Mounting PV Panels on a RV

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addco
addco Registered Users Posts: 11 ✭✭
I'm planning an installation of 2 PV Panels flat-mounted on the roof of my RV. I have a couple of questions.

1. So far, my research is leading me towards the Kyocera KD135GX-LPU. I'm wondering if there might be any better choice with regards to performance under partially shaded conditions. We camp in campgrounds often, and there's many times when it's not possible to park where there isn't at least some partial shading from tree branches, etc. I've heard that some panels perform better under these conditions (more internal bypass diodes?) but have seen little hard data.... I don't think the amorphous panels are a good option for me due to limited roof area.

2. Is it OK to ground the negative leads from the panels to the RV frame? Or do I need to run both leads all the way down to the charge controller?(This would mean 4 runs of MC cable for me, or combining them in a J-box on the roof and running a larger, #8 or #6 cable down.) The instructions for my charge controller (Morningstar SunSaver Duo) show the negative leads grounded to the chassis.) It would be easier just to run the 2 positive leads down from the roof, if grounding the negative leads to the frame is OK. Is there any reason NOT to do this? Will this give me a good, low-resistance path for the PV current?

Thanks in advance for any advice.

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  • BB.
    BB. Super Moderators, Administrators Posts: 33,479 admin
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    Re: Mounting PV Panels on a RV
    addco wrote: »
    I'm planning an installation of 2 PV Panels flat-mounted on the roof of my RV. I have a couple of questions.

    If possible, can you install tilt hardware for the panels? Summer time in the southern US is usually not a big issue for flat panels. However, winter output can be greatly increased with tilt panels.
    1. So far, my research is leading me towards the Kyocera KD135GX-LPU. I'm wondering if there might be any better choice with regards to performance under partially shaded conditions. We camp in campgrounds often, and there's many times when it's not possible to park where there isn't at least some partial shading from tree branches, etc. I've heard that some panels perform better under these conditions (more internal bypass diodes?) but have seen little hard data.... I don't think the amorphous panels are a good option for me due to limited roof area.

    Shade is pretty much an output killer for solar PV panels--Of any type. Kyocera makes fine panels.

    If you will be in areas with shade, perhaps panels that you can place on an extension cord and move the panels into the sun would be helpful. However, you need to secure against wind and theft.

    Amorphous panels are about 1/2 the efficiency, so you would need twice the square footage to get the same solar power. I would recommend staying away from amorphous panels for this, and other reasons.
    2. Is it OK to ground the negative leads from the panels to the RV frame? Or do I need to run both leads all the way down to the charge controller?(This would mean 4 runs of MC cable for me, or combining them in a J-box on the roof and running a larger, #8 or #6 cable down.) The instructions for my charge controller (Morningstar SunSaver Duo) show the negative leads grounded to the chassis.) It would be easier just to run the 2 positive leads down from the roof, if grounding the negative leads to the frame is OK. Is there any reason NOT to do this? Will this give me a good, low-resistance path for the PV current?

    For most controllers, you can bond the negative leads of the panels to local sheet metal/frame... There are a few solar charge controllers that will not work if connected this way (Xantrex MPPT 60 amp charge controller is one--it measures panel current in the negative lead for the MPPT function).

    It is probably better for you to run the +/- leads all the way back to the controller--It is difficult sometimes to ensure that you have a solid electrical connection in sheet metal/frame work.

    You do have a choice between a PWM and a MPPT solar charge controller... One of the advantages of an MPPT type charge controller is that you can put the two solar panels in series--double the voltage and 1/2 the current of two panels in parallel. the MPPT controller will efficiently down convert the higher voltage / low current of the solar panels into lower voltage / higher current to charge the battery bank. This allows you to use lighter wire or run your solar panels a longer distance from the charge controller without higher losses (would be nice if you choose to remote/ground mount them).

    Placing the panels in series can result in a little better performance in partial shade--but I would not plan on this being a great solution (you still can lose up to 50% power with only partial shading on one panel).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • addco
    addco Registered Users Posts: 11 ✭✭
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    Re: Mounting PV Panels on a RV
    BB. wrote: »
    If possible, can you install tilt hardware for the panels? Summer time in the southern US is usually not a big issue for flat panels. However, winter output can be greatly increased with tilt panels.

