RV Rooftop Solar Panels

RV Solar: Part 3 - Installing Rooftop Solar Panels

Rooftop solar panels means effortless, free electricity whenever the sun is shining - and that lets us stay off grid for longer!

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Introduction

We always knew that our Renogy 100W portable solar panel wouldn't be enough to sustain us indefinitely - but it would help us learn about solar. And it did - we learned a lot!

Related:RV Solar: Part 2 - Renogy 100W Portable Solar Panel

We learned how much power we used in the RV. We learned how much power we could expect to get from a given solar panel. We learned how much difference it makes being able to tilt your panel towards the sun. We learned how the amount of power generated changes during the day. We learned about the impact of clouds, hazy weather and shade.

It was a really valuable experience.

And the portable panel worked for a surprisingly long time for us. After returning from our trip to Europe, we hit the road on 1st October 2018. We didn't install our rooftop panels until 2nd February 2019 - that's 4 months later. During this time, we charged what we could with our portable panel, used our DC to DC truck charger to charge the batteries on travel days, and after every 5 days or so of boondocking we'd duck into an RV park for a night or two to fill our batteries and dump & fill our tanks. It worked well.

Related:REDARC BCDC1240D DC to DC Charger Review

But we also learned we wanted rooftop panels. The extra capacity would let us boondock for longer, and that was our goal.

Battle Born Batteries

We want to give a HUGE shout out to Battle Born Batteries who sponsored our rooftop solar panel install. Our three 100Ah Battle Born Lithium batteries deserved more than just a 100W portable solar panel to charge them.

The great thing about Battle Born's lithium batteries is that they can bulk charge much longer than conventional lead acid batteries - in fact, we see them bulk charging to ~99%! That means they can take the full charge from both our solar panels and truck charger until almost completely full, unlike lead acid batteries which slow down on charging once they reach about 80%.

Related:RV Electrical Upgrade: Part 2 – Battle Born Lithium Batteries & Victron Inverter
Related:RV Electrical Upgrade: Part 3 – DC Charger & Truck 12V Socket

Our Battle Born batteries are the perfect complement to a roof-mounted solar array, and the combination of 300Ah of usable battery capacity plus 400W of solar lets us get out there and stay out there for longer!

Always on Liberty

I also want to give a shout out to Dan Brown from Always on Liberty. Dan and Lisa have been on the road full-time for 5 years in a variety of different RVs. Not only was Dan's insight hugely beneficial in refining our design, but Dan volunteered to help us install it.

That's right, Dan gave up his time to climb up on our RV roof with Diana and me, installing the panels and wiring everything up. And at the end of a long, tiring day, Lisa invited us both over for a home-cooked dinner.

We love our full-time RVer family - thank you Dan and Lisa!

Design Overview

Both Diana and I being former engineers, our first step is always to come up with a detailed plan. I actually wrote up an 8-page Google Doc (!!), stepping through everything we planned to do. We reviewed this and iterated on it until we were completely happy that the plan was good. This was especially important since we planned to do the installation while boondocking, miles away from the nearest hardware store or Amazon Locker. Making sure we had everything lined up ahead of time was critical.

Why 400W?

Based on the data we had collected over the past 4 months, we figured we wanted to generate about 120Ah per day to cover our daily electrical usage. A 100W solar panel generates about 8A at full power, and a rough guide for calculating daily generation is to multiply that by 4 hours - i.e. assume you have 4 hours of perfect sunlight per day. Based on that, each 100W solar panel would produce ~32Ah per day.

Four panels, each producing 32Ah per day, would give us 128Ah per day - just over our target of 120Ah. Also, we'd still have the 100W portable panel which we could use for an extra power boost if necessary.

Decisions

It's easy to get carried away when building a solar system on an RV - solar arrays well in excess of 2,000W are not uncommon. We chose to make a series of decisions that would guide our choices later.

