Solar panel placement question

[upgrader]

The available space on my 21’ Travel trailer’s roof limited me to three 100 W panels. However, Rich Solar now offers a “slim” 100W panel. The panel’s dimensions: 58.7 x 13.8 x 1.2 in fits nicely on the very front of the 8’ wide roof. It would sit 2-3” from the leading edge of the trailer.

A forth panel would allow me to connect the panels in series & parallel. I have always wanted a forth panel. This has advantages when one of the panels is in shade.

My question: is it safe to place a panel across the very front of a travel trailer’s roof? I have not seen any pictures of panels located that close to the front of the roof.

 

[RoadTurtle]

will the panel be slightly tipped up from front to rear, acting like a spoiler? I like to place panels all the way to the side edge of the trailer, but in the front, putting it back a bit as you're planning would allow air to go up and over the panel.

 

[Reed Cole]

Maybe less aerodynamic, maybe more likely to have issues driving under low hanging tree limbs.

 

[0truck0]

2-3 inches from leading edge will be fine as long as it sits low. I would go 3, and 4 if thats an option.
No more than 1/2 inch gap under, and I would do less for a leading edge mount, maybe even 1/8 inch on the front and whatever on the back (1/2, 3/4) so the front cannot catch much air under the panel.
If you had the panel on a full sheet of plywood and 2 feet of nothing under the plywood and hit highway speeds where there is no diverted air to flow up and over the plywood, then yes, you would see direct highway speed winds under the panel, but that you have 7 feet of wall at the front of the camper means that air has to go somewhere, and it goes up and way over and swirls around, so there is no direct laminar flow of air at highway speeds.
OR if you were talking about mounting it on a sports car 3 inches from the windshield then you would catch a lot of air under as the front of a sports car (hood to windshield to roof) is way way way more aerodynamic and will not see the turbulent air that a camper would.
As the airflow hits the front of the camper and finds the sharp, yes, very sharp even though it may look rounded and aero, sharp transition to the flat roof the air becomes turbulent. The roof sees a lot of turbulence more than direct wind. Near the rear the airflow will become more laminar, but then hit the transition to the back wall and turbulence at the rear wall is a big aero drag on your mpg's, but thats another story....

edit**
This aluminum angle iron at the front edge would eliminate any air issues. I dont have front pic, but this is what is at the front of panel also. Mine far away enough so I did not do this for speed air, rather to keep the long side of the panel as the air gap for venting, and secure it with the short side.

 

[Rocketman]

Yea more solar!!!

2 comments:

First, the way you talked about the new panel - it sounds like a different panel than the other three - how close are the Vmp and the Isc? If they are different there will be a penalty hooking them up together - if you don’t know how to figure that out just post the specs for both panels and I can walk you through it.

Second, I agree that the lower you can get the front panel the better. If you can’t get it as low as you like add an “air deflector” to the front of the panel. Angled would be better - but an upside down angle aluminum would work too.

Good Luck

 

[upgrader]

Yea more solar!!!

2 comments:

First, the way you talked about the new panel - it sounds like a different panel than the other three - how close are the Vmp and the Isc? If they are different there will be a penalty hooking them up together - if you don’t know how to figure that out just post the specs for both panels and I can walk you through it.

Second, I agree that the lower you can get the front panel the better. If you can’t get it as low as you like add an “air deflector” to the front of the panel. Angled would be better - but an upside down angle aluminum would work too.

Good Luck

@Rocketman: thanks for this post. You’re right, I am thinking of getting an entirely different panel.

Here are the specs for each panel.

Looking forward to your response.



EXISTING PANELS x 3

HQST Compact Design 100w Mono
Specifications
- Maximum Power: 100W
- Maximum System Voltage: 600V DC (UL) - Open-Circuit Voltage ( Voc ): 24.6V
- Optimum Operating Voltage ( Vmp ): 20.6V - Optimum Operating Current ( Imp ): 4.85A - Short-Circuit Current ( Isc ): 5.28A
- Weight: 9.92 lbs
- Dimensions: 39.65x19.61x1.18 in
PROPOSED NEW PANEL - long edge will lay across the rooftop’s front section

 

[Isaac-1]

You can use this calculator to determine mismatch losses in various wiring configurations https://footprinthero.com/solar-panel-series-and-parallel-calculator

In this case with 3 old and 1 new panel, it looks like parallel or series are your only viable options with less than 4% losses, series/parallel, and parallel /series, both get hit with circa 50% losses. Note that series only puts you at 81.3 volts, so if you go with a 100V max MPPT controller, you could be bumping into that 100V max in colder temperatures,

 

[Rocketman]

@Issac-1 I think there was a mistake made…

The way to figure out the losses yourself… (you can also do this exercise with matching panels too).

Volts * amps = watts

In series - volts add - use the lowest amps
In parallel- amps add use the lowest volts
Use Vmp and Imp

So if you connect two of you old panels in series
V= 20.6+ 20.6= 41.2v A=4.85
Connecting an old and your proposed panel
V=19.5+20.6=40.1v A=4.85 (lowest)

Connection those two into parallel
V=40.1 (lowest) Amps= 4.85+4.85=9.7a
40.1v * 9.7a = 388watts

So adding that different panel you have a 12w penalty 12/400 = 3% penalty.

Only you can decide if a 3% penalty is Ok for you - (it’s actually not bad when mixing panels). Look around you may be able to find a different 100w panel that fits with a lower penalty- but you may not either - fit is often the most important thing on RV’s.

One more option… get another SCC and run the new panel directly to it - you will gain 3% - but only you can decide it that is the best option for your RV and budget.

Good Luck