Solar recommendations for a tiny RV....

System
System Posts: 2,511 admin
in Solar Beginners Corner #1
Greetings All -

My partner Cherie and I live, work, and travel most of the year in a solar-powered 16' Tab Clamshell that I've upgraded with solar and much more.

You can see our setup here: http://www.technomadia.com

This is what I have crammed into my current Tab:

+ Siemens 110w solar panel
+ Blue Sky Energy Solar Boost 2512iX
+ IPN Pro Remote control panel / battery monitor
+ 2x Trojan T-145 6V Batteries (260 AH Capacity)
+ Xantrex Pro 1000W Inverter w auto-transfer switch

We are right now we are in the midst of an upgrade to a slightly larger and heavier 17' Oliver trailer that would give us a bit more indoor plumbing and living space. The clamshell Tab is an absolutely brilliant design, but it is a tiny bit tight at times...

Details and pictures of the project are archived here:
http://radven.livejournal.com/tag/oliver

I am considering the new trailer to be a blank slate. We are starting from scratch trying to design the best possible solar and electric system for such a small RV. I would love advice and input from the experts here on this.

The roof is oddly shaped and it will be a challenge to get more than a single panel mounted up there. The primary flat area forward of the AC looks to be around 61" x 30".

Any suggestions on the best panel I could manage to fit into that space?

I've been playing around with an idea - stacking two or three panels on top of each other with drawer-type slides or a trifold system rigged so that the panels can deploy out to either side when parked. While in transit mode, the top panel would provide a charge, and then when in deployed mode you could get 3x the power.

Has anyone had experience trying something like this?

Any other advice on how I can get maximal power generating capacity squeezed into such a small roof area?

I've seen some interesting work done with flexible Unisolar laminate, but the power produced per square foot is low. Is this even worth pursuing?

The basic advice wanted -- if you were designing the electrical system for an off-the-grid Oliver, what would you use? Which batteries? Solar panels? Charge controller? Battery monitor? Inverter / Charger? Size considerations are particularly important considering we have such little space to work with.

I have been disappointed in how most RV inverter / chargers seem to be either too powerful, big and expensive, or way too small and under-featured. The new Xantrex Freedom HF 1800 is intriguing, as is the Prosine 2.0. I also wonder if Magnum or Tripplite have anything worthwhile to offer...

Thoughts? Recommendations?

- Chris // www.technomadia.com
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Comments

  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    #2
    Re: Solar recommendations for a tiny RV....

    i had addressed the pv for that given space in another post and would ask you to try to keep down any duplication. i see you do use an mppt controller now as it wasn't mentioned in the other post and i see no reason you couldn't use that controller with the kc135 pv i proposed. you could run more pvs while parked longer term by remoting the pvs with adjustable mounts placed on the ground and of course i don't recommend walking away from them without putting them away as they could be stollen. you would have to watch you don't exceed an input to the controller of more than 20amps or you should get another controller to handle the excess amps be it paralled with the blue sky controller or one larger controller with getting rid of the blue sky.
    also note that the battery bank you have may be being undercharged with only a 110w pv as this is roughly just under a 2.5% charge rate which is about half as much as we'd normally recommend minimumly. 260ah x 5% = 13amps. even the kc135 by itself won't provide that much current to meet the 5% minimum.
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  • System2
    System2 Posts: 6,290 admin
    #3
    Re: Solar recommendations for a tiny RV....

    I will be selling the Tab with all the solar upgrades included, and I am treating the Oliver as a new blank-slate project so I will be buying all new components.

    The goal is to get as much power and efficiency as possible into the small amount of space I have available.

    What components would you choose if you were starting from scratch?

    I know the single 110W panel in my current system is undersized compared to the battery - but I top off the batteries via the tow vehicle alternator and occasional shore power. There was no way to squeeze more solar onto the roof of the Tab, and maximizing run time was key so I went with the largest batteries I could possibly fit.

    Thanks for the advice,

    - Chris // www.technomadia.com
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  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    #4
    Re: Solar recommendations for a tiny RV....

