Maximizing Solar Off Grid Potential - 740W Build

Patrick

A quick preface to this post.  Before attaching rigid solar panels or other objects to the roof of a moving vehicle, recognize that a realistic worst-case scenario is that the panels could fly off while driving at highway speeds and result in fatalities.  Keep that in mind, and don’t DIY without the knowledge and capability to correctly install and maintain the equipment.


Recently purchased a 2017 Tab 320 S Max and installed an aftermarket roof rack, ~74" in overall length. 
For anyone interested in the roof rack installation, post here: https://tab-rv.vanillacommunity.com/discussion/12592/clarification-on-aftermarket-roof-rack-installation

With the large open surface area on the rear of the trailer, I wanted to maximize the solar production.  I decided to go with commercial size, rigid solar panels, the length of these panels (79") match the width of the tab (78") nearly perfectly.  Mounted horizontally, there is enough room to mount two panels. 

Where I looked, I could find panels up to 410W in this size, but due to the cost, I went with two 370W panels for ~$150 ea.  This also allowed me to stick to a 30amp (24V) MPPT charge controller.

Finished Install:



Base Attachments:
I used 1/8" thick 1.5"x1.5" aluminum angle for the front attachments.  I did not take a picture of the aluminum track mounts, but they were stainless carriage bolts with fabricated metal strips to lock in the tracks. 3/8" stainless carriage bolts were installed upward, aluminum angle was attached with blue locktite, lockwasher, nut.

Overview for top panel base attachments:


Front attachment:
The solar panels use aluminum C-channel for a rigid frame.  The bottom of this C-channel was drilled out  such that there were two 5/8" holes for the alum angle attachments to fit through and that the panel fit flush with the alum angle.  Four 1/4" holes were drilled horizontally through the front of the alum angle and solar panel C-channel to attach the panel to the alum angle.   There was just enough room between the roof and panel to use a driver and a long extension to torque these down.  1/4" stainless bolts, blue locktite, washer, lock washer, nut. 


Rear attachment:
I used the sport rack crossmembers, in combination with U-bolts and reinforcing alum angle to attach the rear of the solar panels to the roof rack. U-bolts are pretty common to attach panels to roof racks.  I added the alum angle reinforcement because the square crossmembers were at a different angle than the panel frame.  
Drilling the alum angle in tandem with the solar panel c-channel. Block of wood helps to not drill out the panels.  A small pilot hole makes sure the larger bit goes where you want it to.:


U-bolts were for 1 1/4" Pipe, with the threads cut to size.  I dont have a good close up picture with them installed. Above the c-channel on the inside is the bracket that comes with the u-bolt, washers, lock washers, and nuts (and blue locktite).


I want to emphasize that although these panels are large, they are very rigid and very well connected.  When pushing the panels at any point on their frames, the entire trailer is pushed.

Patrick

Reserving 2nd post for wiring / electrical / battery install.  

Panels are installed with:
24V 176AH lipofe4 battery
30A/24V MPPT SCC
24V/2000 Watt AC Inverter
40A 24V/12V stepdown converter
24V/10A battery charger when connected to shore power
transfer switches to switch between shore power and the AC inverter
transfer switch between12V battery (which remains as a reserve) and the 24V/12V converter.


I didn't want the new electrical systems to affect weight distribution or take up the limited storage space, so I designed [nearly] everything to fit in the current electrical area under the driver side bench right over the axel.

Breaking this post down into outline format for the remainder of the electrical systems. 

