2023 22MLE Additional Solar Panel Installation

[Melsman]

This post goes into detail about adding an additional solar panel to the existing factory installed solar panel/solar controller package on my 2023 22MLE. I do this in four different sections:

• The Preamble Ramble
• Parts and Materials Required
• Installation
• Testing

In the Preamble Ramble, I discuss the ideas and reasoning behind the decisions and the installation technique. You could skip this part and jump down to the Parts and Materials section if you want, but there’s some important background information that you may want to be aware of.

Preamble Ramble:
In the last couple of years, Grand Design has switched to a 12V refrigerator for the XLS 22MLE rather than the traditional propane/120V refrigerators. In doing so, they also added a 165W solar panel and a 25A Solar controller to help run the 12V refrigerator while driving down the road or in your campsite. This addition of a solar component to the 12V bus is a good start in addressing the additional load on the 12V bus, and the 165W panel will keep up with the demand of an already cooled refrigerator fairly well. However, the load of the refrigerator doesn’t leave a lot of power left over for charging the battery bank or other items on the 12V bus. So, I decided to add another solar panel to our 22MLE mostly because I wanted quicker charging recovery for the battery bank and better power capacity for running the 12V refrigerator. Given that the 22MLE came with one Furrion 165W panel ( FSFP16MW-BL) installed and a 25A (300W) Furrion solar controller (FSCC30PW-BL) capable of handling two solar panels, I felt it would be a fairly straight forward installation. It was and it wasn’t.

The easiest approach would be to simply purchase another 165W Furrion solar panel and connect it in series (as the Furrion solar controller manual suggests). However, a 165W Furrion solar panel costs roughly $600, which is about 3 times more than other comparable solar panels. Additionally, the wire connectors on the Furrion panels are proprietary and not the standard MC4 connectors found in the rest of the industry. Having had some previous experience with RV solar system design and installation, I felt I could overcome these shortcomings and do the whole installation – start to finish – for around $300.

First, I considered other comparable panels. The panel that seemed like the best fit was the Renogy 175W panel (RNG-175D). It was identical in footprint size (26.5”x 52”) and very close in specification. (Furrion- MaxV 18.72V, MaxA 8.82A; Renogy - MaxV 18.1V, MaxA 9.67A.) Close enough that they will work well in series together and max out the power limits of the solar controller (300W). And, at ~$225 to my door, the Renogy panel costs less than half of the Furrion panel!

Why “series” and not “parallel”?
Firstly, that’s how the Furrion solar controller manual suggests adding an additional panel. And since I’m keeping the factory installed solar controller (and the smaller 14 AWG wiring), I’ll go with their suggestion.


Diagram of the Furrion preferred method of adding an additional panel in series.


Secondly, connecting in series increases the voltage, but keeps the amperage the same. (Equal to the lowest MaxA rating of any of the panels in the series.) This way, the smaller gauge of the preexisting solar wiring can handle the additional voltage load yet still handle the amperage load without having to be replaced with larger gauge wire.

A quick discussion about “mismatched” solar panels –
Many may cringe at the thought of connecting two panels of different wattages, and in some cases, that thought is very cringe-worthy. However, that is NOT the case here. These two panels are VERY close in specifications, and – for our purposes – can be considered to be interchangeable. Keep in mind that solar panel specs vary slightly from panel to panel and the output varies significantly depending on the intensity of the light on it. However, to demonstrate the point, if we do the math with the Furrion and Renogy panels, we get the following (for panels in series):
Furrion + Renogy - MaxV = 18.72+18.1 = 36.82V; MaxA (lowest of MaxA ratings) = 8.82; MaxW = 325W
Furrion + Furrion – MaxV = 18.72+18.72= 37.44V; MaxA = 8.82; MaxW = 330W
Note the difference between the two configurations in output is less than 2%, which is well within the normal variation in panel specification and output. Thus, using the Renogy panel is practically no different than adding an additional Furrion panel.

Okay – what about winds and uplift?
Solar panels on vehicle rooftops are frequently subjected to 80-90 mph winds. Hopefully you won’t drive your rig at those speeds but even driving 60 mph in a 25 mph headwind will give an equivalent wind speed of 85 mph across the panel. However, the panels are very low to the roof surface and about 16” behind the leading edge of the roof, which helps keep any possible direct lifting airflow from pushing hard underneath the panel. And each of the four attaching screws on the two front panel brackets has a pull-out strength of about 100 lbs. So, even though in a real-world situation the cumulative pull-out strength may be slightly less than 400 lbs, that is still much greater than the uplift force on the panels (when placed 15-16 inches from the front edge.) Just be careful not to strip out the attaching screws when you install them! It’s easy to do in the 3/8” plywood roof decking.

