400 Watt solar panels.

[Jason]

Hello.

New to the site. And new to solar. Been reading and watching videos on the subject. I'm considering two 400 watt panels (41vmpp per panel with mc4) in parallel for a 12 volt system on a van.  My concerns are amps through the wire and what gauge wire to use. I would be using the Epever 100A mppt charge controller  with 3 100ah lithiums. I would greatly appreciate your knowledge and experience.

 

 

Thanks

Jason

[Al F]

For the wire size, use a wire size calculator like this one:  http://nooutage.com/vdrop.htm

You are planning on putting the solar panels on a van.  A 400watt panel is about 6 feet by 4 feet.  Do you have room for two?  

With the setup you have planned you should have more power than you are likely to need.

[oldjohnt]

As far as wire size Id consult with the manufacturer for their recommendations lest you risk voiding an warranty. HOWEVER that being said let me run a couple calculations FOR EXAMPLES ONLY AND NOT recommendations.

1) If your two panels were producing full 800 watts (Yeah right lol) at lets use ONLY FOR AN EXAMPLE  24 Volts (even though it should be higher) 800/24         =   33 Amps

2) If your two panels were producing 800 watts at 41 volts, 800/41 =   19.5 Amps 

3) Next there will be a line voltage drop from the panels to your solar charge controller which depends on 1) Current 2) Wire size and 3 ) Distance and if its excessive you would increase the wire size

Okay, that all being said and NOT knowing your actual current (depends on sun and panels etc) and NOT knowing the wire length but ONLY what my training and experience has taught me,  if I were doing it and had NO OTHER instructions to follow, I might use a very MINIMUM of say 8 Gauge (subject to length and larger if necessary to reduce line voltage drop) fine stranded copper conductors, Marine grade moisture and UV rated insulation. NOTE if the manufacturer recommends bigger wire USE THAT, I'm ONLY saying I see 8 Gauge AS THE MINIMUM but larger to reduce line voltage drop and/or manufacturers recommendations. Ive seen people use 4 Gauge in similar current applications since THE BIGGER THE WIRE THE LESS VOLTAGE DROP  

Of course use the necessary moisture rated proper connections and prevent the wire from flopping around on the roof. 800 Watts on a small van with three 100 AH Lithiums should provide a great deal of energy storage and harvest.

 Best wishes

John T

 

[Jason]

1 hour ago, Al F said:

For the wire size, use a wire size calculator like this one:  http://nooutage.com/vdrop.htm

You are planning on putting the solar panels on a van.  A 400watt panel is about 6 feet by 4 feet.  Do you have room for two?  

With the setup you have planned you should have more power than you are likely to need.

There is room. Extended van. Empty roof. The solar panels come with attached 12 gauge wire with mc4 pre installed connectors. I plan on using mc4 combine connectors with 20amp fuses to combine the 2 panels on the roof. From the roof to the mppt is going to be 8 gauge. What's your thoughts on the 8 gauge?

Thanks for the information and the calculator. 

[Jason]

1 hour ago, oldjohnt said:

As far as wire size Id consult with the manufacturer for their recommendations lest you risk voiding an warranty. HOWEVER that being said let me run a couple calculations FOR EXAMPLES ONLY AND NOT recommendations.

1) If your two panels were producing full 800 watts (Yeah right lol) at lets use ONLY FOR AN EXAMPLE  24 Volts (even though it should be higher) 800/24         =   33 Amps

2) If your two panels were producing 800 watts at 41 volts, 800/41 =   19.5 Amps 

3) Next there will be a line voltage drop from the panels to your solar charge controller which depends on 1) Current 2) Wire size and 3 ) Distance and if its excessive you would increase the wire size

Okay, that all being said and NOT knowing your actual current (depends on sun and panels etc) and NOT knowing the wire length but ONLY what my training and experience has taught me,  if I were doing it and had NO OTHER instructions to follow, I might use a very MINIMUM of say 8 Gauge (subject to length and larger if necessary to reduce line voltage drop) fine stranded copper conductors, Marine grade moisture and UV rated insulation. NOTE if the manufacturer recommends bigger wire USE THAT, I'm ONLY saying I see 8 Gauge AS THE MINIMUM but larger to reduce line voltage drop and/or manufacturers recommendations. Ive seen people use 4 Gauge in similar current applications since THE BIGGER THE WIRE THE LESS VOLTAGE DROP  

Of course use the necessary moisture rated proper connections and prevent the wire from flopping around on the roof. 800 Watts on a small van with three 100 AH Lithiums should provide a great deal of energy storage and harvest.

