Solar Tilting Logic

[Yarome]

Just my 2 bits with no scientific proof to back it up, but with regard to tilting, there are pros and cons to build in a degree of angle. I'm no scientist but from my days as a pilot, inclining front to back doesn't feel natural to me. If there was no positive pressure flowing along the underside of the panel it 'might' exert a little down pressure... not significantly, but because there will always be air flowing along the underside in smaller volumes, air passing over the top would create vortices along the rump end of the panel. That I do know. That 'might' add a little more stress to the rear mounting hardware, but then again.. probably not enough to matter under normal driving conditions, and I doubt there would be enough drag created to affect mpg.

 

Now.. if you were on the road and were hit with F-scale type winds that might be a different story. However... if you're out driving in that kind of weather, you probably deserve to have your panels ripped off.

 

It's fun to postulate, but the bottom line in my book; I don't think it makes too big a hill of beans. People been doing RV roof installs for a wee time now in all sorts of configurations and orientations. I don't recall ever hearing anything solid about any clear benefit or detriment from any given orientation when you're talking about tilt.

 

Building in a degree of tilt, I would go side to side (not that I do, but if you're set on it...) I say go with what gives you the most confidence in your own particular install. The discussion on why to tilt side to side or not I'll leave for another day.

[Ronbo]

Watch the trees as an 18 wheeler drives underneath them. They never hit the top of the trailer because the cushion of air is compressed on the top. This lifts the tree limbs. There is not sufficient wind in contact with the panels to lift or press them down. They are covered with a bubble of air.

[sushidog]

Sorry for the confusion on my post about the number of panels needed. I can only use 3-4 panels. The information that I had found indicated lots of 15 panels is how they are sold. Perhaps I read it wrong. Anyone know anything about the type of panels? Has anyone used them? Thanks.

 

Safe Travels!

If you are seriously considering some high output panels there are smaller/higher output ones, like the E20 line and the X21 line both by sun. http://www.sunpowercorp.com/solar-panels-technology/facts/

 

Their more affordable E20 435 watt panel weighs less than 63 lbs (12lbs less than the 395 watt model) and its footprint is smaller too. 41.2" x 81.4".

http://global.sunpowercorp.com/cs/BlobServer?blobkey=id&blobwhere=1300260208996&blobheadername2=Content-Disposition&blobheadername1=Content-Type&blobheadervalue2=inline%3B+filename%3De20_435_ds_en_a4_w.pdf&blobheadervalue1=application%2Fpdf&blobcol=urldata&blobtable=MungoBlobs

 

They also make an even smaller footprint, 41lb, 327 watt E20 panel too, if space is a concern. (41.2" x 61.4")

 

I'd call your local solar installers that use the Sunpower brand, as they buy by the container and almost always have a few extra available. You want to pick it up for 2 reasons, first the freight on a panel this large will be a killer (the extra you might pay locally will easily be offset by saving shipping charges) and a panel this big is more easily broken during transit due to its sheer size and weight.

 

Chip

[dennisvr]

Watch the trees as an 18 wheeler drives underneath them. They never hit the top of the trailer because the cushion of air is compressed on the top. This lifts the tree limbs. There is not sufficient wind in contact with the panels to lift or press them down. They are covered with a bubble of air.

 

I sure wish the tree I went under this last weekend knew that. Maybe I better check to see if my bubble of air has a leak in it. LOL

[oldjohnt]

Yo Yarome, not sure if I understand your pilots lingo and air flow and pressures, I think I agree with you??? but here are my thoughts on why to increase DOWNWARD forces the panels rear should be higher then its front. If I'm wrong please explain it to me and you earn one more amp of electrical service lol

 

NOTE I understand how the shape of an airplane wing and the resulting differences in air flow on top versus bottom creates lift BUT THE SOLAR PANELS IVE SEEN ARE NOT SHAPED LIKE A WING, so I'm unsure if panels versus airplane wings is a fair comparison????

 

It seems to me all this "tilt talk" is getting wayyyyyyyyyyyyyyy more complicated then it actually is. Do a mental experiment with a panel hinged in the front,,,,,,,,,,Now drive down the road at 50 MPH and start raising the panels rear,,,,,,,,,WOULDNT EVERYONE AGREE AS THE PANELS REAR IS RAISED THE WIND FORCE IS GREATER AND THERES A DOWN COMPONENT TO THAT FORCE (I think the force will be the vector sum of DOWN and BACK forces) ????,,,,,,,,Imagine If raised to 45 degrees wouldn't everyone agree there's a lot more force???????????? Wouldnt everyone agree if its perfectly flat (not withstanding the front panel edge) that creates the least DOWN force????

 

Next hinge the panel in the rear and start down the road at 50 MPH and lift the panels front,,,,,,,,,,,Can we all agree as the panel front is raised the forces are UP and BACK ??????????? NOT DOWN (what you want) AND BACK

 

I guess what I'm saying is as far as maintaining a DOWNWARD FORCE versus and UPWARD FORCE if your goal is to keep the panels on the roof, ITS OBVIOUS TO ME YOU WANT THE BACK HIGHER THEN THE FRONT.

 

Of course, if they are nearly flat there's little down force but as they are raised it increases dramatically. Im NOT talking about HOW MUCH force (even if slight) , ONLY that there's gotta be "more" DOWN force if the panel is higher in the rear.

