Using Domestic Solar Panels on Motorhomes

Peter Beeston said:
I have used domestic panels now for over 7 years, firstly a 280w panel on my caravan, and then a 360w panel on my M/H. The only difference that I could see is that the domestic panels tend to be higher voltage, so use a good quality mppt controller that can take the higher input voltage. (280w panel vas 57v, the 360w panel is 36v)
The low light performance is a function of the controller, my victron controller will charge down to 8v input.
So at the light level that an 18v panel (Normal 12v panel) is at 8 v, my 32v panel is outputting 16v. So when the light is lower and say is outputting 10 v on my panel, I am still getting some charge whereas an 18v panel will be outputting 5v and not charging.
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Im not sure I understand you correctly, but no charger will do that, to charge with 8v incoming to a 12v output, unless its a buck boost charger. Victron solar controller its not boosting only bucking, so it needs higher voltage to work. It starts charging at 5v above battery voltage, then it keeps on charging as long as incoming PV its 1v above battery voltage.
If you see any charge with 8v PV, thats not charging, its DC leakage to the PV.
 
Raul said:
Im not sure I understand you correctly, but no charger will do that, to charge with 8v incoming to a 12v output, unless its a buck boost charger. Victron solar controller its not boosting only bucking, so it needs higher voltage to work. It starts charging at 5v above battery voltage, then it keeps on charging as long as incoming PV its 1v above battery voltage.
If you see any charge with 8v PV, thats not charging, its DC leakage to the PV.
Click to expand...
This is what an MPPT controller does, it modifies the input voltage/current to increase the charging efficiency.
for example 8v at 2 amps can be output at 16v at 1 amp for charging.
 
Peter Beeston said:
This is what an MPPT controller does, it modifies the input voltage/current to increase the charging efficiency.
for example 8v at 2 amps can be output at 16v at 1 amp for charging.
Click to expand...
Am im telling you that its a boost function, victron solar charge controllers do not have boost, only buck. It can take 24v at1a and deliver 12v at 2a, thats buck.
The only charge controller to do what you said, buck and boost, are only found on wind turbines and hydro generators. Solar charge controllers are only buck, no boost function.
 
Make sure your solar controller can accept the higher voltages that most domestic panels output before you purchase.

The panel will have a maximum output voltage and the solar controller will have a maximum input voltage, make sure these are compatible. I have used a domestic panel on my PVC with great success.
 
Raul said:
Am im telling you that its a boost function, victron solar charge controllers do not have boost, only buck. It can take 24v at1a and deliver 12v at 2a, thats buck.
The only charge controller to do what you said, buck and boost, are only found on wind turbines and hydro generators. Solar charge controllers are only buck, no boost function.
Click to expand...
Apologies, it appears that what I thought was the minimum charge voltage, is in fact the controller start-up voltage, the minimum charge voltage is the battery voltage + 1v.
Peter.

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We have two 100w domestic sola panel's on the roof of our motorhome since 2007 & have covered over 90.000 miles that have included -18c storms at Nordkapp to + 43c in southern Morocco
& some interesting storms whilst traveling with no problems with them coming loose. So we can endorse if fitted properly domestic sola panel's will put up with a lot
 
I have 3 x 425Wp domestic panels on my LWB Transit (yeah, does overhang the back a little) on a standard domestic Renusol rail and bracket system, as I installed on my house. Rails fit to the factory-provided roof rail fixings (8 mm tapped holes); no need to drill. Panels cost about £100 each. I use 3 panels (could have managed with two - 850Wp is enough really) so I could get the Voc up to 150V ( 2 panels give about 100V, not quite enough); this allows me to use a domestic hybrid inverter. I chose the Sunsynk 3.6kW because, I suppose due to popularity, it was cheaper than a 2kW one at the time. This not only manages MPPT solar charging, its also a 3.6kW 230V inverter, 3.6kW mains battery charger and discharger, manages pass-through from grid supply supported by battery as needed, full monitoring, control, battery condition management, web interface, fault protection and programming, cheaper and less wiring that all those Victron boxes, fuses, busbars and cables. Also the Sunsynk (unlike many) also has a 230V Generator input, so I wired a cheap 1kW inverter via switch and fuse to my van battery and so can charge the leisure battery (5 kWh 50V Sunsynk) at 1kW as we drive. The long cable is at 230V, not at 12V as with standard B-B chargers, so is thin and cheap. I did reinforce both the rear cantilever part of the rails, and the leading / trailing edges of the panels, with ali angle pop-riveted on. Cheap, light and easy to do, they are now very rigid. I did a calc, it seems if you want more than about 300 Wp of PV, and more than about 2kWh of storage, you're better off using domestic components rather than van or marine ones. Which perhaps isn't surprising, they exist for a reason. I take the point earlier about traffic wind loads; but domestic panels are designed for snow loads in Canada and wind loading atop skyscrapers in Monsoon countries. The rail mounting system allows for additional attachment points for more stiffness if needed, and components can be reinforced, as I did. On a domestic installation you worry more about the strength of the rafters than about the panels and mountings in case of high winds - if the panels come off, you expect them to take the rafters with them. Having said that, I do worry. Mind you, my daughter hired a camper in NZ earlier this year; the glued-on flexible solar panels blew off. Guess you can't win.
 
