How to put solar panels on top of my RV

[travellinglee]

I want to put solar panels on top of my RV, getting the panels to move in order to track the sun make them nearly 40% more efficient than being static. I have worked out the electronics to control the motors to move the panels by programming an arduino board with light sensors etc but I need help with the actual physical design. The panels weigh 50Kg in total and are 1.5m in length, the electric actuator (piston) can push 130Kg and can extend 0.4m. Take a look at the diagram, can anyone tell me what distances A & B should be?

 

[travellinglee]

 

[hutchphd]

What is the maximum tilt angle required?
What is the minimum actuator length?

 

[travellinglee]

Hi Hutch

Ideally I want the panels to go to/from totally horizontal to nearly vertical so from flat to plus +80 degrees, tx for your assistance my trig is really failing me on this one...:)

 

[travellinglee]

I want to put solar panels on top of my RV, getting the panels to move in order to track the sun make them nearly 40% more efficient than being static. I have worked out the electronics to control the motors to move the panels by programming an arduino board with light sensors etc but I need help with the actual physical design. The panels weigh 50Kg in total and are 1.5m in length, the electric actuator (piston) can push 130Kg and can extend 0.4m. Take a look at the diagram, can anyone tell me what distances A & B should be ?

 

[anorlunda]

[Moderator note: duplicate threads merged.]

 

[travellinglee]

TX Anorlunda - Sorry if I created any confusion...

 

[anorlunda]

I'm envious. I would like to do the same on my RV. It looks like you are planning a one-axis system. Two-axis movement gives you even more energy. Do you have calculations showing how much more energy you will get with 1-axis? 2-axes?

You may be interested in these recent threads. These projects are too big for an RV, but still you could learn.

https://www.physicsforums.com/threads/sharing-solar-home-data.976496/
In that first thread, I mention how the moving panels capture more energy than fixed panels.
I also mention that this installation has a wind speed sensor, and the panels automatically return to horizontal when the wind blows too hard.

https://www.physicsforums.com/threads/pitfalls-in-pv-installations.977703/
I think you'll find that the wind load on non-horizontal panels is much larger than the panel's weight. The RV park where I live won't allow rooftop solar because of fear that the panels can become sharp-cornered missiles flying around during hurricanes or thunderstorms.

At the very least, you need considerable thought into how you are going to fasten the whole thing down to the RV roof. RV structures are very thin. Simple bolts might just rip through the roof material. It may be stronger to anchor the panels to the ground, not to the RV. Perhaps you could search for your questions on an RV forum and find others who have done similar projects.

House building codes usually don't apply to RVs. But they can still be useful to learn from. Perhaps you can find the local code in the UK.

Here is a wind load calculator
https://www.buildingsguide.com/calculators/structural/ASCE705W/

 

[travellinglee]

I am actually building a 2 Axis rig, I only asked about the elevation equation as I have the East/West axis sorted already. I'm going to be pretty much permanently on the move as my visa only allows me in the US 6 out of 12 months so I do spring up the west coast 3 months in Canada, 3 months down the East coast and winter in Mexico, then rinse, dry, repeat So I have set up the control program to activate the panels when the slide outs from my RV are activated and close when the RV gets closed down.

To answer your question re energy efficiency on 1 V's 2 axis systems - The North/South or vertical axis will improve upon a static panel by about 30-35%, the horizontal or East/West axis only gives an extra 5-10%. As I'm on the move all the time and often in desert terrain I need to bleed as much as I can out of the panels hence dual axis but if I was in one place and didn't need every volt possible I'd probably go single axis. I also have a generator which pumps out 10Kw @ 50a which is the same as having a direct shoreline hookup but it eats fuel which is why I want the solar rig to be as efficient as possible.

The reason I am asking about the most effective pivot point (the A & B question) is that I want to make the rig as compact as possible and possibly market it at some stage.

 

[JBA]

What is the total length of your actuator at full extension?

 

[Nik_2213]

First, you need a sub-frame &r roof-rack. Something that will support your not-very-robust panels against mishap & mayhem...

IMHO, putting them on a slanted, south-facing 'easel' may be much safer. Also, readily accessible for cleaning and storage.

 

[travellinglee]

What is the total length of your actuator at full extension?

