series wiring solar

[GlennWest]

Researching for future solar upgrade and got questions. Looking at Mission 355 watt 72 cell panels, VMP 38.98. 10 panels.  If wired in series will have 390 volts and 9.1 amps. This would work with #10 wire if short enough. With these large a setup, the wires going to controller will be long. Wires will come from each end to storage bay. I see no way around not using #6 or #8 wire. Am I correct in this. Not that it is a big deal, just planning now. From what I researched #6 at 10 amps will work up to 29 ft with 2% loss.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Edited December 19, 2018 by GlennWest

[Lou Schneider]

That doesn't sound practical to me.  390 volts is very high voltage and will be hazardous if you come into contact with the panel to controller wires.  You'll have to cover the panels first to avoid getting severely shocked or drawing a  large arc when working on the wiring,  DC rated disconnects for that kind of voltage are also very expensive. What kind of controller are you planning to use?  Most I've seen are only rated for 100-150 volts maximum input voltage.

Five parallel strings of 2 panels each (80 volts and 18 amps maximum per string) would be much safer.  You'll need larger wires and will lose a few percentage points of efficiency under maximum load but it would be a much safer system.

Edited December 19, 2018 by Lou Schneider

[GlennWest]

That is why I asking. Trying to figure this out. Was planning on using Victron equipment. So you saying parallel half the panels and serial them together? Probably the Victron MPPT 150/70-MC4 (12/24/36/48). Yes, I overlooked the 150v limit. Thanks

Edited December 19, 2018 by GlennWest

[Lou Schneider]

No, I suggest making 5 series strings of two panels each, which would give 80 volts at 9 amps for each pair.  Or 45 amps total coming off of the array.

You're also way off on your voltage loss calculations. For 29 ft. one way distance, #6 wire has a 0.059% voltage loss, at 390 volts and 10 amps, not 2%.  The voltage loss is a function of current through the wire and you have to take it as a percentage of the total voltage, so it's less at higher voltages.

Maximum current from (5) 80 volt pairs of two panels each will be 45 amps.  At 80 volts, the voltage drop through 29 ft. one way distance on #6 wire is 1.2%.

What will be your battery voltage?  This will determine the size of wire you'll need between the controllers and the batteries.  Plan for 300 amps at 12 volts, 150 amps at 24 volts, etc.

Voltage Loss Calculator

Edited December 19, 2018 by Lou Schneider

[GlennWest]

I understand below controller. 48v battery, lithium. I was going by charts on line to get those figures. Trying to wrap my head around the solar wiring.

[Lou Schneider]

The key is to use a voltage loss calculator that allows you to enter the source voltage, like the one I linked to above.  You have two voltages to be concerned with, the panel to MPPT controller voltage and the controller to battery voltage.  You'll get different percentages of loss depending on the source voltage

The Victron controllers have an absolute maximum 150 volt input voltage rating.  So you're safe putting two panels in series and then 5 sets of these in parallel and it comes out even for 10 panels.  

Edited December 19, 2018 by Lou Schneider

[GlennWest]

Know it is asking a lot, but can you give me a diagram of your 5 strings of two panels. Also is they a disadvantage to lowering the voltage under 150v to say 100v.

Edited December 19, 2018 by GlennWest

[Chad Heiser]

With the panels you are planning to use you will have 3550 watts at peak output if you run them all in series.  I believe you are talking about running a 24 volt system in your rig, but I can't remember for sure.  Even the bigger Victron MPPT 150/100 can only handle 2900 watts at 24 volts.  If you are planning to run a 48 volt system (which may be the case, I just can't remember for sure), then you could run all the panels in series with the bigger Victron charge controller.  The Victron MPPT 150/70 only allows 2000 watts at 24 volts and 4000 watts at 48 volts.  With this controller you would have to break the panels up into at least two strings at 24 volts (just like the bigger 150/100) and be right near the max capacity at 48 volts.  See the below charts.

