A question about fitting an additional solar panel.

[DaveKerry]

Hi and thanks for reading.
I have a solar panel fitted already, it was fitted when I got our moho, I wish to add to the 100w panel to a much higher wattage if available (about 300w).
My questions are.
1. Would I be able to connect the 2 together and rely on the existing cable to the controller or would I need a bigger cable.
2. Would I need to upgrade the controller.
3. Are there different controllers as the amp increase through controllers.
4. Should I just take it to a workshop and pay to have 1 fitted.
5. Is it better to connect together in parallel or series.
Then there will be a need to upgrade to a larger battery, but later, unless 400w of solar would cook a 90a/h battery.
For those that have questions, I'm unable to answer any due to our moho being in closed storage.

TIA.
Dave

 

[Nixdorfer]

Its something I'll probably do in the near future myself once we are allowed to play out

Cable wise depends on how big the existing wiring is as to whether it can handle the extra power. I read 4 or 6mm cable is recommneded. But for 400w you probably need bigger the better, also depends on distance between panels and controller as voltage drop is the problem not amps.

Controller probably if quadrupling the output but again depends what's already fitted.
You need one that can handle upto 400w, a votronic mpp 350 or one of the victron are a good starting point. Definitely go for an mppt type if changing yours.

A workshop is a good idea if they know what they are doing. Some on here will tell you its not that difficult if you do your research on plan it out. Some have had workshops do it and ended up with a bad job or panels fly off.

90ah is pretty small for a 400w setup, you can produce all the power but have nowhere to store it. A second battery would be a good idea.

Series apparently gives a bit better output but if get shade on one panel it affects both. I'll probably do ours parallel.

I'm no expert but have been doing a lot of searching about it myself recently and that's what I found.

 

[DaveKerry]

Thanks for replying, I'll check the wire sizes, the controller and the size of the battery compartment when I get access to our mh.
I've always fancied a new leisure battery but both batteries were replaced a few months before we bought our mh.

 

[autorouter]

There is a rather long and rambling thread on exactly this subject that you might find interesting.

New system needed

Hi, I’m in a Hymer and underpowered, working from it with my laptop and only lasting up to 2 days without driving, so I need an emergency refresh. After a reasonable amount of research I’ve found how complex this is - I’m hoping not to have to become an expert on this before I buy as I really...

www.motorhomefun.co.uk

Some short answers
1. It's unlikely the new panels would be suitable voltage or amp rating to connect in either series or parallel to the existing panel. You'd need a new cable for that reason. But even if they happened to be suitable, since there will be four times the current, the cable would be inadequate anyway.

2. I'd suggest you leave the 100W panel and controller, and add the extra panels through a new controller. Just connect both controllers to the leisure battery.

3. Yes. Victron, for example, makes a complete range of controllers for 100W caravan systems to 10kW small solar farms.

5. Yes. A less facetious answer is, motorhome installations are usually in parallel, to minimise the shading problem. In series, if there's partial shade on one panel, the output of the whole string reduces. In parallel, each panel acts independently. Cable runs are usually short, compared to house roof or field installations, so voltage drop is less of a problem.

The battery size? The whole purpose of a solar controller is to charge the battery and avoid overcharging it. A 90Ah battery with 400W of solar is unusual, but might be right for off-grid in the winter, when solar yield is low. Depends how much power you use and how many days of bad weather you can live with before it's a problem. You can decide later if you start having problems.

 

[Emmit]

Your Battery is a Bucket that holds no more than 90 amps.

It doesn't matter how much your Solar produces, you can't get more than 90 amps, (and that is really 45 amps because you don't want to go below half it's capacity)

I appreciate that it isn't ideal but if the Battery isn't that long in the Van, another one bolted beside it in parallel would be useful.

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[Lenny HB]

For 300 watts 4mm sq cables are OK 6mm sq slightly better. bear in mind the highest loss will be in summer when the panels are producing the most so not a problem. In winter as the panels aren't producing much there won't be much loss. That's why I say 4mm cables are OK.

I would wire all panels in parallel and fit a decent MPPT regulator. I have 300 watts of panels with a Votronic MPP 350 regulator & 3 x 80a/h Gel batteries.

As a rough rule of thumb 100 watts of solar to 100 a/h of batteries. It won't cause any problems keeping just your 90a/h battery but you won't be making much use of the solar energy available.

 

[DaveKerry]

Thanks Lenny, from what you say, I deduce I need to measure the battery compartment fit the largest battery I can both physically and financially, then upgrade the solar to suit, and wiring if need be.

Thanks everyone for the help.
Dave

 

[68c]

Is it best to fit one large leisure battery or two smaller ones.

 

[Lenny HB]

Is it best to fit one large leisure battery or two smaller ones.

Pricewise often not much different, depends on space and how easy to lift a big one into place. A 200a/h battery with be nearly twice the weight of a 100/ah.
In use electrically no different.

 

[two]

I would not mix panels, but install an additional set-up and gain resilience rather than compatibility issues.
As for batteries, I would go for fewer big ones rather than lots of smaller ones (and all the same).

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[mitzimad]

youll not get anything bigger than 6m in the connections on most controllers two batteries is the norm as one bigone is hard to position and if it fails you left with nothing

 

[Reallyretired]

My batteries are in an awkward position and large ones are heavy. I restrict myself to 110Ah as even going to 125Ah increases the weight beyond what I am prepared to lift.

