Tilted solar panels vs more flat panels for off road use

filippomasoni

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I am planning on installing glass panels on my roof with a 23 degree tilt that is permanent. Two 200w panels on each side of the roof low edge near roof edge, high edge near center of roof. The high point of the installed panels will not be above the other roof installed items so the overall height of the rig is not increased.

I fully agree that having a variable system that requires climbing on roof to adjust is something that won't get utilized much.

I have also read that most of the flexible solar panels don't last long, and degrade over a much shorter time so I am sticking to narrow and long 200w full glass panels. The additional cost of two fixed "struts" that raise the interior edge of each panel is small, and they will connect to the typical feet that are 3m VHB taped to the roof. Just my approach..
What vehicle/camper do you have? I didn't quit understand how are you placing the panels.

Flexible solar panels are less durable, reason why most of them have less than 5 years of warranty compared to 20-25 of the glass ones. They are also a bit less efficient, 2-3% and more expensive.
But if I'm not tilting them and they'll permanently stay on the roof, glued with such a low profile and low weight, then I think it's worth it, much lower center of gravity and better for off-roading. Also much less drag on the freeway an noise.

Do you guys know of good suppliers of solar panels in Europe? Both rigid and flexible. I'm struggling to find different options.
 

Short_Shot

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The downside is the increased heat they will transfer into the roof. If you have limited roof insulation this might be an issue on its own.

Probably not a big issue in many cases but will add extra heat. The other advantages may outweigh this though. Especially if you can fit enough to run ac.
 

OffGridInTheCity

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I put 4 x 300w panels flat on top of my 7 x 14 cargo trailer conversion. I wish I had tilted them 'a bit' (5deg?) so the dirt would wash off over the frame's lip. As it is - they are flat so water pools on them and leaves dirt residue over the cells when the water evaporates.
Live and learn :)
1627683475205.png
 

Short_Shot

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I put 4 x 300w panels flat on top of my 7 x 14 cargo trailer conversion. I wish I had tilted them 'a bit' (5deg?) so the dirt would wash off over the frame's lip. As it is - they are flat so water pools on them and leaves dirt residue over the cells when the water evaporates.
Live and learn :)
View attachment 58238
Oh good point. I'll try to work that into my design lol

Also how do those do at highway speed
 

filippomasoni

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The downside is the increased heat they will transfer into the roof. If you have limited roof insulation this might be an issue on its own.

Probably not a big issue in many cases but will add extra heat. The other advantages may outweigh this though. Especially if you can fit enough to run ac.

I thought about heat, but only that it could lower the efficiency of the panels during hot summer days, not that it might transfer that heat to the camper. I'll have a pretty good insulation with sandwich panels made by a company with 30 mm of styrofoam inside in the middle and fiberglass outside. But I won't have an AC so it could be an issue tecnically.

Solar panels have an efficiency of about 17-20% Is all the other 80% waster in heat?
If that's the case 600W of solar energy will have 2400W of heat to dissipate, sounds like really a lot of heat that could melt plastic to be honest.
I'm very interested in understanding this.

I was thinking of a solution to make those panels dissipate heat, maybe with a thin aluminum sheet underneath? or maybe the hollow polycarbonate sheets, but I know those end up filling with dirt and dead insects and they might be a problem with the wind creating noise when going through. Any ideas?
 

Short_Shot

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Solar panels can hit 150F/65C with ease.

30mm of insulation seems like minimal effectiveness for that kind of temperature.

Also, the flexible panels tend to not be as durable with much shorter warrantees. With the right setup you can harvest that heat for water, but it's usually not all that practical in a mobile application.

I'd want a lot more insulation than that if I were trying to use those personally.

I'm not entirely against them, but they have a lot of downsides.
 

Mcgivor

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Personally I'm not mobile, but if I were I would use heavy duty casement window hinges to provide a tilt, the advantages of tilt is not limited to production, but also shading from other rooftop appendages like vents or A/C units. Should partial shading be an issue on flat mounted panels, MPPT controllers are at a disadvantage to PWM and being distance is not a major factor often PWM would be the better choice.
 

filippomasoni

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Solar panels can hit 150F/65C with ease.

30mm of insulation seems like minimal effectiveness for that kind of temperature.

Also, the flexible panels tend to not be as durable with much shorter warrantees. With the right setup you can harvest that heat for water, but it's usually not all that practical in a mobile application.

I'd want a lot more insulation than that if I were trying to use those personally.

I'm not entirely against them, but they have a lot of downsides.
Is it possible to turn photovoltaic panels into "hybrid" solar heat panels as well? I've never heard of that, sounds great for a house application. Not practical for a mobile one though.

I thought 30mm of insulation was not bad for a camper box with no metal and zero thermal bridging. It's probably fine with 200W of panels but 700W could be too much yeah. I could make it 40mm like the floor, but I'm not sure if it's worth the extra weight. It's probably best to use a gap of air as an insulator since we are outside, but what kind of support do I need for that? It's all about weight, if it has to be too much heavier than eigid panels are probably the way to go. But I didn't want to put 60kg on top of the roof.
 

filippomasoni

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Personally I'm not mobile, but if I were I would use heavy duty casement window hinges to provide a tilt, the advantages of tilt is not limited to production, but also shading from other rooftop appendages like vents or A/C units. Should partial shading be an issue on flat mounted panels, MPPT controllers are at a disadvantage to PWM and being distance is not a major factor often PWM would be the better choice.
Can you explain more why MPPT are a disadvantage with shading compared to PWM ?

