a chance.

SO on that note! why would I not wire the 240 24V panels in series and parralel them with the 12Vers into my Classic 150

Cariboocoot · March 2013

Re: wireing pv array ??'s

shockman wrote: »

SO on that note! why would I not wire the 240 24V panels in series and parralel them with the 12Vers into my Classic 150

Because the 240 Watt panels have a Vmp around 30 so two of them in series would be 60 and way off the two 120's in series operating at 35 Vmp. So much so that the 120's will do nothing then.

And you have three 240 Watt panels just now, which would give you one string at Vmp 60, one at Vmp 35, and one at Vmp 30. That's a formula for low power output.

wireing pv array ??'s

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