Roof Temperature

[deadwood]

I was putting some lap sealant on my van roof today around my heater vent. As I was up there I had to put a towel down so that I didn't burn myself. So I took out my thermometer to get an idea what the roof temp was. A little background: My van is charcoal gray (so it definitely brings on more heat). I live in AZ and it was 109 out today when I took the readings. 

Roof temp on the metal: 170
Temp of my solar panel: 145
Temp of the inside of my my ceiling panel: 109

I was surprised at how hot the roof was. I have taken the temp of the side of the van numerous times and in the sun on a hot day it can be around 130. So seeing 170 on the roof was interesting. I was impressed in how well insulation works. My ceiling panel was the same temp as the outside air. Not sure what to think of the solar panel only being so much lower then the roof metal. The panel is black so I thought it would be around the same as the roof. 

I do have one large 315 watt solar panel. It takes up a nice chunk of real estate up there which shades a good part of the roof below it.

 

[highdesertranger]

what was the temp of the roof under the shade of the panel? highdesertranger

 

[Boyntonstu]

Temp of my solar panel: 145

Perfect to cook steak Sous Vide

 

[highdesertranger]

yeah but when you put your steak on that panel it will basically drop you power output to near zero. considering that this steak is going to take hours to cook I don't believe the trade off is worth it. highdesertranger

 

[Boyntonstu]

yeah but when you put your steak on that panel it will basically drop you power output to near zero.  considering that this steak is going to take hours to cook I don't believe the trade off is worth it.   highdesertranger

Are going to cover the entire panel with a steak or only a tiny portion of it?

I would place the steak beside the panel and gather its heat.

 

[highdesertranger]

do your homework. even partial shading as in one cell will kill a whole panel. highdesertranger

 

[Boyntonstu]

do your homework.  even partial shading as in one cell will kill a whole panel.  highdesertranger

You are correct.  I did not know that even a leaf would be a shut off valve.

That is why I wrote:  "[font=Verdana, Arial, sans-serif]I would place the steak beside the panel and gather its heat."[/font]

[font=Verdana, Arial, sans-serif]We are talking about 1 Amp per hour.  No a big drain.[/font]

 

[deadwood]

what was the temp of the roof under the shade of the panel? highdesertranger

I didn't think to check under the panel. I'll probably be double checking my work tomorrow. I'll try and remember to check that. It would be interesting to see the difference the shade that the panel is making.

 

[John61CT]

Wow that is hot!

Your solar panel would both produce more power and likely last longer if you could find ways to get those temps down.

If I lived there I'd base my build off an ice delivery truck or something.

 

[frater secessus]

This calculator shows 145F is a bit cooler than expected, assuming it's correct.  That temp is associated with ambient 89F.  

At OP's ambient 109F the expected panel temp in full sun would be 164F, losing 72.954W to the panel temp being far above 70F.  

The other day when I was adjusting the mount I had a similar, albeit unmeasured experience.  The white van was too hot to touch for more than a few seconds, the panels were too hot to touch at all, and the roof area under the panels was very warm but allowed unlimited skin contact.

 

[John61CT]

I can see why it's not recommended to bond the semi-flex panels directly to the roof, bet that significantly reduces their lifespan.

Not to mention harder to replace when the time comes.

 

[frater secessus]

I understand the amorphous bendy stuff (while having lower Vmp to start with) is less affected by heat. I don't have any to test with, but if I were car-dwelling I'd give them a serious look.

 

[John61CT]

I believe much much lower power output per area, probably biggest factor to look for in mobile usage.

 

[frater secessus]

The output is lower for sure. But it would mount on a trunk lid or roof without much drama.