Heat generated from solar panels

[Awjuhl]

I'm just starting my build, I have a heartland mpg travel trailer and it is curved like a tear drop. I would like to mount small tiles on it to take advantage of as much surface area as possible. I'm a bit worried about heat generated off the panels. Is there a way to insulate the back of the tiles so they dont melt the roof? Suggestions would be appreciated. 

Thanks

 

[B and C]

I spaced mine up from the roof about a 1/2 inch. Here is my solar build: https://vanlivingforum.com/showthread.php?tid=15681

 

[Awjuhl]

Looking at these, thinking of glueing them on.

 

[B and C]

Wow.  Have you even considered how you are going to connect all those together?  Going to take a lot of connections and wire routing.

Edit to add:  You are losing a lot of surface area from all those edges.  Flexible panels would be the way to go.  Have you measured your mounting surface to see how many watts worth you can fit (with wire)?

 

[Awjuhl]

Electrical is my thing, I can wire a row in series bring voltage up to 72volts. Higher volts means smaller wire. And no just know width of the camper is around 77inch. Debated flexible panels but my budget isn't much. Need money for the batteries. Scary expensive!!

I was thinking c channel, so these can side in the channel so they have space under them. Wire & air can pass under them. Makes them removable as well.

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[Seminole Wind]

general recommendation is to have at least 1 inch of clear air space behind panels for heat removal. i doubt you have to worry about melting you roof people glue down flex panels all the time. but with the higher heat you will lose production. it is just a fact that any and all panels produce less power as the temp goes up.

i only mention this next bit because you mentioned wanting more power from your limited roof space. those cells in the pic you posted look vintage. do you know the % efficiency if they are down around 15-16% or less (very likely) then buying some newer flat residential panels with efficiency around 20% would allow you to get a lot more power from your limited space. panels thes days are the cheap part. charge controllers and batteries hurt more. HDR recently posted about some 435 watt sunpower panels for $200 i think the company is santan solar. you might find the thread or just google them. these panels are over 20% efficiency.

 

[Awjuhl]

It's a combo thing. Limited roof space and curve of the roof, really would prefer not to put holes in the roof as well. I have a gift of making a simple job complicated...lol

Yes they do look dated and, I am still doing research. Thanks for the info.

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[maki2]

I would not glue anything to the roof. Glue them to a substrate and create larger panels out of the small ones. You could have a company with a roller former create long, curve aluminum tubes that go along each side of the roof and then span those sections of panels between those outer rails.

 

[gchristi1]

Why would the watts/meter^2 reaching the roof of your tear drop be greater with solar panels as opposed to without solar panels?

I assume you are addressing a common problem, I'm just having a problem visualizing why it wouldn't be cooler seeing how the the panels reflect some energy and transfer some energy out in the form of electrical power.

I know it's good to keep the panels cool if possible for better efficiency.

 

[Awjuhl]

Panels are traditionally black with out sufficient ventilation they will heat up what they are mounted to, roof of my camper is composite and foam I wasn't sure if it would melt it.

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[Seminole Wind]

Panels are traditionally black with out sufficient ventilation they will heat up what they are mounted to, roof of my camper is composite and foam I wasn't sure if it would melt it.

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the glue down flex panels are quite popular on boat decks. these are glued to foam cored fiberglass all the time. i hear lots of people commenting/complaining they get too hot to walk on with bare feet but never heard about anyone melting their deck

 

[tx2sturgis]

Has anyone tried bonding the flexible panels to a sheet of coroplast (corrugated plastic) and then bond that to the surface of the trailer? 

With a bit of air in the 'flutes', this might work as a thermal barrier, or at least, a partial thermal barrier. 

I haven't tried this myself, but it might work...

 

[Dingfelder]

They sure look like a major weight increase for a little teardrop trailer.

 

[Gr8ful]

I'm putting the 4 320 watt panels, batteries,charge controller all on my alum snomobile trailer putting it in the sun & keeping the ambo in the shade. When I'm moving I'll be plugged into the 250 amp altenator. The panels will be on frames stacked on the trailer so I can set at the correct angle to the sun off one side of the trailer. The ambo's wired for 120v, 12v, insulateded, plumbed for suction, air, oxygen.

 

[DanDweller]

Has anyone tried bonding the flexible panels to a sheet of coroplast (corrugated plastic) and then bond that to the surface of the trailer? 

With a bit of air in the 'flutes', this might work as a thermal barrier, or at least, a partial thermal barrier. 

