Adding a second solar panel

[42208]

Appreciate I will need to ask the dealer this question, however, nothing like being armed with a bit of advance information. I am picking up a van in a few weeks time which has a manufacturer fitted solar panel of just 40w, however, wired by the manufacturer (Autocruise)for 150w (Regulator etc). I need more solar and a second leisure battery, so my question is does this mean I can add a 100w panel and link it to the 40w panel on the van roof without the need to feed any additional cabling through the van, without changing the regulator or the control panel etc.? Have read through as many threads as I can, however, specific point not asked before (as far as I can see)

 

[Ingwe]

Can't answer your question I'm afraid but as I'd like to add a second panel to my van, looking forward to the answers you get.

 

[Lenny HB]

Yes you can just connect them together on the roof using MC4 connectors.

 

[DBK]

Probably is the answer but check how many cells the 40W panel has. If it has 36 then you could wire another panel of say 100W in parallel with it. The panel in the image below has 36 cells arranged in a 4 * 9 pattern. If your panels has less cells then you might be able to wire the 100W panel in series with it but I would be worried about the smaller panel limiting the current from the larger panel - it may not happen but it might.

If you can't easily count the cells disconnect the panel and when the sun is shining measure the open circuit voltage - if it is around 21 or 22 volts you have 36 cells.

The alternative would be to fit the 100W panel with its own controller and ideally an MPPT type for maximum efficiency. The system will work fine with two controllers charging the batteries.

 

[peterc10]

I didn't realise they still made such small ones.

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[andy63]

My understanding is that described above by John...
Ie in parallel the voltage characteristics of the panels should be the same... in series the current output of each panel should be the same...
If not the total output will be affected ...
If it was me id ditch the 40w and fit a decent size panel..
Andy

 

[42208]

Probably is the answer but check how many cells the 40W panel has. If it has 36 then you could wire another panel of say 100W in parallel with it. The panel in the image below has 36 cells arranged in a 4 * 9 pattern. If your panels has less cells then you might be able to wire the 100W panel in series with it but I would be worried about the smaller panel limiting the current from the larger panel - it may not happen but it might.

If you can't easily count the cells disconnect the panel and when the sun is shining measure the open circuit voltage - if it is around 21 or 22 volts you have 36 cells.

The alternative would be to fit the 100W panel with its own controller and ideally an MPPT type for maximum efficiency. The system will work fine with two controllers charging the batteries.

Thanks for the detailed response, will check out how many cells are on the existing panel as a starting point

 

[Ingwe]

At the risk of hijacking the thread (hopefully not) can you please explain the business about wiring in series and parallel of the second panel. My only panel is 120watts and there is space for another. I'd like to fit one and wondered whether the wiring for the second panel could just be joined to that of the first panel (in the small what looks like a junction box on the roof) so that no further wiring needs to go to the regulator. I hope I've been clear enough.

 

[42208]

My understanding is that described above by John...
Ie in parallel the voltage characteristics of the panels should be the same... in series the current output of each panel should be the same...
If not the total output will be affected ...
If it was me id ditch the 40w and fit a decent size panel..
Andy

Assume you mean ditch the 40w and put 150w on the roof. Will this be a lot more efficient than a 40w + 100w? Guess if I end up replacing the controller and wiring then technically I can go to whatever I can fit on the roof? (although 150 w will be sufficient for my needs)

 

[Ingwe]

I think Lenny's reply above may be my answer.

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[Lenny HB]

At the risk of hijacking the thread (hopefully not) can you please explain the business about wiring in series and parallel of the second panel. My only panel is 120watts and there is space for another. I'd like to fit one and wondered whether the wiring for the second panel could just be joined to that of the first panel (in the small what looks like a junction box on the roof) so that no further wiring needs to go to the regulator. I hope I've been clear enough.