Full extension end to end is 1m give or take a few mil

 

[travellinglee]

First, you need a sub-frame &r roof-rack. Something that will support your not-very-robust panels against mishap & mayhem...

IMHO, putting them on a slanted, south-facing 'easel' may be much safer. Also, readily accessible for cleaning and storage.

I plan to have a wide sturdy base to attach to the roof to which I will mount a lazy suzan swivel (500lb capacity) to which I will mount the 'easel'set up you describe. I'll have an actuator that turns the entire 'easel' for east/west tracking and then the vertical tracking it the bit I need help with as described above.

Cheers

 

[JBA]

I did a preliminary analysis of your arrangement and then decided I needed to do the below scaled sketch of a typical result to verify what I had calculated. Unfortunately, both show that it is not be able to accomplish what you want with the current 135 kgf and 1 m extension actuator.

What controls the entire arrangement is the ratio of the 135 kgf vs the 5 kg weight vs the length of the lever required to provide the necessary leverage for the actuator to initially lift the solar panel from it horizontal position. You can see that I used a lever connection point at the CG point of the panel in my example and the limited panel lift angle that is achieved by that location.

The issue is the leverage ratio set by the lever location relative to the panel's CG at .75 m from the pivot. As a result, moving the lever and actuator closer to the solar panel pivot in an effort to get more lift angle is self defeating. For example, if the lever is moved to .375 m from the pivot then the effective panel load for the actuator is 5 kg x .75 m / .375 m = 10 kg and the height of the lever must be correspondingly doubled for the 135 kgf actuator to initially lift the horizontal panel.

At any rate, the diagram shows you how to go about using a diagram to evaluate the alternatives for yourself. Since I retired I no longer have access to CAD, so I had to revert to my prior 20 years of manual drafting with a scale, protractor and compass for the sketch and a lined 8 1/2 x 11 lined pad was the item closest at hand.

 

[travellinglee]

Thanks so much for putting the time in JBA. If I have understood you correctly, my original set up would work from a lift/power perspective but would only elevate the panels to 34 degrees. I have a second identical actuator which I was planning to use for the east west axis but I can use motors for that. I' thinking of keeping the original set up with a twist, use the second actuator to 'pull' the pivot point of the first actuator closer to the pivot point of the solar panels so as actuator 1 extends, actuator 2 retracts (bit like an old school deck chair) - thoughts?

 

[travellinglee]

Thanks again JBA. I have found a 2d modeler called Linkage which should help (still working out how to use it). I'm just working out placement of actuator pivots for max speed/efficiency so one pushes and one pulls at the same time. Tx again.

 

[JBA]

Press on!
For reference: I used my diagram and started at the bracket to actuator connection position with the panel at the 80° elevation angle as the starting point. I then drew a circle of 1 m radius to find the original actuator's extended length intersection with the horizontal base; and, this indicates the horizontal actuator will need to withdraw .75 m from the original actuator pivot starting point to the point required for 1 m actuator to finally lift the panel to its 80° elevation angle.
For safety, I also did some basic actuator force calculations in order to confirm my expected low values and those indicated that at the full lift position the forces from the effective panel weight on both actuators should be less than 1 kg.
Also, a similar calculation indicates the tensile force on the horizontal actuator at the start of the lift will be 125 kgf.
I am sure you realize that all of these values are approximate due to being based on ideal conditions and component locations.
In that respect, one particular note of caution: I took credit for the full 135 kgf ability of the lifting actuator in determining the .22 m height of the actuator bracket above the panel; but, that is not practical for your acual application because it allows no safety factor to address pivot friction loads, etc. You can reduce that 135 kgf required load to correct that issue by extending the height of the actuator to bracket pivot beyond my current .22 m.; however, this will correspondingly result in an additional bit of required travel for the horizontal actuator.
At this point, I will leave the rest to you; but am available to try answer any upcoming questions.

 

[anorlunda]

You can use the calculator below to estimate how much wind load to add to the weight of the panels. Since your angle is variable, so too with the wind load vary. Don't forget to worry about the case where the wind comes from the opposite direction as the sun, thus lifting the panel, and forcing the actuator to hold it down.

I recall a number of 45 pounds/ft² from another thread.