 Best wishes

John T

 

Hi John.

Great information. Truly appreciated. Here's another question.

The solar panels come with attached 12 gauge wire with mc4 pre installed connectors. I plan on using mc4 combine connectors with 20amp fuses to combine the 2 panels on the roof. From the roof to the mppt is going to be 8 gauge.

What's your thoughts on the 8 gauge and amps running through it?

Also, can mc4 connectors be attached to 2 and 4 gauge? I was thinking about cutting the mc4 off and connecting the existing solar panel 12 gauge to the heavier 2 or 4 gauge.

The distance from panel to mppt is 15ft.

Thanks again.

Jason

[jcussen]

IF your charge controller can take 100 volts, why not run panels in series, that way 800 watts at 82 volts would be less than 10 amps and you could use 10 gauge down to controller.

[oldjohnt]

6 minutes ago, Jason said:

What's your thoughts on the 8 gauge and amps running through it?

Also, can mc4 connectors be attached to 2 and 4 gauge? I was thinking about cutting the mc4 off and connecting the existing solar panel 12 gauge to the heavier 2 or 4 gauge.

Jason, thanks for the update, here's my response:

1) 8 Gauge copper is rated FOR AT LEAST 40 Amps, subject to if jacketed or in conduit or single conductors in open air which makes it even greater, so the possible 15 to 30 amps of current I used above should make it adequate being 15 ft shouldn't cause any excess line voltage drop. HOWEVER AGAIN even bigger wire (say 2 or 4 Gauge) = less voltage drop and I have seen 4 Gauge (even if overkill based on current) used under similar conditions PROVIDED all the connections are suitable for that size wire ????  I don't have any MC4 specs or data sheets handy to see what size wire they can accept.  

2) Ive observed situations where MC4 connectors on open rooftops (it can get hot up there in bright sunlight) have failed, but perhaps that was due to excess current ??? I cant say. I have cut them off and used direct burial rated connections/splices in water tight junction boxes with no problems and believe such to be better then MC4 exposed to water and sun BUT DON'T NECESSARILY DO AS I SAY, DO WHAT THE MANUFACTURERS RECOMMEND. 

As far as multiple panel connections are concerned, in series voltage is additive meaning there's less current down to the solar charge controller, however, in series if one panel is shaded that reduces the net energy harvest. In parallel shading is less a problem but current is additive and as used in the examples above. ALL SUBJECT TO any max input voltage range of your charge controller, although many MPPT have a wide input voltage range maybe even as high as 100 volts or more. 

 You are gonna have a nice system when done

John T

[Jason]

All of the research done has been on parallel. I am concerned about sun blocking/ shade over panels. Not clear to me. Does the whole panel/ system suffer if one small (example 12"x6' glass)part of the panels are sun blocked?  Everything thing is 12volt in the van also.

[Jason]

8 minutes ago, oldjohnt said:

Jason, thanks for the update, here's my response:

1) 8 Gauge copper is rated FOR AT LEAST 40 Amps, subject to if jacketed or in conduit or single conductors in open air which makes it even greater, so the possible 15 to 30 amps of current I used above should make it adequate being 15 ft shouldn't cause any excess line voltage drop. HOWEVER AGAIN even bigger wire (say 2 or 4 Gauge) = less voltage drop and I have seen 4 Gauge (even if overkill based on current) used under similar conditions PROVIDED all the connections are suitable for that size wire ????  I don't have any MC4 specs or data sheets handy to see what size wire they can accept.  