AlanandMayya said:
I have 3 x 425Wp domestic panels on my LWB Transit (yeah, does overhang the back a little) on a standard domestic Renusol rail and bracket system, as I installed on my house. Rails fit to the factory-provided roof rail fixings (8 mm tapped holes); no need to drill. Panels cost about £100 each. I use 3 panels (could have managed with two - 850Wp is enough really) so I could get the Voc up to 150V ( 2 panels give about 100V, not quite enough); this allows me to use a domestic hybrid inverter. I chose the Sunsynk 3.6kW because, I suppose due to popularity, it was cheaper than a 2kW one at the time. This not only manages MPPT solar charging, its also a 3.6kW 230V inverter, 3.6kW mains battery charger and discharger, manages pass-through from grid supply supported by battery as needed, full monitoring, control, battery condition management, web interface, fault protection and programming, cheaper and less wiring that all those Victron boxes, fuses, busbars and cables. Also the Sunsynk (unlike many) also has a 230V Generator input, so I wired a cheap 1kW inverter via switch and fuse to my van battery and so can charge the leisure battery (5 kWh 50V Sunsynk) at 1kW as we drive. The long cable is at 230V, not at 12V as with standard B-B chargers, so is thin and cheap. I did reinforce both the rear cantilever part of the rails, and the leading / trailing edges of the panels, with ali angle pop-riveted on. Cheap, light and easy to do, they are now very rigid. I did a calc, it seems if you want more than about 300 Wp of PV, and more than about 2kWh of storage, you're better off using domestic components rather than van or marine ones. Which perhaps isn't surprising, they exist for a reason. I take the point earlier about traffic wind loads; but domestic panels are designed for snow loads in Canada and wind loading atop skyscrapers in Monsoon countries. The rail mounting system allows for additional attachment points for more stiffness if needed, and components can be reinforced, as I did. On a domestic installation you worry more about the strength of the rafters than about the panels and mountings in case of high winds - if the panels come off, you expect them to take the rafters with them. Having said that, I do worry. Mind you, my daughter hired a camper in NZ earlier this year; the glued-on flexible solar panels blew off. Guess you can't win.
Click to expand...
How is the sunsynk below 125vmp behaving? Does the mppt track below 130vmp ish?
 
Raul said:
How is the sunsynk below 125vmp behaving? Does the mppt track below 130vmp ish?
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I chose panels with Voc = 50.9, highest I could find. They have Vmppt = 42.9 so my string is Vmppt = 128.7. The Sunsynk datasheet says Vstartup 125; Vmppt 150, so I did worry! I see they start up as well in low light, and perform as well overall, as my domestic system (on a kWh per day , pro-rata Wp of the installations basis) so i dont thnk there is a constraint there. Looking at the history, it seems to start up at about 120V as promised, and works fine (draws decent PV current) down to 68v (!). But it doesnt start at 100V, so I couldnt have done it with 2 panels.
 
The reason I asked is, I have two Panasonic with 60voc and about 54vmp. A bit low for Sunsynk. What panels do you have? 96 cells? What make?

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The panels are Trina Vertex 425 S+. I bought from ITS, who were also selling Trina Vertex 425 TSM and 425 S Mono, the ones I chose have slightly higher Voc than the others. I dont know how many cells, the panels are 176 x 113 cm, so fairly big.
 
They are normal 120 half cut cells, 60 in parallel with 60, not a high voltage like Panasonic SunPower etc. There are 96cell panels with very high vmp, unfortunately not many available in UK.
 
I did compare inverters; Solis do a 3kW hybrid with Vmin 120V and Vmppt 90V, that should work for you. Don't know how good it is. I have used Solis before, a 3.6kW PV-only one, that worked fine.
 
Thats exactly the problem I ran into! That led me to cram 3 panels in series onto my van, to get the Voc.
 
Lizbiebrowne said:
I want to fit about 400 W of solar panel to my motorhome roof for use in conjunction with my already installed MPPT controller which can handle up to 430 W and Voc of 50 V.

If I look on the 12V Planet website I could buy two 175 W Victron solar panels for around £270, advertised for use with 12 V systems on motorhomes and boats.

However, if I search Google for a 400 W solar panel I find that I can buy various domestic panels at around this power level all for less than £100. For example, the one below is £83, a 405 W panel with a Voc of 37 V.

Is there any reason why I shouldn’t fit this cheaper one?

