Solar Panel Layout and Battery Charging for Teardrop Travel Trailer

kelly · January 2015

I own a Tab travel trailer, with a curved, teardrop roof. I plan to install two flexible 100 W solar panels on the roof. In addition, I want to keep the option to use two additional 100W folding rigid panels to be set up on the ground. My question has to do with the best way to handle the battery charging in this set-up. I expect that the roof-mounted solar panels will have a very low efficiency, since they will be arranged at random angles to the sun and it will be rare that both paels will be in the sun, and when they are, neither will be at a good angle...

If I wire all four panels in parallel, I could use an MPPT controller, like a Bluesky 3000i, or a Midnite Solar Kid, or even something like a Rogue MPT-3048. This plan concerns me somewhat because the flexible panels are not exactly the same technology as the rigid panels; I also am not completely sure what will happen with radically mismatched parallel amperages, although on both points I assume it would be fine and the charge controller would simply find a panel voltage that would maximize total power. However, since I will effectively have three totally independent solar arrays, I am not sure if I wouldn't be better off using three separate controllers instead, although I cannot put into words what doing that would accomplish.

This system will intially be installed with a 12V 80 AH deep cycle battery that was included with the trailer by the manufacturer; I will probably change that to a pair of 6V, 300AH AGM batteries at some point. There is no inverter on the system right now, but I might add a 1000W pure-sine-wave inverter in the future. The main power draw (the reason for the solar panels) is a 3 amp (when running) DC refrigerator.

Does anybody have any advice for the best option for controlling the battery charge on this PV system?

techntrek · January 2015

Re: Solar Panel Layout and Battery Charging for Teardrop Travel Trailer

I own an R-pod, similar in shape. I would mount two rigid panels straight off the rear (parallel to the ground), which may actually improve your mpg going down the road. I run a forum for pod owners and members have run simulations of the airflow coming off the back of these teardrop-ish trailers and they are much less aerodynamic than they appear due to suction created at the rear from the curve.

Ignoring that, two flat PVs will provide more output than 4 flexible panels. Flex panels have a much lower efficiency and the flat panels will catch more sun.

No matter how many panels you put on an RV, due to the other stuff on the roof and random trees at campsites you'll often get shading. Putting each one on its own controller will give you the maximum output.

kelly · January 2015

Re: Solar Panel Layout and Battery Charging for Teardrop Travel Trailer

I like your suggestion, thanks. I think I am going to try to attach it with a hinge at the top edge and install a DC linear actuator halfway down, near the clamshell hinge. Extending the actuator when I am parked will allow me to level out the panel, or even raise it up. It will allow me a lot of flexibility.

AuricTech · January 2015

Re: Solar Panel Layout and Battery Charging for Teardrop Travel Trailer

Here's a half-baked idea that might, if your T@B trailer can support it, turn out to produce a metaphorically-tasty dish of power:

Rig something above the door that would serve as an anchor for a pair of Renogy's 100W flexible panels, with the short edge of each panel anchored to the trailer*. Once you park, set up two such panels as an awning over the door, with two guy-roped poles to support the edge that's away from the trailer. Connect the two panels in parallel via MC4 connectors, then feed the resulting connection into an Anderson Powerpole connector**. Mate that with a partner Powerpole connector leading to your charge controller, and you'll have a simple, lightweight PV system that also provides shade and/or some rain protection for your trailer's front door area.

*Since a pair of Renogy 100W flexible panels, when laid side-to-side, end up as pretty close to forming a square, I would prefer to have each panel anchored to the trailer by two points, for a total of four anchor points, using the grommets on the panels to anchor them.

**A cursory study of the Anderson Web site didn't reveal anything about how waterproof they are, so I would suggest that you make at least some effort to keep rainwater off the connectors.

RandomJoe · January 2015

Re: Solar Panel Layout and Battery Charging for Teardrop Travel Trailer

AuricTech wrote: »

**A cursory study of the Anderson Web site didn't reveal anything about how waterproof they are, so I would suggest that you make at least some effort to keep rainwater off the connectors.

Anderson powerpoles are not at all waterproof. Each terminal is completely shrouded in its own plastic housing, so a drop of water can't bridge the contacts, but water can certainly get inside the housings.

That said, I use them outdoors for lower-current 12V projects (ham radio, small solar setups, navigation lights on my kayaks, etc.) and they do just fine in those applications. The contacts will tarnish a bit but they are silver so it still conducts fairly well and the design of powerpoles is that the contacts "wipe" each other clean when connected. (Or so they claim.)

There are better connectors for this, but these work well enough for me. Nice compact size, fairly robust, easy to assemble, very easy to connect/disconnect, cost per connector is a lot lower than the Molex stuff I used to use.

I like the idea of using a couple of panels for an awning, I'll have to keep that in mind. I'm thinking about getting a cargo van and making a "poor man's RV" of sorts. I was going to put panels on the roof but I'll have racks to haul kayaks on top so that may not work too well... The awning idea is a good alternative.

dropkick · August 2015

We have teardrop style trailer too (socalteardrops.com). I have so far one renogy 100w flexible panel feeding a Morningstar SS-20L-12V PWM charge controller. Don't bother with MPPT if the panels and battery are both "12V". I've gotten the panel up to 89W by just tossing it on top of the roof, or leaving it up alongside the trailer or just tossing it on the ground. Efficient enough! Someone in the family has an adversion to drilling holes in anything (trailer, other trailer, cars, roofs, etc) so it's not mounted.
One thing to consider mounting is that even if you can get 3 or 4 of them up there in whatever optimal robotically controlled direction, you may not want to be parking the trailer in the sun for your own comfort. I ended up putting an inlet (really a 12V marine trolling motor outlet, but its water resistant) for the panel(s) on the side wall near the battery. This way I can park in the shade and toss the panel out in the open however far away that is. The trailer only has some LED lights, a radio and XM receiver, and some usb for phone chargers, so 100W or 30W or whatever it ends up being is more than enough. If we had an ARB fridge or something, I'd consider adding to the system.

kelly · October 2015

I went ahead and mounted three Renogy flexible panels on the roof. Just as an update, two of the three completely failed under warranty. I had them replace all three - and of the replacements, one is defective right out of the box. The problem seems to be the plastic junction boxes. They are cheap, unsealed plastic. On most panels, they are mounted underneath, so they can get away with not being well sealed, but with the flush mounted flexible panels, rainwater can get in and short them out. The flexible panels looked good and were easy, but I think that building the rack for rigid panels might be the only way to go.

scrubjaysnest · October 2015

Our experience with a roof mounted 120 watt panel and two 80 watt panels in portable mode; just parallel the panel outputs to a single controller. Keep panel Vmp within a volt of each other and it all works fine. Our 120 watt panel Vmp is 16.9 and the 80 watt panel Vmp is 18.1

dropkick · October 2015

Renogy discontinued the 100W flex panels due to an overheat issue until they re-work the design (as of two months ago). U may have gotten some in that bunch

Hope they get it worked out cause it's still a good idea and I would like to more.

Solar Panel Layout and Battery Charging for Teardrop Travel Trailer

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