Two 440 watt Panels - Series or Parallel ?

[BobJones]

Hi folks!

I'm gearing up to do my first solar install and don't know much about it yet.

I picked up two 440W panels and was going to put them in parallel with MC4 branch connectors. I also ordered up a crimper to make the ends so I could use bulk cable and make them the correct length. To that end, I was going to order some bulk wire and that's where I ran into some concerns. What thickness of cable to use?

It seems that if you parallel the panels you increase the amperage and that is where you run into real cable thickness problems. Ie, the more amps, the thicker the cable required and distance becomes an issue. Ie, it's all about resistance.

From Renology, "The downside to parallel systems is that high amperage is difficult to travel long distances without using very thick wires. Systems as high as 1,000 Watts might end up outputting over 50 amps which is very difficult to transfer, especially in the systems where your panels are more than 10 feet from your controller, in which case you would have to go to 4 AWG or thicker...." (makes sense, that explains why the 50 amp power cable from my RV is so thick)

I haven't measured it all out yet, but I am pretty sure I will be a lot further away than 10 feet.....it could be 20 depending on routing from the panels, through the roof, and down to the compartment.

So then it looks like the panels can be run in series, also from Renology;

"Strictly series connections are mostly utilized in smaller systems with a MPPT Controller. Connecting your panels in series will increase the voltage level and keep the amperage the same. The reason why series connections are utilized with MPPT controllers is that MPPT Controllers actually are able to accept a higher voltage input, and still be able to charge your 12V or more batteries. The benefit of series is that it is easy to transfer over long distances. For example you can have 4x100 Watt panels in series, run it 100 feet and only use a thin 14 gauge wire.

The downside to series systems is shading problems. When panels are wired in series, they all in a sense depend on each other. If one panel is shaded it will affect the whole string. This will not happen in a parallel connection."

I am using a MMPT 100/50 controller. The panel specs are (each);

PMAX = 440W
VMP = 41.1V
IMP = 10.71A
ISC = 11.46A

The battery bank that is being charged runs at 12v.

It seems that the 10 AWG wire in a MC4 connector is limited to 30A....

If you can use a 14 AWG wire for 400 watts of solar going a whopping 100 feet, I'm wondering if that might be the way to go? I'm probably only going, at most, 25 feet for the feed wire from the panels down to the controller. I'm a little over double the power output in their example, but in that case, wouldn't the standard 10 AWG solar wire and a series installation be the way to go?

I really don't know what I'm doing, this is my first solar install, we will not be adding more panels to the roof other than these two. The motorhome is short (29 feet) and the panels are probably going to be roughly 10 feet apart. So if there's shading, I would assume it's likely they would both be shaded. But hey, what do I know?

Thoughts, ideas, suggestions ? Am I on crack?

[Perryb67]

Originally Posted by BobJones

Hi folks!

I'm gearing up to do my first solar install and don't know much about it yet.

I picked up two 440W panels and was going to put them in parallel with MC4 branch connectors. I also ordered up a crimper to make the ends so I could use bulk cable and make them the correct length. To that end, I was going to order some bulk wire and that's where I ran into some concerns. What thickness of cable to use?

It seems that if you parallel the panels you increase the amperage and that is where you run into real cable thickness problems. Ie, the more amps, the thicker the cable required and distance becomes an issue. Ie, it's all about resistance.

From Renology, "The downside to parallel systems is that high amperage is difficult to travel long distances without using very thick wires. Systems as high as 1,000 Watts might end up outputting over 50 amps which is very difficult to transfer, especially in the systems where your panels are more than 10 feet from your controller, in which case you would have to go to 4 AWG or thicker...." (makes sense, that explains why the 50 amp power cable from my RV is so thick)

I haven't measured it all out yet, but I am pretty sure I will be a lot further away than 10 feet.....it could be 20 depending on routing from the panels, through the roof, and down to the compartment.

So then it looks like the panels can be run in series, also from Renology;

"Strictly series connections are mostly utilized in smaller systems with a MPPT Controller. Connecting your panels in series will increase the voltage level and keep the amperage the same. The reason why series connections are utilized with MPPT controllers is that MPPT Controllers actually are able to accept a higher voltage input, and still be able to charge your 12V or more batteries. The benefit of series is that it is easy to transfer over long distances. For example you can have 4x100 Watt panels in series, run it 100 feet and only use a thin 14 gauge wire.

