solar panels on rubber roof, what did/would you do?

[mannebk]

Hi together,


Manny from Germany, with the sight unseen, bought and paid for 97 National Dolphin 535 "mechanics" motorhome via Craigslist from last year.

If you want to go straight to my questions, go all the way to the end to the bold headline secion.


If you want the background, read on.


So last year we had lots of fun after I got my Vortec 7400 up and running. With some hick-ups, true, but in the end it was a fun holiday.


Except, we had not so much fun with the availability of power (and a long laundry list to fix before the next trip).

Mostly cause I went cheap on batteries, as I wanted some sort of metal hybrid and a decent inverter, but since I had no clue what I did actually had bought sight unseen, and no time to wait for deliveries after I knew, I went cheap on the batteries, and we made it through, barely though.


So what were our issues? Obviously, our (EU) stuff works just fine with 120V if it's wide-range input; unfortunately, some of my medical stuff isn't wide-range, but works just fine on a 240V split-phase outlet. So I had an 8-week holiday with no oxygen. Not good. But again, I made it though and had to pay for it.


Besides that, since we are from Germany, we would also like to use our "not wide range" but 230V only stuff, e.g., a 3kW water kettle that boils a quart in 90 seconds flat. So hot water for a cup of tea or coffee is only 20 seconds away. In the 8 weeks I was in the US last time, I really got upset with our gen set friendly 800w water kettle... First start the gen set, then wait till warmed up, then start the kettle, then wait 10 minutes till water boils. No, sir, I'm not going to have 20 mins for a cup of coffee again. Sure, I could have used the propane stove, but not THAT much faster, and the electric kettle was up front and the switch for the gen set too, and I've been the only driver and kind of tied to that pilot's chair up front with a handicapped and a kid on board...


So I set out to find a 12V-based true sine wave true split phase 240V inverter with a decent power range. Like 130% of my preferred water kettle as continuous power, plus a decent peak overhead of 200% a few seconds. Since a 3kw 50Hz water kettle is an inductive load, at 60Hz we are talking about 3600 Watts. The maximum a Schuko (Typ F / CEE7/4) plug can handle continuously is 16A at 230V equals 3680W. Since we run at 240, we can have a bit more, like 3840W. So it should be just fine. But the inverter needed to be up for it.


I had not much luck finding one last year, but I was basically looking at Voltronic clones (EASunPower comes to mind and is widely advertised on YT). But they have nothing in the 12V range that gets even close to what I need, but lots to choose from in 24/48V, but I did not want to refit my RV to 24 or 48V. But just a few days ago I tried again and stumbled over sungoldpower, not affiliated in any sort or form, and ordered this true split phase 4kw 12V unit with charger:


https://sungoldpower.com/products/40...r-with-charger


This one comes with a gen set remote start, grid failover and includes a charger, so when I am at a campground, I don't need to worry; I can just plug in and the RV is switched over to the campground 15 seconds later, and batteries will get charged. And if I overpower the shore power, the inverter kicks in under 10 ms. We won't even notice. The same goes with the gen set. If I need power, I can charge with this inverter from the gen set, while switching my old stock charger and all my load to the starter battery during charging.



After ordering that inverter, I tried to find sodium ion batteries, but had not much luck, so I ordered 8 pcs 210ah lifepos and two JK BMS B2A8S20P-Heat-CAN including heater outlet and CAN capability for a start.


I aim to use a Raspberry Pi with Venus OS to monitor them, since the JK BMS display options are a sad joke with the usual Chinese usability score of minus something. Where something fantastic would score +100 and something terrible would get zero, they would get minus a lot for those displays.


I usually do substantial driving, last time it was I think 4000 miles, this time we start again in central Colorado and go all the way to LA and San Diego and then up all the way to Vancouver, BC, the first two weeks of my 10 weeks stay is already over 2000 miles, and it won't get any better.


I therefore elected to add a DC-DC charger. Reasoning behind this is I don't want to burn up my alternator with a 420AH lifepo load. An empty bank can suck up 1C 420A easily from the 120A alternator. Clearly that doesn't mix well, and especially since with the big US engines the alternator spins slowly at just 1500 highway rpm, it's likely to burn up trying to stabilize the voltage at 13.8v with a 400A load on it and not much airflow through the alternator.


After some research, I chose this one:


https://www.aliexpress.us/item/3256802619013003.html

With it, I can have the chargers display up front next to my seat and monitor my batteries and alternator while driving. And pushing 60 amps into the lifepo banks is a start.


But keep in mind that any time I'm on shore power or the gen set runs, my inverter pushes also 120A into the batteries.