Edit: oops, I forgot the link,
https://www.buildingsguide.com/calculators/structural/ASCE705W/

 

[revesz]

At optimal angle to horizontal, for your latitude and time of year, there is a single angle if you do not have the lazy susan. The sun should move through a plane at perpendicular to the plane of the panel. The sun should pass through a point normal to the panel at high noon. With the panel oriented south, any tracking will only turn the panel further from the sun. There is no tracking that can improve this unless you add the lazy susan as well.. then you keep the sun normal to the panel all day, and you get a big increase in efficiency.

 

[travellinglee]

Here's where I got to, can anyone help with the equation I need?

 

[JBA]

First, simplify your diagram by using a simple perpendicular line to connect P2 to the face of the solar panel because that is a critical dimension in this analysis.
(Once you determine the critical dimensions for the design then you can start working on the actual bracket design).

The maximum compression load on A1 and A2 occurs at the start of the solar panel lift from its horizontal position. As a result the ratio of the from the panel CG to the perpendicular bracket base location and the bracket height are what determine the amount of compression loadings on A1 and A2.
For your current configuration, the vertical force to lift the panel from flat = 44 Kg x (1.48 / 2) / .55 = 59.2 Kg; and, (assuming the .2 m dimension is vertical height of P2 from P3) then the resulting compression load on A1 = 59.2 x .42 /.2 = 124.3 Kg; which means you can shorten the the bracket to .2 x (124.3/150) = .165 m

With that required bracket length determined, you then have to determine the combined extended lengths for A1 and A2 required to raise the solar panel to your target elevation angle.

 

[revesz]

I took a course relating to this sort of thing a few months ago. The topic was "Dynamics of Machines". You can break this problem down and get to the solution, using techniques that have been developed.
Here's a course a found online that will certainly have the technique in it somewhere, I have no looked through it.
https://nptel.ac.in/courses/112104114/

 

[travellinglee]

First, simplify your diagram by using a simple perpendicular line to connect P2 to the face of the solar panel because that is a critical dimension in this analysis.
(Once you determine the critical dimensions for the design then you can start working on the actual bracket design).

The maximum compression load on A1 and A2 occurs at the start of the solar panel lift from its horizontal position. As a result the ratio of the from the panel CG to the perpendicular bracket base location and the bracket height are what determine the amount of compression loadings on A1 and A2.
For your current configuration, the vertical force to lift the panel from flat = 44 Kg x (1.48 / 2) / .55 = 59.2 Kg; and, (assuming the .2 m dimension is vertical height of P2 from P3) then the resulting compression load on A1 = 59.2 x .42 /.2 = 124.3 Kg; which means you can shorten the the bracket to .2 x (124.3/150) = .165 m

With that required bracket length determined, you then have to determine the combined extended lengths for A1 and A2 required to raise the solar panel to your target elevation angle.

That's brilliant JBA, thank you. I think I'll leave the measurements as they are as the motors should last longer and will also be able to lift on occasions when water/snow/wind may effect the lift weight. You are a star my friend.

Cheers

Lee

 

[parkland]

At work we have large satellite dish for internet and it is actuated by hydraulic rams for inclination and azimuth using a little hydraulic pump powered by electric motor. I realize this might be heavy, but thought I would mention it since at least one company saw it as a good solution.

 

[travellinglee]

Thanks Parkland, do you know the name of the company?

 

[parkland]

Yes it is pason systems they do oilfield computer and electronics but they rent everything out so they'd be no help as a source for parts, but my point was that they must have spent some money on deciding that hydraulics were the way to go to point big satellite dishes and those have wind loading and such like you will so maybe it's worth a think

 

[travellinglee]

Cheers buddy, when I get the bugger built I'll post pics etc.

 

[parkland]

Sounds good. A long time ago me and some guys looked into focal point solar dishes and aiming a gang of them at once, and we found that on paper anyways it made sense to have an azimuth motor and inclination motor and common shafts and worm gears on each dish.
For aiming, I wrote a program in quick basic on a pc, and got a program off the internet called fwink which saved a webcam picture every second. My qbasic program would look at the picture and figure out where the sun was and control motors. The camera would be outside on a dish with tinted glass in front of it.

 

[DEvens]

After you run this puppy for a while, please report back on how it performs. I'd be curious to know if it pays off.