The downside to series systems is shading problems. When panels are wired in series, they all in a sense depend on each other. If one panel is shaded it will affect the whole string. This will not happen in a parallel connection."

I am using a MMPT 100/50 controller. The panel specs are (each);

PMAX = 440W
VMP = 41.1V
IMP = 10.71A
ISC = 11.46A

The battery bank that is being charged runs at 12v.

It seems that the 10 AWG wire in a MC4 connector is limited to 30A....

If you can use a 14 AWG wire for 400 watts of solar going a whopping 100 feet, I'm wondering if that might be the way to go? I'm probably only going, at most, 25 feet for the feed wire from the panels down to the controller. I'm a little over double the power output in their example, but in that case, wouldn't the standard 10 AWG solar wire and a series installation be the way to go

A 14 gauge wire can only handle 15 amps, while a 10 gauge wire can handle 30 amps. As the gauge size gets smaller the wire gets larger. Make sure you purchase pure copper, not copper tinned aluminum.

Appears you purchased 24 volt panels. On a perfect day that never happens you'll be putting 22 amps through your wire at 24 volts. A 10 gauge wire is plenty at that nominal voltage and you'll actually be around 40 volts, so better yet.

The minimum wire installed by any knowledgeable solar installer is 10 gauge. Don't go smaller! Fourteen gauge is too small. Ten gauge is cheap, but a PITA to run to your batteries where your controller should be located. It's more about pulling the wire, than wire size, but 8 gauge or smaller is harder to pull in an existing camper. Ten gauge still pulls easily, but the smaller the gauge (i.e. 8 or 6 gauge) the harder to pull.

With a 24 volt system you have plenty of voltage to run parallel in case of shading. You probably bought household panels that usually don't include diodes for shading, so I'd definitely wire parallel.

I'm currently installing three 100 watt 12 volt panels to add to our 170 watt panel, so after the slight VMP mismatch will have 465 watts available. I'm wiring in parallel.

Despite all the solar you can put on your roof, you'll run into a campsite with full shade. We carry a 100 watt portable with 45' of cable for those situations.

Enjoy,

Perry

[astrocamper]

Your 10 AWG will work fine to the MPPT controller. Your panel specs as you posted:

PMAX = 440W
VMP = 41.1V
IMP = 10.71A
ISC = 11.46A

You will be installing the pair in parallel. IMP will double and only be 21.42 amps total. I would recommend a bigger cable between the controller and batteries since the amperage will be much higher at the lower battery charging voltage.

[Persistent]

Good advice posted above. Use 10 gauge or 8 gauge. 8 gauge will be more efficient for longer distances, but will be harder to pull though blind spaces and will cost more. There is a cost benefit action here. Your solar equipment supplier can probably give good general advice. Tell him the panel specs and the distance.

Two 40 volt panels in series is 80 volts. Will your mppt controller handle that? Check specs.

There is "Ampacity" and there is efficiency. Ampacity is the current the wire can carry without getting hot and failing. You still must consider efficiency.

Smaller diameter wire will have more voltage loss (less power delivered) for any given distance. Longer wire will have more voltage loss.

So, never exceed ampacity rating for safety. Consider current and distance for efficiency.

If you are running a string of lights, you may be less concerned about power loss. If you are charging batteries, voltage loss has an outsized effect. Between solar panel and controller is not as sensitive as battery charging but is more sensitive than a string of lights.

I wish you good luck and happy trails ahead!

[astrocamper]

I recommend doing the panels in parallel and the amperage will easily be handled by 10 AWG.

[BobJones]

Excellent - thanks everyone!

Stay tuned for some posts with pics as I go along

[BobJones]

Hi guys!

On my solar install I was told I should have a fuse on the line from the battery to the controller (I guess to protect the controller). Given that my controller maxes out at 50 amps he suggested a 60 Amp fuse.

If you agree, is it OK to use a 60 amp resettable circuit breaker instead?

