New Guy PV Wiring Help & Ground

ki7fxki7fx Registered Users Posts: 10
Thanks to all the experts who provide tons of information here!

I just installed a (hobby, hobby, hobby) single 250w panel, 160 feet from the basement mounted Morningstar MPPT60 controller using 6g copper. All loads are DC (ham radio, internet, security cameras, etc). Battery load to these components is about 8 amps average 24 hours a day. No immediate plans for an AC inverter, maybe later....

If someone could help me with some basics here, it would be much appreciated...

First, I sunk an 8' ground rod at the base of my PV panel outside and grounded the panel at the designated location on the frame. Should I also connect this ground to the PV - (negative) side of the feed into the house (black)? It would just be a short 4" jumper, but not sure if i should do this. That would cause the negative feed to be at earth ground potential. Would that be the only ground on this leg of the run, or --> I also grounded the controller inside the house to the cold water pipe in the basement. I am not looking at the lightning/EMP issue yet (that's another book), just the basic safe grounding.

Since I have a 160 foot run of cable (320' both ways), should I twist the cable a few turns every foot to reduce noise (I'm a ham radio op too). One of the reasons I bought the Morningstar MPPT60 is because of the low noise FCC Certification.

System has been running for two days now. All seems well, but that grounding issue is haunting me...

I came across a new wind generator (400w) at the local big box store. If I buy this thing, can I just connect it to the PV array combiner (like an additional PV)??

Thank you all for your help in advance... Mike

Comments

  • nielniel Solar Expert Posts: 10,311 ✭✭✭✭
    Re: New Guy PV Wiring Help & Ground

    welcome,
    the - pv lead does not need to be at ground potential, but the nec has a little thing that a 3rd wire must be run with the pv wires for grounding at the main rod, in your case the water pipe. i have issues with this rule because it draws in lighning and emp into the house. if it were me i wouldn't run the 3rd wire, but i dissavow any responsibility if you don't do it per nec.

    with the distances between the pvs and the controller i don't believe you would have any ground loop issues, but you could lose quite a bit of power with that long of a wire run, even if large gauged. use a voltage drop calculator to see how bad it really is.

    btw, i do hope you have a large enough battery capacity for those long qsos and note that you don't want to draw it down beyond 50% or you will have some life expectancy issues.

    i don't know how effective it would be to twist the wires very much, but a turn every 4 or 5 feet couldn't hurt. this could add to the length needed if too many turns are utilized though and the length you currently have is farther than would be ideal.

    forget the turbine and stick with solar as turbines don't output that much like many think and are very high maintenance due to moving parts. costs are high too after all accessories are factored. for the record you can't do what you had in mind to use it as an input like an extra pv and turbines require their own controllers.
  • ki7fxki7fx Registered Users Posts: 10
    Re: New Guy PV Wiring Help & Ground

    Niel,
    Thanks for the quick response and the advice (grounding). Unfortunately, the PV panels had to be mounted this distance, as all my roof peaks run East/West. My only clear view to the south sun was on the far north corner of my lot. I think the trade off was living with the voltage drop and 400 ft of FREE 6g new copper. Other than the loss, is there any other problem/danger with the loss (heat, etc)? I am sticking with high voltage panels to help compensate (31+ volt).
    I am watching the battery bank very closely now with the new controller. It will send me an email if the voltage drops below 12v.
    I haven't buried the conduit in the yard yet, so I thought that BEFORE I bury it, I should resolve this twist issue. :-)
    Turbine forgotten... thanks. Will save cash for another PV. Thanks again for your advice!! Mike
  • BB.BB. Super Moderators, Administrators Posts: 29,511 admin
    Re: New Guy PV Wiring Help & Ground

    Hmmm... How much power is that 250 watt panel giving you. Assuming near Minneapolis/Saint Paul area, using PV Watts, fixed mount, tilted to latitude:
    Month    Solar Radiation (kWh/m 2/day)
    1      3.85     
    2      4.72     
    3      4.97     
    4      4.91     
    5      5.74     
    6      5.91     
    7      5.89     
    8      5.64     
    9      5.21     
    10      4.28     
    11      2.95     
    12      2.85     
    Year      4.74
    

    Toss the bottom three months, that leaves February at 4.72 hours per day. Assuming 0.77 derating for panels and 0.80 for battery eff (DC only system, no inverter):
    • 250 watts * 0.77 derating * 0.80 battery eff * 1/14.5 volts charging * 4.72 hours of sun = 50 AH per day (Feb-long term average)

    You said:
    Battery load to these components is about 8 amps average 24 hours a day.

