Voltage Loss - Impact of >3%

mjp24cohomjp24coho Solar Expert Posts: 104 ✭✭✭
I'm working on some voltage loss calcs for a new array I'm contemplating, and the distance will be quite large. I'm looking to do 6 panels in series for ~220v, and then two series in parallel. The calculated total system voltage loss would be 3.75% with 6 AWG THHN wire. I understand that is over the magic 3% rule, but I wanted to understand what the impact is of being over 3%. What am I risking/sacrificing by being between 3-4%?

Comments

  • zonebluezoneblue Solar Expert Posts: 1,218 ✭✭✭✭
    Looking at the PV home run cable is a real horse trade. Theres no such thing as a perfect cable there. With copper costing so much these days 3% isnt actually that much when you consider that 3% of 6x 250W panels is 45W, and even at a buck a watt thats only 50 bucks of lost or addtional PV to compensate for the cable loss. Odds are you are talking about quite a bit more for your cable, yeah?

    The only thnig to watch is that you have enough voltage at the controller to do its job. At such a high array voltage that isnt an issue for you, however, also watch your controller losses at that voltage, they tend to be high. Also, esp if you are in 230V land, consider putting the inverter at the array.
    1.8kWp CSUN, 10kWh AGM, Midnite Classic 150, Outback VFX3024E,
    http://zoneblue.org/cms/page.php?view=off-grid-solar


  • vtmapsvtmaps Solar Expert Posts: 3,738 ✭✭✭✭
    mjp24coho wrote: »
    I'm working on some voltage loss calcs for a new array I'm contemplating, and the distance will be quite large. I'm looking to do 6 panels in series for ~220v, and then two series in parallel. The calculated total system voltage loss would be 3.75% with 6 AWG THHN wire.

    What are the panel specs, how far is the distance, and what controller will you use? You must have some cold winters in the Utah mountains... if your Vmp is 220 volts, the cold temp Voc will be too high for most controllers.

    As Zoneblue points out, its all just a matter of how many watts you lose in the cable.... and it may be more cost effective to buy an extra panel than to invest in more copper.

    You might even be better off configuring the panels four in series per string (three strings in parallel)... sure your cable losses will be higher, but your controller may be much more efficient (what controller are you planning to use?).

    By the way, the wattage losses you calculate go as the square of the current in the cable, so at typical power levels your losses are much less than what you calculate at full power production.

    vtMaps
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
  • mjp24cohomjp24coho Solar Expert Posts: 104 ✭✭✭
    400 feet each way with 8 awg wire (not 6 as I misstated above), and Midnite Classic CCs. I've run the calcs using Midnite's tool, and I should be ok using 6 in series and 2 series in parallel for each sub-array. The panels I'm looking at are the Kyocera 255 our sponsor sells (30.4 Vmp, 8.39 IMP, 37.6 Voc, 9.09 Isc). I'm in southern utah, so it doesn't get nearly as cold as northern utah (though we'll get below zero a few times). The price difference between 6 awg and 8 awg wire for that distance is much more than just adding an extra panel.
  • vtmapsvtmaps Solar Expert Posts: 3,738 ✭✭✭✭
    mjp24coho wrote: »
    400 feet each way with 8 awg wire (not 6 as I misstated above), and Midnite Classic CCs.

    Doing what you propose will be a disaster with any Midnite controller.

    First of all is the issue of cold Voc. Your Voc at standard conditions is 225 volts. On a 24 volt system that may damage a Midnite Classic 200 without even taking into consideration cold temperatures. Even with a 48 volt system on a Classic 250 you are pushing the envelope in cold weather.

    Secondly, for a 24 volt system you are over the power limits of either a Classic 200 or a Classic 250. Midnite's power charts for a Classic 200 only go up to a PV input voltage of 160 volts. At that voltage (160 volts) the maximum capacity of a Classic 200 is 2066 watts (and even less for a Classic 250).

    At higher voltages the controller is less efficient. That means that it makes more heat. Heat is the enemy of electronics. To run the controller at maximum capacity AND maximum inefficiency will shorten the life of the controller. Of course, with your proposed configuration the controller will probably die first from exceeding hyperVoc.