  1. Install four 100W solar panels now, leaving an option to install two more (and maybe more) later if we needed them.
  2. Use Renogy solar panels, since they're a company we don't think is likely to disappear meaning it'll be easier to find matching panels if we do want to expand later.
  3. Configure the panels in 2s2p. This means two parallel strings, each with two panels in series, making it easy to add pairs of panels in future. This is a reasonable compromise between the benefits of series (higher voltage means lower current and less loss on the wires) and parallel (less vulnerable to partial shading).
  4. We will not tilt the panels, since although this would improve solar power generation by up to 30% in winter, we move too frequently and I don't want to be climbing up on the roof all the time. Plus, with our small and heavily domed RV roof, tilting without shading other panels would be tricky.
  5. Replace rooftop combiner box with a new box from AM Solar. We had serious concerns about the safety of the factory-installed combiner box from Zamp, so we wanted to remove this.
  6. Fuse each pair of panels with an inline fuse, then hardware these into the combiner box. The AM Solar combiner box does not include a fuse, so this keeps everything safe on the roof.
  7. Remove all MC4 connectors and hardwire everything together with butt-splices. I'm not a fan of removable connectors in hardwired applications (more potential for failure), and we can always pull a fuse if we need to cut the power.
  8. Use the wire in the front cap that runs from the roof down to the front electrical bay. Our RV came with this wire in place, and although it's only 8AWG (not bad, but I'd probably have chosen slightly thicker if I could), it's secured in the front cap in such a way that pulling a new wire would be next to impossible. It's good enough.

Based on these decisions, we came up with a plan.

Parts List

Below is a summary of the components we used for this installation. Some of these were purchased in larger quantities because we would be using them later, or we had purchased them for other mods for the trailer. You may need more or less depending on your exact requirements, including the number of panels, location of electrical connections, and size of your RV.

Components

These are the major components that our system needed.

ItemQuantity
100W Renogy Solar Panel (Compact Design)4
Renogy Curved Z-Bracket (4 pack)4
Victron SmartSolar MPPT 100/50 Solar Charge Controller1
AM Solar Roof C-Box1
Blue Sea Systems 40A DC Breaker1
Blue Sea Systems 60A DC Breaker1

There are a few items in the list above that are sized to suit our system. The Victron SmartSolar MPPT 100/50 is actually able to support a larger installation than we have (up to 700W), and the Victron SmartSolar MPPT 100/30 would have been sufficient - it can handle up to 440W. However, since we were designing the system to potentially scale in future, we elected to oversize this component.

Similarly with the DC breakers: 40A and 60A. These are larger than necessary for this size of system (according to the solar panel specifications, the maximum current we should see would be 12.48A on the input side, and ~33A on the outside side of the solar charger controller), but are rated appropriately for the wiring we're using and to allow future expansion. If you are planning a larger system, then make sure to size these accordingly, and select an appropriate wire gauge for your install.

Also notable is that these DC breakers are rated up to 48V DC. The 100W Renogy panels have an open-circuit voltage (Voc) of 21.6V, so two in series totals 43.2V - less than the 48V maximum. However, if you're intending on running more than 2 strings in parallel (or panels with a higher Voc), you would need to find an appropriate DC breaker - this was one of the reasons we chose to only use strings of two panels.

Materials

I've grouped together all the miscellaneous items here that we used, but you may need to adjust the quantities to suit your needs.

ItemQuantity
VHB Tape1
TEMCo Welding Cable - 6 AWG Black25ft
TEMCo Solar Wire - 10 AWG100ft
6 AWG butt-splice connectors4
10 AWG butt-splice connectors10
1/4" 6 AWG ring terminals4
3/8" 6 AWG ring terminals2
Adhesive-lined heat shrink tubing
Inline fuse holder2
15A fuses2
Butyl tape1
Dicor Self-Leveling Lap Sealant (White)3
1/2" Liquid Tight Connector4
10 AWG Hexagonal Ferrules4
UV Resistant Zip Ties1
Clear RTV Silicone Sealant1

Tools

Below are the specific tools you'll need, but I'm assuming you also have access to screwdrivers, wrenches, sockets, etc. For installing Renogy panels, a couple of 10mm ratcheting wrenches would be very useful too!

