Flexible panels

Ger08 · Senior Member

Flexible panels

Brenda and Alan · Guru

We have had flexible panels now for 2 years and the best efficiency we have had in southern states in winter is 75% of panels rating. I think this is pretty good for any panel under the same conditions. All panels suffer from efficiency reduction as they heat up in use and a rigid panel with an air gap may run a little cooler, but the overall out put of both types would not be that much different. That said flexible panels are dearer than rigid but a hell of a lot lighter so to over come any perceived loss just fit an extra panel. One thing I would suggest if contemplating fitting flexible panels is to buy the best quality and stay away from el'cheapos.

Alan

Peter_n_Margaret · Guru

One seller tested flexible panels and concluded that air cooling the under side gave 9% better output.
There are reports of aluminium backed panels having more problems than plastic backed panels possibly due to differential expansion.

Cheers,
Peter

Ger08 · Senior Member

Thanks for the quick responses.

Aus-Kiwi · Guru

They are less efficient . But if your roof is curved ? They are ideal, some can be walked on . Fitted 20% more panel makes up for efficiency loss . Was thinking of fitting some flexable top rear of old bus conversion if panels where cheap enough . Using up space not used .,

Dunnp · Member

I put 5 100w flexible panels on van. Stuck down with Sikaflex 252. They worked pretty will for a while and occasionally saw 320-odd watts. But after about 6 months, max output was noticeably down (even accounting for seasonal differences). Under ideal conditions I could barely get 180w.

Some troubleshooting revealed 2 of the 5 panels were way down - one or two watts in full sun.

One test proved very interesting - I had one panel connected and it was producing 18w in full sun. As an experiment I poured a bucket of water over it to cool it down. Bingo 36w! As the water evaporated and the panel heated up, it gradually dropped back to around 18w again. So it seems heat is a big killer and having them glued down gives the heat nowhere to go. And the ceiling under the panels is noticeably warmer then elsewhere.

These 100w panels are the cheap plastic backed ones you can buy of evil-bay. I also have two 65w aluminium backed flexible panels glued elsewhere on the van. They seem more efficient (around 70w) and much less affected by heat. When I get a the chance I'll repeat the bucket of water test.

I also have a pair of 50w aluminium backed panels setup up as a folding portable setup & they also seem quite efficient.

While experimenting with different configurations before I glued the panels on the van roof, I managed to destroy one panel. The supplier replaced at no charge and it wrote it off as bad luck. But now I have 2 more dead ones so now exactly impressed!

I have removed four of the panels and in the process of refitting 2 with an air gap below to help cool them and also keep the heat away from the van ceiling.

Lessons: Be wary of cheap panels; they run hot and heat causes problems; direct bonding to the roof wasn't a great success; limited number of physical sizes available; expensive (per watt) but much much lighter than glass panels; metal backed panels seem better than plastic ones but harder to find and more expensive.

Still learning after all these years!

Phil

T1 Terry · Guru

I fit a lot of them, the latest job will be 20 x 100w panels. Had problems in the early days but it is all due to how they are mounted, don't glue them down as they need to expand and contract and the backing may expand at a different rate. Mount them via the eyelets, Lexan Thermoclear makes an excellent heat dispersing backing material. Quality isn't cheap but cheap is expensive in the long run so if weight is an issue then spend the $$. The last job out last week the 100w panels put out 5.25 amps @ 14v, 73% efficient and through a PWM controller, not bad for flat mounted in South Australian spring sun shine so again, quality makes the difference

T1 Terry

Dunnp · Member

Terry

What make & type of panel did you use? Plastic or metal-backed?

Phil

Krusty · Senior Member

I'm following this thread as if they're reliable it would solve all my problems.

T1 Terry · Guru

OK, a bit of an update. We have had a run of failures from the original shiny surface 6 eyelet mount type panels, still unknown if it was the mounting method used that caused the problem, but all the 8 eyelet dimple finished panels have performed well so far with no issues to date.
All the panels were plastic backed, the latest mounting method is via the 8 eyelets so no glue between the panel and the Lexan thermoclear so the panel is allowed to move with expansion and contraction independent to the Lexan thermoclear. In defence of the earlier type panels, it may have been the expansion of the thermoclear that tore the panel modules apart rather than panel failure as the panel that came unstuck on all but one corner and flapped for 200kms is still working like new in a proto type light weight portable panel set up I made using U shaped extruded aluminium for the outer frame and flyscreen door outside part aluminium lattice behind the panel to stop it from falling out of the frame. It is well over 18 mths of continuous use now and shows no signs of loosing performance or failing even in the harsh Mannum SA sun and heat.

T1 Terry