    Here is a quote from Robin Gudgel (cofounder of both Outback and Midnite):
    Max power for the Classic 250 is somewhere between 3000 and 3500 watts depending on your system configuration.
    <snip>
    I would not put more than 3000 watts on the Classic 250 myself. It will just run hot. That is never a good idea to run the controller flat out at its maximum day after day.

    In this quote Mr Gudgel was discussing a 48 volt system on a Classic 250 which has a maximum capacity of 3212 watts with an input voltage of 180 volts. The point is that it not good design to run a system at max power continuously.

    --vtMaps



    Edit: you might want to read this also:
    http://midnitesolar.com/Forum/index.php?topic=2008.msg18796#msg18796
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
  • zonebluezoneblue Solar Expert Posts: 1,218 ✭✭✭✭
    vt is right. Can you run 240V from the array? Maybe use a auto transformer? There is one other route for that kind of distance, kind of expensive though, run 600V array into a grid tie inverter, then into a hybrid inverter. Ac coupled.
    1.8kWp CSUN, 10kWh AGM, Midnite Classic 150, Outback VFX3024E,
    http://zoneblue.org/cms/page.php?view=off-grid-solar


  • Ethan BrushEthan Brush Solar Expert Posts: 231 ✭✭
    mjp24coho wrote: »
    I'm working on some voltage loss calcs for a new array I'm contemplating, and the distance will be quite large. I'm looking to do 6 panels in series for ~220v, and then two series in parallel. The calculated total system voltage loss would be 3.75% with 6 AWG THHN wire. I understand that is over the magic 3% rule, but I wanted to understand what the impact is of being over 3%. What am I risking/sacrificing by being between 3-4%?

    I will offer some opinions and suggestions:

    1. Use aluminum conductors
    2. As other said, consider the watts lost in PV cost - I have an array with 10 percent loss but adding a panel was cheaper than adding more wire.
    3. I think you are probably fine with 2 classic 250's
    4. take a look at the schneider mppt-600-80 CC. Costs the same as two classics. The schneider will only give you about 2300 watts but your 3000 watt array will work pretty well for that consideringwith losses, less than perfect conditions, mismatch panels, VD, etc. you will be around low to mid 2000's often anyway. You can usually do 13 - 250 Watt panels all in series with that controller - I would load it all the way,series is a free lunch in terms of losses and more output on cloudy days.
  • Ethan BrushEthan Brush Solar Expert Posts: 231 ✭✭
    Also with 13 panels in series using #6 AWG aluminum you would have 1.1% drop. #6 XHHW is around .20 per conductor per foot - cheap. Put it in 3/4 PVC.
  • mike95490mike95490 Solar Expert Posts: 8,653 ✭✭✭✭✭
    I have a 980' run to my water system and used #6 aluminum wire. It is light and pulled real easy. You can order spools with the footage you need, so there is no need to splice. Just be sure the gear has aluminum rated connectors (nearly everything does)

    Re Array Voltage. Schneider or Morningstar 600V charge controller. { I think this is the way I would go, and I'd use the Morningstar fanless & nice ethernet 16V min turn on voltage, can be programed via computer and MSView software for 24V bank}
    http://www.morningstarcorp.com/wp-content/uploads/2014/02/600V-TS-MPPT-Operators-Manual.pdf page 35 lists switch 3 as being able to config with MSView for 24V

    Or I suggest you re-think the array. 250V into a 24V battery will be a heavy loading on the classic. My 170V array on a Classic 200 @48V, sits and cooks all day long and you are considering an even worse PV-Bat volt mismatch, Consider 2 or 3 panels in series, #4 alum wire and combiner box.
    Powerfab top of pole PV mount | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
    || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
    || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