ItemQuantity
Plastic Putty Knife1
Wire Cutter / Stripper / Crimper1
Cable Cutters1
Hot Air Gun1
Hydraulic Cable Crimping Tool1
Hexagonal Ferrule Crimping Tool1

Installation Procedure

I always like to break down an installation like this into steps, with each one being as discrete as possible. Given the realities of everyday life, I also like to start with the least disruptive things so it's easier to stop at any point.

Step 1: Install Solar Charge Controller & DC Breakers

Our trailer came “pre-wired for solar”, but it assumes that your battery is installed on the trailer tongue. We needed to extend these wires into our electrical bay and install the solar charger plus two breakers - one on the input and one on the output. The input breaker protects the wiring but also gives us a convenient switch to disconnect incoming solar power if we need to. If the solar charge controller shorts on failure, it would short across the battery so it’s important the output is fused.

We chose to install the Victron MPPT solar charge controller and DC breakers under the bed, next to our batteries, inverter, etc. As with some of the other components, I mounted these on the back wall using double-sided VHB tape and self-tapping screws. Ensure both DC breakers are open (i.e. not connected).

I've been saving this spot for the solar charge controller.
I've been saving this spot for the solar charge controller.

The wiring in our trailer also assumes that the solar charge controller will be mounted above the bed, near the front cap of the RV. There is an access panel in the cabinet here, and behind the access panel are some wires. One pair of wires comes down from the rooftop combiner box, and the other pair of wires (red and white) extends down to the electrical bay. These are 8 AWG wires, but I was able to securely splice them together using two 6 AWG butt connectors and some adhesive lined heat shrink tubing.

Using two more butt connectors, adhesive lined heat shrink tubing and some 6 AWG wire, I extended the red and white wires from the front electrical bay into the space under the bed. I now have a pair of wires extending from the roof of the RV, all the way to the near the Victron MPPT solar charge controller. I crimped a 1/4" ring terminal onto the positive wire and connected it to the 40A DC Breaker. I stripped the end of the negative wire and connected it to the "PV —" screw terminal on the solar charge controller. I then crimped a 1/4" ring terminal on one end of a short jumper cable to connect the 40A DC Breaker to the "PV+" screw terminal on the solar charge controller. I used adhesive lined heat shrink tubing over all the ring terminal crimps.

Finally, I made 3 more short cables to connect the output side of the solar charge controller into the 12V system. One cable from the solar charge controller "Battery —" to my ground bus bar; one cable from the solar charge controller "Battery +" to the 60A DC Breaker; and one cable from the 60A DC Breaker to my positive bus bar. I crimped 1/4" ring terminals on the breaker connections, and 3/8" ring terminals on the bus bar connections. Again, I used adhesive lined heat shrink tubing over all the ring terminal crimps.

Our solar charge controller is now installed, protected by breakers on the input and output sides, with wires running all the way to the roof.

Step 2: Install AM Solar Roof-C Box

The existing rooftop combiner box is unfit for purpose - it contains a thermal breaker rated to only 14VDC and our system will be operating at 35.6VDC and peaking at 43.2VDC. Further, it expects SAE connectors but we’ll be hard-wiring our system. We therefore need to remove the existing rooftop combiner box and replace it with the new AM Solar Roof C-Box, but keep the existing wires that runs down to the electrical bay.

Related:Unsafe Zamp Solar Combiner Box

We chose to use the AM Solar combiner box - this is a well-made, sealed rooftop box with a positive and negative bus bar inside. It has knock-outs for Liquid Tight connectors on the sides to connect the panels into the bus bars.

The AM Solar Roof C-Box is a well constructed combiner box with sturdy bus bars inside.
The AM Solar Roof C-Box is a well constructed combiner box with sturdy bus bars inside.

