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Topic: How hot do solar panels get ?

mikael

11/12/2014 at 11:04pm
Location: WEST DORSET
Outfit: Nissan NV200

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As there are a proliferation of different types of solar panels ranging from flexible through to rigid type, my question refers to the potential damage to fibreglass pop up roofs. Solar panels get hot as they generate and store electricity, but how hot do they get ? If I chose flexible panels which can be glued to the roof, will these melt the fibreglass ? Also if one chose rigid ones connected via mounting frames, do these cause wind whistling ? I think the flexible type look better. Any advice gratefully received.

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-mojo-

12/12/2014 at 1:16am
Location: None Entered
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Quote: Originally posted by mikael on 11/12/2014
Solar panels get hot as they generate and store electricity

Solar panels don't generate any significant amount of heat themselves, and they certainly don't store electricity.

They get hot because the sun heats them, and they can get significantly hotter than other materials around them because they are typically almost black, which means they absorb heat from the sun well.

I have a 100W flexible panel bonded to my fibreglass roof, and this is standard practice for the company that made my conversion. They have been doing this for many years, and I've never heard of a bonded-on flexible panel getting hot enough to damage a fibreglass roof.

There does seem to be a widely held misconception that getting hot damages solar panels, and it is true that their efficiency drops steadily as they get hotter. However, this effect is completely reversible as the panel cools down again.

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mikael

12/12/2014 at 9:36am
Location: WEST DORSET
Outfit: Nissan NV200

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Thanks Mojo,

Just been fed a line from my converter ! I think he has a reason he wants to fit rigid type and advised the heat from flexIble bonded solar panels may damage the fibreglass roof. I have read there may be delineation where the panel peels away a layer of fibreglass. I'm not read up really at all on the subject. Just want a solar panel that will last for a good 10-20 years or so. I think the bonded type look better anyway. Perhaps if someone can enlighten me. I think maybe my converter has a solar panel supplier who only does the rigid type.

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pepe63

12/12/2014 at 11:11am
Location: Shropshire
Outfit: Toyota Granvia (Wellhouse)

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I would've thought that just a big a consideration would be whether or not the adhesive used was going up to taking such temperatures?..and whether or not it could cope with any differing expansion rates...?

..I used some Sika' 512 to fasten the outer section of my lightweight "plastic" mushroom vent. I carefully keyed the area and cleaned it down with panel wipe etc and still it came loose and leaked..

I wondered whether it was down to the vastly differing expansion rates between steel roof and the plastic vent, causing the Sika' to let go ?

-mojo-

12/12/2014 at 2:13pm
Location: None Entered
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Quote: Originally posted by pepe63 on 12/12/2014

I wondered whether it was down to the vastly differing expansion rates between steel roof and the plastic vent, causing the Sika' to let go ?

Yes, almost certainly - as you say, they have significantly different expansion rates.

Fortunately the situation with a fibreglass roof is different - the substrate for most flexible panels these days is aluminium, and this has a thermal expansion rate that is very similar to fibreglass.

The one real disadvantage of bonded-on flexible panels is that it would be a lot harder to remove and replace if the panel fails than with a rigid, framed panel. I have never seen any evidence that flexible panels are any more or less reliable than framed ones - so that aspect is just a gamble as far as I'm concerned. But if mine fails, removing it will not be easy, as Sika-221 (the variant I used) is pretty tenacious stuff...

iggycamper

12/12/2014 at 6:54pm
Location: Devon
Outfit: Dreamer(Rapido) D.55 select Plus

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Have had 2 vans with a rigid framed solar panel. The actual surface never feels really hot, at least in british summer sunshine. (E.g. no hotter than than say the roof of a black car ...)

Was advised that framed panels - with a air gap underneath - will always be more efficient than a flexi-panel bonded directly to the roof as there will be a greater degree of air-cooling to the panel itself.

Have never noticed any 'wind-noise' and appearance not really a problem - even when viewed from our bedroom window! But agree that bonded flexi panels would look better on a smaller campervan.

P.s. Wish I was young enough to consider needing a solar panel to last up to 20 years, mikael!

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mikael

12/12/2014 at 7:02pm
Location: WEST DORSET
Outfit: Nissan NV200

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To all
Thanks for the advice and info offered. Am now looking more towards a rigid panel as if a flexible bonded one failed, trying to remove may cause too many problems . Also, I see the logic in more efficiency achieved by rigid because of air cooling. Maybe a wind deflector to eliminate potential whistling ? To Iggycamper - not that young (60th year) just hoping for longevity !

