New RV Solar Installation

jmayerjmayer Registered Users Posts: 8
I'm looking for comments on the solar/electrical system I'm planning to put on a new RV. I'm not a novice to solar and electrical RV mods, but I know there are people far more experienced than I am that post here and I'm soliciting comments and suggestions.

The system is intended to be expandable. I am a full-time RVer that boondocks for months at a time, primarily in good solar conditions. I've had solar on several rigs in the 10 years we have been fulltiming. We use about 125-150Ah per "overnight". There will be 5500 watt LP genset which will be rarely used, but available.

Intended system:

- Inverter will be a Xantrex RS3000. Reasoning - I can get a very good installed price from the RV manufacturer. I may move to AGM batteries in the future and I like the large charge section. Also, I can wire the inverter "inline" (no subpanel) on a 50-amp RV if I ever pull it out and move it to another RV (I do understand the ramifications of doing this).

- Charge controller will be the Xantrex XW MPPT 60. Reasoning - integates easily with the Xantrex network. Saves me buying separate instrumentation. Gives me enough "head-space" to expand the system into the 40A range (panels). If I did not use this, I would likely use the Outback 60, but it will cost me far more to fully set it up.

- Xantrex SCP for monitor/control.

- Trimetric 2025RV for battery monitoring. I want cummulative amphours and nothing in the Xantrex instrumentation gives it to me.

- Midnite Solar MNPV6 combiner with breakers on the roof, properly mounted for water shedding. I don't anticipate having more than 6 panels. #4 welding wire feed to the controller and on to the bank. I'll use an airconditioner "pull-box" to isolate the in/out to the solar controller.

- Battery Bank will be six (6) Trojan T105s. The price I'm getting from the RV manufacturer makes this selection a no-brainer. I'd love to have AGMs but for now the 105's will have to do. L16s would be great alternative for now, but my good pricing is on 105s.

Panels: I have not decided on what panels to use. Likely they will be 24-volt. I have the space for the larger form-factor. I'm planning on at least 600 watts initially. So likely this will be 3x200 watts or so. Any recommendations on panels would be appreciated.

Suggestions for alternative equipment is appreciated. I've worked with Outback and Magnum products and am familiar with them. I like Outbacks a lot, but it is quite a bit more $$ to go "all Outback" and I can not justify it.

Thanks for your help....

Comments

  • nielniel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: New RV Solar Installation

    welcome. there's not too much to say in your choices as you are experienced and familiar enough to know what's going on. there are 2 points to bring up that you did not mention and the first is how many pvs can you fit on the rv? along those lines will they have adjustability or lay flat as flat is not efficient or able to stay clean very well and adjustable means watching that you don't go down the road without putting them flat again. of course putting them on the rv means parking in the sun which can present different problems so mounting pvs remotely may be an option with an increased theft risk involved.
    the 2nd point is your choosing flas in a confined space means they must be ventilated. you could, depending on the rv, have them external to the normal living space, but i doubt you'll fit that many batteries externally. if you managed an external mounting of the batteries it would, in all likelyhood, expose the batteries to more temperature extremes and possibly weather. in any case the bts is vital as i'm sure you know already.

    edit to add:
    reminder to be sure you have enough in pvs to supply at least a 5% rate for the charge and pvs not optimally oriented to the sun will output far less than their rating.
  • BB.BB. Super Moderators, Administrators Posts: 30,502 admin
    Re: New RV Solar Installation

    By the way, take a look at Jack's home page... A very serious RV'er... :D

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • jmayerjmayer Registered Users Posts: 8
    Re: New RV Solar Installation

    Thanks Niel. I was not complete in my description:

    1) the panels will remain flat. That causes some compromise, but any solar on an RV is all about compromise. I don't like tilting the panels under "normal" circumstances on an RV. Too many issues, including wind, and falling off the roof :)

    2) There will be a BTS. Fortunately, the the X network all components can share a single BTS. So I think that is covered.

