Adding additional solar panels (1 Viewer)

[Henry Walpole]

Hi
I'm looking to add two additional solar panels to my existing setup and would appreciate any advice.
I currently have 2x125w Wattstunde flexible solar panels factory fitted, linked to a Victron MPPT 100/50 controller. I have 300Ah of Lithium batteries.

I would like to add 2 more panels and can see that the biggest Wattstunde panel of the same type as mine is 150w so my thoughts were to add 2x150w panels to give me a total of 550w. I have checked the roof and there is plenty of space. The Victron controller is rated up to 700w according the manual.

I can see that the existing panels feed into a junction box which goes into the van as shown on the picture. My questions are as follows:

1. Can I simply add two panels and wire them into the existing junction box by just adding the new cables into the existing connectors shown?
2. I don't really understand the wiring, the red cable from one panel is joined to the black cable of the other panel but then doesn't go anywhere. The red cable from one panel is joined to a brown cable that goes into the van. The black cable from the other panel is joined to a black cable that goes into the van. Does this indicate they are joined in parallel or series?
3. If it is possible to add the two panels as per point 1) above would I just replicate how the panels are currently wired i.e. join one red / one black to the existing connector which goes nowhere and then join the other red / black to the brown / black going into the van?
4. Is it ok to add 2x150w to a 2x125w setup? I could get 2x125w panels if it's important that they match exactly.

Thanks in advance for any help.

 

[autorouter]

The two existing 125W panels are wired in series, which is unusual but acceptable. You could wire two new 125W panels of the same make/model in the same way, which would give you a series/parallel arrangement, ie two series strings in parallel. There would be no problem doing that.

You could wire in two 150W panels in the same way, but you'd need to check the voltages are the same. It looks like you can easily find the specs of both panels, so maybe you could post the details if you are not sure.

I'm a bit concerned about those wire colours, you need to be very careful the positive and negative are correct. British colours are red = positive, black = negative. German colours vary, but black = positive, brown = negative are quite standard. So best to double-check the pos/neg polarity with a meter to be sure.

Panels are usually wired in parallel on motorhomes, because of the shading problem. A small patch of shade on one panel will drastically reduce the output of both panels if they are in series, but will only affect one panel if in parallel. But it's not absolutely necessary to wire them in parallel, and if you know the problem you can take steps to avoid it when choosing a stopping place.

The MPPT 100/50 will be fine with the extra output. The '50' means the maximum output current (amps) from the solar controller, which is OK for the 500W or 600W of panels that you mention.the '100' is the solar controller voltage input limit, which would be fine for two panels in series, or two series strings of two panels each.

 

[Henry Walpole]

The two existing 125W panels are wired in series, which is unusual but acceptable. You could wire two new 125W panels of the same make/model in the same way, which would give you a series/parallel arrangement, ie two series strings in parallel. There would be no problem doing that.

You could wire in two 150W panels in the same way, but you'd need to check the voltages are the same. It looks like you can easily find the specs of both panels, so maybe you could post the details if you are not sure.

I'm a bit concerned about those wire colours, you need to be very careful the positive and negative are correct. British colours are red = positive, black = negative. German colours vary, but black = positive, brown = negative are quite standard. So best to double-check the pos/neg polarity with a meter to be sure.

Panels are usually wired in parallel on motorhomes, because of the shading problem. A small patch of shade on one panel will drastically reduce the output of both panels if they are in series, but will only affect one panel if in parallel. But it's not absolutely necessary to wire them in parallel, and if you know the problem you can take steps to avoid it when choosing a stopping place.

The MPPT 100/50 will be fine with the extra output. The '50' means the maximum output current (amps) from the solar controller, which is OK for the 500W or 600W of panels that you mention.the '100' is the solar controller voltage input limit, which would be fine for two panels in series, or two series strings of two panels each.

Many thanks for the response. It's a German van (Niesmann). I've checked the voltages of the two panels (125w/150w) and they are different so presumably this means I should stick with adding 2x125w panels and not the 150s?

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[Lenny HB]

You could rewire the existing panel in parallel then add the two new panels in parallel, that would overcome the shading problem and make the wiring easier.

