I could use your advice.

TommyBoy
TommyBoy Registered Users Posts: 9
Hello,

Over the last few days, I have been reading this excellent forum and getting components together for a small/midsize solar setup. I've used the search function but I still feel like I have a very limited grasp which I come here now to ask advice of. My plan is to start with the basics and then move on to better components later. I am at the point where I need to start getting cables, fuses, and wires together. My system:

Offgrid
7x 100w 17.5V panels
fused combiner box
xantrex 60A CC
BLS desulfator
8x 12V 125Ah DeepC Batteries
Cobra 2500W Inverter


1. Is it ok to use 12-2 awg outdoor romex through conduit to connect panels to combiner box (span=25ft)?

2. I am using super/unistrut from home depot with the spring clips/bolts to fasten the panels to the roof. Are these galvanized steel fasteners enough to create electrical continuity with the aluminum panel frames?

3. Is there a safe low-cost grounding solution avail from the local hardware?

4. What do you recommend I should do for fuses in this system? Between batteries and inverter for sure but how about between combiner and charge controller? What do you recommend?

If you have any suggestions, please feel free to let me know.

Thank You, Tommy

Comments

  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: I could use your advice.

    Welcome to the forum.
    Let's see what we can come up with by way of answers.
    1. Is it ok to use 12-2 awg outdoor romex through conduit to connect panels to combiner box (span=25ft)?

    Have you done a Voltage drop calculation? www.solar-guppy.com/forum/download/voltage_drop_calculator.zip
    I'd do it for you, but the Linux netbook doesn't run it. :blush:
    Depending on how your 700 Watts of panel is wired (not sure which Xantrex controller you're using) you could be in the 50 Amp current range, which is over what 12 AWG will handle.
    2. I am using super/unistrut from home depot with the spring clips/bolts to fasten the panels to the roof. Are these galvanized steel fasteners enough to create electrical continuity with the aluminum panel frames?

    You don't want to use galvanized fasteners here; the dissimilar metals will set up an electrolytic reaction. This means something's going to corrode eventually. Use of stainless steel and/or some plastic insulation (with separate ground wire linking panels) would be better if you can't spring for the aluminium structure.
    3. Is there a safe low-cost grounding solution avail from the local hardware?

    Not sure I understand the question but, wire is wire. Most hardware/electrical outlets sell 6 AWG and 8' grounding rods et cetera. Grounding issues can create lively discussions, btw. :p
    4. What do you recommend I should do for fuses in this system? Between batteries and inverter for sure but how about between combiner and charge controller? What do you recommend?

    You need circuit protection http://www.solar-electric.com/cipr1.html on the line from the batteries to the inverter that will handle the full potential current of the wire, which should handle the full potetnial current of the inverter (maximum output at minimum input Voltage - the manual will have recommended sizing). You should also have CP on the output of the charge controller, again sized for wire and wire sized for maximum current potential. There should be fuses on the panels (not the combiner box output) as per their Isc to prevent problems if any one of them should short - you don't want it "backfed" by the remaining good panels.

    Now it's my turn for questions.

    Have you got a figure for expected loads? Off-grid systems need to be designed around how much power you intend to use. Vital to have numbers for peak Wattage and daily Watt hours.

    You've got eight 12 Volt batteries. Are these to be wired in parallel? If so, that's a problem. That many batteries in parallel creates difficulty in keeping current flow even throughout all the batteries. The net result is that some of the batteries do all the work and some just sit there. They all end up dying prematurely. 1000 Amp hours is huge for a 12 Volt system, and presents problems getting enough current to charge (50 Amps minimum, 100 is better) and a charge controller to handle it. Your stated panels would barely meet the minimum on a good day with no loads. If you have got potential load numbers perhaps we can suggest a more functional alternative.