2) Ive observed situations where MC4 connectors on open rooftops (it can get hot up there in bright sunlight) have failed, but perhaps that was due to excess current ??? I cant say. I have cut them off and used direct burial rated connections/splices in water tight junction boxes with no problems and believe such to be better then MC4 exposed to water and sun BUT DON'T NECESSARILY DO AS I SAY, DO WHAT THE MANUFACTURERS RECOMMEND. 

As far as multiple panel connections are concerned, in series voltage is additive meaning there's less current down to the solar charge controller, however, in series if one panel is shaded that reduces the net energy harvest. In parallel shading is less a problem but current is additive and as used in the examples above. ALL SUBJECT TO any max input voltage range of your charge controller, although many MPPT have a wide input voltage range maybe even as high as 100 volts or more. 

 You are gonna have a nice system when done

John T

I am very grateful for your feed back. 

Thank you very much.

[jcussen]

https://www.solarchoice.net.au/blog/partial-shading-is-bad-for-solar-panels-power-systems/#:~:text=In conventional solar panel strings,as the shadow sitsI

 

Interesting read on solar panels and shading, especially the part about bypass diodes. I have a bluetooth readout on my phone for the solar controllers, and have shaded panels on the roof with a piece of cardboard, in both series and parallel operation, found very little difference in output, probably because of the bypass diodes. All home systems run in series or series/parallel at high voltage because it is just not practical to run high amperage cables. I am running 120 volts on series panels on my coach, and 240 volts on my series/parallel panels on the house.

[oldjohnt]

2 hours ago, Jason said:

Everything thing is 12volt in the van also.

Jason, that DOES NOT mean you cant have multiple solar panels configured in say 24 or 48 or even more volts provided your charge controller allows, and besides the Vmp is higher then the panels nominal (like 24 volt) voltage. The charge controller can still take that energy at whatever volts INPUT and use it to charge a 12 volt battery bank and in your case it should be suitable to charge your Lithium batteries. I'm running my four RV rooftop "24 volt" panels in series/parallel and in bright sun there's something like 70+ volts at the controllers input and its charging my 12 volt three AGM battery bank.

You got this  

John T

[Al F]

If you already have the panels, then be sure you test them for shading before making decisions about parallel or series.  Attach each one to your controller put it in full sun and then shade part of the panel.   Many panels, if you just shade one square section it kills just about all power from that panel.  Wire them in series and you loose both panels.   

I have heard about panels with diodes, but have not seen diodes mentioned in the panels specs I have looked at in the past.  Not that I have looked at very many panels. 

I would love to know of a website demonstrating the shadowing of panels, with the diodes, to see the actual measurements.    

Wire size: 

-- The 12 gauge wire that is included on the panel is only 2-3 feet long, so that part is fine.

--  From your panels to your combiner box on the roof, I would use #10 wire.

--  For the wire run to your controller: Measure the distance from the combiner box to the controller, then in the voltage drop calculator use the max amperage & voltage output of both panels, and buy the wire size that gives you less than 1% loss.   Lots of places recommend 2% to 3% loss, however the extra cost of the larger size wire, to go to 1% or less, is minimal compared to what you have invested in the system.  

--  Also use welding cable for any wire of 8 gauge or larger.  You can buy it on amazon or a local place which sells welding cable.   Trying to bend #8 or larger stranded wire you buy at a hardware store around tight corners is a real pain.  #10 is bad enough to work with. 

I have heard about panels with diodes, but have not seen diodes mentioned in the panels specs I have looked at in the past.  Not that I have looked at very many panels.  On my RV I have two 325watt panels.  I know if I shade one small corner I loose 95% or more of the power output.  

I would love to know of a website demonstrating the shadowing of panels, with the diodes, to see the actual measurements. 

For an excellent example of "shading" for panels w/o the diodes take a look at the link to a video below. 

