Solar Panel Airfoil profile for 3030 extrusion for roof mount

sebcbien

Member
Hello,
I designed this 3D profile to help save fuel.
I'm still waiting for my solar panels to be delivered, but in the meantime I designed and tested this:
It's a 3D printable wind deflector to reduce the front drag with an airfoil profile
The front air pressure is responsible for the most of the drag created by a solar panel.
I made this airfoil profile for the 3030 extrusion that will support my solar panels.
I designed to be printable with no supports and with minimal material.
Preferably print with ABS to prevent UV wear.
Snug fit, it wont go anywhere !
Length: 20cm
Photos of printed sample where 2,5cm for testing..
Can be cut to size.

For a front panel size of 57cm for example you can print 3 of them and cut 3cm at the end off one of them.

2021-01-05_14-31-56.jpg2021-01-05_14-34-21.jpg2021-01-03_23-19-47.jpg2021-01-04_00-25-24.jpg2021-01-04_16-02-14.jpg
 
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autostaretx

Erratic Member
Very good ...
Airfoil considerations played a part in my choice of a steel "pipe" roof rack to support my panels from the front, not from underneath.

Your design has a better airfoil shape than my cylinders.

Fan-to-Rack-Gap.jpg

My choice may survive low-hanging tree branches a bit better. (i can hope)

--dick
 

sebcbien

Member
Good idea !

If someone would like other sizes, I could try to find some time.
I'm thinking of making just a D profile to glue or screw.
Doing this my object took me around 8 hours with prototyping. The hardest part is to have a snug fit.
 

autostaretx

Erratic Member
It comes to mind that you want to put those fairings on the rear bar as well ... otherwise they're just (miniature) barn doors creating energy-robbing turbulence.

--dick
 

sebcbien

Member
Indeed, but they should have another shape (tail of a drop)
What is concerning me also is the "internal" edges of the solar panel. I already thought about something but I need to "take care" of the cooling
 

sebcbien

Member
Any ideas/suggestions on how to solve the aerodynamics of the internal frame without compromising airflow/overheating ?
The internal rear frame is the most inefficient one, even more than the external front one.

1610500885252.png
 

Dendisch

New member
Any ideas/suggestions on how to solve the aerodynamics of the internal frame without compromising airflow/overheating ?
The internal rear frame is the most inefficient one, even more than the external front one.

View attachment 167131
The effect can be reduced by directing most of the airflow above the panel just like front spoilers on cars.
 

sebcbien

Member
Interesting.
So better make like this ?
1610541909440.png

As we need to make the panels not too close to the roof for venting, will this huge spoiler not make things worse ?
 

Dendisch

New member
Interesting.
So better make like this ?
View attachment 167182

As we need to make the panels not too close to the roof for venting, will this huge spoiler not make things worse ?
I think as long as the sides allow for venting it is fine. Venting is only an issue while stationary. Poor venting results in lower efficiency with high sun intensity. My thinking is that I have enough power when the sun is shining strong, even if the efficiency is a little lower. Worst case is always overcast days or sun at low angle. Under the those conditions the venting is not making much of a difference. For that reason I installed my panels very close to the roofline. See https://sprinter-source.com/forums/index.php?threads/93498/
 
So you guys are attaching the solar panels behind the leading edge of the 80/20. Not sure how you do that. I was going to place them on top and use two hinges on each panel (they go front to back) so that I can lift them for cleaning, maybe prop them up for orientation on rare occasions. I can build with fiberglass and resin, maybe one of you aeronautical engineers could design a front edge shape for me. It will have to allow for hinging up in the middle. Well, now my brain is working on that instead of finishing out the van. :smilewink:

Gene
 

autostaretx

Erratic Member
If i recall correctly, the coefficient of drag for the T1N Sprinter was 0.39. I don't know the NCV3's.

All ya' got'ta do is plop your Sprinter in a 100 mph wind tunnel, put a spring scale at either end and turn on the fans.
Measure the force the wind is applying to the Sprinter with and without your solar panels.
Easy peasy.