The 150 wat panels may have a slight different voltage maybe 1v higher if paralleled with the 125 panels you will get a slight loss but it won't be enough to worry about.

 

[autorouter]

The maximum power voltage of the125W panel is 35V, and for the 150W it's 43.5V. I'd have thought, with 8.5V difference, that the 150W panels would not produce much more than the 125W panels.

 

[Hoovie]

from what I working out, if you want to combine all the panels to use a single controller, you may as well just get 2 more of the 125W panels to match.
You will gain very little extra (if anything) from the 150W panels over the 125W if they are all in parallel.
the best way to setup If you DID get the 150W would be 150+125 in series. Next 150+125 in series and than connect those pairs in parallel. you could get close to the maximum possible that way.

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[Henry Walpole]

Thanks for all the replies so far. Looking at the Victron MPPT 100/50 manual it shows the setup I currently have as follows (albeit I have 125w panels not 120w):

It also shows a typical 4 panel set-up (i.e. what I am aiming for). What confuses me is it is describing both setups as 24v setups (whereas other examples given are described as 12v setups). Why would I have a 24v setup on a 12v system?

 

[Hoovie]

Thanks for all the replies so far. Looking at the Victron MPPT 100/50 manual it shows the setup I currently have as follows (albeit I have 125w panels not 120w):

It also shows a typical 4 panel set-up (i.e. what I am aiming for). What confuses me is it is describing both setups as 24v setups (whereas other examples given are described as 12v setups). Why would I have a 24v setup on a 12v system?

View attachment 750734 View attachment 750735

Just one thing initially to clarify....
A "12V" panel is around 20V. a "24V" panel is around 40V. And putting 2 12V panels in series = 24V panel.

having higher voltage panel setups means the current from panel array to controller is lower (thinner cable possible). Higher voltage means less voltage drop. So should be more efficient in the ideal (lab) environment which these wiring diagrams are based on.

It is the job of the MPPT Solar Controller to convert the power into a form the battery (be it a 12V battery or a 24V battery) can accept.

The second picture is what I described to do if you did go for 150W new panels, except you would have more like an 80V system. Which is fine with your controller.
for example, I have on my van a 270W "12V" array (3 x "12V" panels in parallel), and a 300W "36V" array (3 x "12V" panels in series), each array to its own controller.

 

[Henry Walpole]

The second picture is what I described to do if you did go for 150W new panels

Thanks again, would this second picture setup also work if I went for 125w new panels?

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[Hoovie]

Thanks again, would this second picture setup also work if I went for 125w new panels?

absolutely.
What you are asking is a fairly common question, but yours is more interesting as you have given the actual specs (so we can look at reality, not theory) AND they are high voltage, so other factors come into play.
I will reply in a while with some actual numbers for different setups which may be useful for you and others?

 

[Henry Walpole]

absolutely.
What you are asking is a fairly common question, but yours is more interesting as you have given the actual specs (so we can look at reality, not theory) AND they are high voltage, so other factors come into play.
I will reply in a while with some actual numbers for different setups which may be useful for you and others?

Yes thanks, that would be useful. Also for installation is it sufficient to just remove the fuse for the controller before connecting the new panels and then re-insert it after connection? The manual describes this as the shutdown and restart procedure:

 

[buzz1]

You guys are very helpful for your information to op, credit to you all ,
Absolutely above my skill set

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[Hoovie]

Yes thanks, that would be useful. Also for installation is it sufficient to just remove the fuse for the controller before connecting the new panels and then re-insert it after connection? The manual describes this as the shutdown and restart procedure:

View attachment 750753

OK, these are the numbers based on the figures quoted. the first "Wattage" is just the number they provide and what when you combine panels you might think you should get (a bit rounded up! The 125W panel is really a 119W panel and the 150W is a 145W panel).
the last "Calc Wattage" number is what the sums tell you for different configs.
Rules of the game are ....
Add panels in SERIES, you add the voltages together and only use the LOWEST current number
Add panels in PARALLEL, you add the currents together, and only use the LOWEST voltage number
if you do a Series/Parallel combo, you work out the numbers for each group and build it up.

