A newbie seeks fridge guidance

I'm not sure if you're fully set on how you plan to add solar but I just finishedy 350w solar panel project and I am very pleased with it. My thread is on here also and I pretty much just copied Titos work and recommendations. There's a few tweaks I'm going to do to breaker sizes but overall did it in a day and was very simple with the preexisting wiring etc.

Here is his video link

https://youtu.be/uJIEXhnF8MU

Freddydcruz said:

I plan on doing this exact same set up with my Grandby (to be delivered next fall). I’m still in the process of figuring it all out, but trying to come up with the most economic solution with the greatest flexibility. The camper is coming stock with (1) 12V and I planned on having mainline overland handle the battery and solar system. Do you have any recommendations on the best path forward?

I’ve been looking at the bluetti AC300 it EP500pro which can double as an emergency system for my home. What system are you looking at?

Click to expand...

I have not looked at portable units in depth; However, I'd recommend staying away from all chemistries other than LiFePO4
mainly because of cycle life. I hear Jackery is going to a big announcement and sale in a couple days.

Just a crazy idea I had is to buy a couple more 50/60ah bicycle packs and swap them back and forth between the camper and my diy power box. Our camper can run a couple days on a 50ah battery. Having three would offer infinite possibilities and configurations.

Most likely, I'll buy a 100aH SOK battery - with heater - for the camper when the time comes to replace the factory AGM's.

Cbessler, et al,

Relative to the video and Tito's mounting technique for the semi-flexible solar panels:

Solar panels get hot. If that heat is not removed somehow it can cause damage leading to failure of the panel. This premature failure problem due to heat has been seen in many semi-flexible panels that were bonded directly to RV and camper roofs.

People assumed that the Aluminum roof was thermally conductive but failed to consider that the roof coatings and the adhesives might not be (typically aren't) thermally conductive. As a result the back of the panel gets very hot causing material degradation of the panel and premature failure.

A problem is that the adhesives typically used in home construction and RV/Camper work are non thermally conductive. In addition the roof coatings and sealants on RV and camper roofs are typically not very thermally conductive. This is why most manufacturers recommend mounting any solar panel with an air gap between the back of the panel and the mounting surface.

Getting to Tito's mounting approach:

Polycarbonate has a very low thermal conductivity. In fact it is a superior insulator material. As a consequence I suspect that the channels in the polycarbonate sheet are not facilitating much thermal transfer but the way he bonded it to the panel with only a couple of long beads of adhesive does leave a small air space between the Solar panel and the polycarbonate sheet. However, Sikaflex 715 is a silane terminated polymer. These types of adhesives generally have low thermal conductivity unless a thermally conductive filler material such as Al203 is added to it. Again a good insulator not a thermal conductor.

I suspect that the adhesive contact lines will get hotter than the surrounding solar panel areas because of the low thermal conductivity of the adhesive thus creating local hot spots because the heat will not be removed very well. This could lead to discoloration along the adhesive lines and ultimately local failures in the solar panel over time.

Another consideration is that polycarbonate generally has poor resistance to Solar UV radiation which causes it to become brittle and crack and fall apart.

It seems to me that:
1) Mechanical attachment with a fastener and/or a thermally conductive adhesive is best for attaching the solar panel to another surface. Thermally conductive adhesives tend to be a specialty material and often significantly more costly.
2) The best supporting surface would be a good thermal conductor such as bare Aluminum.
3) Perhaps fastening the panel directly to a supportive Aluminum frame or bonding it to a thin Aluminum sheet would allow the appropriate conduction of heat from the hot back side of the solar panel and also provide a secure mounting configuration that will hold up over time and seasons

I like the use of the Aluminum L-track (T-Track) to hold the panel assembly to the RV roof but I wonder if it would be better used in short lengths rather than long lengths to minimize mechanically "working" the bonded interface to the camper roof and gradually breaking down the bonded connection which may result from the constant and frequent length changes of the Aluminum channel over large temperature swings from day to night and season to season as it expands and contracts.

Aluminum contracts and expands 0.0000129" per degree F. Consider that the temperature change of a piece of Aluminum exposed to direct sunlight and then a clear night sky can easily swing 100 to 150 degrees F every 24 hours. A four foot long piece of Aluminum channel will shrink by as much as 0.093" and expand 0.093" each 24 hour period. That mechanically exercises the adhesive interface a lot in shear and can lead to de-bonding.

Now the adhesive used is sufficiently compliant that it should be able to accommodate the minimal length changes of a short piece of Aluminum track of say 6" or so without breaking down.

An alternative is to add mechanical fasteners to ensure that if the track starts to de-bond that it cannot peel off or just do away with the adhesive altogether and rely on mechanical fasteners.

All adhesives even those extremely strong in tension and shear tend to be very weak in peel and once peeling starts they can come right off very easily.

Crazy Aerospace engineer thoughts.

Craig