over paneling a controller to compensate for long runs and or lower insolation?

i have run as much as 405(rated) watts of panel ( 3 kyocera 135's) on my bluesky solar boost 3024 mppt charge controller. i know for certain they over power and trip the charge controller at home in colorado on clear cool days at 8000 ft. my problem is i am often NOT in such a high insolation area and often have to run my panels out quite a ways from the motor-home in order to get to the sun. my current situation for the sumer has my panels 120ft from the controller and i am in oregon. so i am losing a lot to line loss and less than ideal sun. my 135's were stolen out of storage a while back and i am in the market for a re-power. i want to explore the possibility of taking advantage of todays ridiculously low prices on panels to get a couple extra to be able to use to max out my charge controller when i have to use the long wires or in low sun times of year. i am happy with around 400 watts making it to the battery and i am cool with stashing the extra panels seasonally when not needed. i can practically double my panels for less than what it would cost to get a larger or extra charge controller.

i figure i am facing 2 different problems that i will need to deal with to keep from tripping the controller. first i have the static/consistent issue of approx 120 ft of wire between the panels and controller. using the standard 10ga solar mc4 extension cables and running a 24v nominal panel or some combination of panel that keeps my input voltage max bellow 40v. how would i best calculate how much extra panel i could add. if i figure out the voltage drop due to the wire length how can i relate that? if my voltage drop is 20% does that mean i could add 20% more panel wattage (rated) to compensate

the second aspect is that i would like to set something up to block or redirect excess panel wattage away from the controller in the event it gets to high and approaches a predetermined set point. this question project may warrant a separate thread?

again i would like to take advantage of cheap panel prices. my thought was to say put 50% more rated watts in the array than recommended but use an over current or over voltage switch to connect a load ( water pumping) direct to the panels before the charge controller or maybe it would be more complicated and i may have to set up an arduino to measure actual wattage and program it to operate the load (pump) some sort of system like this would allow me to more fully utilize the charging capacity of my current charge controller without burning it up and to be able to get extra water pumping done if the sun was cooperative.

i am hopeful some of the guru's out there will have some input to tell me i am crazy or point me in the right direction.



  • BB.BB. Super Moderators, Administrators Posts: 30,638 admin
    Re: over paneling a controller to compensate for long runs and or lower insolation?

    Welcome to the forum Kenny.

    What exactly BlueSky 3024 controller do you have (i, iL, etc.)? I am not real familiar with the different Bluesky models, but sometimes the exact model matters (I think).

    Next, what physical size of solar panels are you looking for? ~140 watt panels are about the maximum size you can ship via UPS/Fedex/bus/etc... ~175 watt panels are about as big as one person can safely move around (at least on a roof top--Depending on how big a person you are).

    And, in general, the "cheaper" solar panels are >~200 Watts...

    So, you have shipping, storing in the motor home, and moving them around. I suggest you look at a few different panels here (or similar stores) and find the optimum size panel(s) you want to use first.

    As you know, the typical glass in a solar panel is ~1/8" thick tempered glass--And any hard knocks/serious scratches in the class will leave you with a work of modern art (rather than a work solar panel).

    Is there any way you can mount your panels (or at least some of your panels) to the RV? I know it means parking out in the sun--But it may be "safer" all the way around (less chance of breakage, less chance of them walking away).

    Once you pick the solar panels, then we can look at the Bluesky... I would be suggesting a more modern controller--but at ~$300-$500+ -- These may not be your first choice where you want to spend your money.

    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: over paneling a controller to compensate for long runs and or lower insolation?

    Get a different charge controller.

    Your two problems are a need to run higher array Voltage to overcome distance to the controller when the panels are 'remote' and a need to limit current which can be greatly increased due to sometimes high elevation location.

    The Blue Sky units have a lot of quirks and limitations. The primary one is not being able to handle high input Voltage the way a MidNite Classic or Kid can. Nor do they manage current well.

    Regrettably the better controllers are more expensive, but on the other hand they work better.
  • rice81rice81 Registered Users Posts: 25
    Re: over paneling a controller to compensate for long runs and or lower insolation?

    I'm not sure what the actual answer is from a real world perspective (adding panels to compensate) but you should realize that the open circuit voltage of your boosted array (Voc) could exceed the rating of your controller and lead to damage or perhaps shutdown or blowing some kind of input protection. If you had a fixed load on the panels then that solution would seem acceptable.

    Your controller will only see the 'normal' or acceptable voltage under load through voltage drop in both the internal resistance of the panel and the voltage drop of the wiring. I would be concerned that being under digital control, the controller might sample Voc prior to beginning its algorithm and thus register an overvoltage fault. If your controller can take the added Voc of the enlarged panel then I would say to go for it.
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