    I hadn't really planned on a tiltable mounting system. Most of our camping is in the summer months. In the winter the RV is parked outdoors & the solar would mostly be for charge maintenance. Also, I figured I'd soon tire of climbing on the roof to tilt the panels. (We don't usually stay in one place for very long). However, I might give it another thought, might be nice to have the capability....
    Shade is pretty much an output killer for solar PV panels--Of any type. Kyocera makes fine panels.

    So, there aren't any particular makes/models of panel which are more "shade tolerant"?? (other than the amorphous panels which I've ruled out for the space / efficiency considerations as you've mentioned.)
    If you will be in areas with shade, perhaps panels that you can place on an extension cord and move the panels into the sun would be helpful. However, you need to secure against wind and theft.

    Sounds cumbersome. We do move quite often, and as you said I'd worry about theft.
    Amorphous panels are about 1/2 the efficiency, so you would need twice the square footage to get the same solar power. I would recommend staying away from amorphous panels for this, and other reasons.

    Pretty much what I had figured. Looks like we are going to be best off just trying to park in the sun whenever we can, and live with the inefficiency when we do get hit by shade.
    It is probably better for you to run the +/- leads all the way back to the controller--It is difficult sometimes to ensure that you have a solid electrical connection in sheet metal/frame work.

    OK. It looks like that's what I'm going to do. I had hoped to avoid mounting a junction box on the roof of the RV (One more potential leak point), but the MC cables used by most panels is only #10 ga. So I'll likely run a pair of #6 cables from the charge controller to the J-box and tie the panels into that. (A plus is that I could easily add another panel later if needed.)
    Placing the panels in series can result in a little better performance in partial shade--but I would not plan on this being a great solution (you still can lose up to 50% power with only partial shading on one panel).

    Now this is news to me. I was under the impression that a parallel configuration was better for partial shade. (If only one panel has shade, the other panel is free to produce full output without the series resistance of the shaded panel.)

    How can the series configuration be better in this respect?

    Thanks for your reply and advice.
    Much appreciated.
  • BB.
    BB. Super Moderators, Administrators Posts: 33,479 admin
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    Re: Mounting PV Panels on a RV

    Basically, imagine you have 3x 12 volt batteries in series powering a switching power supply that can output 12 volts... Each 12 volt battery has a bypass diode (or three)... If one one or all cells in one battery "fails", the bypass diode continuous to pass current from all the cells that are still functioning, and the 12 volt power supply is still able to output 12 volts.

    If, you have all 12 volt batteries in parallel--if any one cell fails, the 12 volt battery falls to 10 volts, not the 12 volts needed by the power supply to power your load--so one cell failure knocks out the output from the rest of the 5 cells in one 12 volt battery. Leaving the other two x 12 volt batteries to handle the load.

    Where as if the batteries where all in series, one cell outage would only take out 1/18 cells, and the other 17 cells would still be able to power the loads through the switching power supply (AKA MPPT solar charge controller).

    In the end, any shading is an output killer--even the shade from a vent pipe on your trailer roof...

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • System2
    System2 Posts: 6,290 admin
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    Re: Mounting PV Panels on a RV
    BB. wrote: »
    Placing the panels in series can result in a little better performance in partial shade--but I would not plan on this being a great solution (you still can lose up to 50% power with only partial shading on one panel).

    I'm also just getting into solar for my RV, and I've been researching the whole serial/parallel issue as well. I understand your example using batteries, but I also read the following papers http://www.ccsenet.org/journal/index.php/mas/article/viewFile/3937/3464 (PDF link) and http://www.sustainableenergy.com/fileadmin/user_upload/product_information/Parallel_Wiring_for_Increased_Energy_Yield_-_Whitepaper.pdf (PDF link) that claim that parallel is much better for partial shade. Here's the money quote from the second article:

    "A real life study was completed at the University of Hong Kong to demonstrate the performance difference between parallel and series. The study found that when modules are wired with short strings in parallel, the array consistently performed better than when wired in series. Typical performance advantages were in the range of 6-7%1, showing that as different variables came into affect such as partial shading, the parallel array became increasingly beneficial to system performance."

