Solar - voltage difference on 2 panels

[Insider]

Hi,

looking to upgrade my solar and have a query about the different voltages. Going to wire in parrallel and have an existing 90W panel that has Vmax of 17.8V and open-circuit voltage of 22V. The panel I am looking at is another 90W and has Vmax of 19.6V and open-circuit voltage of 24.06V. Will the differences in voltage be OK or should I go in series. The solar controller will be fine with either - Victron 75/15

TIA

 

[Gromett]

You should not put these panels in parallel to feed a single controller.

If you want to use both, then a separate controller for each of them would work.

The best option though would be to put 2 matching panels up in parallel and dispose of the old panel.

 

[jwells]

I have 3 different panels in parallel on my van, 2x 40w and 1x 80 all fed through a Votronic solar controller. Everything has appeared to be working perfectly okay since I fitted them some time ago!
My question, am I missing a trick here regarding output/miss matching, maximum efficiency and where is the best resource for information?

 

[Lenny HB]

I would measure the open circuit voltage of the panels if within a volt they should be OK. Most 12v panels are 21.5 to 22.5v

 

[Guigsy]

If you mix and match panels, you'll pretty much always get less than optimal performance. If they are in parallel, one will always drag the other down to the same voltage. If you wire them in series, then they current limit each other instead. I wouldn't be surprised if you max out at ~150w in optimal conditions.

If you're trying to maximise your solar collection, consider getting a matched pair of new 90w panels, replace them both with one bigger one, or just have the two panels on separate controllers.

Edit:
More info here:

Mixing solar panels – Dos and Don’ts • SOLAR POWER SECRETS

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[RedFrame]

It's absolutely fine to mix differing panels, but just be aware you won't get the absolute best performance out of ALL the panels.

As has been said, if you mix differing panels in Series the whole will be limited by the weakest panel's Amperage; In Parallel then the whole will be limited by the weakest panel's Voltage.

Your panel's, if matched and in an ideal world, would produce 180W, but because they are mixed...

In parallel - System limited to 17.8V and Total Current of 9.64A (5.06+4.59), so theoretical max = 17.8 x 9.64 = 171.6W

In series - System limited to 4.59A and Total Voltage of 37.4V (17.8+19.6), so theoretical max = 37.4 x 4.59 = 171.6W

This obviously becomes much more of a problem if you introduce a 16v 90w panel into an existing parallel system with 3 22v 200W panels (Total 690W, but theoretical max 526W...degrading the original 600W system by 74W!!)

On your current setup, with a theoretical loss of 8.4W but an increase on the original system of 81.6W, I wouldn't worry about it.

Cheers
Red.

 

[Insider]

The original plan was to get an additional Victron 90W(780x668) and place it to the right of the existing panel as you look down. The Victron 90W is €135. I can get the Victron 175W(1485x668) for €201and remove the existing panel. Below is the roof - I'll be removing the VisionPlus TV aeriel and I'll design and print a cover to feed a cable out for a small magnetic TV aerial. One of the reasons to do this(other than more solar) is to feed the cables down to the right of the toilet skylight so that they only have to drop down to the batteries. Currently my controller is at the back and the 12V lines have to travel 3/4 of the van - even going thru the EC400 system to get to my batteries. I reckon selling the exising panel and aerial will cover the difference in the panels. Sourcing exact kit in Ireland is a struggle. I can get the panel easily enough but the gland and brackets etc are a pain!!!

 

[RedFrame]

What are you trying to achieve by increasing your solar...?

Edit: Ignore, just re-read your last post....

Cheers
Red.

 

[Insider]

It's absolutely fine to mix differing panels, but just be aware you won't get the absolute best performance out of ALL the panels.

As has been said, if you mix differing panels in Series the whole will be limited by the weakest panel's Amperage; In Parallel then the whole will be limited by the weakest panel's Voltage.

Your panel's, if matched and in an ideal world, would produce 180W, but because they are mixed...

In parallel - System limited to 17.8V and Total Current of 9.64A (5.06+4.59), so theoretical max = 17.8 x 9.64 = 171.6W

In series - System limited to 4.59A and Total Voltage of 37.4V (17.8+19.6), so theoretical max = 37.4 x 4.59 = 171.6W

This obviously becomes much more of a problem if you introduce a 16v 90w panel into an existing parallel system with 3 22v 200W panels (Total 690W, but theoretical max 526W...degrading the original 600W system by 74W!!)

On your current setup, with a theoretical loss of 8.4W but an increase on the original system of 81.6W, I wouldn't worry about it.

Cheers
Red.

Red - I had my reply done and only saw yours after posting! Didn't know it was a simple case of taking the lower voltage - another case of w=av making life nice and simple! A loss of 8.4W is negligle so this gives me food for thought as to the better approach although I am liking the idea of a single panel as it means I don't need to worry about MC4 connectors on the roof which will add in additional cost. My big gain from either solution will be changing the 12V run from the controller from 6+meters down to 1.5 with much better cabling used.

 

[Insider]

What are you trying to achieve by increasing your solar...?

Cheers
Red.

Here's where you're going to think I'm a bit mad. I have a 60A Sterling B2B feeding into 2x90W LA which I want to change over to lithium but not for a while. I know the B2B is oversized and sufficient by itself(when moving) but having solar means I'm not under pressure to move and solare keeps the batteries in better nick(battery master installed). The other main reason to do this is I'm unhappy with the cabling for the solar in the van. Its not run in kopex and it goes into the Sargent EC400 on terrible pin connectors. I want to do a proper job on it and that means moving the controller closer to the batteries. I thought why not put in a panel at the same time and that's why I'm not here.

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[RedFrame]

Red - I had my reply done and only saw yours after posting! Didn't know it was a simple case of taking the lower voltage - another case of w=av making life nice and simple! A loss of 8.4W is negligle so this gives me food for thought as to the better approach although I am liking the idea of a single panel as it means I don't need to worry about MC4 connectors on the roof which will add in additional cost. My big gain from either solution will be changing the 12V run from the controller from 6+meters down to 1.5 with much better cabling used.

More "food for thought" You could also take into account the positioning of the two 90W panels, what if your 175W single was in partial shade...? Would two 90's spaced apart provide you with a more flexible soloution...?

Also, just thinking outside the box, and a throw away comment, have you considered blanking off the forward vent (or blanking it off and moving it back/forward) to create more space?

Losing 9m in total of Solar cable will go a fair way into offsetting the additional weight of the new panel...

Cheers
Red.