I personally do not like to run mobile set ups in all series wiring.  It creates potential shading issues and some other draw backs.  With 10 panels, I would do at least 2 strings of 5.  I prefer at least some split in the panel wiring rather than having them all in one big series on an RV roof.  If you were planning a 12 volt system, then I would most likely go 5 strings of 2, but I don't think that you plan on a 12 volt system.

I also do not like the idea of running the smaller charge controller so close to its maximum rating with one large string.  I would probably opt for at least the Victron 150/85 (not shown below) for that large of an array and maybe would go up to the 150/100 just to have a comfortable overhead.

 

On Edit: some other posted while I was typing and I see you are planning a 48 volt system, so ignore my information about 24 volts above.  Everything else remains the same.  I would still break the panels into at least two strings of 5 and would strongly consider 5 strings of 2.

Model	MPPT 150/70
Battery voltage	12/24/48 Auto Select (software tool need to select 36V)
Rated charge current	70A
Maximum PV power	1000W (12V) / 2000W (24V), 4000W (48V)
Maximum efficiency	98%
Charge voltage (absorption)	Default setting: 14.4 / 28.8 / 43.2 / 57.6 V
Charge voltage (float)	Default setting: 13.8 / 27.6 / 41.4 / 55.2 V
Charge algorithm	multi-stage adaptive

 

Model	MPPT 150/100
Battery voltage	12/24/48 Auto Select (software tool need to select 36V)
Rated charge current	100A
Maximum PV power	1450W (12V) / 2900W (24V), 5800W (48V)
Maximum efficiency	98%
Charge voltage (absorption)	Default setting: 14.4 / 28.8 / 43.2 / 57.6 V
Charge voltage (float)	Default setting: 13.8 / 27.6 / 41.4 / 55.2 V
Charge algorithm	multi-stage adaptive

Edited December 19, 2018 by Chad Heiser

[Lou Schneider]

Here's a quick sketch.  The Victron MPPT 150/70 or above controller will handle this for a 48 volt battery.  Note the Victron controllers are rated for an absolute maximum 150 volts input voltage, which rules out more than three panels in each series string.

https://www.victronenergy.com/upload/documents/Datasheet-BlueSolar-charge-controller-MPPT-150-45-up-to-150-100-EN.pdf

 

Edited December 19, 2018 by Lou Schneider

[Chad Heiser]

16 minutes ago, GlennWest said:

Know it is asking a lot, but can you give me a diagram of your 5 strings of two panels. 

The wiring would be similar to running series and parallel 6 volt batteries.

Positive from Panel 1 goes to negative of Panel 2.  The remaining positive cable from these two panels goes to a common positive buss bar and the remaining negative from these two panels goes to a common negative bus bar.  The wiring between panels and to the bus bars is typically 10 gauge wire.  The bus bars are typically located in a combiner box on the roof somewhere.  You then repeat this four more times for the remaining 8 panels.  Then you run one positive wire and one negative wire (larger gauge than between the panels determined by voltage drop calculator) down from the roof combiner box through to the charge controller.  You will also want to add some type of disconnect in the positive line between the combiner box and the charge controller.  

Here is a link to the wiring diagram of my system.  I have three strings of two panels in series (for a total of six panels) on my roof.  My system is based on a 12 volt battery bank, but other than that would be no different than what you are planning to do.

 

On edit:  Lou typed faster than me.  The only difference between my explanation and his diagram is that I use end runs between each series pair back to the combiner box whereas he diagrammed out interconnecting all the pairs and then continuing on without using a combiner box.  I would make one change to Lou's diagram in that I would have the positive and negative leads coming out different ends on the series pairs rather than the same ends as he depicted.

Edited December 19, 2018 by Chad Heiser

[GlennWest]

Reason I was considering all series is as I understand all modern panels have diodes in them.