    Forget the desulphator; there's no real evidence they work. That money would be better spent getting the system more in balance.
  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: I could use your advice.

    you can use the romex as far as i know, but you won't want to use 12-2 as you'll see.

    well i did the voltage drop calculation and going with a current output from the pvs at 5.71a (rough guess for each pv) at 25ft with #12 yielded a .578v drop and is at 4.82% drop for a 12v system.:cry: #10 would give about a 3.03% drop, but you still have to deal with the drops from the combiner to the cc and the cc to the battery as all vdrops are additive. these drops should not exceed about 3% totally and some would say even as low as not exceeding 2%. that means the #10 would roughly work at 3% if the rest of the wires had no vdrops and that would mean no resistance in those wires. that's impossible as we currently know it.
    here's a few more results,
    #8-1.9%
    #6-1.2%
    #4-.75%
    remember that is only the vdrop %s between the pv and the combiner.

    btw, each pv should be fused when paralleling more than 2 pvs or strings of pvs and the fuse rating should be listed by the manufacturer. if it's not then figure the imp x1.5 and round that up to the nearest commercially available fuse. if my 5.71a guess is correct then it's 5.71a x 1.5 = 8.565a. the next highest commercially available fuse would be 10a.
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: I could use your advice.

    Niel's calculations look right to me. Based on those and the over-all array size I'd suggest considering an MPPT controller here, with an even number of panels (either drop one to 6 or add one to 8) so that you can at least double the array Voltage.

    Again there is still the matter of how much power you need to supply and for how long. Everything hinges on that.

    A sample re-adjustment:

    600 Watt array using two strings of 3 in parallel (no panel fuses required) ; Vmp 52.5, Voc likely <70, Imp 11.5.
    Peak charge current potential < 35 Amps, so a Tristar 45 MPPT controller. This would give an 8.5% peak charge rate for three of your 125 Amp hour batteries in parallel.
    Those three batteries could supply up to 187 Amp hours or about 2.2 kW hours daily, which is fairly good power.

    Just a suggestion; not a precise calculation or recommendation.
  • dwh
    dwh Solar Expert Posts: 1,341 ✭✭✭
    Re: I could use your advice.
    I'd do it for you, but the Linux netbook doesn't run it. :blush:

    If your Linux box has Wine installed (many do):

    http://www.winehq.org/

    then you can probably run it under Wine.
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: I could use your advice.
    dwh wrote: »
    If your Linux box has Wine installed (many do):

    http://www.winehq.org/

    then you can probably run it under Wine.

    Thanks; I'll look in to that.
    Don't hold much hope, though, as this original version of the Aspire One has very limited resources and hasn't looked kindly on updates. I have to reboot several times a day as Firefox jams repeatedly! :grr
  • TommyBoy
    TommyBoy Registered Users Posts: 9
    Re: I could use your advice.

    Thanks very much for this detailed response. I apologize for the delay in replying as I am overwhelmed right now with current events. I have a real sense of urgency to get this system built as the global problems grow out of hand. My problem is my needs exceed my knowledge, I can admit that. This is a few steps beyond my electrical experience but I am committed to building a safe system. I will answer your questions and comments:


    not sure which Xantrex controller you're using

    >>>Xantrex C60




    You don't want to use galvanized fasteners here; the dissimilar metals will set up an electrolytic reaction. This means something's going to corrode eventually. Use of stainless steel and/or some plastic insulation (with separate ground wire linking panels) would be better if you can't spring for the aluminium structure.

    >>>Thanks for that. Would rubber or nylon washers be ok to isolate the panels from the unistrut? If I insulate the panel frames from the unistrut, do I need to ground the unistrut too? Grounding is somewhat complicated to me, sorry.




    Not sure I understand the question but, wire is wire. Most hardware/electrical outlets sell 6 AWG and 8' grounding rods et cetera. Grounding issues can create lively discussions, btw. :p

    >>> What I mean is that after reading that PDF about grounding in another thread, it seems grounding is much more complicated than simply drilling a screw into the frame and winding a wire around it. I was wondering if there was a fail-safe way to ground an alum frame using certain parts from the hardware store.