1. Battery

• The Battery is a 24V 176AH lipofe4 battery that I built from 8 individual aluminum cased cells.  lipofe4 batterys are incredibly safe in comparison to other battery chemistries.  Between the increased safety and the damage that could occur to the battery if charged or discharged below 32F, I wanted to install inside the cabin.
• I chose this size in order for the battery to fit between the current electrical box and the wheel well.  You could go up to 190AH for more $$$.
• Installation: I needed to relocate the 12V negative bus bar and install a raised platform with two strips of 1" lumber so that the battery wasn't resting on the pex piping:
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• The four vertical dowel segments line up with the battery base  to keep it from sliding around.
• 
  
• I moved the 12V negative bus bar to between the outlet and the breaker box here:
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• I want to keep this TAB focused, so if you want details on how to build a lipofe4 battery from cells, this website and forum are great resources:  https://www.mobile-solarpower.com/raw-lifepo4-deals-page.html  /// https://diysolarforum.com/
• I did not have room for a hard case, but raw cells do need to fit snuggly to prevent expansion under heavy loads, so I used a ratcheting cable strap around a three sided box with the above base.  This is encased in stretch wrap to insulate the terminals and keep the BMS balance leads from moving around.  I mounted the BMS on the right side.
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• This then slides into place like so.  This picture also shows the 
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• I considered that the battery could bounce off the dowels and start sliding around, but the battery weighes ~70 lbs, the top of the ratchet strap is ~1/8" from the bottom of the bench plywood, and I do not have any intention of off-roading.  If I have any issues here, I can put in a L bracket to secure the battery to the floor.

2. MPPT Solar Charge Controller

• Solar charge controller is a 30A / 24V EPEVER that is sized appropriately for the two 370W solar panels.  I went with this model based on the good reviews and the remote panel I could mount outside of the electrical cabinet. 
• I installed an extra horizontal crossbar (1"x lumber) for support and mounted this with 3 of 4 mounting screws + VHB tape on the right side of the battery.

3. AC Inverter

• Inverter is a Novopal 24V DC / 2000W Pure Sine Wave Inverter.  Did not have the best reviews, but I went with this model solely for it to physically fit in the space that I had for it and low cost through amazon warehouse.  In a perfect world, I would have gone for a 1500W model that had a lower standby electrical usage.
• The grey CPVC pipe was just barely in the way, the penetration where this comes through the left side of the cabinet had to be enlarged for it to raise up ~1".
• I installed 1"x lumber to keep the "bottom" of the inverter from sitting flush against the left side of the electrical cabinet.
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• Installed the inverter here with 3 of 4 mounting screws and VHB tape:
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4. 24V DC / 12V DC Stepdown Converter

• This is a 40A (at 12V) step down converter.  Went with 40A as that is the fuse size for the factory AC / 12V DC converter.
• This is mounted below the 120V outlet here: 
• 
• This converter is wired into a transfer switch to where the 24V / 12V Stepdown converter can feed the 12V fuse box OR the factory 12V inverter and front tub 12V battery can feed the 12V fuse box.  This transfer switch is important because both the 12V battery and the factory 12V inverter operate at a higher voltage than the stepdown converter and the converter doesn't have a diode that would prevent current backflow.

Have to take a break - will finish later!

5. AC Transfer Switch

6. DC Transfer Switch 

7. 24V Battery Charger from Shore Power

8. Heat Management

9. Solar Panel Wiring / Routing to the Interior

10. Overall wiring diagram

4ncar

Dag! I wanna party with you!

pthomas745

That trailer will hover all by itself.

ChanW

I think @pthomas745 has a point.
Have you done a wind tunnel test with this design?
And I see a possible future with your Tab powering your electric tow vehicle!
  

Denny16

O wouldn’t tow that setup any faster than 55-60 mph.  Go faster and those solar panels may act like a spoiler, pushing down on the rear of the trailer and induce sway.
cheers

Patrick

ChanW said:

I think @pthomas745 has a point.
Have you done a wind tunnel test with this design?
And I see a possible future with your Tab powering your electric tow vehicle!
  

Lol, no wind tunnel testing.  Although they will increase drag for sure, I tried to minimize it by having the leading edge of the panels as close to the roof as possible (~1/2” gap), following the roof line as much as possible, and sharp trailing edges tend to reduce drag more than rounded trailing edges.