LONGi Solar Hi-MO 5m 405WP Full Black PV Module LR5-54HIB-405M

LONGi's high-efficiency PV modules are widely used all over the world, from alpine grasslands to desert wastelands, and from ponds and vegetable beds to household dwellings. LONGi's ultra-high-value PV module products continue to benefit customers and local economy with its advantages of higher...
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Click to expand...
Hi
I have scrolled through the replies before posting my reply for your consideration.
Some of the replies should not concern you because they are just theoretical and the members haven’t tried it.
I myself fixed 3 heavy duty domestic panels onto my van roof. 750w 37.5v each. Very efficient panels. They secure no problem and work very well. They hang over the side of the van a bit because they are so big, but they provide a lot of electricity. So I would say that it is no issue whatsoever. My panels cost me £80 each, so I got a lot of bang for my bucks. They are of course second hand.

However, whilst it works, and is considerably cheaper than buying new ones, or ones branded for your van, there are 2 downsides for me.
1. The weight is enormous. Each panel weighs 20 kg. I don’t like that weight on top of the van and certainly not permanently. There is zero wind noise and no drag, but I can definitely feel the weight.
2. I found that for my use of the van, I didn’t need them. I invested £1700 on a Roamer 460Ah lithium battery which lasts for days on one single charge. I generally stay on campsites and I only have to pay for electric hookup every few days at a cost of a few euros to fully charge the battery, so I don’t need solar at all. That is why I am removing them.
I am not suggesting that what I have found is going to be right for you, but it is a suggested way to power your van. Invest your “power” money in the best battery you can afford and charge it whilst driving or for the odd night on hookup instead.
I started off thinking that I would be off grid most of the time whilst planning, but the reality for my wife and I is that we do stay the odd night off grid or on free aires but it is much more of an enjoyable experience to be on a nice campsite. So that is what we do.
I am considering purchasing a portable solar panel which is very lightweight and can be rolled out for emergency use but I am not sure I even need that.

Some people have said why would I not use the free energy from solar?
Because hookup is 3 euros every few days to fully charge a good battery set up.It is for nothing.

Just my views.
Lots of ways to achieve a functioning electrical system.
I hope my views give you some provoking thought?

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where is the best place to buy domestic panels? also what is the best make to buy.
 
chrisandbev said:
where is the best place to buy domestic panels? also what is the best make to buy.
Click to expand...
I compare several sellers and always end up with either ITS Technologies or Trade Sparky. Comparing prices, look out for delivery charges - some, especially ITS, like to use pallet delivery which can be £50 or more - a lot if its a small order. I reckon the best is the cheapest that is the physical size, power, and Voc (open circuit voltage) that I need for the system Im building. So physical size set by your roof; the electrical parameters set by your solar charge controller or hybrid inverter. I never look at the make, just the data sheet figures and price.
 
I fitted a single 415w panel from Bimble, 25/May/2022 , they are big and a tad heavy but extremely pleased with the quality and service, this is the purchases:

415W Canadian Solar Mono Half Cell Panel - Super High Power
Mono PERC HiKU (MCS approved) C415 1 £162.39
Premade MC4 6mm Solar Cable 5 meter - (Cut in half to make
two MC4 to bare wire cables when used in our kits) 5M length mc4-cable-5m 1 £10.68
Solar ABS Mounting System for Caravans, Boats, Sheds 7
piece set - BLACK ONLY absmountkit 2 £30.77 £61.54
BLACK CT1 Sealant & adhesive - Bonds everything, Works
Underwater - 290ml - Stick down panels & ABS Mountings ct1-black 1 £11.97
MultiSolve CT1 multi-purpose solvent for the safe removal of
adhesives and sealants. multisolve-ct1-spray 1 £8.55
Sub-Total: £255.13
Bank Transfer Discount 2.5%: £-6.38
Standard - UK - Panels usually 2-5 Days: £41.50
VAT (20%): £58.05
Total: £348.30

Copied so apologies for the layout, from memory the mounts from Bimble were used as well as the alley mounts available off Amazon, I have posted somewhere on the fitting of this panel, as you will get into mounting brackets, adhesive, bolt or not to bolt, a whole new can of worms!
 