 

[froli's]

If you’ve got different size panels it’s better to fit them in series.

 

[Lenny HB]

If you’ve got different size panels it’s better to fit them in series.

Doesn't make any odds providing the panels are the same voltage.
Series is a waste of time on a Motorhome, any shade on one panel and you have lost all your output.

 

[Trout bum]

Hi folks there are several good You Tube videos relating to the fitting of solar panels either first installations or adding on if you want some info on do it yourself, a good one is a channel called Gadget John he has built a van and is now helping other folks with questions about fitting all types of stuff to motorhomes he has a Question answering slot every Tuesday called vantech Tuesday but if you go on his channel and contact him anytime I'm sure he would help guide you he has loads of videos and knows his stuff .

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[Chris Sykes]

The most efficient way to do things is to leave the existing panel and controller as fitted and fit a new Victron Controller for the new panel. on my Swift Bolero I have the existing manufacturer supplied panel, which Eddie’s team at Vanbitz Moved & relocated on the roof to make room for 3 more additional solar panels each with its own separate Victron Controller these feed into 3 x 100amp batteries (2 extra fitted by Vanbitz) this provides me with complete flexibility to Wild Camp (Off the Grid) for months at a time without ever having to worry about the batteries - I also have the Victron bluetooth battery monitor fitted so can easily keep an eye on the state of the batteries and am always most happy when it says batteries 100% charged infinite days useage available!

 

[autorouter]

If you’ve got different size panels it’s better to fit them in series.

If they are the same voltage, parallel connection works.
If they are the same current (amps), series connection works.
If they are different voltage and current, use separate controllers for each panel.
Separate controllers will work in all cases.

 

[autorouter]

he has loads of videos and knows his stuff .

His videos have been discussed on here before, and some of us would not agree that he is very knowledgeable. The incident with lithium batteries for example.

 

[two]

It's often difficult to judge the value of advice given.
Many seem prepared to offer it with little or no experience or understanding.
I imagine that the mission of many U-Tubers is to increase their following rather than inform.

 

[TR5]

Several have advocated separate controllers / regulators. I may be totally wrong, but doesn't a controller work like a battery charger, reducing the charge (amps) as the voltage increases, so as not to overcharge?
If that is the case, surely fitting two controllers wired to the same battery bank, won't one controller (the one giving out the greater voltage), cancel out the second controller, as it will see the higher voltage and cut right back on it's own amperage output, thinking the battery is fully charged?

If that is the case, would it not be better to wire the smaller panel and controller to the vehicle battery, and fit a suitable larger panel and controller to the leisure batteries? Or, wire both panels into one suitably sized controller?

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[Lenny HB]

Several have advocated separate controllers. I may be totally wrong, but doesn't a controller work like a battery charger, reducing the charge (amps) as the voltage increases, so as not to overcharge?
If that is the case, fitting two controllers wired to the same battery bank, won't one controller (the one giving out the greater voltage), cancel out the second controller, as it will see the higher voltage and cut right back on it's own amperage output, thinking the battery is fully charged?

My thoughts as well but it does appear to work even Victron recommend it. Personally not something I would do.

 

[autorouter]

doesn't a controller work like a battery charger, reducing the charge (amps) as the voltage increases, so as not to overcharge

Smart (multi-stage) chargers don't work quite like that. If the battery is fairly discharged they push out a constant charging current, watching as the voltage slowly rises to the 'absorption voltage'. As soon as it reaches the absorption voltage, it fixes that voltage and waits for the current to slowly fall as the battery becomes fully charged. At a predetermined low current limit it switches to trickle charge (float) mode.

In the first stage, all the chargers will contribute to charging the battery as much as they can. At the end of the first stage the battery is about 80% charged. So maybe there's a bit of confusion in the last 20%, but it's not a big problem.

If that is the case, would it not be better to wire the smaller panel and controller to the vehicle battery, and fit a suitable larger panel and controller to the leisure batteries?

The starter battery usually doesn't require much more than a trickle charge. You arrive on site or at home after a drive which has charged up the starter battery, and then it's just self-discharge and the alarm/tracker to be powered. Unless of course you power your disco and sub-woofers from the starter battery when parked up.

 

[King Warwick]

Simple, look on YouTube for Gadget John. All your questions answered and instructions. Search Gadget John then look for solar panels information.

 

[Lenny HB]

Simple, look on YouTube for Gadget John. All your questions answered and instructions. Search Gadget John then look for solar panels information.

Please don't he gets so much wrong.

 

[Bill and Tracey]

Do you need a 400w set-up? If you do then the 90ah battery should be the first thing to address. My personal rig is a 100w monocrystalline panel to a 75/15 victron mppt to a pair of isolated 130ah battery's. Not had a problem with this, it keeps us wild camping over the potters fortnight in the sunny of UK. Hope you get it sorted.

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[the1andonly]

Please don't he gets so much wrong.

Thanks for putting it in a more succinct and diplomatic way than i was thinking.
Ps i aggree.

 

[DaveKerry]

Thanks everyone for your help and advice, when the mh is out of storage and we are able to be out to play, I'm going to measure the battery compartment and go from there.

 

[TR5]

Simple, look on YouTube for Gadget John. All your questions answered and instructions. Search Gadget John then look for solar panels information.

I wasn't over-impressed on some information I have seen on his video's.