Parts and Materials required:
Now that we have decided on the Renogy panel, we need to gather all of the necessary parts and tools. Here is a parts and materials listing for the entire installation project:

• (1) Renogy 175W 26.5”x52” solar panel (RNG-175D)
• (1) Renogy Solar Panel Mounting Z-brackets, set of 4 (MTS-ZB)
• (1) 6 ft 14AWG Solar Cables with extra connectors
• (1) Dicor 501LSW Self-leveling sealant (10.3 oz tube)
• (8) ¼”x1” zinc-coated lag screws
• (8) ¼” nylon washers
• (8) Zip-tie adhesive-backed mounts
• (8) small zip-ties

Materials needed for installation


And here are the tools/supplies you’ll need:

• Multimeter (for checking voltages and continuity)
• 10mm wrenches (for mounting panel to brackets)
• Blue locktite (optional)
• 7/16 wrench or socket (for driving ¼” lag screws)
• 1/8” drill bit (for lag screw pilot holes)
• Soldering iron and resin core solder (for panel connector surgery)
• Caulk gun (for Dicor)
• Wire cutter and wire stripper
• Crimpers and/or needle nose pliers (for connector attachment)
• Isopropyl alcohol (to clean roof area before attaching zip tie mounts )
• Tape measure (to measure stuff… duh!)

(INSTALLATION FOLLOWS IN A NEW SECTION) (The web page won't let me have more that 10,000 characters.)

[Melsman]

(Continued)

Installation:
First and foremost, read through these installation procedures a few times so that you understand how this all went together and the different options that are mentioned. This is how I did it; you are responsible for your own installation, so do it to the best of your abilities. If you’re not comfortable with all of the procedures discussed, pay a professional to do it. Also, this whole process took me 4-5 hours to complete. Now… on with the show.

The first thing I did was to check the actual amperage supplied by the installed 165W solar panel. I did this by checking the measured amperage being fed to the partially-drained battery bank. The measured value (via my battery monitor) was 8.49A (with a solar radiation value of 1106 W/m²). This value is very close to the rated value of 8.82A found in the Furrion nomenclature. (Side note - I also found that the 12V bus was drawing 2A from my truck’s 7-way connector).

My next step was to verify that the new Renogy panel was indeed functional and undamaged. I did this by setting the panel in the sun and checking to see that it had the correct voltage across the cables. In the case of the Renogy, the “open circuit voltage” (no load) of 21.6V is what we were looking for, and found 20.7V… which is close enough given the varying levels of sunlight I was experiencing at the time.

Once I verified that the Renogy panel was functional and the project was a “go”, I climbed on top of the trailer to prep the Furrion panel for its new sibling. This involves removing the negative (-) plug/wire from the rooftop solar electrical box and running the wire underneath and to the right side of the panel, extending it as far as possible without straining it.



Furrion panel's negative wire extended from underneath panel


(IMPORTANT NOTE: The length of this panel wire and the length of the positive (+) Renogy panel wire will determine the spacing between the two panels.) Cut the connector off of the Furrion panel negative (-) wire as close to the connector as possible. (We will be using this Furrion connector to make a connecting wire, so don’t lose it!) At this point, attach the extra MC4 connector (that mates to the Renogy panel’s positive (+) wire connector) to the Furrion panel’s wire. You may crimp and solder the connecter or simply crimp it. Just be sure to get a good, solid electrical connection. The Furrion panel is now ready to connect to the Renogy panel.



New MC4 connector on Furrion panel's negative wire


Next, begin prepping the Renogy panel to mount on the roof by attaching the z-brackets to the panel frame using the stainless steel bolts/nuts/washers that came with the z-bracket kit. I also used a dab of blue locktite to ensure that the nuts will not come off with road vibration, but this is optional. The lock washers alone will probably suffice… probably. Note that I mounted the bolts with the head on the bottom. This helps ensure that the bolts don’t protrude into the roof. Also note that the brackets are mounted as far forward as possible on the panel frame (similar to how the factory mounted the Furrion panel). This best counters any uplift experienced by the panel as the trailer moves down the road (as mentioned earlier).



Stainless steel bolts on mounting z-brackets


After the Z-brackets were mounted on the panel, I lifted the panel onto the top of the trailer and set it beside the Furrion panel, ensuring that BOTH of the Renogy panel wires exit the left side of the panel. I then connect the Furrion panel’s negative (-) wire (which has the new MC4 connector on it) to the Renogy panel’s positive (+) wire. The panels are now connected in series. I then measure the distance from the Renogy panel’s negative (-) wire to the vacant negative terminal on the rooftop solar electrical box. That length (plus 6” for slack) will be the length for the new negative connecting wire we’re going to make, so don’t forget this value. (In my case, the wire length was 6 feet exactly.)

