Adding another solar panel

[headlight]

Due to the lack of space on my roof, when I had solar fitted the installer could only fit a single 100 watt panel.
My intention is to fit, wired in parallel, an identical 100 watt panel to my roof rack there by doubling my solar.
I have a Victron 75/15 MPPT controller with the blue tooth app.
The most amperage I have seen from my existing panel is 6 amps (last summer in the UK and I don't intend to go abroad) so presumably with the two panels in parallel I will see 12 amps which is within my MPPT controllers max 15 amp rating.
I have also confirmed with the installer that the cables from my existing panel to my MPPT and from MPPT to my batteries is rated at 20 amps.
My intention is to connect the two panels wiring together, positive to positive negative to negative, on the roof before it goes through the roof to the MPPT there by not having to put another hole through the roof and not fitting a second controller.
My present panel is fixed to the roof via plastic corner brackets so I can't see which wire is positive and negative and both wires are white.
If I temporarily connect the wires together then if the amperage doubles I have connected in parallel.
However if the amperage stays the same but the voltage doubles, it would still be well within the controller's 75v max, then I have connected in series and need to swap the connections around.
Does this sound correct and make sense ?

 

[stevec]

If you have MC4 connectors on the leads from the panels you can get 2 into 1 adaptors which will make adding the second panel straightforward

 

[headlight]

I've got 2-1 MC4 connectors.
I just want to check that what I am proposing doing is ok ie 2 identical panels into the one controller and using the amperage/voltage reading to determine which wires are positive and negative ?
I can see which wire goes to negative and positive on the controller but have no idea which is which on the roof, both wires being white and unmarked.

 

[Stealaway]

I've got 2-1 MC4 connectors.
I just want to check that what I am proposing doing is ok ie 2 identical panels into the one controller and using the amperage/voltage reading to determine which wires are positive and negative ?
I can see which wire goes to negative and positive on the controller but have no idea which is which on the roof, both wires being white and unmarked.

A multi meter set to 25 volts will tell you which is positive (+) and which is negative (-) and the current voltage of the solar panel

 

[68c]

Deleted.

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[68c]

Do you already have MC4 connecters fitted to the original panels and to the two white wires? They should have a red ring indicating positive, assuming the original install was done correctly.

 

[headlight]

Do you already have MC4 connecters fitted to the original panels and to the two white wires? They should have a red ring indicating positive, assuming the original install was done correctly.

No I don't.

 

[headlight]

A multi meter set to 25 volts will tell you which is positive (+) and which is negative (-) and the current voltage of the solar panel

Aren't you not suppposed to have the panels producing electric when they're not connected to a battery ?

 

[tonka]

As above.. Just use a multimeter to test..
The panel will produce and be live even when not connected to a battery, hence why you should cover them up when working on the regulator / battery end.

You should get around 18-24 volts ish..
If you get a - (minus) in front of the reading then you have the connections the wromg way around.

 

[Emmit]

I will preface this comment by saying that I am not a professional, however;

If you cover your present panel with lightproof material (assuming you are
NOT going to connect the panels after dark)

You can then disconnect the wires at the Controller end.

You have already been pointed in the direction of 2 into 1 MCA Connectors

You can then cut the cable between your extant panel and as previously stated
use a multimeter to ascertain which wire is Pos. and which is Neg.

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[headlight]

Does it matter whether I use a multimeter or the Victron app to tell me what the voltage is to determine positive and neg ?
I thought you shouldn't have the panel in light if not connected to a battery ?
Won't I have to uncover the panels to get a voltage reading with a DMM ?

 

[68c]

Just a bit of fun, apparently you can use half a potato to determine polarity. Stick the wires into a spud, after a while a stain will appear around onoe wire. Sad thing us I cannot remember which.

 

[Emmit]

Does it matter whether I use a multimeter or the Victron app to tell me what the voltage is to determine positive and neg ?
I thought you shouldn't have the panel in light if not connected to a battery ?
Won't I have to uncover the panels to get a voltage reading with a DMM ?

That's why you cover the extant panel up. It will think it's midnight!

 

[Stealaway]

Aren't you not suppposed to have the panels producing electric when they're not connected to a battery ?

It don't matter.
Like all electrical supplies. It simply sits there waiting for you to find it something to do
If not, it's just a big piece of glass.

 

[Guigsy]

I'm in a similar position. I've got a 175w panel and a Victron SmartSolar 75/15 and I need more power... although I'm mainly interested in harvesting more when light levels are poor.

I'm thinking of simply adding a second identical panel and running it though the existing controller and wiring. My understanding is that if I connect the panels in series, I'll still be well under the 75v maximum the charge controller can take. The maximum current the controller can take is 15 amps [edited!], but if I add panels that can exceed that, it doesn't matter. So on bright days, despite having 350 watts of panels, I'll be topping out at about 220 watts. But when light is lower, I won't be limited. Is this correct?

At a later date, I might upgrade the controller, but I might also need to change the wiring...

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[nicholsong]

Excuse my barging in, although I think the answers so far have already answered the OP's questions.

I am proposing to add 2 x 100(?)W panels to my existing 80W. I have read that wiring them in series, with the correct Victron MPPT Controller which can convert the resultant 36v to 12v, will give an earlier and later in the day charge.

Any comments please and does anyone have the best number for Victron to get advice on this installation, please?

 

[Stealaway]

At a later date, I might upgrade the controller, but I might also need to change the wiring...

I would be fitting this controller - now ----- to both batteries

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[cyberyacht]

It's always considered best to have matching panels to get the best from them.

 

[Guigsy]

I would be fitting this controller - now ----- to both batteries

Victron Solar Dual Battery Charger Duo PWM 12/24V 20A LCD USB Lead Acid Lithium | eBay

New model by Victron Energy. BlueSolar PWM DUO-LCD&USB. Protected against reverse polarity connection of the solar panels and/or battery. Load output protected against over load and short circuit. BlueSolar PWM-LCD&USB.

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I've already got a trickle charger for the cab battery. And I've got a lithium battery pre-ordered.

It's always considered best to have matching panels to get the best from them.

I'll be getting another Victron 175w monocrystalline. Apart from 2 summers of aging, they should be well matched.

 

[headlight]

Another question.
After re-measuring I think that an identical panel to the one I already have will foul on my Heki.
I have found a slightly narrower panel that will not foul the Heki.
The specs are almost, but not quite identical.
These are the specs of the 2 panels.
Existing panel Second panel
36 cells (4x9) 36 cells (3x12)
100W. 100W
Max power 5.62A. 5.6A
Max volts 17.8V. 18V
Short circuit
current 6.07A. 6.12A
Open circuit
voltage 21.3V. 21.6V

I assume these specs are close enough to connect the 2 panels in parallel ?

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[Guigsy]

Another question.
After re-measuring I think that an identical panel to the one I already have will foul on my Heki.
I have found a slightly narrower panel that will not foul the Heki.
The specs are almost, but not quite identical.
These are the specs of the 2 panels.
Existing panel Second panel
36 cells (4x9) 36 cells (3x12)
100W. 100W
Max power 5.62A. 5.6A
Max volts 17.8V. 18V
Short circuit
current 6.07A. 6.12A
Open circuit
voltage 21.3V. 21.6V

I assume these specs are close enough to connect the 2 panels in parallel ?

You will lose some efficiency. I think one will cap the other at 17.8V. Whichever is performing worse in varying light conditions will drag down the other. But if they are the same technology (e.g. monocrystalline) you won't be losing much.