    You need circuit protection http://www.solar-electric.com/cipr1.html on the line from the batteries to the inverter that will handle the full potential current of the wire, which should handle the full potetnial current of the inverter (maximum output at minimum input Voltage - the manual will have recommended sizing). You should also have CP on the output of the charge controller, again sized for wire and wire sized for maximum current potential. There should be fuses on the panels (not the combiner box output) as per their Isc to prevent problems if any one of them should short - you don't want it "backfed" by the remaining good panels.

    >>> That is awesome information right there. My inverter manual recommends #2AWG. I was planning on using #2 for the batteries as well, is that ok?





    Have you got a figure for expected loads? Off-grid systems need to be designed around how much power you intend to use. Vital to have numbers for peak Wattage and daily Watt hours.

    >>> Thanks, I am estimating 7500 Watt Hours.




    You've got eight 12 Volt batteries. Are these to be wired in parallel? If so, that's a problem. That many batteries in parallel creates difficulty in keeping current flow even throughout all the batteries. The net result is that some of the batteries do all the work and some just sit there. They all end up dying prematurely. 1000 Amp hours is huge for a 12 Volt system, and presents problems getting enough current to charge (50 Amps minimum, 100 is better) and a charge controller to handle it. Your stated panels would barely meet the minimum on a good day with no loads. If you have got potential load numbers perhaps we can suggest a more functional alternative.

    >>> It was my understanding that taking the leads from opposite ends of the bank would alleviate the imbalance. You mean this doesnt work? OH CRAPPPPPPP NNNNNOOOOOOOOOOOOO!!!! Im broke now!!!! OH NOOOOOOOOOOOO!!!





    Forget the desulphator; there's no real evidence they work. That money would be better spent getting the system more in balance.

    >>> I already got it. I am planning on trying it on a moderately sulfated battery to test it. I will let you know how it goes.
  • TommyBoy
    TommyBoy Registered Users Posts: 9
    Re: I could use your advice.
    niel wrote: »
    you can use the romex as far as i know, but you won't want to use 12-2 as you'll see.

    well i did the voltage drop calculation and going with a current output from the pvs at 5.71a (rough guess for each pv) at 25ft with #12 yielded a .578v drop and is at 4.82% drop for a 12v system.:cry: #10 would give about a 3.03% drop, but you still have to deal with the drops from the combiner to the cc and the cc to the battery as all vdrops are additive. these drops should not exceed about 3% totally and some would say even as low as not exceeding 2%. that means the #10 would roughly work at 3% if the rest of the wires had no vdrops and that would mean no resistance in those wires. that's impossible as we currently know it.
    here's a few more results,
    #8-1.9%
    #6-1.2%
    #4-.75%
    remember that is only the vdrop %s between the pv and the combiner.

    btw, each pv should be fused when paralleling more than 2 pvs or strings of pvs and the fuse rating should be listed by the manufacturer. if it's not then figure the imp x1.5 and round that up to the nearest commercially available fuse. if my 5.71a guess is correct then it's 5.71a x 1.5 = 8.565a. the next highest commercially available fuse would be 10a.

    Thanks so much for all your work on that. Thats the kind of information a beginner like me needs to know. I need to minimize the spans between components as my orig plan will not work. IM going to take some measurements tomorrow, thanks a TON!!!
  • Photowhit
    Photowhit Solar Expert Posts: 6,002 ✭✭✭✭✭
    Re: I could use your advice.

    Batteries age together, I hope your not using a bunch of older batteries with different past lives."....I am planning on trying it on a moderately sulfated battery..." Great information in the battery FAQ's!

    Grounding aluminum is a real art, start with Lay in lugs. From what I have read, the pictutre does NOT represent a good connection! you need to remove the oxidated coating of the aluminum with emery cloth/fine sand paper, then apply a light coating of dielectric grease, aluminum starts oxidating the instant it is exposed, then install the lug. The WEEB grounding system is likely better but not universally excepted.
    Home system 4000 watt (Evergreen) array standing, with 2 Midnite Classic Lites,  Midnite E-panel, Magnum MS4024, Prosine 1800(now backup) and Exeltech 1100(former backup...lol), 660 ah 24v Forklift battery(now 10 years old). Off grid for 20 years (if I include 8 months on a bicycle).
    - Assorted other systems, pieces and to many panels in the closet to not do more projects.
  • SCharles
    SCharles Solar Expert Posts: 123 ✭✭
    Re: I could use your advice.

