Running panels in series.

nobody928
nobody928 Solar Expert Posts: 62 ✭✭✭✭
in Off Grid Solar & Battery Systems #1
I am thinking about upgrading my system. Right now I have 3x 140 watt panels ran parellel. I also have a 20 ft drop to the charge controller wich is a C40 pwm charge controller.

I am going to be purchasing the "Midnite kid" 30a mppt.

I was wondering once I upgrade charge controllers what my benifeits would be to run my panles in series? I would like to have my Vdrop decreased. I would also like to be able to add more panles using a 24 volt system instead of 12. My question is if I run my system with all 3 panles in series(36v), will there be a big " loss" in the conversion process of going down to 12 volt battery bank?

What will my benifits be? Smaller wire? Less Drop? Please explain advantages and disadvantages.

Lastly my work computer never lets me respond to posts but it lets me start them. Anyone know why this would be?
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  • ggunn
    ggunn Solar Expert Posts: 1,973 ✭✭✭
    #2
    Re: Running panels in series.
    nobody928 wrote: »
    I am thinking about upgrading my system. Right now I have 3x 140 watt panels ran parellel. I also have a 20 ft drop to the charge controller wich is a C40 pwm charge controller.

    I am going to be purchasing the "Midnite kid" 30a mppt.

    I was wondering once I upgrade charge controllers what my benifeits would be to run my panles in series? I would like to have my Vdrop decreased. I would also like to be able to add more panles using a 24 volt system instead of 12. My question is if I run my system with all 3 panles in series(36v), will there be a big " loss" in the conversion process of going down to 12 volt battery bank?

    What will my benifits be? Smaller wire? Less Drop? Please explain advantages and disadvantages.

    Lastly my work computer never lets me respond to posts but it lets me start them. Anyone know why this would be?
    Any series string needs to be evaluated for maximum open circuit voltage. For this you'll need to adjust the module Voc to account for the lowest temperature the system will ever see (I use the all-time record low temperature for the location) and multiply it by the number of modules in the string. This voltage needs to be less than the maximum DC voltage your inverter or charge controller can accept. Higher voltage for the same power means less current, which means that you can use smaller wire or that you will see less voltage drop for the same size wire. As long as you do not subject your inverter or charge controller to an overvoltage condition, there really is no down side.
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #3
    Re: Running panels in series.

    Your actual panel specs are likely to be around 17.7 Vmp, 22.1 Voc, and 7.91 Imp (based on the KD 140 panel).

    As such three in series would give you a Voc of 66.3 before the effect of cold temperatures on them. I believe the Kid is rated for up to 100 Volts, so it should work even if the array Voc hits 86 (about the maximum likely).

    The Vmp will be up at 53 Volts, which moves it away from system nominal and reduces controller efficiency a couple of percent (haven't seen an actual curve for the Kid yet).

    There will be an improvement in V-drop for a given wire size. For example you would be going from 12 Volts @ 24 Amps over 20' on let's say 10 AWG and suffering about 8% drop to 53 Volts @ 8 Amps
    over 20' on 10 AWG resulting in less than 1% V-drop. So in this case the improvement in Voltage drop makes up for the decrease in controller efficiency.

    On the whole it should work fine.

    I can't think of any reason why you would not be able to click "Reply" and respond to posts.
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,613 admin
    #4
    Re: Running panels in series.

    For some reason, you were able to do one Reply back on November 10th:

    http://forum.solar-electric.com/showthread.php?21754-First-time-using-a-generator-and-battery-charger&p=175520#post175520

    Regarding posting--I changed your settings a little bit (newest posts at bottom, WYSIWYG what you see is what you get editor) to see if that forces cookies or something to refresh on your computer.

    Otherwise, make sure you have javascript/java enabled for the forum. You might try deleting all wind-sun.com cookies and re-login.

    Are you seeing a big blue button "Reply to Thread" above or below the posts (on right)? At the bottom of each post in a thread, there should be an "twisted arrow" and "Reply" and a quote symbol and "Reply With Quote" button. do you see those?

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • vtmaps
    vtmaps Solar Expert Posts: 3,741 ✭✭✭✭
    #5
    Re: Running panels in series.
    ggunn wrote: »
    As long as you do not subject your inverter or charge controller to an overvoltage condition, there really is no down side.

    There is a down side as Cariboocoot points out:
    Cariboocoot wrote: »
    The Vmp will be up at 53 Volts, which moves it away from system nominal and reduces controller efficiency a couple of percent (haven't seen an actual curve for the Kid yet).

    But I do have a comment on Cariboocoot's conclusion:
    Cariboocoot wrote: »
    There will be an improvement in V-drop for a given wire size. For example you would be going from 12 Volts @ 24 Amps over 20' on let's say 10 AWG and suffering about 8% drop to 53 Volts @ 8 Amps
    over 20' on 10 AWG resulting in less than 1% V-drop. So in this case the improvement in Voltage drop makes up for the decrease in controller efficiency.

    On the whole it should work fine.

    Yes it will work fine. And if nobody928's only option is to use 20 ft of #10 wire, I would reach the same conclusion.
    But nobody928 can use thicker cable and reap the benefit of increased efficiency in both the cable AND the controller.

    --vtMaps
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #6
    Re: Running panels in series.

    Keep in mind that three panels in parallel also means three fuses/breakers (one per panel) to combine them.

    On the whole the reduced efficiency of the controller is not that severe compared to the higher V-drop and/or more expensive wiring for all panels in parallel.

    And if you increase the system Voltage to 24 the problem is nonexistent.
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