However, I might add a second DC-DC one later if I add more capacity and also upgrade the alternator to a high current version.


I also will be able to read the BT part of that DC-DC thing with the Venus OS on my Pi, to track it more closely than I ever could while driving.


But mostly, I wanted to make sure, it charges even when the engine is just idling, something an alternator usually doesn't do too well with lead acid sock installs.


In the end, I want to be able to run the rear roof A/Cs off that link while driving, and still charge my battery bank at a decent rate. So I probably will have to go to a 400A alternator and get a 300A DC-DC charger. But that's for future me. The same goes for some Victron smart shunts that I want to add for even more monitoring, because these can be monitored with the Pi and Venus OS too; these BMSs are just not the right thing to track battery SOC levels.


So my choice of DC-DC charger comes with a MPPT tracker, for less than 30 bucks extra. A stand alone MPPT would have cost about the same and would not have the integration and monitoring option, so I went with it and took the option.


So much for the background, and now my questions:


Since I have an MPPT that's good for 30A at max 50V, I would like to add some solar panels to the roof.

Thought about 2KWp if I can fit it. Since when I get more than the MTTP can handle, the MPPT will just run at full capacity and cap the rest. But if I have shading, I want the maximum that I could get from my roof. And if I see it too often capping and/or my batteries too often empty, I'll just add a second MTTP unit.

So I have a rubber roof on my 97 Dolphin.

1. Did/would you go with flex or rigid?
2. What size panel did/would you choose?
3. How did/would you mount it?
4. Someone got a roof layout from a 97 National Dolphin 535?

I've got dual A/C, the fridge vent, an old TV antenna over the copilot seat, and 4 roof vents, one in the bathroom on the driver side, and 3 down the middle. So I guess smaller panels would be better.


What's your take on this?


Cheers Manny

[Bobby F]

I'm only going to jump in here with one point, which I didn't consider before mounting my panels and now regret.

I mounted my panels onto my roof - rubber, with thin paneling beneath - using the standard Z-brackets:

They work great, I've never had any issue with them not being secure, and they're cheap.

But . . .

Once mounted, the only way to pull up a panel is to remove the screws that go into the rubber and paneling of the roof. The panel-to-bracket screws are inaccessible. From a machinist standpoint, a wood-screw attachment is not meant to be a reusable attachment.

I would find a different bracket that would allow for the removal of the panel from the bracket, leaving the bracket screwed to the roof.

Small point, I know, but I wish I knew better back then. I'd probably choose a rack system if I had a do-over.


(As I think about this, I'll add one more comment: )


I have 600w of panels, and a Victron 100/30 controller. I agree that overpaneling a controller is a viable option, but based on how often I clip off the 30-amp limit, I think that 2000w of panels on a 50/30 controller is too much for that controller. Too much will be clipped.

[mannebk]

Thanks a lot for your insights.


I look into a mounting system with C rails then, probably, and fabricate some L-brackets to rivet to the panels. So if I have to take em off or want to change to another form factor, I can unscrew the bracket from the C rail and remount what ever I need.


Thanks for that hint :-) exactly why I asked here.


And regarding the clipping, indeed, I agree 50v/30a at best delivers 1,5kW, but that's clearly total nonsense. Since the 50V is the input side limit, but the 30A is the output side limit, and 30A at 12V is only 360W, and I never thought about that...


THANK YOU for saving me a lot of headaches.


again exactly the reason why I asked here.


i will add an other MPPT with more capacity


but guys, keep your insights coming pls.

[ttavasc]

Renogy sells a curved Z bracket for mounting panels which is what I used. This allows for the panel to be removed without removing the bracket that is screwed to the roof. They also work better for roofs that have more curve to them.

Renogy Curved Z Brackets

[SafariBen]

I bet it will be quite the puzzle to get 2kw on that roof. You can cover the A/C's, as long as it doesn't cause them to recirculate air.



Should have gone with 48V, put the 12v house loads on the chassis battery, and charge the chassis with a DC to DC. 4kw 12v inverter and 8 batteries is crazy town. I'm sure you'll make it work, but why?

[mannebk]

Originally Posted by ttavasc

Renogy Curved Z Brackets

thats a nice one, thanks.

Originally Posted by SafariBen

I bet it will be quite the puzzle to get 2kw on that roof. You can cover the A/C's, as long as it doesn't cause them to recirculate air.