The first step is to remove the existing Zamp combiner box. We took our time with a plastic putty knife, removing the existing sealant and butyl tape without damaging the roof, then unscrewing the box from the roof. I cut the wires leaving plenty of slack to make it easy to reattach to the new AM Solar combiner box.

Following the instructions provided with the AM Solar combiner box, I mounted it and secured it in place. I cut the wires coming up from below to length, and screwed them into the combiner box bus bars. Don't seal it with Dicor or attach the lid just yet - we need to put the solar wires in first.

Step 3: Prepare Solar Panels

We need to do some wiring for the solar panels, and it's much easier to do this on the ground than on the roof of the RV!

Each Renogy solar panel has a junction box on the back with two pigtail wires coming out - one positive, one negative - terminated with MC4 connectors. Since we didn't want to use MC4 connectors, I cut these off about 9" from the junction box; but not before clearly marking the back of the panels with + and - symbols next to the respective wires! Use a multimeter to double check these if you're in any doubt. Careful also that the bare wires don't touch each other once you've cut them.

This is also a good chance to test all the panels and make sure you're seeing a voltage across them! It's much easier to replace a faulty panel now than when it's mounted on the roof.

As an aside, the original plan was to remove their wires completely, and then install my own wires through the Liquid Tight connectors into the junction box - unfortunately the wires are soldered to the panel, so this seemed more hassle than it was worth. Cutting the MC4 connectors off is much easier!

The plan is to have two parallel strings, each containing two panels in series. I numbered the strings 1 and 2, and lettered the panels A and B; where A is the positive side and B is the negative side. I used a permanent marker to label the panels: 1A, 1B, 2A, 2B.

On the A panels, I connected an inline fuse holder to the positive side using 10 AWG butt connectors, putting adhesive lined heat shrink tubing over the connection. I then crimped one side of another butt connector to the other side of the inline fuse holder.

Adventurous Tip: I made a mistake in our install and used ATC automotive fuses, however I later discovered that these are only rated to 32V. In the parts list, I have linked to glass fuses and inline holders that are rated to a much higher voltage.

Do not install the fuses yet: this reduces the risk of accidentally shorting something or being electrocuted during the installation.

I then attached one side of a 10AWG butt connector to each of the other solar panel wires - the negative wires on the A panels, plus both positive and negative wires on the B panels.

Lastly, we mounted the Renogy Curved Z-Brackets onto the four solar panels, according to the instructions provided. We didn't tighten the mounts too much though, as we would be removing them shortly.

Here's what a finished A panel looks like. You can see it's labeled 2A with + and - wires marked, the inline fuse is installed, butt connectors are spliced onto the ends, and the mounts fitted too . Much easier to do this on the ground!
Here's what a finished A panel looks like. You can see it's labeled 2A with + and - wires marked, the inline fuse is installed, butt connectors are spliced onto the ends, and the mounts fitted too . Much easier to do this on the ground!

Incidentally, one of our panels had a slightly different layout of mounting holes on the rails, even though it was an identical model number to the others, so we drilled new holes that aligned with the other three panels for consistency.

Step 4: Mounting the Solar Panels

We had already measured out on the roof where we would be placing the solar panels, but there's really no comparison for actually getting the panels up there and maneuvering them. The 100W panels aren't too heavy so it's easy to do, but Dan's ladder helped a lot since then someone could stand at the side while another was up on the roof.

Based on our measurements, and verifying by placing the panels, we found we could fit 10x 100W panels on our roof! Far more than we needed - for now, at least! We chose the locations for these four panels, electing to mount them near the front of the roof where they would least likely be shaded. Once they were all in position, we carefully mounted each panel, one by one.

This was by far Diana's least favorite part as it meant screwing holes into the roof. The Renogy brackets come with sturdy-looking self-tapping screws, and our roof has a thick plywood layer underneath. But each bracket takes 4 screws, there are 4 brackets per panel, and we were installing 4 panels - that means 64 holes in the roof!

The process was the same for each one: tilt the panel to one side and put a strip of butyl tape under the bracket, then lay it carefully back down and screw in the 4 self-tapping screws. Tilt the other way and repeat until all four brackets are taped and screwed.