[Chad Heiser]

5 minutes ago, GlennWest said:

Reason I was considering all series is as I understand all modern panels have diodes in them.

This is typically true, but if you get a faulty panel for whatever reason it can kill your entire string.  With multiple series strings, a faulty panel will only kill the string it is in rather than the whole system.  In the mobile environment, I plan for redundancy.  You may never need it, but it is nice to have.  What if a tree limb or some other hazard smashes a panel as you are going down the road.  With one big series string, your whole array is dead.  If you break them up into at least two strings or potentially five strings, then you will still have productivity from the remaining strings in the array.

Edited December 19, 2018 by Chad Heiser

[GlennWest]

1 minute ago, Chad Heiser said:

This is typically true, but if you get a faulty panel for whatever reason it can kill your entire string.  With multiple series strings, a faulty panel will only kill the string it is in rather than the whole system.  In the mobile environment, I plan for redundancy.  You may never need it, but it is nice to have.  What if a tree limb or some other hazard smashes a panel as you are going down the road.  With one big series string, your whole array is dead.  If you break them up into at least two strings or potentially five strings, then you will still have productivity from the array.

That is very sobering, thank you

[Lou Schneider]

BTW, Chad and I are giving you different answers because he's assuming you're using 12 volt panels, not 36 volts.

[Chad Heiser]

5 minutes ago, GlennWest said:

That is very sobering, thank you

When I design the systems I use or build, I always hope for the best but plan for the worst.  In my case that meant having two inverters (one whole house and one dedicated to the refrigerator for redundancy and efficiency when traveling).  My large inverter is also a Hybrid inverter that allows the system to augment low output shore power with inverted battery power.  I also broke my panels into three series strings of two rather than two strings of three or one string of six, again for redundancy.  Finally, I have a built in 240 volt capable generator just in case all else fails. 

My system is all based on Magnum equipment because DRV started with a Magnum inverter from the factory.  As I have mentioned in other threads.  If I were designing a new system from scratch, I would probably go all Victron.  I like some of the advanced technology they have for remote monitoring that Magnum does not offer.  I also like the fact they offer more options for solar controllers.  I would run two large inverters, one on each leg of the 50 amp panel and program them to be capable of 240 volt operation (because I have a 240 volt dryer in my rig).  This would also offer some redundancy if one happened to die on me.  I would probably also run multiple (at least two) smaller charge controllers in series for a large solar array.  Again for some redundancy in case I ever had an issue with one of the controllers.  The only thing I haven't decided on is whether I would go with a high voltage battery bank (48 Volt) or stay with a 12 volt bank.  I like the advantages a higher voltage bank offers, but I am still not convinced a step down DC to DC converter will work in the long hall to run things like leveling jacks and slides.  There are some out there doing it, but no one has been doing it for a long time yet.  By the time I am ready to build my next system, hopefully there will be enough data on the DC to DC converters to see if they will handle high amperage loads over the long hall.  Of course I would build all of this around a lithium battery bank (regardless of what voltage I decided to go with).

[GlennWest]

Chad, planning to run entire Teton on battery. This likely be 10,000 watts. Two 5k inverters are lots more money over a single larger unit. But I have had one Freedom inverter/charger fail so far. So they will go out sometime. I will need 240 but my panel allows that as long as both legs are hot.

[oldjohnt]

Glenn, sorry I got here late FWIW here's my opinion. I would NOT want to wire them all in series such that you're transmitting at such highhhhhhhhhh voltage down to the controller due to  A) Voltage withstand and insulation and voltage breakdown considerations.  b) If you stick to more typical 24 or 48 or 96 volt systems, more solar charge controllers are suitable ALTHOUGH my (and many other) MPPT will accept up to 100  or even 150, but I've NOT seen 300 volts !!!!! C)  With that many panels wired in series there's more potential of shading problems. In series if one panel is drastically shaded or isn't producing for whatever it decreases the net output, although you're still gonna end up with some series connections if you go with my plan below...........