Panels wired in series are slightly more efficient but not many regulators can handle the voltage of panels in series. The big disadvantage is if you get shade on one panel you loose the output from both.
With panels wired in parallel with a decent MPPT regulator the difference in output will be negligible but if one panel is in shade you still get the output from the other one.
Parallel is the prefered way on Motorhomes.

You don't need a junction box just a pair of MC4 couplers.

 

[Silver-Fox]

If it was me id ditch the 40w and fit a decent size panel..

That was my first thought.

If he can do the work himself mucho savings to be had

I’ve just taken one 100w panel off and replaced with two 150w panels and changed cabling and fitted a MPPT controller.

 

[gus-lopez]

. I'd like to fit one and wondered whether the wiring for the second panel could just be joined to that of the first panel (in the small what looks like a junction box on the roof) so that no further wiring needs to go to the regulator. I hope I've been clear enough.

That is all I do.

 

[Lenny HB]

That was my first thought.

If he can do the work himself mucho savings to be had

I’ve just taken one 100w panel off and replaced with two 150w panels and changed cabling and fitted a MPPT controller.

You finally plucked up the courage to do it.

 

[andy63]

Assume you mean ditch the 40w and put 150w on the roof. Will this be a lot more efficient than a 40w + 100w? Guess if I end up replacing the controller and wiring then technically I can go to whatever I can fit on the roof? (although 150 w will be sufficient for my needs)

I'm just assuming without looking things up that it would be difficult to match panel characteristics unless you fitted another panel or panels of the same sort of size..
It may not make a huge difference..I have no practical experience.. some have panels of various sizes and claim it is ok... but from my reading on the subject is suggest its most probably not ideal..
My thoughts are why fit something that cant operate at its full potential and as has been said a 40 w panel is in today's world rather small.. find it hard to believe a manufacturer would fit that to a new van for servicing hab batteries..
Andy..

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[Richard n Ann]

I would remove all the solar, sell it on ebay as 'new other' and start again.

That's just me though

 

[42208]

I would remove all the solar, sell it on ebay as 'new other' and start again.

That's just me though

Not a bad option, if starting again what route would you take?

 

[Silver-Fox]

You finally plucked up the courage to do it.

I know, it’s the unknown that held me back a bit

It was a pain pulling the the new main cable in though

I’ll let you drool over the install next time we meet

 

[Richard n Ann]

Not a bad option, if starting again what route would you take?

I'd definitely buy another Votronic Duo mppt controller, they maintain the starter battery too and are made for motorhomes rather than a lot that are made for houses.

Check out photonic universe for panels, when I bought mine they had 2 ranges, German and Chinese, I emailed their technical department asking what was the difference. The answer was that the German panels were, on paper, better in low light, but this had not been proven. I went for the ones made in China and they're very good.
I did hear the German solar plant had ceased production after.

 

[Lenny HB]

I'd definitely buy another Votronic Duo mppt controller, they maintain the starter battery too and are made for motorhomes rather than a lot that are made for houses.

I use a Votroinc Duo but I don't use the second output as it is only 1 amp, I fitted a CBE split charge relay.

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[Silver-Fox]

I use a Votroinc Duo but I don't use the second output as it is only 1 amp, I fitted a CBE split charge relay.

This may well be my next move

I think we need to talk

 

[Lenny HB]

I think we need to talk

10 words per pint.

 

[Richard n Ann]

I use a Votroinc Duo but I don't use the second output as it is only 1 amp, I fitted a CBE split charge relay.

Why would you need more than 1 amp? you must have one serious alarm drain... Or perhaps a pimped up stereo?

 

[Silver-Fox]

10 words per pint.

Yikes that’s already half a pint

Maybe we’ll make it a visual thing

 

[Lenny HB]

Why would you need more than 1 amp? you must have one serious alarm drain... Or perhaps a pimped up stereo?

Working on theory that on a series of dull UK winter days when my 300watts of solar is only producing about 2 amps the second output is only producing a percentage of that so probably sod all.
Also I had the relay around, its capable of delivering up to 4 amps from the leisure batties and doesn't rely on solar.

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