    Are you saying 8 amp*hours per day or 8a*24h=192AH per day?

    It would appear that you may be severely under paneled if it is 192 AH per day (at 12 volts) usage.

    Twisting cables helps a lot--But you need to wrap at least as tight as the 1/4 wave length of the highest frequency you are trying to control. It probably is not worth it with these heavy power cables.

    Since you like cool "toys"--You might want to look at a Battery Monitor (Victron is another good brand)--Will tell you what is happening with your battery bank without having to measure specific gravity or resting voltage.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • BB.BB. Super Moderators, Administrators Posts: 29,511 admin
    Re: New Guy PV Wiring Help & Ground

    Forgot to add--Do not ground the negative lead at the panel ground... Just tie the panel/frame ground to your local array ground rod.

    All the rest of the grounding should be done with a ground rod at the edge of the home (or water pipe/per code) and a single ground wire from the battery negative to the ground rod (you can share the AC mains ground rod too--You want everything at zero potential).

    Grounding your array at 160 feet away will pick up a lot of potential from the array to the home/radio room if there is a nearby lightning strike or even a downed power line.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • vtmapsvtmaps Solar Expert Posts: 3,738 ✭✭✭✭
    Re: New Guy PV Wiring Help & Ground
    ki7fx wrote: »
    I think the trade off was living with the voltage drop and 400 ft of FREE 6g new copper. Other than the loss, is there any other problem/danger with the loss (heat, etc)? I am sticking with high voltage panels to help compensate (31+ volt).

    You didn't specify your exact Vmp or Imp, but I can tell you that the resistance of 320 ft of 6 AWG is 0.12896 ohms. I would guess that your power loss (at full power) in the 160 ft cable would be about 6 or 7 watts.

    --vtMaps
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
  • waynefromnscanadawaynefromnscanada Solar Expert Posts: 3,009 ✭✭✭✭
    Re: New Guy PV Wiring Help & Ground

    And when you get you're next PV, make sure if at all possible that it's an exact match, identical at least in current ratings, to you're existing PV and wire them in series, doubling the voltage. Then at the other end of that long wire run, next to the batteries, let your TS-MPPT-60 do it's magic :)
    Cases like yours with long runs between PV and batteries, are where MPPT controllers can really shine if given the chance.
  • ggunnggunn Solar Expert Posts: 1,973 ✭✭✭
    Re: New Guy PV Wiring Help & Ground
    BB. wrote: »


    Twisting cables helps a lot--But you need to wrap at least as tight as the 1/4 wave length of the highest frequency you are trying to control. It probably is not worth it with these heavy power cables.

    This is DC, isn't it?
  • BB.BB. Super Moderators, Administrators Posts: 29,511 admin
    Re: New Guy PV Wiring Help & Ground

    Yes--But if you have AC radio frequencies (differential noise) from the switching of the MPPT/PWM charge controller (FETs turning on and off), twisting the wire will make the cable a "less good" antenna for "broadcasting" the RF energy.

    Twisting the cable also makes the cable less susceptible to picking up lightning induced surges (again, only helps with differential signals/power, not common mode signals). Not sure that it would be actually helpful to twist the cable in real life. Much of the lightning energy is in the ~7kHz frequency range. That is about a 35,000 foot 1/4 wave length. Not many people are going to run a ~6 mile solar array feed.