Should have gone with 48V, put the 12v house loads on the chassis battery, and charge the chassis with a DC to DC. 4kw 12v inverter and 8 batteries is crazy town. I'm sure you'll make it work, but why?

jep, it needs more copper. otherwise, not much change compared to converting over to 48V. Aside from finding the inverter. And with staying on 12V i have direct access to the 12v li bank with no conversion in it. Im not full time. just 8 weeks at a time. and i have friends use this RV too, so it must be fire and forget. turn on this, and just drive. dont worry if the genset starts, that just means its charging the battery. real fiere and forget, use as you need, turn that swich when you leave the RV for the next guy.


regarding 2kw on the roof. Sorry I'm a metric one, so in metric 1 m² (all imperial converted roughly: 10sqft) gives about 200wp.

I dont think a 11x2,5m (36x2,5ft) rig should have problems to get 10m² (100sqft) of solar out of the roof, sure the front is curved, and youve got all the stuff on it, but still its 28,6 m² (or 286sqft) of base surface, if i fit like 40% of it with solar, ive overachived already.


I think the main question is, to find cell sizes that fit this roof best. and have several mppt units, so you dont combine funny cell values into one MPPT and thereby kill the output.

over the master beed room alone i can have about 1350Wp installed. (3 panels with 2x1m 6,42ftx3,25ft 72 cells (450Wp)). Maybe up to the shower overhead window it fits an other panlen and we are up to 1800wp. And Im sure Ill find enough space left and right of the AC and hatches over the livingroom to fit an other 1800Wp on there.

So without using the rounded front, Im already somewhere way past 2kWp, more like 3.6kWp.


So, no, I dont think 2kwp on the roof is difficult, its just a question what cell sizes to use and how to fit the most area onto the roof and then how to wire and manage them efficiently.

And i think 60 cell panels with 5,5x3 foot and about 380Wp should fit most of the places pretty good and get me way past 2kWp. And still leave me with a foot of walking space around each panel.

[sushidogchip]

I racked mine on my roof then coated it with Henry's 887 Tropical sealant. I used 1/4" toggle bolts to attach it to the roof - 54 of them in total. It's not going anywhere as each bolt holds 600lbs of tensile strength.

[mannebk]

wow, that really looks amazing.

no issues with wind catching underneath? e.g. when passing a truck.

that air gap is probably also good to keep them cells cool and the RV too.

probably even good for aerodynamic considerations since all the stuff sticking out from the roof is covered up in one smooth surface.

what did you use 69 cell ider u2 cell panels? thr long way?

[Ivan Pacheco]

Originally Posted by sushidogchip

I racked mine on my roof then coated it with Henry's 887 Tropical sealant. I used 1/4" toggle bolts to attach it to the roof - 54 of them in total. It's not going anywhere as each bolt holds 600lbs of tensile strength.

Hi sushidogchip and everyone else,

That is a nice workaround. How's the roof coat handling up to date? How long ago did you complete the project? Thank you for your time.

[sushidogchip]

My array is 15" off the roof so it clears my front A/C shroud by 1 inch. The front 2 of 8, 550w Sungold Power panels drop down to the roof at a gentile 9.5-degree angle to ease air over the array creating a laminar airflow, so the RV is more stable going down the road, when big rigs pass, etc. I'm old and built it myself, so it took about a week to clean, prep, install and caulk the 18 feet and coat the roof with Henry's 887 lifetime guarantee 100% waterproof silicone coating. Building the rack, drilling all the holes and bolting it on the roof took another couple of days. I was able to lift the panels on the roof and bolt them in place in a single day. I threw a rope over the roof and used a couple gallon jugs of water as ballast to help me lift these heavy, bulky panels up onto the roof. It was worth the effort though.

I also have a 620-watt side mounted array that charges my 560ah 12v battery, while my 4,400w roof array charges my 320ah 48v battery.

[mannebk]

thanks for the detailed description, awesome work!!!!!

[mannebk]

Originally Posted by sushidogchip

I also have a 620-watt side mounted array that charges my 560ah 12v battery, while my 4,400w roof array charges my 320ah 48v battery.

While playing with my kid I fell and injured my back, so my wife is doing the heavy lifting regarding trip preperation, on Tuesday we board the plane, i hope it gets better till then, casuse i need to tend to kind and father, my wife stays home for the first weeks till we are all settled in... but in the mean time I got some time and more questions :-)


I figgure you got a bit above 40kwh in batteries, probably 50-80% of it being available, depending if its LiFePo or lead accid.


And you charge with two arrays totaling to 5kWp, I presume you mostly park in a way so the sun is on the passenger side to give that panel the best exposure?


Im also sure it suits you well with just one AC to have that shading on the roof and bedroom?


May I ask, how much time do you spend hooked up to power or running your genset, are you charging the 48V from your alternator too while driving? And is this configuration sufficent for beeing selfsustained?


And was there a special reason to go with sungoldpower, (i just bought my Inverter there) ?


Thank you kindly.