While the video is about tilting, what is most amazing, is that, not until they tilt the very last of 6 panels do they see the large jump in power output.  You may want to skip forward to about the 2:30 minuet time to see the last panel go up. 

https://www.youtube.com/watch?v=G01A51L-5Vc&feature=youtu.be

 

[Al F]

For what it is worth, we are sitting at 44 degrees north (in the mountains near Bend, OR.   It is 1pm PDT on a very clear day and my pair of 325 watt (650 watts for the pair) are attached to my MPPT solar controller.  The controller shows that it is putting out: 520 watts.  The solar panels are probably a little dusty, I have not cleaned them in a while.  The panels are not tilted.   The panels are 4.5 years old.

The solar panel voltage as measured by the controller is 35.4V.   

The Keocera panels are rated at the following  "nominal" specs:

Vmp:  36.2V

Pmax:  254 Watts  (508 watts for the pair)

Voc:  45.5V

 

My panels are working very well IMO. 

 

Here is what conditions the spec sheet states is Nominal, as versus "Standard Test Conditions" which would only happen in a lab environment.

        Nominal Operating Cell Temperature Conditions (NOCT)
        NOCT=800 W/M2 irradiance, 20oC ambient temperature, AM 1.5 spectrum
 

 

 

[jcussen]

1 hour ago, Al F said:

If you already have the panels, then be sure you test them for shading before making decisions about parallel or series.  Attach each one to your controller put it in full sun and then shade part of the panel.   Many panels, if you just shade one square section it kills just about all power from that panel.  Wire them in series and you loose both panels.   

I have heard about panels with diodes, but have not seen diodes mentioned in the panels specs I have looked at in the past.  Not that I have looked at very many panels. 

I would love to know of a website demonstrating the shadowing of panels, with the diodes, to see the actual measurements.    

Wire size: 

-- The 12 gauge wire that is included on the panel is only 2-3 feet long, so that part is fine.

--  From your panels to your combiner box on the roof, I would use #10 wire.

--  For the wire run to your controller: Measure the distance from the combiner box to the controller, then in the voltage drop calculator use the max amperage & voltage output of both panels, and buy the wire size that gives you less than 1% loss.   Lots of places recommend 2% to 3% loss, however the extra cost of the larger size wire, to go to 1% or less, is minimal compared to what you have invested in the system.  

--  Also use welding cable for any wire of 8 gauge or larger.  You can buy it on amazon or a local place which sells welding cable.   Trying to bend #8 or larger stranded wire you buy at a hardware store around tight corners is a real pain.  #10 is bad enough to work with. 

I have heard about panels with diodes, but have not seen diodes mentioned in the panels specs I have looked at in the past.  Not that I have looked at very many panels.  On my RV I have two 325watt panels.  I know if I shade one small corner I loose 95% or more of the power output.  

I would love to know of a website demonstrating the shadowing of panels, with the diodes, to see the actual measurements. 

For an excellent example of "shading" for panels w/o the diodes take a look at the link to a video below. 

While the video is about tilting, what is most amazing, is that, not until they tilt the very last of 6 panels do they see the large jump in power output.  You may want to skip forward to about the 2:30 minuet time to see the last panel go up. 

https://www.youtube.com/watch?v=G01A51L-5Vc&feature=youtu.be

I also have not seen an actual website that has measured  the difference between  shading on parallel compared to series panels, only my own experience getting on the roof and reading the solar controller output in both modes. I used a piece of cardboard to shade the same amount of cells first in series and then in parallel, did not see much difference. Many home systems run panels in series up to 600 volts, so shading cannot be much of a factor for home installations. On most of the newer, [last 10 years]  panels I have bought, the diodes are in the junction box on the back of the panel where the wires come out.  This video explains some of it.

 

I put 5200 watts on my house in series/parallel and use two sets of 8 gauge wire to bring it down to the solar controllers, can't even imagine the cost and weight of the wiring I would have needed if I had run them all in parallel.  But to each his own.

[oldjohnt]

2 hours ago, Al F said:

  It is 1pm PDT on a very clear day and my pair of 325 watt (650 watts for the pair) are attached to my MPPT solar controller.  The controller shows that it is putting out: 520 watts. 

Good information Al, thanks for posting. Just for a comparison in say January in South Central Florida subject to the suns intensity and angle of course, my flat rooftop mounted 1080 watts of solar might ??? yield me 700 watts. Now if it was summer and the sun was bright and direct overhead I'm sure I would harvest more. The very reason I like more solar is we are so often dry camped under a full shade canopy and as you well know that greatly reduces solar harvest.