    Also when wiring up a system--Try to keep the +/- (and AC wiring too) running next next to each other. Don't make big loops of positive vs negative cables around the battery shed. This makes a loop antenna and will help broadcast RF noise too (and receive energy interference from portable transmitters, electrostatic discharge, etc. into your system too).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • nielniel Solar Expert Posts: 10,311 ✭✭✭✭
    Re: New Guy PV Wiring Help & Ground

    i guess we should've elaborated that you could feed the cables through large toroids near the cc to give the same effect as the wire twists. more turns through it is even better yet as you may know. in fact you could do both if you are that worried about it. if burying conduit then make it larger than you think you'd ever need and run a rope or strong string through it so as to allow a future wire or wires to be strung through it. saves redigging and replacing what you've already done. imho with the wire in conduit and buried i really doubt you will have much of a problem with rfi or even lightning emp bursts showing up on the pv wires. as long as some wire is above ground though, it will still be able to pick it up some.

    as was pointed out already, do be sure the pvs can be sufficient in keeping your batteries fully charged. you will also find that by putting another pv in series with the one you originally planned for that it doubles the voltage while keeping the current the same. plugging that into a v drop calculator will show an improvement in the percentage due to the v drop now being divided into double the voltage. this will cut the v drop % in half. more pvs placed in series later will also improve the v drop %.8)

    i should say that most times the noise generated will be below the general noise floor of the received background noise. when they appear they are usually in frequency multiples, like for example, every 50khz. it will vary with the controller makes and models and any of them could have a spike that could interfere. this is more likely to happen when a controller is operating on the high end of its capability. few have complained with today's mppt controllers of noise, but it is good that you are taking precautions even though it may not actually be necessary.
  • ki7fxki7fx Registered Users Posts: 10
    Re: New Guy PV Wiring Help & Ground

    Wow... many thanks to all of you for your insight. Very useful information!
    So.. as I see it, I will just go ahead and give the 6g a few twists every few feet before I sink it in the ground - can't hurt. I also have a run of RG6, CAT5 and whatever else I could stuff in there - as well as a nylon pull string for future bright ideas...

    Also, I do understand that my PV wattage output is low. I will be adding more panels as time and $$ permit. My goal was to get that voltage up to 60+ volts and reduce the distance loss, so that will come in time as well. I am sticking with the Helios 6T 250 panels. They are made in Milwaukee which is close by, and my local distributor has hundreds of them available. And, lastly, I will ground the negative side of the PV feed in the basement at the controller, but not outside at the panels/combiner box.

    Yes, I am consuming about 192Ah per day <-- thanks to BB and thanks for the statistics/specs. Right after I put the system on line, I noticed that I had more "output" than "input" <--- for lack of a better term :-). So... more panels = happy batteries.

    I have been slowly piecing this together for a year or more. Started out as a DC UPS with this 8-10 amp load. Powered by a 30 amp Samlex charger/conditioner/power supply. It would idle along every day consuming 75-100 watts and provide plenty of backup power for the Ham radios when necessary. With the solar input, it hums away at 7 watts - however the lack of adequate solar current does cause the Samlex to go back to 75 watts at night because the batteries are not getting a full charge under this constant load. So I am at least saving during daylight/sunshine hours. I consider my experiment a success - so far. Now to just add more solar and more battery capacity and permanently unplug the Samlex charger. Does this make any sense? BTW - Don't check my numbers too closely as I haven't done my basic OHM's law on this setup - just ballpark figures. If I have to get the calculator out it will be too much like work! :-) That's more of a winter project in Minnesota!
    Thanks to all...
    Mike
  • BB.BB. Super Moderators, Administrators Posts: 29,511 admin
    Re: New Guy PV Wiring Help & Ground

    The mix of solar vs Grid/Utility power vs backup genset--Purely your choice. As you say--the end result should be "happy batteries". ;)

    Check the Vmax input for your chosen charge controller. Many MPPT charge controllers (45 amps and larger) will take a Vmp~100 volt array pretty easily (although, check--in very cold weather, Vmp/Voc rise)--That will help reduce copper costs/losses too (Midnite and a few other brands offer even higher input rated controllers).

    By the way, I would suggest burying multiple larger diameter conduits (2" minimum, if I did it again, I probably would go 6" or larger--much easier to pull more cable later) in your trench. If you are "to code", the AC wiring should (usually) be in "rated" PVC electrical conduit. The other cabling/signal lines could be in a second conduit (I am cheap, I use ABS sewer pipe--better UV resistance vs PVC white water/irrigation pipe. Keeping cables separated (by even a few more inches will reduce noise coupling too).