Denny16 said:

O wouldn’t tow that setup any faster than 55-60 mph.  Go faster and those solar panels may act like a spoiler, pushing down on the rear of the trailer and induce sway.
cheers

I always agree with reducing speeds while towing!  So much safer and saves money at the pump.  But I disagree that this could push down on the rear of the trailer and induce sway.  Spoilers that increase downward force for traction are angled up on the trailing edge to create that downforce, opposite of these panels.  To @pthomas745’s point, the angle of the panels would create a low pressure zone above the panels, but negligible in comparison to the weight of the camper.

DougH

@Patrick  In awe! 

When I had a heavy wildlife camera mount on the roof, I used steel cable wrapped around the vent top as a redundant means of preventing anything flying away. But it sounds like your rack design is more than strong enough, so no second or third line of defense needed. Impressive.

I wish I'd done rigid, as I keep losing flex panels to hail. And while flexible panels have their pluses, if you avoid hail, or cover them before every storm, they start to age and the surface will haze just like plastic headlight lenses. No such worries with rigid glass panels.

And I love the ironic shore power connection in the picture, when you'll never need it again.  Five heated Battleborns distributed throughout the cabin?

pthomas745

I was not intending anything about aerodynamics with my comment.  I was thinking with that much power available, the trailer could become a TabHovercraft.

Patrick

pthomas745 said:

 I was thinking with that much power available, the trailer could become a TabHovercraft.

Sounds awesome, let’s do it

NovaTab

Nice job

I laughed when I open your pictures, I'm adding a 265W panel in very similar fashion in the next few weeks an I'm looking into tilting then with motorized linear pistons similar to gas shocks used on RV doors that way no climbing on a ladder or the roof.

I think you should consider tilting those or you will lose a high percentage of output

they will not fly off,

There are many people that use 3M tape on the brackets no fasteners at all, see

4950 VHB Tape

I had a class A motorhome 4 years ago. I put 650 watts on the roof with an Outback controller and 8 6V golf cart batteries n one bank, there were times that drove 75-80 mph, kept it for two years drove about 15,000 miles no issues.

Marceline

NovaTab said:

Nice job

I laughed when I open your pictures, I'm adding a 265W panel in very similar fashion in the next few weeks an I'm looking into tilting then with motorized linear pistons similar to gas shocks used on RV doors that way no climbing on a ladder or the roof.

I'm pretty sure that @AldebaranJill has a rigid panel with some kind of lift mechanism.

pthomas745

That was a beautiful mod, too.

https://tab-rv.vanillacommunity.com/discussion/4971/t-b-solar-panel-roof-mount-with-tilt-able-brackets-mod-for-under-300/p1

Patrick

NovaTab said:

Nice job

I laughed when I open your pictures, I'm adding a 265W panel in very similar fashion in the next few weeks an I'm looking into tilting then with motorized linear pistons similar to gas shocks used on RV doors that way no climbing on a ladder or the roof.

I think you should consider tilting those or you will lose a high percentage of output

Yeah definitely.  I'll see how it goes and if the performance is too low, I may add a manual tilt mechanism to the lower panel.  I am also not happy about the shading from the overlap and might move the lower panel back.  I've got a little room to do that without the lower panel overhanging the back of the trailer.

Hoping the top panel is close enough to horizontal to not need it.

Patrick

Performance Testing!

TLDR: Had a sunny day today and got to do some testing.  Learned that partial shading is a big problem and I'll have to move the lower panel back ~4".   But, when oriented in an optimal way, system has no problem powering everything incl. AC.

Partial shading:
Today was the first sunny day with the panels and the output was lower than expected. I used a clamp ammeter to test the individual panels.  Top panel was giving 4.5-6.5A (panels output ~45V) which is good.  Bottom panel was outputing 0.2-1.6A - not good.

The top panel was shading the entire top row of cells on the lower panel, I should have recognized that if this happens, the entire output of the panel is lowered.


When I rotated the camper 90 deg to get that panel to face the sun, the output went up to 6A.