Adventurous Tip: Use an electric screwdriver with a torque control, and gradually ramp it up. I put all the screws in at setting 3, then went back round at setting 5 afterwards. This was enough torque to put the screws in tight without stripping the holes.

At this point, we then removed all the panels from their mounts, leaving just the mounts on the roof. This is fiddly (really fiddly!), especially working in tight conditions on a curved RV roof, but a couple of ratcheting 10mm wrenches would make this a whole lot easier! We didn't have those, so we made do with a standard 10mm wrench, a socket and a crescent wrench.

So why did we remove them? To put Dicor Self-Leveling Lap Sealant over the brackets. Although you can do this with the panels in place, it's much easier to get the Dicor thoroughly around the back of the brackets underneath the panels when the panels aren't in place. A leak in the roof is one of the worst things in an RV, so we decided it was worth taking the time to do this properly.

The goal with Dicor isn't to be neat, it's to be thorough - a little messy is far better than leaving gaps uncovered!
The goal with Dicor isn't to be neat, it's to be thorough - a little messy is far better than leaving gaps uncovered!

While we had the Dicor out, we sealed around the bottom of the AM Solar Roof C-Box too.

Wait for the Dicor to dry, or, if like us you're too impatient, be very careful when you mount the panels back on so you don't get Dicor on the panels, your hands, clothes, shoes, tools....yeah, it gets everywhere!

A finished solar panel mounted in place. The tiny solar panel on the left is the trickle charger that came with our RV. It puts out up to 10W and is designed to counteract the natural self-discharge of lead acid batteries - we don't need it on our setup, but it's easy to leave it than remove it and fill the holes.
A finished solar panel mounted in place. The tiny solar panel on the left is the trickle charger that came with our RV. It puts out up to 10W and is designed to counteract the natural self-discharge of lead acid batteries - we don't need it on our setup, but it's easy to leave it than remove it and fill the holes.

Step 5: Wiring Up the Panels

We had plenty of slack underneath the panels to reach the wires, but again, if you've been too impatient (like us) to wait for the Dicor to fully cure, then try and avoid getting the wires in the Dicor! The process for connecting the panels is identical with each string.

Starting with string 1, use 10 AWG solar wire and some heat shrink tubing to connect A- to B+, using the butt connectors you attached earlier.

Then run a length of wire from B- to the negative bus bar inside the AM Solar combiner box. You'll need to use a 1/2" Liquid Tight connector for the knockout in the side. I also put a generous dose of Clear RTV Silicone Sealant in the connector to help seal it too.

At this point, most people would then just strip the wire, put it in the bus bar and screw it down. However, I really don't like putting thin, stranded wires into a screw terminal - the screw can damage the wires and cause issues over time. So we decided to crimp on hexagonal ferrules. They provide a solid terminus on the wire for the screw terminal to press into.

We did the same thing on the positive side, splicing a wire into the positive side of the inline fuse holder, and running it to the positive bus bar, again, crimped with a hexagonal ferrule.

Dan helping us to wire up all the solar panels on the roof.
Dan helping us to wire up all the solar panels on the roof.

The process is then simply repeated on the other string however it was getting late in the afternoon, so we decided not to rush to connect up the other string. We would do that the next day. But, we couldn't call it a day without testing it! We did some quick preliminary tests, temporarily installed the fuses and fired things up (spoiler alert, we did step 6 a little out of sequence).

We turned it on at 5:40pm, just before the sun went down, and saw 2W coming in! By 6pm, the sun (and solar power) were gone.

As the sun rose the next day, we saw rooftop solar power coming in - we earned our first 1W at 7:58am. We turned the system off, disconnected the fuses, removed the breakers, and climbed back up on the roof to connect up the second string of panels.

Dan climbed up on the roof with us the next morning to help us get the final solar panels connected. At least the Dicor wasn't as sticky in the morning!
Dan climbed up on the roof with us the next morning to help us get the final solar panels connected. At least the Dicor wasn't as sticky in the morning!