Ciao for now

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pepe63

13/12/2014 at 4:09pm
Location: Shropshire
Outfit: Toyota Granvia (Wellhouse)

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On the subject of the mounting panels(rigid), rather than bonding on "size specific" mounting brackets, I think I 'd rather something that allowed some degree of variation/adjustment, so they could accommodate a different panel size/type IF a panel ever failed/got damaged...

-mojo-

13/12/2014 at 5:08pm
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I'm not convinced that the reliability is such an issue - I've not heard of significant numbers of failures, of any type, flexible or not.

The efficiency really isn't (IMO) an important factor. When the sun is blazing down and your panel is putting 5 amps into your batteries, you won't really care much whether it's 5.1 amps or 4.9 amps. You only really care about efficiency when the sun is ~not~ blazing down, and then the temperature effects will be almost nil.

The thing that really puts me off a rigid, boxed panel is the aesthetics. On a high top van it's not so bad, as it's less visible, but having one sitting 40mm or more as a rectangular box above a curved pop-top just looks (to me) horrible.

And the other thing is that I didn't want holes drilled in my roof for the fixing brackets. Some people glue these on, but I would not trust that, given the windspeeds that it will have to deal with...

mikael

13/12/2014 at 7:35pm
Location: WEST DORSET
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To Pepe63 - thanks. If I do go with rigid, a form of flexible mounting is a very good point.
To Mojo - I agree with your point as to their reliability on reading up. It certainly has thrown a cat amongst the pigeons whether to go rigid or bonded flexible. I did see quite a few bonded type at the recent NEC show in particular the Nissan NV200 electric version which had a very neat panel bonded directly to the pop up roof. As I too am having an NV200 converted, I am now pulling towards this type. However I might have to go to a different fitter for this.
My only concern is if for any reason I need to replace the panel whilst I have the van, can the panel be removed without wrecking the roof, or can another panel be glued either on top or where the previous panel was located so the job doesn't look like a dogs dinner. A new roof is expensive !
Ciao

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-mojo-

14/12/2014 at 12:58am
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Quote: Originally posted by mikael on 13/12/2014
My only concern is if for any reason I need to replace the panel whilst I have the van, can the panel be removed without wrecking the roof, or can another panel be glued either on top or where the previous panel was located so the job doesn't look like a dogs dinner. A new roof is expensive !

If you need to replace the panel, it should not (at least in theory) be significantly harder than the replacement of a windscreen - both bonded in place with a PU adhesive sealant, and cut off using a steel wire.

When I fitted mine I deliberately put it on fairly deep fillets of sealant so that it sits up a couple of mm - which should make removing it with a cutting wire easier. But I hope I never need to find out whether the theory is correct...

Not sure if this will work, but if it does, this is what my DIY fitted one looks like:

[/IMG]

mikael

14/12/2014 at 2:15am
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Thanks Mojo,

Thanks Mojo,
I see exactly what you are saying. It seems the answer to my problem. I always thought a flexible bonded panel was the correct decision. However, I just needed the right practical advice so I could make right informed decision. After all we are not born with the knowledge, and need to get the answers in the best way we can. Great site.
Ciao

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pepe63

14/12/2014 at 7:11pm
Location: Shropshire
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That flex panel looks really neat.

...and as you say the reliability and efficiency is up to scratch, on something T5-like, it'd be hard for anyone to argue in favour of a rigid panel (which after all, can resemble the door from a pub's drinks cooler! )

iggycamper

15/12/2014 at 3:03pm
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Agree - looks really good Mojo!

Just a couple of final thoughts .. In the unlikely event of such a bonded panel failing I would be tempted to fix a new one on the top rather than trying to remove old one.
On same subject I don't like the idea of removing old stuff to fit on a new van - can give problems and not good for new owner to see sometimes badly filled holes etc!

My current 100W solar panel with a MPPT controller works really well, charging both batts even in 'UK sunshine' and looks good, at least the bit you can see from the ground!(Fitted professionally by a respected specialist company.)
The company 'screw and glue' the panel and said it would not 'fly-off' at speed even without the screws. (Can I quote you on that said I :-) ) There was no problem with the Adria warranty either. Note that leading edge of panel is fitted with a spoiler so look quite neat should a very tall person pass by ...

All that said I agree with all that the only way to go with a camper-van - especially a rising roof one, is for a bonded panel. (Understand these have been used on boats & narrow-boats for years.)

All above assumes of course -
a) You really need a solar panel ...
b) You have got plenty spare cash!

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