    1 pv to fit in those dimensions will not be sufficient for charging the batteries of the size you indicated you will be selling. the kd135 is about the biggest i'm aware of that'll fit, but you may wish to research that further if you would be ok with a new mppt controller that'll downconvert the higher voltages those pvs would present. i am not aware of any 12v pvs over 135w. i'm assuming that the previous battery size was conducive to your needs.
    speaking of the batteries, if you are buying new batteries too, then go with the agm type as you'll have more efficiency in charging, no gassing unless overvoltage, and low maintenance. they cost a bit more though.
    personally i'd go with 2 kd135 pvs and have at least one mounted on the tab, if that'll be the right term for it, and have at least one other kd135 you can at least temporarily mount elsewhere if not on the tab. your current blue sky controller would handle this just fine and you'd need the bts to monitor the temps and adjust the charge voltage accordingly. these 2 pvs would be about 270w stc total and should handle up to about 304ah at 12v in batteries. if you elect to go with a larger battery bank then you need even more in pvs as well as another controller to handle the current of all of the pvs.
    alternator charging may help supply a good part of the bulk charge, but you cannot top off a battery from the alternator as the voltage usually is not high enough to do this. solar and/or utility sources will be needed to finish the charging. use at least a 2 stage charger with 3 stages prefered when using utility type battery chargers. if going with agms then i'll recommend no less than 3 stages.
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  • System2
    System2 Posts: 6,290 admin
    #5
    Re: Solar recommendations for a tiny RV....

    Thank you for the great response.

    The roof space I have will allow for at most 62" x 33" of space, maybe even a tiny bit less. There will be no room for a second panel, but I like your suggestion of designing the system to allow a second stowable panel to be deployed when stopped for extended periods.

    Is it preferable to wire the two panels in parallel or series - particularly considering that they will likely have very different sun angles and shade exposure?

    Right now the top choice panel is a 130W Kyocera KD135GX-LP, but I
    am researching larger panels that might fit, like the Mitsubishi PV-MF170 or Sharp NT-180U1.

    The charge controller I am looking at is the MorningStar SunSaver MPPT, so I am not tied to 12V panels.

    The charge efficiency advantage of the AGM batteries is tempting, but I haven't ruled out the flooded lead Trojans yet. I have seen claims that the LifeLine AGM's can handle more 80% discharge cycles over a lifetime than the Trojans, which is another big plus for AGM's. Hmmm...

    I will probably end up with around 210 amp hours of capacity if I go with the LifeLines. In the same physical space, I can fit 300 amp hours of flooded lead Trojans.

    The big question mark is around the inverter / charger - but I will continue that conversation in a different thread.

    Thanks for the wisdom!

    - Chris // www.technomadia.com
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  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    #6
    Re: Solar recommendations for a tiny RV....

    ok you may find a pv within 62x33 inches and using such a pv is ok by itself, but the controller will not handle 2 or more pvs with the kind of wattage that the 24v pvs have. that means get a bigger mppt controller or multiple sunsavers. each controller should have a battery temperature sensor. i do not recommend you series the pvs as you want to be able to use just the roof mounted pv by itself if need be so any remote pvs will be paralleled.
    yes the concordes peak on the cycles a bit over 70% depth of discharge by a graph they had provided me, but i recommend no more than about 60% to be on the safe side and still being in the ball park for good cycling rates. you will have outgassing with the trojans that you'll have to deal with if you go with them.
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  • Solar Guppy
    Solar Guppy Solar Expert Posts: 1,989 ✭✭✭
    #7
    Re: Solar recommendations for a tiny RV....

    Actually Neal, series is fine, if the second panel is shaded, the bypass diodes conduct, you only have a small loss of the diode and it's automatic.

    Parrallel shaded is no better, no bypass diode losses but there is the leakage load of the shaded panel.

    I would only use AGM in a trailer
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  • Telco
    Telco Solar Expert Posts: 201 ✭✭✭✭✭
    #8
    Re: Solar recommendations for a tiny RV....

    Since you say you also use the vehicle alternator for power charging, what about setting a second panel on the roof of that SUV you're hooked up to? Sure, it wouldn't be charging when you are away from the trailer, but when it's with the trailer it would be.

    Also, how would you feel about having a covered porch on that trailer for when you are parked? Use two or three panels on a hinged mount that you can swing up when parked for both solar exposure and shade on the side of the trailer. Set them up to fold like an accordian when not in use. You'd want to make sure the mount was set to one side so as to not block the door when folded, and would want a protective lip to keep road debris from flying by the side of the vehicle and smacking the frame.
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