    It does not cost too much, and will save you having to cut another trench just to pull one more wire.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • nielniel Solar Expert Posts: 10,311 ✭✭✭✭
    Re: New Guy PV Wiring Help & Ground

    if you intend to add more battery capacity you should do it now as it is not advisable to mix old and new batteries. if not abused up to about a year we kind of say ok, but adding new to old brings the new battery or batteries down to the level of the worst battery you already have. do not disconnect the grid charger until you are sure you have enough charge capacity to fully keep your batteries happy. even after that you may have need to reapply that charger for extended bad weather periods. it may even be helpful if you get a battery monitor, but one can become too complacent in trusting these as there isn't a good substitute for tracking things like voltages, specific gravity, and so on assuming that there could be a small degree of error. i guess i should reword this to say they are ok to have, but don't fully trust them.

    btw, i too use my setup for ham and backup to my refrigerator and a few lights. n3ghx
  • ki7fxki7fx Registered Users Posts: 10
    Re: New Guy PV Wiring Help & Ground

    I plan to do a 100% battery replacement after I get one or two more PV panels and get my incoming solar votlage up to 60-90 plus volts.

    For budget vs efficiency, is it better to run a 24v system? If so, four 12v batteries or eight 6v? And... if I do 24v, then I cannot split off my 12v loads... correct? Maybe I have to stick with a 12v system? Just starting to research and understand this particular part of the topic.

    As you can tell, I am just putting pieces together here with the goal of a complete system in the next few months.

    Thanks again for all the assistance.
    Mike
  • BB.BB. Super Moderators, Administrators Posts: 29,511 admin
    Re: New Guy PV Wiring Help & Ground

    Mike,

    A lot of the battery bank voltage choices really depends on your loads... More or less, I like to recommend 1,200 watts of load as the break point between 12 volt and 24 volt systems... For example:\
    • 1,200 watts * 1/0.85 inverter eff * 1/10.5 cutoff voltage * 1.25 NEC fuse/wiring/breaker derating = 168 amp minimum rated wiring/fuses/breakers

    As you can see, the current adds up very quickly and you are starting to talk about some pretty hefty wire. Add voltage drop for running the 134 amp current 10 feet through a pair of cables--even more copper needed.

    Similar using 2,400 watts at 24 volt break point (48 volt bank for higher power requirements).

    There is also the charge controller selection... You have about 4-8 hours to pump the batteries full... so, if you have a 24x7 load that of say 15 amps--Then you have ~6 hours to replace all that current--or about 4x15 amps = 60 amps average in that time frame--Many controllers max out at 60 amps--So if your array/controller combination needs to output >60 amps--You have a choice of adding a second controller--Or doubling the bank voltage (from 12 to 24 volts) and now the 60 amp controller can handle 2x the array (power=volts*amps -- double the voltage at the same current, double the power).

    I usually ask about loads--Then that defines the battery bank capacity. Battery bank size and Watt*Hours per day define the array size. Then we look at the "magic" break points (60 amp charge controllers, 100 amp wiring limit (i.e., 100 amps * 12 volts = 1,200 watts), etc...

    Some times, the lower voltage wins out... For example the 12 volt 300 watt TSW inverter for MorningStar is about the "perfect" inverter if you do not need high peak current (or get a second/cheaper inverter to run some power tools, etc. on demand). There is no inverter with its features in the 24 or 48 volt arena until you hit several thousand dollars and multiple kW output.

    Long way around for a "hand waving" "it depends".

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • vtmapsvtmaps Solar Expert Posts: 3,738 ✭✭✭✭
    Re: New Guy PV Wiring Help & Ground
    BB. wrote: »
    For example the 12 volt 300 watt TSW inverter for MorningStar is about the "perfect" inverter if you do not need high peak current (or get a second/cheaper inverter to run some power tools, etc. on demand). There is no inverter with its features in the 24 or 48 volt arena until you hit several thousand dollars and multiple kW output.

    Victron makes 800 watt TSW 'Phoenix' inverters at 12, 24, or 48 volts.
    The no load draw at 24 volts is 5 watts (Very Impressive) and the search mode is 2 watts. :D
    As far as I can tell, they have built in sockets for the output. I would like to see a hard wired option :cry:

    I have never seen or used one, but Victron seems to have a good reputation on this forum.

    --vtMaps
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
  • BB.BB. Super Moderators, Administrators Posts: 29,511 admin
    Re: New Guy PV Wiring Help & Ground

    Nice find vtMaps.

    Here are the Victron data sheets.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
Sign In or Register to comment.