    Have you seen these and can you comment on them?

    Thanks,
    Ted
  • notsobright
    notsobright Solar Expert Posts: 247 ✭✭
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    Re: Mounting PV Panels on a RV

    hi addco, I have that controller on my RV. originally I wired it to chassis ground and it worked fine but I was seeing some voltage spikes above 14.2v and since I have AGM batteries I decided to rewire the grounds to the controller to see if that would change but it made no difference so I would say do whats easiers.

    the techs at MorningStar say its OK to ground @ the chassis also BTW (I was wondering the same thing)

    let us know how yours does! I still see voltage spikes but I have no way to tell the duration as the remote meter only stores high and low info. MorningStar said these spikes should only be for milliseconds but if I have problems with it they will honor the 5yr warranty at anytime.

    I plan to get a better meter that stores this info soon. I really wish the MS one did this, it should.

    I run my panels parrallel and mouted flat and partial shading doesnt seem to have a huge effect on thier output. I even get upto 2a out of them with full cloud cover but in full sun I get 20a.
  • K4GAA
    K4GAA Registered Users Posts: 4
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    Re: Mounting PV Panels on a RV

    There is a difference between two or three panels in series and a large array with panels in series and the strings in parallel using a single charge controller.

    When you have a single series string then a partially shaded panel will loose a portion of the panel output and the isolation diodes will do their job. When the panels are in parallel then that whole panel output will be lost since the panel voltage will be less than the panels in full sun.

    The newer MPPT controllers are efficient at converting the higher voltage array output to battery charge current. If you have the panels in parallel then then you could use a less expensive PMW charge controller.

    I have two 90 watt panels on my RV and I've had them wired both ways. While I haven't seen a huge difference between the two configurations, I prefer the series configuration to reduce the I squared R losses in the 10 gauge wiring. I'm using the Morningstar MPPT 15 amp charge controller. Note that half the current results in one fourth the power loss in the wiring.

    My panels are permanently mounted and fixed. I keep an eye on my Trimetric meter but otherwise just leave it alone. Last year I switched to 200AH AGM batteries and I don't even have to worry about checking the batteries and adding water anymore.

    I hope you enjoy solar camping. Ray
  • addco
    addco Registered Users Posts: 11 ✭✭
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    Re: Mounting PV Panels on a RV
    hi addco, I have that controller on my RV....

    I run my panels parrallel and mouted flat and partial shading doesnt seem to have a huge effect on thier output. I even get upto 2a out of them with full cloud cover but in full sun I get 20a.

    346w total w/4 Kyoceras | 400 total AH w/3 isolated AGMs | 25a MS SSD charge controller w/remote meter | 300w MS SS300 TSW inverter | 1500w Duracell/Xantrex MSW inverter | B&D VEC1093 40A charger | 80a GMC altenator | Honda EU2000i

    Thanks to everyone for all the info.

    Notsobright, Since we're running similar hardware (same panels, only I will have 260watts, same controller, same MS SS300 inverter.) I'm wondering about the real-world performance of your system. You say you are seeing 20A in full sun? (so I might expect 15A) How many Ah do you get into your batteries on an average sunny day???
  • notsobright
    notsobright Solar Expert Posts: 247 ✭✭
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    Re: Mounting PV Panels on a RV
    addco wrote: »
    Thanks to everyone for all the info.

    Notsobright, Since we're running similar hardware (same panels, only I will have 260watts, same controller, same MS SS300 inverter.) I'm wondering about the real-world performance of your system. You say you are seeing 20A in full sun? (so I might expect 15A) How many Ah do you get into your batteries on an average sunny day???
    I dont yet know the max ah per day yet because I keep changing things and resetting the meter.

    I have it setup with switches to toggle between batt2 and Batt3 and aux output too so Im not sure how that affects the readings yet either.

    I hooked up the laptop to it today and adjusted the settings to closer match the batterry specs. Im just now getting it all figured out.