    While everyone is on the subject, or one of them, and refering to the advice to add a circuit breaker/fuse between PV panels, what fuse are you recommending? Is this a simple, in-line sort of fuse?

    I am using 8 ga. and in some places 6 ga. wire to hook up the panels to one another. [I happen to have a bunch of pieces of those gauges and the lugs to use them]. The in-line fuse holders I've seen over the years are all very small gauge things.

    I have the usual circuit breakers for the combiner box and controller and the big fuse for the battery cable to inverter, but I hadn't known about needing anything between the panels and am trying to imagine which sort of fuse I'd want to use.
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: I could use your advice.

    Big problem: 7500 Watt hours is enormous for off-grid, and your battery bank & panels will not support that much power. Vis:

    7500 / 12 = 625 Amp hours which means a 1250 Amp hour battery bank at least and more than 2 kW array (with two charge controllers) to support it.

    This is shut down time: it will not work with the equipment described in your original post.
    You should make some concerted effort to reduce the load potential.
    If you can't, you need to up the system Voltage and increase the battery bank and array size. You will not get that amount of Watt hours from 700 Watts of panel and 1000 Amp hours of 12 Volt battery.

    Time for a total re-think.
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: I could use your advice.
    SCharles wrote: »
    While everyone is on the subject, or one of them, and refering to the advice to add a circuit breaker/fuse between PV panels, what fuse are you recommending? Is this a simple, in-line sort of fuse?

    I am using 8 ga. and in some places 6 ga. wire to hook up the panels to one another. [I happen to have a bunch of pieces of those gauges and the lugs to use them]. The in-line fuse holders I've seen over the years are all very small gauge things.

    I have the usual circuit breakers for the combiner box and controller and the big fuse for the battery cable to inverter, but I hadn't known about needing anything between the panels and am trying to imagine which sort of fuse I'd want to use.

    Most panels don't put out more than 10 Amps. Some do. Some are "12 Volt" and some are "24 Volt" and some are "other". You need to size fuses (or breakers) based on the specs of your particular panels: able to handle the current and interrupt the Voltage.

    With some systems it is possible to install an automotive fuse block and use the blade fuses. Others need the more expensive circuit protection: http://www.solar-electric.com/sopawiinco.html
  • Paul54
    Paul54 Registered Users Posts: 18
    Re: I could use your advice.

    Tommy,
    I have used the Unistrut or Superstut for a frame. I use their cone nuts or spring nuts, but use stainless steel screws or bolts through the PV panel, and let the panel sit on top of large stainless steal fender washers so that the aluminum panel frame is only touching the stainless steel. This helps to avoid any corrosion between the different metals. You can get the stainless hardware at Lowes or Home Depot.

    I use the lay in lugs that were recomended in an earlier post. You can get them at a local electrical supply house, but I have not seen them at Lowes or Home depot. Attach them with stainless screws and a special star washer to dig into the panel's aluminum. Run one continuos ground wire through each panel lug down to your central grounding point. You can add an extra lug or lugs to the unistrut frame, but you need to scrape off the galvanized finish and treat the connection to avoid corrosion.

    Ideally you end up with one continuos grounding wire. You can remove individual panels with out interupting your ground connection to the others. My mount is adjustable for over 45 degrees of tilt. I use bare #6 copper with a little slack so I can tilt the panels repeatedly without stressing the ground wire.
  • TommyBoy
    TommyBoy Registered Users Posts: 9
    Re: I could use your advice.
    Big problem: 7500 Watt hours is enormous for off-grid, and your battery bank & panels will not support that much power. Vis:

    7500 / 12 = 625 Amp hours which means a 1250 Amp hour battery bank at least and more than 2 kW array (with two charge controllers) to support it.