I haven't tried this myself, but it might work...

Anyone?  This sounds like a great idea.  I'm searching through this forum trying to find out whether flex panels are worth getting.  Bad reviews because of overheating kind of turned me off to flex panels, even though they are what I would prefer since they don't stick up too high off the roof, affecting fuel economy.  Have they improved in the last year or two?  What is the actual recommended way to mount them?  

Anyway, a layer of corrugated plastic sounds great since it doesn't raise the profile too much.  I wonder how would it sound while driving?  While stopped in the sun, perhaps the plastic could end up getting too hot and melting?  If not, it would also help cut down on the transferring of heat from the solar panels to the vehicle body.

 

[B and C]

I used the packing closed cell foam that came with the panels to make 2" squares mounted to the back of my flex panels. This raised them up from the roof a little and allows for airflow underneath. I then fastened them down with industrial strength velcro around the perimeter of the panel that left a gap at the ends for airflow. It has been holding well for over three years now. Be sure to thoroughly clean (I used windex) both surfaces before sticking the velcro down.

 

[maki2]

Solar panels nowadays are a lot more efficient and a lot less labor to install. You will be saving on the cost of the wires and the cost of the adhesives. It simply does not make economic sense to install those archaic voltaic panels. Some projects will not give you a good return for the effort involved and what you are presenting is one of those types of projects. Becoming "green" by recyling something that does not give you as much power as a newer option that produces considerably more energy as well as having a longer life span of use is not a very green thing to do. Plus you will need to buy adhesive and that installation will be next to impossible to ever remove without the use of a lot more environment harming chemicals as well as the cost of yet more chemical products to repair the damage to the roof caused by the installation and remove of the inefficient panels.

 

[future_vandweller]

Anyone?  This sounds like a great idea.  I'm searching through this forum trying to find out whether flex panels are worth getting.  Bad reviews because of overheating kind of turned me off to flex panels, even though they are what I would prefer since they don't stick up too high off the roof, affecting fuel economy.  Have they improved in the last year or two?  What is the actual recommended way to mount them?  

Anyway, a layer of corrugated plastic sounds great since it doesn't raise the profile too much.  I wonder how would it sound while driving?  While stopped in the sun, perhaps the plastic could end up getting too hot and melting?  If not, it would also help cut down on the transferring of heat from the solar panels to the vehicle body.

This response is to all the posts in this thread on the topic of heat loss.  There's a fundamental difference between how rigid, glass-on-top panels and flexible panels lose heat.  The rigid panels lose heat thru the back since the 3 mm glass acts as a high resistance thermal path.  Hence the recommendation for an air gap below the panel.  Flexible panels lose heat thru the Sun facing side since the thick polymer backing acts as an insulator.  Mounting flexible panels by gluing them to the support substrate is not going to limit their performance.

 

[DanDweller]

This response is to all the posts in this thread on the topic of heat loss.  There's a fundamental difference between how rigid, glass-on-top panels and flexible panels lose heat.  The rigid panels lose heat thru the back since the 3 mm glass acts as a high resistance thermal path.  Hence the recommendation for an air gap below the panel.  Flexible panels lose heat thru the Sun facing side since the thick polymer backing acts as an insulator.  Mounting flexible panels by gluing them to the support substrate is not going to limit their performance.

I see, thanks for clarifying that   So, about their performance, can you say anything about that?  Have you tried them?  Thanks.

 

[future_vandweller]

I see, thanks for clarifying that   So, about their performance, can you say anything about that?  Have you tried them?  Thanks.

Flexible panels use thinner (60-80 microns) mono-crystalline silicon cells vs 150-200 micron thick cells of the rigid panels.  A brand new flexible panel can be almost as efficient as rigid panels - 'almost' because thinner cells don't capture as many photons as thicker cells.  However, after a year or so in use, the thinner cells develop a number of cracks, essentially becoming poly-crystalline cells.  The cracks impede the flow of electrons liberated by the PV process, leading to a loss of current & voltage.

In addition, tot he above limitation, the clear, protective top coating becomes less clear with UV exposure and decrease the amount of light reaching the cells (~3-5% over a few years).  Add to this, surface scratches other mechanical damage that scatter light away from the cells and you have 10-20% drop in power production over a few years.  It'll take 20-25 years for a similar loss in good rigid panels.

I have a few flex panels and have used them.  I like them for what they offer - light weight, portability & ease of storage.  I also have rigid panels.