AlanandMayya said:
I have 3 x 425Wp domestic panels on my LWB Transit (yeah, does overhang the back a little) on a standard domestic Renusol rail and bracket system, as I installed on my house. Rails fit to the factory-provided roof rail fixings (8 mm tapped holes); no need to drill. Panels cost about £100 each. I use 3 panels (could have managed with two - 850Wp is enough really) so I could get the Voc up to 150V ( 2 panels give about 100V, not quite enough); this allows me to use a domestic hybrid inverter. I chose the Sunsynk 3.6kW because, I suppose due to popularity, it was cheaper than a 2kW one at the time. This not only manages MPPT solar charging, its also a 3.6kW 230V inverter, 3.6kW mains battery charger and discharger, manages pass-through from grid supply supported by battery as needed, full monitoring, control, battery condition management, web interface, fault protection and programming, cheaper and less wiring that all those Victron boxes, fuses, busbars and cables. Also the Sunsynk (unlike many) also has a 230V Generator input, so I wired a cheap 1kW inverter via switch and fuse to my van battery and so can charge the leisure battery (5 kWh 50V Sunsynk) at 1kW as we drive. The long cable is at 230V, not at 12V as with standard B-B chargers, so is thin and cheap. I did reinforce both the rear cantilever part of the rails, and the leading / trailing edges of the panels, with ali angle pop-riveted on. Cheap, light and easy to do, they are now very rigid. I did a calc, it seems if you want more than about 300 Wp of PV, and more than about 2kWh of storage, you're better off using domestic components rather than van or marine ones. Which perhaps isn't surprising, they exist for a reason. I take the point earlier about traffic wind loads; but domestic panels are designed for snow loads in Canada and wind loading atop skyscrapers in Monsoon countries. The rail mounting system allows for additional attachment points for more stiffness if needed, and components can be reinforced, as I did. On a domestic installation you worry more about the strength of the rafters than about the panels and mountings in case of high winds - if the panels come off, you expect them to take the rafters with them. Having said that, I do worry. Mind you, my daughter hired a camper in NZ earlier this year; the glued-on flexible solar panels blew off. Guess you can't win.
Click to expand...
interesting re your use of the sunsynk inverter. makes me wonder if other domestic inverters would offer the same, especially as you can still buy G38 brand new inverters for under £100 .... no use for new domestic installations, but can be used as replacements on existing domestic installations. whether that would have the same functionality as the Sunsynk would need to be checked of course and if they do then it might open up few avenues for self builds or self installs? This one for instance, what size (watts/voltage?) would the panels need to be for the charger to function? Also shows (i think) a MPPT start up of 150 VDC, same as the Sunsynk ..?


Raul
 
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That one is a PV inverter only, not a hybrid one. It works as a grid-tie inverter, producing 230V AC to synchronise with the grid. In the absence of grid power it shuts down - this is called "anti-islanding protection". A Hybrid inverter by contrast will do that, but will also charge and discharge a battery, and will supply AC power to a "LOAD" or "UPS" output, 230V even in the absence of grid power. Thats what you really need for a MH.
 
Some very good info on this thread and just what I've been searching for.

Thanks to all contributors 👌
 
MisterB said:
interesting re your use of the sunsynk inverter. makes me wonder if other domestic inverters would offer the same, especially as you can still buy G38 brand new inverters for under £100 .... no use for new domestic installations, but can be used as replacements on existing domestic installations. whether that would have the same functionality as the Sunsynk would need to be checked of course and if they do then it might open up few avenues for self builds or self installs? This one for instance, what size (watts/voltage?) would the panels need to be for the charger to function? Also shows (i think) a MPPT start up of 150 VDC, same as the Sunsynk ..?

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Raul
Click to expand...
Sorry seen this to late, but as already mentioned, it’s just a string inverter, and won’t work. Another low voltage hybrid is as you may already know Dyee, Solis and maybe growatt. Not sure about sunsynk MPPT range, but looks AlanandMayya is using one with 3 panels. It’s a interesting concept and of course it needs a 48v battery and a converter for the 12v loads
 
Raul said:
Sorry seen this to late, but as already mentioned, it’s just a string inverter, and won’t work. Another low voltage hybrid is as you may already know Dyee, Solis and maybe growatt. Not sure about sunsynk MPPT range, but looks AlanandMayya is using one with 3 panels. It’s a interesting concept and of course it needs a 48v battery and a converter for the 12v loads
Click to expand...
The Sunsynk is a badged Deye, albeit apparently with a few specific tweaks. i have a Sunsynk 5kw and its working really well ! Though they may be a bit too expensive and may not be really the best choice for a motorhome? I know you far more knowledgable than me on these matters ! (y) (y)

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Last edited:
MisterB said:
The Sunsynk is a badged Deye, albeit apparently with a few specific tweaks. i have a Sunsynk 5kw and its working really well ! Though they may be a bit too expensive and may not be really the best choice for a motorhome? I know you far more knowledgable than me on these matters ! (y) (y)
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Good point! I bought the Sunsynk because I’ve got an 8kW one at home so I know them, they have an AUX input that allows you to charge from a 230v inverter from your alternator, and ITS were selling the 3.6kW one really cheap that day. But I’m not a fanboy and for a couple of quid less would have bought SoFar, Growatt, Solax , etc. I guess they all use the same chips and FETs and only the box is different. It’s a very competitive market, compare the specs and prices it’s down to what they want to shift that day.
 

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