--dick
(who (of course) actually did measure his Sprinter's stiction and rolling friction with a bathroom scale between the Sprinter and my hands as i pushed it from the rear)
 
Well, my fertile brain, which can't remember anything, had an epiphany. I can attach a wooden strip to the top and bottom of the cross member and attach a stiff rubber sheet to each just long enough to resemble the front of an airplane wing when attached to each. Now the rear one presents a horse of a different color.

Gene
 

sebcbien

Member
Aluminum air dam with leading edge tucked into the roof indentation. Door edge trim avoids metal to metal contact.

View attachment 167389
Hi, I saw your design, very well executed, congrats ! :thumbup:
That said, I'm not sure that the added front surface is beneficial in regard of the small front surface of the solar panel.
The depression created will (I think) create a low pressure vortex on the sides of the panels and at the end.
I also asked here on a forum more aerodynamics oriented: https://ecomodder.com/forum/showthread.php/reducing-drag-rigid-solar-panels-mounted-van-39013.html

The best would be someone who can use an aerodynamics software and study those solutions more scientifically.

I created this post because I think that with the number of fan/campers with solar panel, I found nowhere a real scientific experiment and recommendations.

A definitive answer on an easy DIY solution would save tons of fuel around the globe.
 

sebcbien

Member
So you guys are attaching the solar panels behind the leading edge of the 80/20. Not sure how you do that. I was going to place them on top and use two hinges on each panel (they go front to back) so that I can lift them for cleaning, maybe prop them up for orientation on rare occasions. I can build with fiberglass and resin, maybe one of you aeronautical engineers could design a front edge shape for me. It will have to allow for hinging up in the middle. Well, now my brain is working on that instead of finishing out the van. :smilewink:

Gene
Hi Gene,
I will simply drill a hole trough the 3030 and the solar panel aluminium profile and bolt them with loctite.
I also plan to do a lifting setup with 3030 hinges attached to the sprinter roof rails

1610656882495.png
 

gltrimble

Well-known member
Hi, I saw your design, very well executed, congrats ! :thumbup:
That said, I'm not sure that the added front surface is beneficial in regard of the small front surface of the solar panel.
The depression created will (I think) create a low pressure vortex on the sides of the panels and at the end.
I also asked here on a forum more aerodynamics oriented: https://ecomodder.com/forum/showthread.php/reducing-drag-rigid-solar-panels-mounted-van-39013.html

The best would be someone who can use an aerodynamics software and study those solutions more scientifically.

I created this post because I think that with the number of fan/campers with solar panel, I found nowhere a real scientific experiment and recommendations.

A definitive answer on an easy DIY solution would save tons of fuel around the globe.
My goal was not so much aimed at aerodynamics as it was at noise reduction. My air foil was a success with regard to noise reduction. I believe my design is still more aerodynamic than what you are proposing. Any air flow under the solar panels is going to create a large amount of turbulence unless you completely covered the bottom of the solar panels. You then have to deal with other obstacles such as the roof fan for any chance of laminar flow between the panels and the roof. Better to just direct a smooth air stream over the panels as suggested above by @Dendisch.
 
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Dendisch

New member
Hi, I saw your design, very well executed, congrats ! :thumbup:
That said, I'm not sure that the added front surface is beneficial in regard of the small front surface of the solar panel.
The depression created will (I think) create a low pressure vortex on the sides of the panels and at the end.
I also asked here on a forum more aerodynamics oriented: https://ecomodder.com/forum/showthread.php/reducing-drag-rigid-solar-panels-mounted-van-39013.html

The best would be someone who can use an aerodynamics software and study those solutions more scientifically.

I created this post because I think that with the number of fan/campers with solar panel, I found nowhere a real scientific experiment and recommendations.

A definitive answer on an easy DIY solution would save tons of fuel around the globe.
I found an interesting paper studying roof rack designs (https://www.beta-cae.com/events/c8pdf/6D_2_CALDICHOURY.pdf). The study was done using a Sprinter model and found 8 % difference between their initial (bad) design and the optimized design.

Unfortunately the study doesn't directly address the benefits of a leading edge air dam as used by @gltrimble. I think there is not a single answer, because the drag reduction depends on the spacing between panels and roof, or in other words, how much extra front surface is added. For small gaps typical for panels the dam eliminated air turbulence due to the poorly shaped underside of the panels. A key benefit of this is the reduced wind noise that @gltrimble noted.
 

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