43 replies to this topic

[ri-f]

Jack, I do think that there will be little change in the temp coefficient, since you are only providing an air gap the height of your velcro straps. You'd likely see more of a difference with, say, a 1-2 inch gap as if you had mounted the panels on an aluminum z-bar frame. I know that scientific papers in this subject matter indicate that a 4 inch free-air gap is ideal for thermodynamic flow to dissapate heat, which will improve cell efficiency. I
Of course that is not practical for a camper roof install. But 1-2 inches is practical and typical. So, just as a test, on a sunny hot day, it might be interesting to temporarily un-velcro one of your panels and raise it 1 to 2 inches off the roof with some 2x4 blocks, and take some measurements that way. Then you'll know if there is any significant difference in incoming current between that and the panels with no air flow. If there was, say, a temp differential that resulted in a 20% efficiency increase, that would be valuable info. Then you'll really be having some fun! 👍

Rich

Edited by ri-f, 17 February 2021 - 12:54 AM.

[Stokeme]

Here is a link to a long build thread that started with mounting flex panels. Started out to cut & stack (like Lincoln Logs) aluminum tube attached to my Yakima tracks. Later welded by a friend but original idea was functional. My 2- flex 100W panels have held up surprisingly well after 3 years, they ably maintain my parallel 150ah LFP4 system. Not quite as efficient now but they were cheap commodity panels from Solar Blvd. I list all materials & hopefully my links are still current. I wanted airflow under my panels & an easy roof lift. Frame weighs ~5lbs, 2- panels=~10lbs, so total roof solar is ~15 lbs.
I purchased 2 of these last year which have the top cells on the market, IMO, plus improved weather resistance. I will probably install them next year. Will have to slightly reframe or add a brace as they are not the same dimension. Found $20 discount code (Cseeker), worked last year. Consideration ... if u need to replace a panel(s), what will be required?

https://www.expertpo...00w-solar-panel

https://www.wanderth...+takes +village

Edited by Stokeme, 17 February 2021 - 10:14 PM.

[RC Pilot Jim]

We used 3M VSB 4950 tape. to tape our 26 pound Renogy 150 pound soler panel to the roof of our Eagle which is mounted on our Tacoma full time February 2016. 36,556 miles ago.

I check it onece a month and it is still solid on the roof. 

 

If you want to see the details click on the following link:  Renogy solid panel glued to roof.

[ri-f]

Like the j-box.

Rich

[Stokeme]

Yes, heartily agree with the j-box thought. It will not be fun but I will be replacing the SAE roof outlet with an MC4 outlet (w/extra cable) as that is such a superior connection. I had a SAE prong crumble off on my roof plug, last year, only a matter of time before the roof outlet crumbles off.

Edited by Stokeme, 16 February 2021 - 11:26 PM.

[ri-f]

Worth it, if you've experienced that level of corrosion. Good info. And good luck with the swap out.

Rich

[ntsqd]

I used a typical house wiring sealed duplex sized j-box on our old camper. That gave me room to install a two conductor terminal strip. I sealed it to the roof with 5200 and all wires exited through cable glands like RCP Jim's install. Might be where I got the idea from, don't recall. Looks like I never took a pic of it.

 

I'm OK with the MC4 connector, I don't like or trust the stiff wire that all of mine came with. That install was done before MC4's could be bought un-assembled.

[ri-f]

I used a typical house wiring sealed duplex sized j-box on our old camper. That gave me room to install a two conductor terminal strip. I sealed it to the roof with 5200 and all wires exited through cable glands...

ntsqd -  used to do exactly the same thing  (terminal strips) in a j-box. Never had any issues at all within the plastic, sealed j-box itself.  Even though I thought there could be a problem with condensation within the box, it never was an issue - connections were always dry and bright showing no signs of corrosion (and that was on the foredeck of a sailboat in an ocean environment with salt spray and waves washing across the deck). I've even used the bare minimum of butt connected wire covered only by weather proof heat shrink, exposed to the elements (and it worked fine for many years. The panels gave out but the wires were fine. For extreme conditions I used to use LanaCote on my electrical connections. My only issues were with delamination off my old flexible solar panels and corrosion of the connections under the sealed housing where the panel's wires exited. Of course, that was 20 years ago when flexible panels first made their exciting debut on the market and those panels typically came with bare wires and no connectors. I do believe that some of today's high-quality panels are much better when it comes to frustrating, physical delamination, and of course exponentially better when it comes to cell efficiency. So, originally I used semi-flexibles (for a curved deck), and then later used heavier weight, glass-covered rigid panels (where I had flat surfaces for mounting), and now back once again to the current generation of semi-flexibles, which have proven excellent, so far, mounted with z-bar aluminum on the roof of my camper. And while I like the idea of MC4 connectors or like you said, bare wires buried in a weatherproof j-box, I must admit that I have been using the FWC installed SAE to MC4 connection (with 90 degree bend) method and I have not had issues with either disconnection and/or corrosion. I've been in terrible hail storms, snow, rain, high winds, cold, hot, you name it, so far so good. If that changes, and I start seeing issues develop, I wouldn't hesitate to switch to a j-box, either with or without MC4s.

 

Rich

Edited by ri-f, 18 February 2021 - 07:23 AM.

[ntsqd]

The rigid panel that I put on our old camper came with MC4's and cutting them off voided any warranty. So I bought a pre-terminated jumper off amazon and cut it instead. Both jumper wires into the j-box's terminal strip. Then much more finely stranded plated marine wire down into the camper.

 

I too, worried about condensation in that little box and it didn't happen for me either. Didn't stop me from checking it periodically.

 

Now that I can buy MC4 terminals and terminate them myself I'm not sure that I'd bother with the terminal strip. I'd just bring the good wire out thru some weather/water tight wire glands and install the MC4 terminals directly.

[ri-f]

Now that I can buy MC4 terminals and terminate them myself I'm not sure that I'd bother with the terminal strip. I'd just bring the good wire out thru some weather/water tight wire glands and install the MC4 terminals directly..
 

Roger that.