Apart from connecting fuses and closing breakers, everything was wired up. We used some zip ties to tidy up all the wires and keep them secure on the roof.

Step 6: Check, Connect & Test

Now is a great time to double check all your connections. Make sure all wires are going where they are supposed to, all crimps are tight and sealed with heat shrink tubing. If you forgot to heat shrink any butt splice connectors then do this now. And if you forgot to put extra heat shrink tubing over the top of any connections, you can use some electrical tape - it's better than nothing.

I installed 15A fuses in each of the fuse holders in turn, and checked we had voltage across the positive and negative bus bars. Check!

Then, with Diana in the RV, she turned on the Victron SmartSolar MPPT charger by closing the 60A DC breaker on the output side. Although this may sound counterintuitive, the charger uses a small amount of power from the batteries to operate, including running its Bluetooth system. Once it was turned on, I was able to pair it with my phone and get it set up.

Once the app was working on my phone, Diana closed the 40A DC breaker on the input side of the solar charge controller, letting all that sunny goodness flow in!

And it did; the system worked!

Step 7: Seal Everything

Now that everything is tested and working, it can all be sealed up. We screwed the lid onto the AM Solar combiner box, using generous amounts of Clear RTV Silicone Sealant in and over the screw holes.

Sealing up the AM Solar Roof C-Box. The nice thing about the RTV silicone sealant is it stays fairly soft so if you need to open the box in future, you can.
Sealing up the AM Solar Roof C-Box. The nice thing about the RTV silicone sealant is it stays fairly soft so if you need to open the box in future, you can.

I had one last look over all the Dicor to make sure there were no gaps, and we set about tidying up.

Installation complete!

The finished install - 400W of solar panels on the roof of our RV. Free, effortless power whenever the sun is shining!
The finished install - 400W of solar panels on the roof of our RV. Free, effortless power whenever the sun is shining!

Results

We turned the system back on at 10:45am but, as is always the case in these situations, Saturday 2nd February 2019 was a cloudy day in Kofa, AZ.

However, as the sun peeked through the clouds, we saw it register on our system - we were generating solar power from our roof! 52W!

Here's our power generation from Saturday. You can see where we turned off the system to connect up the final 200W of panels. The curve is jagged because of clouds moving across the sky.
Here's our power generation from Saturday. You can see where we turned off the system to connect up the final 200W of panels. The curve is jagged because of clouds moving across the sky.

Fortunately, Sunday was a much sunnier day, and we could really see what the system was capable of. We peaked at a little over 220W for a couple hours or so around lunchtime, which for February isn't too bad at all. Along with our portable panel, it was enough to take us from 42% battery at 8am on Sunday morning to 75% by 5pm - we had picked up 33%, or a net increase of about 100Ah during the day. That was pretty much inline with our expectations, and over the next few days we saw our overall battery levels start to rise slowly.

Sunday was much better - we generated solar power from 8am until 6pm. Barely a cloud in the sky!
Sunday was much better - we generated solar power from 8am until 6pm. Barely a cloud in the sky!

Conclusion

The whole installation process took us less than a day, and we were taking our time so as not to mistakes. Plus, filming and photographing these things adds a lot of time too! That being said, Dan's help was invaluable - again, thank you! And another big thank you to Battle Born Batteries for sponsoring this installation - the new solar panels work great alongside our batteries!

Once the installing is complete, rooftop solar is an effortless way to produce free electricity in our RV. As I write this now, it's been over six months since we installed it. I actually struggle to remember what life was like before we had it - it seems so intuitive to us now that we should be generating power for free all day long. Plus, although our roof is small, because of where we mounted the panels we don't have to worry too much about orienting the RV to face a particular direction.

Make sure to join us for Part 4, when we'll be talking through why we no longer have a portable solar panel and instead installed another 200W on the roof of our RV!

Hope you enjoyed this post, and let us know in the comments below if you have any questions!

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