    3) the batteries are in their own box which is well ventilated. I'd love to have AGMs,but it is not in the cards for me right now.

    4) the panels will go on a 42' 5th wheel, so I have plenty of "roof space". I will start with at least 600 watts, and don't anticipate exceeding the limits of the controller (around 40-ish amps allowing for the boost output). My goal is to rarely or never use the genset. With my current bank size it does not make a lot of sense to go with many more panels...

    Most of the experienced guys on here have forgotten more than I know about this stuff, so I thought I would run it by "y'all".

    The area I'm not totally comfortable with is the 24-volt + panels. I've installed lots of panels on RVs over the years but have usually worked with 12-volt panels. So I'm not that familiar with the "residential" market with the higher-volt panels. Any suggestions on panels are appreciated, otherwise I'll likely shop for 24-volt (nominal) panels with lots of cells. And use cost per watt as a primary selection critera.
  • nielniel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: New RV Solar Installation
    BB. wrote: »
    By the way, take a look at Jack's home page... A very serious RV'er... :D

    -Bill


    wow, you aren't kidding.:cool: the truck cab would almost be like a mini rv unto itself to me.:D
  • jmayerjmayer Registered Users Posts: 8
    Re: New RV Solar Installation

    Thanks, guys. Yeah, the truck really is a mini-RV. And titled as a MH. It has shore power, inverter (small), sink, portapotti, refigerator, microwave. Two bunks.

    It is great for overnight or several-day trips. Just hook the Jeep to it and go offroading. (I sometimes refer to it as my "fiberglass tent"). It is easy to drive, tunrs in less space than a CC pickup, and can pull anything out there with ease. Not for everyone - but it works well for us.
  • nielniel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: New RV Solar Installation

    lmayer,
    1> no problem. remember you will need to access them for frequent cleanings.
    2> good.
    3> you have all bases covered for the batteries and that's good also.
    4> ok on the vast area to mount as you will need more pvs to reap that power.

    don't worry about the 24v pvs too much as it will be fine to use them as the mppt controller will downconvert it. in fact why don't you consider raising the battery bank voltage and go to a higher voltage inverter? smaller amps to flow makes life a bit easier.
  • BB.BB. Super Moderators, Administrators Posts: 30,502 admin
    Re: New RV Solar Installation

    Regarding the panels... To a large degree you will want to purchase them based on $$$/Watt pricing... Large format panels (>100 watts) tend to have better pricing, but many times are setup for Grid Tied Inverters which can accept inputs up to 600 VDC.

    So--many have Vmp > "12 volts" (really Vmp>17 volts for a 12 volt panel)... The MPPT controllers do a very nice job of down converting panels (roughly Vmp=100 volt maximum to fall withing the 140-150 VDC max for many of the larger MPPT controllers).

    There is one "problem" point for high voltage panels vs battery bank voltage... There are some "48+ volt" panels available and when connected to 48 volt battery banks--one 48 volt panel does not have high enough voltage to charge a battery bank-->60VDC on hot days), and two panels in series is too high of voltage for the controllers (Voc>150 VDC on cold days).

    Assuming you run 12 or 24 volt battery banks--you should not hit the 48+ volt panel issue.

    In the end, the rough "sweet spot" for an MPPT controller is Vmp=2x the battery bank voltage. But if you run high voltage (100 Vmp panels, and 12 volt battery bank) -- you may get a couple percent more losses in the charge controller. But, you can use smaller/less wiring for putting all of the panels together.

    Also, remember if you parallel more than two strings of panels, you will need a series protection fuse/breaker (typically a combiner box) to protect one panel short from being "fried" by having the other strings back-feeding the short).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • jmayerjmayer Registered Users Posts: 8
    Re: New RV Solar Installation

    Interesting info on the 48-volt + panel issue. As you said, it likely will not be an issue with my 12-volt bank. I feel restricted to the 12-volt bank because of the 12-volt systems in an RV. Everything is basically based on 12-volts. It is not worth the problems of converting (to me, anyway).