 My preference would be to wire them in series/parallel such that I'm sending NO MORE THAN 96 volts down to the controller. One possible method using ten panels would be five sets of two in series. That's 77.96 Vmp using your figures. That's wiring two in series and then parallel five such sets. That will work with the majority of controllers and be safer and more standard and typical when it comes to selecting your wiring and it and connections  and combiner and junction box voltage ratings.

VOLTAGE DROP CONSIDERATIONS: Once you know the max current and wire lengths its easy to use a voltage drop calculator and Id prefer it be kept to a minimum like less then one percent. Sure bigger is better, but I don't like the idea of too big heavy cumbersome less flexible cables all over the roof either.    If you're looking at lets use 3550 watts at lets use say 77.96 volts (just for an example and illustration NOT intended in any way as exact) that's 45 amps in which case No 6 wire "could" suffice for ampacity purposes BUT bigger would give less voltage drop so No 6 from the final combiner box down to the controller looks like the MINIMUM   NOTE this is based on a 5 x 2 series/parallel configuration but this would change if you wire it different !!!!!!!!!!

CONNECTIONS: Although these are solar panels instead of batteries THE WIRING METHOD TO ACHIVE BETTER BALANCE IS MORE IMPORTANT THEN MOST REALIZE. To decide how best to wire them I would definitely take a look at  AT SMART GAUGE http://www.smartgauge.co.uk/batt_con.html  because a simple ladder is NOT the best way so the panels are balanced. To get the most bang for the buck and realize ALL the benefits those panels have to offer I strongly suggest you study their findings even if sure it will still "work" if wired in a simple 5 x 2 ladder, Im sure people have used such for years NO problems HOWEVER the panels are simply NOT balanced as well as if wire correctly.........….YOUR MONEY YOUR CHOICE WHICH I SUPPORT 

Great question fun discussion for us "sparkies" at least lol

NOTE I approach this more from a power distribution standpoint as that's my background Im NOTTTTTTT in any way a solar expert so do as the solar experts say NOTTTTTTTTTT me 

 

John T  Long retired n rusty engineer and no solar expert so NO warranty, ONLY my thoughts and opinions.

Edited December 20, 2018 by oldjohnt

[Chad Heiser]

7 minutes ago, Lou Schneider said:

BTW, Chad and I are giving you different answers because he's assuming you're using 12 volt panels, not 36 volts.

My answers are based on using high voltage panels.  If using an MPPT controller, I always recommend higher voltage panels because of the advantages the MPPT controller has when supplied with higher voltages.  If using 12 volt panels with an MPPT controller, then you would definitely want some series wiring involved somewhere to get to a higher voltage to take advantage of the MPPT technology.  With higher voltage panels you can get away with parallel only wiring, but it still can be advantageous to have some series wiring for efficiency purposes.  I just do not like one large series string in a mobile environment for the reasons I mentioned above.  In a static/residential environment then I would use one large series string, but not in a mobile environment.  This is just a personal preference of mine.  There are some who have gone with one large series string in the mobile environment with no issues.  I just prefer not to.

[GlennWest]

35 minutes ago, Lou Schneider said:

Here's a quick sketch.  The Victron MPPT 150/70 or above controller will handle this for a 48 volt battery.  Note the Victron controllers are rated for an absolute maximum 150 volts input voltage, which rules out more than three panels in each series string.

https://www.victronenergy.com/upload/documents/Datasheet-BlueSolar-charge-controller-MPPT-150-45-up-to-150-100-EN.pdf

 

Learned something here. Did not know one could wire like this and get these results. According to this it is 5 times panel amps and doubles volts.

[Lou Schneider]

Yes.  Panels (or batteries) in series add voltages while the current stays the same.

Panels (or batteries) in parallel keep the voltages the same while the currents add up.