To make the connecting wire, take a section of cable with the MC4 connector that connects to the Renogy panel’s negative (-) MC4 connector, and cut it to the length measured above. Then, cut and strip the bare end and attach the cut-off Furrion connector that you saved when you were prepping the Furrion panel. Attaching this Furrion connector to your new connecting wire will require unsoldering the remnants of the old cable and soldering the new cable into the connector’s terminal. Once this is completed, you’ll have a wire with an MC4 on one end and the Furrion connector on the other that connects the Renogy panel’s negative (-) wire to the vacant negative terminal on the rooftop solar electrical box.

But before making this final connection with the connecting wire, we have a quick test to perform.

Connect the new connecting wire to the Renogy panel’s negative (-) wire connector. Then, disconnect the Furrion panel’s positive (+) wire from the rooftop solar electrical box. Connect your multimeter to the Furrion panel’s positive (+) wire and the Renogy panel’s negative (-) wire. Verify that voltage is present. (It will vary depending on the intensity of the light on the panels. The key here is simply to see SOME voltage to verify that your connections are all working properly. Once this test is complete, go ahead and connect wires to their associated ports on the rooftop solar electrical box. The only thing left now is to mount the Renogy panel.

Move the Renogy panel into its final position so that the front edge is parallel to the front edge of the Furrion panel. (Around 15-16 inches back from the front edge of the roof.) Then slide the Renogy panel towards the outer edge of the trailer roof until the connecting wires are extended, but with a little slack in them.



Renogy panel in place and ready to mount.


Once you’re happy with the alignment, you can begin drilling pilot holes and anchoring the brackets with the ¼” lag screws. Note that I used a depth collar on the 1/8” pilot hole bit to keep from accidentally over-drilling the holes and into some unseen item below the roof deck. (A piece of tape works well too, though it won’t physically stop you from over-drilling.)

I used ¼”x1” zinc-coated lag screws (shiny, not hot-dipped galvanized, though those would work too) from my local hardware store. I also used ¼”x1/16” nylon washers as an insulating washer between the zinc-coated bolts and the aluminum brackets to prevent dissimilar metal galvanic corrosion. Probably not necessary… probably.

I chose to use ¼” lag screws instead of the smaller (but longer), self-tapping screws that came with the Renogy bracket kit mostly because I wanted the bigger ”bite” that the lag screws offer. And since we’re attaching to 3/8” plywood, the bigger bite is preferable, especially when the panels are exposed to those 80-90 mph winds we discussed earlier.

Drill an 1/8th inch pilot hole and then drive a lag screw w/nylon washer into each of the eight mounting holes on the z-brackets. Hand tighten each lag screw to ensure that you do NOT overtighten and strip them out! Again, it's easy to do with 3/8" plywood and an impact driver.

Next, clean the roof surface with a little bit of isopropyl (rubbing) alcohol (or your favorite cleaner) to prepare the surface for the zip-tie mounts. Then, place the mounts under the wires running between the panels. Give the adhesive a few minutes to stick well, and then zip-tie the wires to the mounts. This keeps the wires from flapping about in the turbulent airflow on the roof. Be sure to place a couple of the mounts around the wire connectors since their larger diameter will induce more movement in a slip stream.

Once the wires are zip-tied down and the panel mount lag screws are in, it’s time to seal everything with Dicor self-leveling sealant. I cover the zip-tie mounts with Dicor to lock everything together and add a bit of adhesion. However, the Dicor on the panel z-bracket mounts is for corrosion resistance and water-proofing. Be sure to get good, continuous coverage around the mounting bolt heads and the edges of the brackets. Plan to use the entire tube of Dicor during the installation of the panel.



Panel installed and sealed with self-leveling Dicor.


A word about the z-bracket mounts and water-proofing and/or sticking them down.
Before driving in the lag screws, many people like to use butyl two-sided tape to adhere the mounts to the roofing. I chose not to do this because a.) I don’t believe the extra “uplift” protection is necessary, and b.) I’ve had to remove and replace a panel before; not fun when you have to carve tape off of the brackets. However, putting a thin layer of Dicor down under the bracket has some value towards helping with water-proofing without adding much adhesion. If you want to take this step, then you’ll need to add a small bead of Dicor under the bracket foot BEFORE driving the lag screws into their final place and thoroughly covering them with Dicor.

Final Testing:
And you’re done with installation! Now, perform a final test by once again measuring the total amperage supplied to your partially charged battery bank. You should see the amperage (from the solar controller to your battery bank via your battery monitor) double in strength. I noticed that in full sun (solar radiation value 1096 W/m2), my two panels were producing 18.2A, which was a significant increase from the single panel output in similar sunlight conditions, and should run the already-chilled 12V refrigerator and still have ~10 amps to add to the battery bank/12V bus. Your mileage may vary.
Good luck!

Melsman

[Country Campers]

Fantastic write up! Thanks for sharing.