Pleasure sparky chatting with you

John T

[Al F]

1 hour ago, jcussen said:

I put 5200 watts on my house in series/parallel and use two sets of 8 gauge wire to bring it down to the solar controllers, can't even imagine the cost and weight of the wiring I would have needed if I had run them all in parallel.  But to each his own.

Thanks for the video, it was very informative.  

There is a great deal of difference in solar panels on a house and on an RV.  

With 2600 watts per series string you probably have at least a couple hundred volts coming down to each controller, allowing you to use 8 gauge wire and your wire run is most likely much longer than with the typical RV.

The difference in cost for 20-30 feet of #8 welding wire compared to #6 or even #4 not a huge amount.  Especially in relation to the total cost of the system.  The same goes for the 2 to 4 feet of the heavier cable (#2 to 4/0) to go from the controller to the batteries or battery to inverter.  It is a minor cost to go from 3% loss to 1% loss.  

 

 

[Al F]

Caution with cutting off the MC4 connector on the solar panel.  It is my understanding that cutting off the MC4 connector will void the solar panel warranty.  

I have used #10 wire into a MC4 connector which plugs into the solar panels connector.  The #10 wire from each panel then goes to a combiner box where you attach whatever size wire you need to go to the controller. 

[jcussen]

6 minutes ago, Al F said:

Thanks for the video, it was very informative.  

There is a great deal of difference in solar panels on a house and on an RV.  

With 2600 watts per series string you probably have at least a couple hundred volts coming down to each controller, allowing you to use 8 gauge wire and your wire run is most likely much longer than with the typical RV.

The difference in cost for 20-30 feet of #8 welding wire compared to #6 or even #4 not a huge amount.  Especially in relation to the total cost of the system.  The same goes for the 2 to 4 feet of the heavier cable (#2 to 4/0) to go from the controller to the batteries or battery to inverter.  It is a minor cost to go from 3% loss to 1% loss.  

I am using two strings on the coach, one at 120 volts, the other at 60 volts. Two runs of 10 gauge wire, lot easier to run than 6 or 4 gauge I would need if I was running in parallel. $40 for 50 ft of 10 gauge,  $100+ for 50 feet of 4 or 6 gauge. Of course from controllers to batteries is  4 gauge on my coach. This is my 5th coach will solar, and am starting to learn the easy way,  That"s why I did the parallel series test, getting older and looking for the easier way. haha.

 

 

[hemsteadc]

I don't think fusing solar panels is necessary.

[Sehc]

Fusing from panel to controller is not needed, and causes an extra voltage drop. You will need a switch, but that can be sized to little to no voltage drop. I have and used 8 awg uv resistant wire from Windy Nation. But they no longer list any over 10 awg. There are two types of mc-4 connectors. Renogy for one has a different than standard. 

[Jason]

On 8/4/2020 at 3:35 PM, Sehc said:

Fusing from panel to controller is not needed, and causes an extra voltage drop. You will need a switch, but that can be sized to little to no voltage drop. I have and used 8 awg uv resistant wire from Windy Nation. But they no longer list any over 10 awg. There are two types of mc-4 connectors. Renogy for one has a different than standard. 

Hi.

Thank you for the information. I was wondering about the fuses available. I will put the switch in

[Darryl&Rita]

On 8/4/2020 at 1:35 PM, Sehc said:

Fusing from panel to controller is not needed, and causes an extra voltage drop. You will need a switch, but that can be sized to little to no voltage drop. I have and used 8 awg uv resistant wire from Windy Nation. But they no longer list any over 10 awg. There are two types of mc-4 connectors. Renogy for one has a different than standard. 

A switch has just as much of a chance of voltage drop as a fuse. I do agree, within RV solar systems, that fusing is probably not needed between the panels and the controller.

[Sehc]

No. A 500 amp battery disconnect doesn't have near the resistance as a 50 amp fuse or CB.