Getting the 150W panels to add to the 125W panels could be either the WORST option, OR the BEST option! it is all down to how you cable it

All in parallel, BAD. you are actually LOWER than if you had all 125W panels!
But connect a 150W in series with an existing 125W, do the same with the other new 150W and the other existing 125W, and then connect both in parallel - you are only loosing 4 Watts of the theoretical CALCULATED absolute maximum.
Series/Parallel combo done wrong though .... 125W+125W in series, 150W+150W in series, and then Parallel those pairs, you are back in worse case scenario.

Getting more 125W Panels, it doesn't matter how you cable (all parallel or series/parallel), you get the same power (I am ignoring cables losses and volt drops entirely in these numbers BTW).

Sticking to 125W and connecting in parallel would be the easiest (and IMO, best) option. It would also be the most resiliant option. lose one panel (it fails/smashes) in a mixed array and you could lose that entire string. Have 4 panels in parallel and you just loose that one panel. Whilst it is tempting to max the power potential, simplicity can be a great advantage.


Series vs Parallel argument ....
In the ideal world, Series is better. less power transmission losses, plus earlier wakeup and later sleeping means a longer day for the panels to work. That is the theory.
In the real world, the transmission losses are virtually unnoticable for the sizes of arrays Motorhomes have (for a solar farm with panels covering fields, it is a different matter); the extra harvesting time is in minutes and the power gained at that time is in the order of around 0.1Ah-0.2Ah total per day; the real world has clouds and shadows that will kill harvesting on a panel - and one panel in a series array is compromised by shadow, the entire string is affected. In parallel, only that panel is affected.

I have, as I mentioned, two different arrays of similar size (270W vs 300W), one in series and one in parallel, each going to identical controllers (Victron 100/20 MPPT). I did them differently so I could compare them. I see no real difference in the performance of one over the other which would relate to the cabling method.

HTH.

 

[Hoovie]

Also for installation is it sufficient to just remove the fuse for the controller before connecting the new panels and then re-insert it after connection? The manual describes this as the shutdown and restart procedure:

View attachment 750753

I would not recommend to go against the manuals instructions, but I would say not what I would do myself

for a Victron controller, I would do something like the following on my own MH ....
1) go into VE.Connect and put the controller into "maintenance mode" by turning off the charger in the settings.
2) on the roof, once the panels were installed, join them together in the method you have chosen. If parallel, plug into the splitter/combiners (I will assume I am using MC4 connectors and not making my own junction box).
BEFORE I make the connections into the splitter/combiner, I will cover up the panels with blankets/cardboard/etc so they are "dead".
3) uncover the panels
4) in VE.Connect, re-enable the charger in the MPPT.

I don't know if I would remove any cables from the controller. unlikely. If the fuse was easy to get to, maybe, but don't know if I would bother IF I was covering all the panels.

 

[Henry Walpole]

Sticking to 125W and connecting in parallel would be the easiest (and IMO, best) option. It would also be the most resiliant option. lose one panel (it fails/smashes) in a mixed array and you could lose that entire string. Have 4 panels in parallel and you just loose that one panel. Whilst it is tempting to max the power potential, simplicity can be a great advantage.

Thanks again that's really useful. Just to clarify is the above the third option in your table? Does this match the diagram from the manual (image below).

I do have the space for a third pair of 125s but it looks like this would require upgrading the MPPT controller? Or could I add an additional single 125 over and above what I've mentioned (i.e. existing 2x125+ new 2x125 + new 1x125) or do they need to be in pairs?

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[Hoovie]

Thanks again that's really useful. Just to clarify is the above the third option in your table? Does this match the diagram from the manual (image below).

the first and second ones in the table are ALL panels in parallel. the third option onwards is pairs of panels in series, and those pairs connected in parallel, like in the diagram you posted.

I do have the space for a third pair of 125s but it looks like this would require upgrading the MPPT controller? Or could I add an additional single 125 over and above what I've mentioned (i.e. existing 2x125+ new 2x125 + new 1x125) or do they need to be in pairs?

If you had 6 of the 125W panels, that is a theroretical 750W, but the maths suggest 712W in truth. I would not bother changing the controller for being just 12W over (the 100/50 covers upto 700W), especially as you will over ever get that maximum power very very rarely.