    This is shut down time: it will not work with the equipment described in your original post.
    You should make some concerted effort to reduce the load potential.
    If you can't, you need to up the system Voltage and increase the battery bank and array size. You will not get that amount of Watt hours from 700 Watts of panel and 1000 Amp hours of 12 Volt battery.

    Time for a total re-think.

    Sorry, I meant 750, I used 120V to multiply the current instead of 12V, whoops.
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: I could use your advice.
    TommyBoy wrote: »
    Sorry, I meant 750, I used 120V to multiply the current instead of 12V, whoops.

    Are you sure? You don't want to change the amount again? Is that your final answer? :p
    Because you've now just gone from the ridiculous to the sublime.

    For 750 Watt hours you don't need eight 125 Amp hour batteries. It's more like this:
    750 Watt hours / 12 Volt system = 62.5 Amp hours, times 2 for maximum 50% DOD allowance = 125 Amp hour battery. Two such batteries would allow 25% DOD. How did you calculate for eight?

    Just to check the obvious: 1 Watt hour = Volts * Amps * hours. As in 12 Volts * 10 Amps = 120 Watts * 1 hour = 120 Watt hours. (None of this includes compensating for system inefficiencies/losses.)

    And no, the standard "diagonal wiring" method for parallel batteries will not work with eight batteries. Two is fine. Three, okay. Four ... gets a bit "iffy". By the time you reach eight in parallel it's a pretty safe bet that at least one of them will actually be left out of the mix, no matter how good the wiring. If not at first, certainly later as resistance values change.
  • TommyBoy
    TommyBoy Registered Users Posts: 9
    Re: I could use your advice.
    Photowhit wrote: »
    Batteries age together, I hope your not using a bunch of older batteries with different past lives."....I am planning on trying it on a moderately sulfated battery..." Great information in the battery FAQ's!

    Grounding aluminum is a real art, start with Lay in lugs. From what I have read, the pictutre does NOT represent a good connection! you need to remove the oxidated coating of the aluminum with emery cloth/fine sand paper, then apply a light coating of dielectric grease, aluminum starts oxidating the instant it is exposed, then install the lug. The WEEB grounding system is likely better but not universally excepted.

    No, lol the sulfated battery is an old trolling marine motor. Can I get dielectric grease at the local store?
  • TommyBoy
    TommyBoy Registered Users Posts: 9
    Re: I could use your advice.
    Are you sure? You don't want to change the amount again? Is that your final answer? :p
    Because you've now just gone from the ridiculous to the sublime.

    For 750 Watt hours you don't need eight 125 Amp hour batteries. It's more like this:
    750 Watt hours / 12 Volt system = 62.5 Amp hours, times 2 for maximum 50% DOD allowance = 125 Amp hour battery. Two such batteries would allow 25% DOD. How did you calculate for eight?

    Just to check the obvious: 1 Watt hour = Volts * Amps * hours. As in 12 Volts * 10 Amps = 120 Watts * 1 hour = 120 Watt hours. (None of this includes compensating for system inefficiencies/losses.)

    And no, the standard "diagonal wiring" method for parallel batteries will not work with eight batteries. Two is fine. Three, okay. Four ... gets a bit "iffy". By the time you reach eight in parallel it's a pretty safe bet that at least one of them will actually be left out of the mix, no matter how good the wiring. If not at first, certainly later as resistance values change.

    I will use this as an emergency system so I dont expect massive loads. Do you think I should make 2 banks instead? I got 8 batteries based on instinct, not a calculator. I figured its better to have too many than too little in an emergency.

    What do you think about making a battery buss like 2mantoyz's setup? Would that fix the issue? If not, I could get a switch and use 2 banks of 3 each and keep 2 spares.
  • SCharles
    SCharles Solar Expert Posts: 123 ✭✭
    Re: I could use your advice.

    Last yr. I bought dielectric stuff at Lowe's. I had to as someone where it was back in electrical, but they had it.