Edited December 19, 2018 by Lou Schneider

[Chad Heiser]

10 minutes ago, GlennWest said:

Learned something here. Did not know one could wire like this and get these results. According to this it is 5 times panel amps and doubles volts.

Correct. 

The amps in series stay the same.  So two panels in series will have the same amps as one panel. 

The voltage in a series will add.  So two panels in series will have double the voltage. 

When you connect in parallel, it is the opposite.  The voltage stays the same and the amperage adds.

In the above example, five sets of two panels in series will give five times the amps and two times the volts of a single panel.  Two panels in series keeps the same amperage and then five of those series in parallel gives five times the amperage.  Two panels in series gives double the voltage and five of those series in parallel keeps the same voltage. 

 

On edit, Lou typed faster than me again.  Although his second line should say parallel instead of series. 

Edited December 19, 2018 by Chad Heiser

[GlennWest]

Ok, don't get this. trying to draw it out and just can't grasp it. What is 5 strings of 2? 

[Chad Heiser]

3 minutes ago, GlennWest said:

Ok, don't get this. trying to draw it out and just can't grasp it. What is 5 strings of 2? 

5 strings of 2 is in reference to 5 sets of 2 panels wired in series which is what Lou depicted above.  The two panels wired in series make one series string.  Then each additional set of two panels wired in series is another string.  With 10 panels, this gives a total of 5 strings of two panels each wired in series.

You could also wire 2 strings of 5 panels wired in series.

[GlennWest]

1 hour ago, Chad Heiser said:

When I design the systems I use or build, I always hope for the best but plan for the worst.  In my case that meant having two inverters (one whole house and one dedicated to the refrigerator for redundancy and efficiency when traveling).  My large inverter is also a Hybrid inverter that allows the system to augment low output shore power with inverted battery power.  I also broke my panels into three series strings of two rather than two strings of three or one string of six, again for redundancy.  Finally, I have a built in 240 volt capable generator just in case all else fails. 

My system is all based on Magnum equipment because DRV started with a Magnum inverter from the factory.  As I have mentioned in other threads.  If I were designing a new system from scratch, I would probably go all Victron.  I like some of the advanced technology they have for remote monitoring that Magnum does not offer.  I also like the fact they offer more options for solar controllers.  I would run two large inverters, one on each leg of the 50 amp panel and program them to be capable of 240 volt operation (because I have a 240 volt dryer in my rig).  This would also offer some redundancy if one happened to die on me.  I would probably also run multiple (at least two) smaller charge controllers in series for a large solar array.  Again for some redundancy in case I ever had an issue with one of the controllers.  The only thing I haven't decided on is whether I would go with a high voltage battery bank (48 Volt) or stay with a 12 volt bank.  I like the advantages a higher voltage bank offers, but I am still not convinced a step down DC to DC converter will work in the long hall to run things like leveling jacks and slides.  There are some out there doing it, but no one has been doing it for a long time yet.  By the time I am ready to build my next system, hopefully there will be enough data on the DC to DC converters to see if they will handle high amperage loads over the long hall.  Of course I would build all of this around a lithium battery bank (regardless of what voltage I decided to go with).

On the jacks and slide outs, I am considering to just use 1 battery and leave converter in place. Know I be using inverted power to run a converter but it is simple.

[oldjohnt]

33 minutes ago, GlennWest said:

What is 5 strings of 2?

FWIW I agree with Chad, just to put it in different terms Id say:  Simply means you start by wiring TWO panels in series,,,,,,,Next you PARALLEL five of those combinations. Again for "best" (although will still work no problem if not) balance of that ten panel complex arrangement take a look at the Smartgauge tests results. Same as batteries in series or parallel, voltage adds in series but amps adds in parallel...…...NOTE 5 x 2 is ONLY one method to wire all ten panels there are others that can "work: its just how I would choose to do it based on the considerations I cited above

Fud discussion

John T

Edited December 20, 2018 by oldjohnt