    I don't anticipate any feed-wire issues with t e#4 welding cable. It may be overkill, but it is easy and cheap to do in relative terms. And the runs in an RV are relatively short. I can buy #4 for around $1/ft. retail.

    With the MPPT controller I was anticipating getting a pretty good benefit from the higher cell panels with Vmp far greater than I could utilize with the smaller nominal-rated panels. I think I just have to be careful not to exceed the specs of my chosen controller, especially under good solar conditions, which we do encounter in the desert in the winter sometimes (granted the sun is low, and the panels flat, but it is cool out and the batteries just suck it up....). I can probably put on slightly more panel than a residential situation since I am never in an ideal environment like a good house system would be. My panels will never be properly oriented, and they are always hotter than a good residential system.

    On edit: I'll be using the Midnite PV6 combiner on the roof of the RV. That should protect the individual panels and make any debugging easier....at least that is the idea.
  • BB.BB. Super Moderators, Administrators Posts: 30,502 admin
    Re: New RV Solar Installation

    The Voc maximum is based on just a minimum amount of sunlight + very cold temperatures... Vmp minimum is based on Hot panels (those mounted flat against roof are even going to get hotter).

    You can play with Xantrex's string calculator tool (for their XW 60 Amp MPPT controller) and see what the various options will work for you.

    Xantrex XW Sizing Tool

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • jmayerjmayer Registered Users Posts: 8
    Re: New RV Solar Installation

    Looking at the X calculator using a Kyocera KD205GX-LP panel I get a charger amp of 40 for 3 panels, and a charger amp of 54 for 4 panels. This is under PTC.

    Does this mean that I could go with 4 of these panels? In other words, are boost conditions accounted for in this calculator or am I going to blow it out of the water with 4 panels?
  • BB.BB. Super Moderators, Administrators Posts: 30,502 admin
    Re: New RV Solar Installation

    In general, a well designed MPPT type charge controller will both current limit (60 amps max) and power/temperature limit (hot area, poor ventilation/cooling).

    So, you can put more solar panels than the controller can support under ideal conditions (say noon time summer sun in high southern mountains)--and make up for those times when conditions are not ideal ( low winter sun with high clouds)...

    I am sorry -- but I do not have the time at the moment to look up the absolute maximum Vmp*Imp that you can connect to the XW 60 MPPT charge controller--but I don't think you will have any problems with some amount of "over panelling" other than just the cost issues.... Certainly can make up for flat mount/poor conditions (you could also have tilt panels as an option--will help a lot more during winter and for northern latitudes).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • jmayerjmayer Registered Users Posts: 8
    Re: New RV Solar Installation

    Thanks for your help Bill. It sounds like it will be fine to go with four panels. That is probably all I would ever need.
  • Solar GuppySolar Guppy Solar Expert Posts: 1,962 ✭✭✭
    Re: New RV Solar Installation

    I have one tidbit to add to this discussion, the XW is not the best choice for large Vin to Vout differentials. This is due to the fact its not a synchronous design, meaning it had diodes instead of active FETS for the low-die switch of the buck supply

    In configurations of nominal 12V -> 12V or 24V -> 24V ect. its a non issue, but if your staying with a 12 volt battery bank and a 48V nominal PV input the efficiency start falling off pretty sharp for the XW unit. There is no question the networking is nice, its a good solid unit, but strictly on an efficiency there are better choices
  • WindsunWindsun Solar Expert Posts: 1,164 ✭✭
    Re: New RV Solar Installation
    jmayer wrote: »
    Looking at the X calculator using a Kyocera KD205GX-LP panel I get a charger amp of 40 for 3 panels, and a charger amp of 54 for 4 panels. This is under PTC.

    Does this mean that I could go with 4 of these panels? In other words, are boost conditions accounted for in this calculator or am I going to blow it out of the water with 4 panels?