If you had 5 panels, you could configure them all in parallel. no series option is available.
If you had 6 panels, you could again configure them all in parallel, or you could have 3 pairs of (125W+125W series) in parallel. So like the diagram again but with one more identical pair.
If it were me, I think I would have 3 parallelled pairs in that situation.


Ref going over the ratings ....
With the Victron controllers, there are two numbers quoted - Voltage and Current. so yours is maximum 100V IN and Maximum 50A current OUT.
The Voltage is a HARD maximum. exceed it and you will likely damage the controller. That is why with your panels, you can never have more than 2 panels in series as a third one will take you over 100V
The Current is a 'SOFT' maximum. anything greater than the value just gets chopped and no harm comes to the controller.
The above may not be true of other non-Victron solar controllers.

 

[Lenny HB]

The maximum power voltage of the125W panel is 35V, and for the 150W it's 43.5V. I'd have thought, with 8.5V difference, that the 150W panels would not produce much more than the 125W panels.

It was late so I didn't look up the spec on the panels, that's a big difference and rules out putting them all in parallel, as said probably better to fit two more 125 panels.

 

[Hoovie]

Yes thanks, that would be useful. Also for installation is it sufficient to just remove the fuse for the controller before connecting the new panels and then re-insert it after connection? The manual describes this as the shutdown and restart procedure:

This would be your cabling for 4 panels, either all parallel, or two pairs of panels in series, then combined in parallel. the S/C are MC4 Splitter/Combiners

For ALL Parallel

For Series/Parallel Combo

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[Henry Walpole]

This would be your cabling for 4 panels, either all parallel, or two pairs of panels in series, then combined in parallel. the S/C are MC4 Splitter/Combiners

For ALL Parallel
View attachment 750822

For Series/Parallel Combo
View attachment 750823

Really useful thanks very much. Where you have S/C could I instead feed the extra cables into the existing connectors I have (pictured in my first post)?

 

[Hoovie]

Really useful thanks very much. Where you have S/C could I instead feed the extra cables into the existing connectors I have (pictured in my first post)?

the Splitters are the same as you have electrically - just with connections ready to use.
If you went all parallel, you would need a 5-way block so you can accept cables from 4 panels and then one out. then the same again for the other set of cables.
If you went series/parallel, you would need to move some cables so you have a cable going from panel to panel.
either way, you will need to do some work on your connections when you add the new panels.

 

[autorouter]

Are these Wattstunde panels the glue-on type? The ones I looked at on the website were. Glue-on solar panels don't have a great reputation for reliability on here, I don't know if these are better quality and more reliable. Presumably you are happy with the existing 2 x 125W panels?

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[Henry Walpole]

Are these Wattstunde panels the glue-on type? The ones I looked at on the website were. Glue-on solar panels don't have a great reputation for reliability on here, I don't know if these are better quality and more reliable. Presumably you are happy with the existing 2 x 125W panels?

Yes they are glue on ones. No problem encountered so far with the existing panels (factory fitted from new in March 2021). Having said that, on a recent enquiry to Niesmann in Polch they said they no longer fit them so perhaps they have had issues?

 

[autorouter]

Where you have S/C could I instead feed the extra cables into the existing connectors I have (pictured in my first post)?

In your picture, both wires from the panel go into that junction box, the link from panel to panel is made inside that junction box too. You could route all four wire pairs from the four panels into the junction box.

Make a link between the new series panels with a terminal block, like the one in your picture.

Then connect the other two positives, one from each panel string, into the terminal block going to the solar controller. Also connect both negatives from each panel string to the terminal block going to the solar controller. You may need a bigger terminal block, or you could get a 4-way terminal block and link two positives together to the controller, and also link the two negatives together.

 

[Henry Walpole]

In your picture, both wires from the panel go into that junction box, the link from panel to panel is made inside that junction box too. You could route all four wire pairs from the four panels into the junction box.

Make a link between the new series panels with a terminal block, like the one in your picture.

Then connect the other two positives, one from each panel string, into the terminal block going to the solar controller. Also connect both negatives from each panel string to the terminal block going to the solar controller. You may need a bigger terminal block, or you could get a 4-way terminal block and link two positives together to the controller, and also link the two negatives together.

Thanks for the clarification, I was hoping to be able to do that but it's nice to have it confirmed.

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