Brian

[Melsman]

Thank you, Brian.

Melsman

[howson]

Melsman -- I agree with Brian. Superb documentation. The rationale for the way you wired in the Renogy in series (along with the "mismatching" rationale) is excellent, too.

Howard

P.S. Added the "modification" tag to your first post so it's found when individuals are searching the Solar channel (and that tag).

[Melsman]

Thanks for the kind words, Howard.

Melsman

[Speakeasy]

Melsman Thanks for the detailed write up.
I followed your post to add a 175w Renology panel to my 2024 XLS 23LDE. The only difference in my install is a vent that forced me to move the new panel a couple of inches forward, and the factory connectors were actually MC4 connectors. Maybe a change for 24?
I didn’t have to cut any connectors, just make a short jumper from the Renology - minus connector to the rooftop solar box.
Super simple, but drilling that first hole in a new roof was a high pucker factor event…

Thanks again!

[Eleven99]

I love modifications.....This is about one of the best write-ups that I have seen for a modification. I would really like to add another panel...unfortunately my fake knees will no longer allow me to kneel. So, I will have to find an RV tech to do the install using your write up as a reference. Thanks for the awesome effort....I appreciate it. 👍 👊

[BobnJen]

Kudos for taking the time to write such an easy to follow procedure. May I ask what batteries are you powering?

[COReflection]

This post goes into detail about adding an additional solar panel to the existing factory installed solar panel/solar controller package on my 2023 22MLE. I do this in four different sections...

Good write-up and very similar to what I did on my Reflection about a year ago. I added (4) of the Renogy 100 w panels to my existing 165 Furrion for a total of 565 watts. I used my Furrion solar controller for a few trips but then decided to switch to a Victron. I've taken in over 500w during direct sunlight with my setup and couldn't be happier. All my (5) panels are also running in series and used to refuel my 560ah of LiP04 batteries for boondocking. I did all the work myself and am quite happy with the results. I also added a 2K watt inverter and can now run all the outlets in the camper too. Great job!

[Melsman]

Kudos for taking the time to write such an easy to follow procedure. May I ask what batteries are you powering?

My coach batteries are two (2) 6 volt deep cycle lead acid batteries connected in series. The batteries are Deka ProMaster batteries (supplied by the trailer dealer).

[Mitchell & Kitty]

Excellent writeup! I've wanted to add a panel to mine since day 1 but was a little leery of what panel to add. My first thought was to remove the existing Furion and just add 2 new identical panels; but the cost is doubled that way. hmmm... I think I see a future project brewing.

[steveluannj]

I am following your procedure, but am adding 2 panels. So far I have confirmed that the way you attached the brackets is correct- you need either a Nylock or loctite to keep the bolts that hold the panel to the brackets tight- the locking nut is rendered ineffective by the flat washers underneath- assuming you used them. I used red high strength loctite- and I hope I never need to remove them! I also looked at the included self drilling screws, and they are designed to drill and form threads in thin metal, so they are not the correct option for the wood in the roof- I think the hole would be too big and the threads too shallow to develop much strength in wood- so good choice switching out the screws there as well. I am going with 3 panels, to max out my controller, and hopefully have plenty to boondock with. Your clear directions and technical explanation gave me the confidence to start on this upgrade. I owe you a beer if we ever meet in person!

I am installing on a 280RS, 5th wheel, and I felt nervous about putting the panel as far forward as the factory one. The roof starts to curve so severely the front that the brackets did not sit well, and rather than torque it down and bend it, I moved the panel back and used the flat part of the roof.

I have been trying to convince myself that this is all working as designed. I can't trust the shunt meter I bought- but the most the charge controller reported today was 14 amps. I did see over 60V open circuit, which seems right, but the solar voltage dropped into the 40s when I pulled power from the unit. I checked all of the connections, and none seem loose or were getting hot, and I used larger wires than the panels had for my wire extensions. I do worry that the charging was slowing because the battery was over 90% full, but I plugged in to the shore power and the converter added 25 amps no problem. I do have some shading of the panels in the afternoon, so tomorrow I will drain down the battery in the morning, and pull the trailer into full sun around noon and see if I can get more than 175 watts

EDIT: After several conversations with Amped Outdoors, they sent me a new shunt meter, and that fixed the problem. I do like this meter because it attaches directly to the battery terminal, and is bluetooth, so the install was easy. Now I have seen over 25 amps the battery, and conditions have not been ideal yet. The one night I checked, the loss in the battery was about 10% overnight, so I have more than enough when the furnace does not run. I still plan to apply for solar credit on the system, so I should be getting $300 back on my taxes next year. I also will be considering selling my 2 generators if we don't end up needing them for A/C- we did not do that for the last 3 years, so ny net cost for this upgrade might end up to be zero!