[Tomahawk]

You might want to consider 2 100/30 Charge controllers. With the 100/50 seems like the Charge Controller could be limiting the charging. Seems like the manual is saying for a 12V nominal battery system the max nominal panel wattage is 700 versus the 880 you have. The 100/30 has a max nominal of 440 Watts. I guess if you don't mind being limited the 100/50 will work. I am not an expert and would defer to some of the other guys on this form, maybe you never see the limiting because the actual power output will be lower and charge voltage will be 14.4 or so, reducing the max current down. Curious to others opinions.

[BobJones]

That's interesting....I was not aware of that at all. I checked the specs and it appears you are correct, the controller will limit it 700 watts at 12v.

At 24v it goes up to 1400 watts. I'm not sure what to say!

[Perryb67]

Originally Posted by BobJones

That's interesting....I was not aware of that at all. I checked the specs and it appears you are correct, the controller will limit it 700 watts at 12v.

At 24v it goes up to 1400 watts. I'm not sure what to say!

With 24 volt panels you'll be just fine with a 100/50. Don't scrimp on your controller! Buy the best you can!

Yesterday I had 16-18 amps at my controller at high noon and it got to absorption in a heartbeat. I covered my panels until high noon to see what was possible. I didn't order enough roof wire so I'm only using 365 watts. I'll have the wire by early next week to get my system to 465 watts and 20 or more ah's input at high noon.

Enjoy,

Perry

[YC1]

Originally Posted by BobJones

Hi guys!

On my solar install I was told I should have a fuse on the line from the battery to the controller (I guess to protect the controller). Given that my controller maxes out at 50 amps he suggested a 60 Amp fuse.

If you agree, is it OK to use a 60 amp resettable circuit breaker instead?

Yes. The breaker or fuse protects the wire from melting and going up in smoke. Without protection a wire will glow in seconds.

If some component shorts dead to ground and has the ability to carry a lot of current the fuse still protects the wire, the short is just from the component versus a rubbed wire.

[astrocamper]

You should bring your battery connection to the MPPT controller before the solar connection. Being able to switch each is useful. When taken the solar off line disconnect the panels before the battery. When bringing it back online connect the batteries on before the solar. If you use a master battery disconnect for your system turn off the solar to the MPPT controller first.

I use an inline MC4 fuse at each panel in my system.

https://www.amazon.com/PowMr-M-C-4-W...ustrial&sr=1-3

I recommend a breaker/disconnect between the MPPT controller and the batteries.

https://www.amazon.com/gp/product/B0...e?ie=UTF8&th=1

I recommend a disconnect switch between the panels and the MPPT controller.

https://www.amazon.com/dp/B07DPNRWXW...xpY2s9dHJ1ZQ==

[BobJones]

Way to go guys - once again you're saving me a lot of work and headaches . I'm trying to get all the parts in quickly but on that front it seems there is a two week lag time before anything will arrive so getting all the bits and pieces ordered ASAP is a real big help

Jeff, I ordered up the inline fuses, the circuit breaker and the disconnect switch.
I'm also working on getting in those brackets you suggested.

I'm guessing you put the inline fuses on the positive output on each panel? I ordered up 20 AMP fuses for those. On the disconnect switch before the controller I'm guessing it doesn't matter which side you switch, just switch the positive? Same thing on the breaker between the battery and the controller, switch the positive?

I think the install is starting to come together in my mind. If I can get all the bottom bits (controller, breakers etc) together I can get that end done ahead of time because I think I'm going to get stuck on the brackets.

[astrocamper]

Yes. I put the MC4 fuses on the positive cable. I use the disconnect switch and the breaker disconnect on the positive cables.

I would recommend a 6 AWG cable between the MPPT controller and the breaker/ disconnect and the breaker/disconnect and the batteries because you may see up to 50 amps on this cable.

If you ever need to work on wiring and you switch off the battery main disconnect also remember to turn off the disconnect switch from the solar panels. You can leave the MPPT output at the breaker/disconnect enabled because there will be no solar output once the disconnect switch feeding the solar panel power to the MPPT controller is off.

It is easy to forget and if the sun is shining your 12 volt system will still be energized from the power coming from the solar panels if you forget to turn off the solar panels.