Solar Planning

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This topic contains 11 replies, has 6 voices, and was last updated by  J J 3 years, 2 months ago.

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  • #30857

    J J
    Member

    Hi folks! Just doing a little planning here for my solar system and wanted to test my logic with those in the know. First off I will be using a MPPT type controller and my RV is pre wired from the factory with a MC 4 panel on the roof wired to the inside of the RV. The only downside here is they used 8AWG wire. I am thinking that if I were to do a series / parallel type connection with the solar panels I can keep the current on that line down to acceptable levels.. For example if I use 4 100w panels with max output of 8A, two in series gives two banks of 24v at 16A running to the controller. The length of the wire run from the roof to the controller is about 15 feet or so.

    So, an I on to something here or off track in my thinking?

    #30859

    Ray
    Keymaster

    4 GA would be nice but 8 GA shouldn’t be too bad for that load at 15 feet, I get good power off my 4 -100 watts running in parallel with approx 7 GA at a similar distance, but also important how far is the controller from the battery bank? I have mine about 18 inches away.

    RVHH Chief Cook and Bottle Washer - LoveYourRV.com

    #30861

    J J
    Member

    Hi Ray, thanks again for the info on the battery box. Picked it up in Newmarket for 90 bucks. I now have the same battery setup as you. As for my run from the controller to the battery, well I’d say it’s no more than a foot, maybe less. I’m wondering if you have ever heard of putting two sets of panels in series, then connecting them in parralell, just like we do with the battery bank?

    #30863

    Ray
    Keymaster

    Sounds good. Sure, that’s one of the benefits of an MPPT type controller. You could also likely wire all the panels in series and reduce the current even more if the controller can handle the voltage which it probably can. Although if shading occurs there may be more power loss than with a parallel/series arrangement.

    RVHH Chief Cook and Bottle Washer - LoveYourRV.com

    #30866

    J J
    Member

    Well, looks like I may to do some experiments on this. Do you find the 400w keeps your battery bank topped off? If you were to start from scratch again today, knowing what you have learnt over the last 5 years, what solar equipment / setup would you go with given money is not unlimited?

    #30868

    always go with as big a cable as you can afford. I would go with 4 ga wire  min. As you never know if you want to add more solar panels later. With solar it is true bigger is better. The cost is not that much more but it does make a difference in power loss due to how long the wire run is from panel to charge controller. The main feed cable from panels to charge controller is the one of the most important part of the solar system. It’s the biggest cause of solar systems not functioning properly.You can buy big output solar panels and mppt charge controller but they will not produce enough amps on small cable. Go to Handy Bobs Blog and read what he has to say about solar installations.Very good Information. ( handybobsolar.wordpress.com )

     

     

    #30871

    Ray
    Keymaster

    Well, looks like I may to do some experiments on this. Do you find the 400w keeps your battery bank topped off? If you were to start from scratch again today, knowing what you have learnt over the last 5 years, what solar equipment / setup would you go with given money is not unlimited?

    Yes, it does except in the mid-winter if we don’t watch our usage due to the short days and low sun angle. More time spent indoors. Also, cold weather plays a big factor since the furnace fan eats a lot of juice and the batteries lose capacity as the temps drop.

    Last December/January I was peaking at about 16.5 amps and only for a couple hours but by March/April I was seeing 22.5amps or more plus solar output for more hours.

    I recently added a 100w ground panel so hopefully, that will help out for those mid-winter times as a quick test the other morning at 10.30 am saw 27 amps of solar output out of the Bogart controller as reported by the Trimetric monitor.

    I don’t think I’d change much unless I could spend quite a bit more. The thing with solar is the system needs to be balanced all the way through. If I go with more panels I then need larger wire, a bigger controller, and more batteries and I would likely end up craving a larger inverter, too. 😉

    I like the way my system is matched up now and it should meet our needs.

    RVHH Chief Cook and Bottle Washer - LoveYourRV.com

    #30873

    John
    Participant

    The wire size should be taken off the chart based on distance and load. I agree that getting your voltage up using series/ parallel makes sense in the context of an MPPT controller, which needs a lot of headroom to function optimally. Also, the amps will be lower and this reduce wire size requirements. Some will say parallel is better, because of shading issues. However, no much shade in the desert, but shading is an issue you must be aware of if you configure in series. Having said that, the higher voltage and MPPT controller combo is better. Some parallel applications might be better off not using the MPPT controllers, because the headroom voltage is inadequate to get the MPPT’s benefits.

    Northern Arizona Wind and Sun has a decent forum. If you call them on the phone, however, they tend to oversize everything because they are in the sales business, but the forum is useful. For example, the add the panel labels and divide by 12 (if a 12 volt batt system) and use that to size your amps for your controller. This is fine if you want a 25% cushion, but to tell you that this is the minimum is suspect at best, IMHO.

    I would try to use higher amp panels if you can. If you’re taking up real estate on your roof, why not at least use a 180 panels and worry less about future upgrades? Grape sells some decent little 180’s. I just put 6 of those on my roof.

    #30875

    J J
    Member

    Thanks everyone for the input. I have lots of choices to make over the next little while.

    #30877

    Curious by Nature
    Participant

    You are still going to need a generator for the occasions when you get several gray days in a row, or if there are hot days and you need the AC. Large exhaust fans in the vents can help reduce AC usage, but most of them pull 4-5 amps each.

    I believe a battery monitor and a volt/ammeter should be the first investment, audit your actual usage under a variety of conditions, learn what each component actually draws, how much does your furnace run per hour under different temperature conditions. Fifth wheels tend to have much larger internal volumes of air than taildraggers, and generally have larger furnaces with larger electrical draws.

    RV’s tend to vary quite a bit in construction, plus personal habits of the owner, ie sleeping with windows open, vents up, cool sleepers, hot sleepers and  so on, makes a power audit a necessity to determine what your actual size configuration will be.

    #30885

    Eddie & Aileen
    Participant

    Hi JJ, If your running a MPPT controller you go by the watts of your panels not the amps.

    So your 400-watt panel array in a 24-volt configuration on 20′ (one way) of #8-AWG will give you a 2% loss, that’s good. If you go in the 24-volt set-up you wont need to upgrade your wiring and still have room for more watts. The only thing you may go to a 3% loss with more panels, but most systems work on a 3% loss anyway.

    When you set your series panels, if you plan to put two on each side of your 5er,  make sure to series each set that slope in the same direction to cut down on shading loss. (Morning/Evening):good:

    Happy Trails!!! :bye:

    P.S.- What type/brand of MPPT controller are using?:scratch:

    #30893

    J J
    Member

    Hi all, much appreciate the feedback. Eddie, thanks for jumping in as I know you have a lot of experience with this stuff. I plan to run the EP Solar, EPS-MPPT -40 controller, it’s just an entry level unit but on a retirement income the budget is not unlimited. I would like to keep this project to around $1500 so I’m trying to get the biggest bang for that amount. My plan is to acquire all the bits and pieces over the next little while and once I have everything I will do the install. In the meantime I do have a Honda 3000i generator to fall back on. 😀

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