 

Sorry, I just cant see why anyone would tilt their panels with the front higher then the rear, but I'm an electrical NOT an aerodynamics engineer, so if any aerodynamics experts or pilots can explain how there's more panel DOWN force if the front is higher, IM ALL EARS ENLIGHTEM ME PEASE Again panels NOT shaped like wings

 

John T NOT a Pilot, NOT an aerodynamics engineer and may be wrong as rain, its happened before (wife says lol)

[Tom_M]

Alternate plan 22 (or 28, your choice) Throw a couple of plug in panels on the ground and tilt them to your hearts content.

 

No roof, gather them in the wind, align them to the moon, all kinds of options.

 

Besides, tilting is a 360 degree option really, as opposed to a side to side. What do you do when your parked north to south? Raise the front of the trailer to 45 degree's? Kathy would have you by the ...belay that, and your frig level would be off, (yeah I knew if I thought long enough that another reason would come up) I can see all the coffee cups on gimbals in the trailer just so they don't spill. And trying to chock the tires. Oh boy!!

 

In Michigan, my 4-100 watt flat mounted, 12 year old panels with poor wiring (paralleled wiring 10 gage) were putting out 25 amps the other day. About 75% of rated cap. We had a number of bad heavy overcast days and this was the first bright and sunny. I was down 230 AH (35%) and the boys were cranking. I got back about 80% of that the first day and topped up the second day. I was almost thinking of turning on the charger.

I mounted my panels on the side of my coach. I rigged them up so that they can be tilted if I'm parked with the driver side toward the sun. Otherwise I lift them off and set them out on the ground and tilt them toward the sun.

 

 

 

Here's a slide show of my install: http://s1095.photobucket.com/user/tomzpix/slideshow/Solar%20Slide%20Show?sort=4

[kinseypw]

I'm feeling so underpowered after reading all the posts! We run 380watts on our rig and we ran our generator only a couple of hours on 2 days last winter in Yuma. Our panels are free standing and so we have them tilted to optimal angles depending on where we set up. The benefit to free standing is that you can adjust the panel to maximize solar pick up on cloudy days. We were camped in BC and had a full week of mainly cloudy days and tons of rain. I adjusted the panels every 3-4 hours and was able to keep up with our power needs even without any full sunshine. it surprised me how well we were able to keep up with demand. In Yuma we just set the panels up facing south and are fully charged by noon most days. Stowing and setting up the panels takes about 15 minutes and seems like a small price to pay for the extra flexibility and the cost savings on the initial set up. I have some photos of the set up here http://pjsnowbird.ca/index.php/tutorials/installation

[hemsteadc]

. If I secure them adequately to the aluminum frame structure and the frame in turn to the roof trusses, will my trailer, or at least it's roof, be transported to Kansas by a heavy blow? I think it could stand up to typical winds encountered in most areas and only need to be lowered occasionally.

Jim

 

l tilt.

 

I have 6- 135w panels mounted with the 'standard' 4-point brackets secured with 2 wood screws at each corner. I have been in very strong winds in So Cal in winter, and those panels and brackets have never suffered any damage. There's no way I'd be getting on the roof DURING that kind of wind. I would consider taking them down before a wind, but, as you may know, wind predictions can be very inaccurate.

 

The worse "damage" I see from panels up in the wind is the noise. They can keep me awake.

[oldjohnt]

Tom M,

 

Nice lookin set up. I've considered something similar but with the top hinge point higher (to avoid roof shadow if headed East) so you could elevate them to say 45 degrees if parked headed West (to see southern sky), but if parked facing East, lift them even higher to 135 degrees (same as 45 if facing opposite direction) .

 

Kinsey,

 

Don't feel UNDER powered, as long as you harvest in daylight what you typically require over 24 hours, hey youre keeping up SUBJECT OF COURSE to sunlight hours and angle and your use. There are two of us in a smaller 29 Ft Class C Motorhome with four Golf Cart Batteries (460 Amp Hours) and modest energy requirements (vent fan, water pump, LED lights, computer and chargers etc.) and we were getting by with only 200 solar watts and now we have 400 watts so life is good. We often ran the genset maybe 15/30 minutes per day for coffee or microwave or hair dryer etc at which time my Smart Charger was pumping nearly say 60 amps into my batteries so that factors in and helps of course. Now if you want to run the microwave or coffee makers or other energy hogs strictly off solar and batteries, you're gonna need MORE solar and/or batteries and hey, some have the need for 500 to over 1000 watts of Solar and that's fine and I'm happy for them, but my energy requirements are modest so I don't need all that. I'm NOT into keeping up with the Jones', I have a hard enough time just keeping up with myself lol and yes I may have to run my genset more then others who have more solar capacity.

 

PS as the old saying goes (sort of), any solar is better then no solar and you cant have too much solar. More allows for future expansion and a lot depends on your rooftop real estate and other factors, to each their own, not much of a right or wrong answer to these type of questions.

 

John T

[bigboomer]

I tilt with my mobile lifting system. Generally speaking it takes me about an hour to remove the panels from the top of the truck and about the same going back up. Since we usually spend a few months at a time when at one location either workamping or at Q the setup and take down is no big issue. I can tilt the panels at several angles and can turn and locate the panels to optimize direction to the sun with out moving the rig.

 

I use a combination of stakes and weights to tie down the panels which held up well during 50+ mph winds in the desert.

 

If we are short term in a location (under a month) I leave the panels flat on the truck and can unplug the panels from the rig so we can use the truck and upon return I plug the back in when they are not under load.

 

Here is link to our set up...

 

http://s962.photobucket.com/user/mybigboomer/library/RV%20Solar%20System

 

I designed our system to have options since we use energy as needed (tv, convection micro, furnace, frig, etc.) and conserve as needed.

 

Everybody has their opinions and each situation is unique. We like our setup and like anything have learned for future what to improve and do differently.