    In theory, yes you can. But in actual practice, the efficiency of MPPT controllers tends to fall off somewhat with larger voltage differences between input and output. We usually recommend a max ratio of 2:1. That of course varies a lot - often the reason for using an MPPT is because of long wire runs, in many of those cases running say a 6:1 ratio into a 12 volt battery would be more efficient - or at least save a ton of money on copper wire costs.

    We had one case not long ago where the panels had to be mounted almost 300 feet away from a 24 volt cell phone site. In that case it made sense to feed 130'ish volts into the input side rather than 48.
  • jmayerjmayer Registered Users Posts: 8
    Re: New RV Solar Installation

    OK, so for sake of discussion I'll assume that this efficiency drop is so great that something has to be done about it. How much drop are we talking about here? 5%, 50%?

    If this is a great drop and I have to go with something else what would you recommend? I'd lean toward the Outback, but that causes me other issues that need to be balanced with the lack of efficiency. I'm commited to the RS3000. It sure is nice to not have to add another monitor to the mix. Along with the additional cost.

    I was planning on this being a single string of 4 parallel panels (or perhaps 3 to start with), so I think my voltage is not too high....and with my #4 cable I should have no significant voltage drop.

    So what does NAWS recommend?

    On edit: I found the efficiency curves for various voltages for the Outback 60. On a 12-volt battery system at 100-volts input it is down to about 92% efficiency. So I'm loosing 8% potential (but not really, since it is never 100%). If the X is similar (I assume somewhat worse, though) I can live with that loss. I'll try to find the curves for the XW. But since I have parallel panels it should not matter - right?
  • jmayerjmayer Registered Users Posts: 8
    Re: New RV Solar Installation

    So after looking at all this, I'm going to use 4 panels with a Vmp in the 24-26V range. Which ones are not determined yet - some of the Sun panels look very attractive at $1.98/watt.

    These will be wired in 2 strings of 2 panels. That should keep my voltage in a reasonable range for the XW controller and the cable run I have from the roof should support the voltage/amperage at those rates.

    Thanks for the pointer to the XW calulator...that is one nifty tool. And I appreciate the "higher voltage" education, especially having not worked with panels running the higher Vmp's.
  • BB.BB. Super Moderators, Administrators Posts: 30,502 admin
    Re: New RV Solar Installation

    You would probably be loosing closer to 2-3%--most controllers pretty much peak out at 95-96% or so... Not a lot to worry about.

    The the Xantrex (at least right now) has the highest/best MPPT Tracking algorithms right now...

    I would be very careful with the "Sun" panels (common name, many manufacturers and distributors/retailers/aftermarket businesses and products)... There are a lot of different types out there and some of them work "better" with positive grounding (panels can slowly lose some 10+% of their output if negative grounded). It probably has only become more confused as time goes on.

    Also, check the maximum voltage of the panels--The major brands are rated to 600+ VAC (for grid tied strings). At least one product line of "Sun" panels is rated for a maximum of 70 Volts (DC?). If you plan on using the panels at higher voltages (now or later)--these may not be the best choice for you.

    Also, does your building dept/application/homeowner's insurance require UL/NRTL/NEC compliance? You need to check the major components (panels, wiring, fuses, controllers, etc.) to make sure that the meet your requirements.

    -Bill

    PS: I have not purchased any product from any of the vendors listed (including NAWS--our host)--Just do your due diligence before you buy.
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • QuabillionQuabillion Registered Users Posts: 22
    Re: New RV Solar Installation

    I think that 24V for the panels will work best.
    That is gonna be one nice power system for your rig there
  • KamalaKamala Solar Expert Posts: 452 ✭✭
    Re: New RV Solar Installation

    Quabillion gave me advice for my system. I am some orders of magnitude below what is being discussed here. But I suggest that Q knows what he is talking about.
Sign In or Register to comment.