Went inside, switched everything to battery power and this is the 24V Battery BMS data.  Below is the baseline with all the lights on and 2kw inverter running on standby:


When I switched the fridge on 12V power, the charging dropped to 6.5A.

Turned off the fridge and turned on the AC to max:


Good to know that if there is an extremely hot / sunny day I can run the AC intermittently. 

Patrick

DougH said:

@Patrick  In awe! 

When I had a heavy wildlife camera mount on the roof, I used steel cable wrapped around the vent top as a redundant means of preventing anything flying away. But it sounds like your rack design is more than strong enough, so no second or third line of defense needed. Impressive.

I wish I'd done rigid, as I keep losing flex panels to hail. And while flexible panels have their pluses, if you avoid hail, or cover them before every storm, they start to age and the surface will haze just like plastic headlight lenses. No such worries with rigid glass panels.

And I love the ironic shore power connection in the picture, when you'll never need it again.  Five heated Battleborns distributed throughout the cabin?

Thanks for the feedback!  I have thought a lot about how I could install  backup safety cables, but I am not sure what I could mount them to that would be more secure or as secure as the roof frame.  I'll update if I add them.

I had read a bit about early failures on flexible panels but did not know that they get hazy 

No battleborns, but a single custom built 24V / 176AH lifepo4.  That's equivalent to ~4 100ah 12V agm batteries or 3.5 battleborns.  I just update the second comment with the battery install, rest of the electrical install to follow.

dragonsdofly

@Patrick, absolutely awesome! So impressive for a t@b. I am floored that you built your own custom LiFePo battery. When do you plan to market your solar powered t@b hovercraft/time machine/warp drive capsule?

DougH

@Patrick Well I guess they use several bonded layers of plastic on the EFTE flex panels, and cannot exactly use a UV blocking additive since it would defeat the whole purpose.  The pic below shows me starting to use the Rain-X headlight restorer kit on the three 100W panels I have taped down on the back of my clone of your T@B (same model, year, color). The kit takes the top oxidized layer off. Hopefully power levels go back up (or they'll drop to zero?). But on my next camper I'm definately going the route you went.

P.S. I had an Epever MPPT controller but wasn't getting the amps out of it I should for 300W. Only 6A or so. Asked around on this forum and everyone said I should get Victron for faster charging.  Switched to the Victron 100/20 and saw a huge jump in power to the 375Ah bank. Just something to keep in the back of your mind if you don't see anything close to 30A into your 24V battery.

Patrick

@DougH

Cool.  Definitely interesting to know how much removing the oxidation layer will help.  

I think I'll be okay with the epever controller.  Today the panels maxed out around 530 watts which I think is as good as I can hope for with a 740W system with relatively poor angles and winter sun.  

DougH

Excellent! That's great for a winter sun.

And I think I read Lithium chemistry batteries can charge faster than leads acid, so my Epever slowish charging was probably just due to using AGMs.

NovaTab

Patrick looking good I just ordered the power linear lifts for my big panel see the link below, I ordered two one for each end I could have did one in the center but was concerned with high wind or storms twisting the panel thus shattering the glass.

I also intend to put light gauge safety wires if a wind on the back of the panel tried to over extend the max 60 degree position.

It has remote control to and angle I want

https://www.amazon.com/gp/product/B00NM8H6VS/ref=ppx_yo_dt_b_asin_title_o04_s00?ie=UTF8&psc=1

https://www.amazon.com/gp/product/B079K8D3YK/ref=ppx_yo_dt_b_asin_title_o05_s00?ie=UTF8&psc=1

so about $100 for the whole setup, as U R aware tilting increasing the power upto 30%

I found this system on a U tube where a guy did 1000 watts and traveled all over the US & Mexico. He said it's been working great.

I post the details in the future.

Bob

tomgiar

Bob,
Please post photos of the lifts . I would like to do the same on my tab 320. thank you

Sharon_is_SAM

@NovaTab - can you help @tomgiar?