I'm planning on having the least amount possible of stuff on the roof to keep the center of gravity low. No AC and no storage, only one vent/fan and solar panels.
 

Mcgivor

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With MPPT the panels are arranged in series, any shading, be it full or partial can render a single panel void, therefore if a single panel disabled it renders the entire string void.

With PWM each panel is able to provide it's output independent of the others, so partial shading wouldn't affect the whole array, only the individual shaded or partially shaded one.

Being that mobile applications are in general relitivly short in distance, the wiring costs are minimized but the added cost of balance of system components with PWM, over current protection (OCP) etcetera has to be considered.
 

Boondock Saint

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I put 4 x 300w panels flat on top of my 7 x 14 cargo trailer conversion. I wish I had tilted them 'a bit' (5deg?) so the dirt would wash off over the frame's lip. As it is - they are flat so water pools on them and leaves dirt residue over the cells when the water evaporates.
Live and learn :)

THANKS. Can you please provide the links to the HW you used for this installation? Thanks in advance.


.
 

Short_Shot

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With MPPT the panels are arranged in series, any shading, be it full or partial can render a single panel void, therefore if a single panel disabled it renders the entire string void.

With PWM each panel is able to provide it's output independent of the others, so partial shading wouldn't affect the whole array, only the individual shaded or partially shaded one.

Being that mobile applications are in general relitivly short in distance, the wiring costs are minimized but the added cost of balance of system components with PWM, over current protection (OCP) etcetera has to be considered.
That is definitely not the whole story and running parallel panels with mppt is not necessarily a problem.

Bypass diodes are a thing.
 

Short_Shot

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In fact here's what a 100 watt suitcase panel, two 20 watt panels, and a 10 watt panel all in parallel got me on a day out where roughly 1/2 of said day was with my 3 small panels flat mounted and in the shade (hence only 94w peak from 150w)

You'll note it is an mppt controller.
Screenshot_20210703-195553.jpg
 

fratermus

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We all know tilting solar panels yield a better efficiency but is that worth it?

I overpaneled my flat array to deal with varying yields, which results in excess capacity under good conditions. I also have a couple of portables on a separate controller; they are primarily used when forest canopies or other obstructions are interfering with harvest. There are times when the small (200w) tilted portable array makes more power than the flat main array (750w) but when this happens harvest is already trivial, like at sunset.

My opinion on the matter is to take advantage of tilt if you can and it's not too much trouble -- but I wouldn't rely on it in vehicle-mounted systems to cover the solar nut.
 

filippomasoni

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I overpaneled my flat array to deal with varying yields, which results in excess capacity under good conditions. I also have a couple of portables on a separate controller; they are primarily used when forest canopies or other obstructions are interfering with harvest. There are times when the small (200w) tilted portable array makes more power than the flat main array (750w) but when this happens harvest is already trivial, like at sunset.

My opinion on the matter is to take advantage of tilt if you can and it's not too much trouble -- but I wouldn't rely on it in vehicle-mounted systems to cover the solar nut.
I didn't know about RVwiki that's so cool, thanks for sharing that!
Makes perfect sense, we can't rely on tilt in a vehicle, so it's better to overpanel.

From your picture I see you have a Ducato/Pro Master. What panels do you have? Looks like it perfectly uses the available space and it's what I'd like to but I can't find a European supplier with many options and decent prices
 

OffGridInTheCity

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THANKS. Can you please provide the links to the HW you used for this installation? Thanks in advance.
This guy (on ebay) sells rails and mounting hardware. They rails are short enough for 'regular' shipping. The rail kit + some extra fasteners is what I used.
He's been around over 3 years now - so I was able to buy extra fasteners recently that matched the original purchase a few years ago. Its nice when someone is around a long time so you can get compatible stuff down the road.

FYI
- On my roof I used IronRidge. Perfectly good system as well, just longer rail pieces that require expensive (freight) shipping.
- On my yard array I used universal strut and accessories - this also worked well.
 

Boondock Saint

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Thanks for that. I posted in one of my own threads about just using flat aluminum and two types of brackets for a low profile set, that will breach the distance from the edge of my roof.

.
 

Mcgivor

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That is definitely not the whole story and running parallel panels with mppt is not necessarily a problem.

Bypass diodes are a thing.

No its not the whole story which is why the words can and may were used, in leu of will.

Partial shading depends on how a shadow is cast, the orientation of the module itself and the cell arrangement within. Take a regular module with cells arranged vertically along its length, each row is in series with a bypass diode, should a single cell in a single row become obscured, that row becomes disabled. With the same arrangement, this time the entire horizontal portion, one or more cells in all rows being obscured, the entire module becomes disabled.

When the single module is part of a series string using an MPPT controller, it renders the ballance of models in the string void if the absence of the module's voltage input decreases the aggregate string voltage below the MPPT's requirements, thus dropping output. The same scenario with modules arranged in parrallel using a PWM controller would only affect the single module without affecting the others. Since its impossible to predict where or how a shadow will be cast in every circumstance, it's impossible to make a definitive statement, hense the deliberate choice of words.

There have beem many studies done on the subject, a simple Web search will link to them, it's worth the time to study the effects, particularly if shading is an issue in one's situation.

That is false.

Three words to make a point is a weak argument not worthy of an individualized response.
 
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