    solar: http://tinyurl.com/LMR-Solar
    gen: http://tinyurl.com/LMR-Lister ,

  • mjp24cohomjp24coho Solar Expert Posts: 104 ✭✭✭
    I should have clarified in my original post - this potential new array would have a new inverter and battery bank, both of which would be 48V, not 24V. I ran the calcs using Midnite's tool (see attached), and it appeared it would be fine at 6 in series, 2 in parallel. Running it at 4 in series, 3 in parallel would be even better (also attached), but my wiring losses even at 6 awg would be 5.5%. I wouldn't want to run anything lower gauge than that, so maybe I could just add extra panel (likely cheaper) to account for the loss, or run aluminum instead of copper, as others have suggested. My voltage loss calculator doesn't allow for an aluminum wire input - anyone know how to calculate with aluminum? I also would prefer not to put the inverter/batteries at the array and run 240V into the new cabin, as the array will be 450' away on a hilltop. I'd like to avoid having to make that walk everytime I'm checking on all the system components. I'd like to put it all in a room I want to build in the basement of the new cabin.
  • inetdoginetdog Solar Expert Posts: 3,123 ✭✭✭✭
    I have been happy with the online calculator from Southwire, at http://www.southwire.com/support/vol...calculator.htm
    It take a little getting used to, and you have to choose between inputting wire size and %VD and getting run length or %VD and length and getting min wire size.
    It does not give you %VD for a particular wire size and length AFAIK. But it is easy to work that out yourself from the output it gives.

    Aluminum will need to be between 2 and 3 AWG numbers larger than copper for the same VD.
    SMA SB 3000, old BP panels.
  • Ethan BrushEthan Brush Solar Expert Posts: 231 ✭✭
    Here is one I like most of the time:

    http://www.nooutage.com/vdrop.htm
  • Dave AngeliniDave Angelini Solar Expert Posts: 5,082 ✭✭✭✭✭
    The rule for commercial solar is design at 2% loss. A good article this month in solar pro talks about the trade offs and costing for large projects to bend the rule upwards. They basically say the cost of wire on the solar side of the controller is cheaper to size correctly and skimp on the output side of the controller.

    That does not really relate to you as you should just buy the Schneider hi voltage controller as the Morningstar will not work at 24VDC. XW-80 will give you room to expand later and its cost is the price you pay to run an array that far.
    "we go where power lines don't" Sierra Mountains near Mariposa/Yosemite CA
     http://members.sti.net/offgridsolar/
    E-mail [email protected]

  • mike95490mike95490 Solar Expert Posts: 8,653 ✭✭✭✭✭
    .......the Morningstar will not work at 24VDC. XW-80 will give you room to expand later and its cost is the price you pay to run an array that far.

    How do you determine that ?
    http://www.morningstarcorp.com/wp-co...ors-Manual.pdf page 35 lists switch 3 as being able to config with MSView for 24V

    Powerfab top of pole PV mount | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
    || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
    || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

    solar: http://tinyurl.com/LMR-Solar
    gen: http://tinyurl.com/LMR-Lister ,

  • Dave AngeliniDave Angelini Solar Expert Posts: 5,082 ✭✭✭✭✭
    Mike, I was hoping someone like you might come back and correct me. The older 600vdc Mstar did not have a 24vdc option. So this new model does? --Dave
    "we go where power lines don't" Sierra Mountains near Mariposa/Yosemite CA
     http://members.sti.net/offgridsolar/
    E-mail [email protected]

  • mjp24cohomjp24coho Solar Expert Posts: 104 ✭✭✭
    As mentioned above, I plan for this to be a 48V system, not 24V. I'm a big fan of Midnite's CCs, so I plan to use those instead of a high voltage Schneider.
  • Ethan BrushEthan Brush Solar Expert Posts: 231 ✭✭
    mjp24coho wrote: »
    As mentioned above, I plan for this to be a 48V system, not 24V. I'm a big fan of Midnite's CCs, so I plan to use those instead of a high voltage Schneider.

    I really think in this situation, one of the 600V CC's is a much more logical choice.
  • mike95490mike95490 Solar Expert Posts: 8,653 ✭✭✭✭✭
    Well, then you are all set. The Morningstar View SW will let you tweak the settings beyond what the dip switch can select.
    Powerfab top of pole PV mount | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
    || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
    || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

    solar: http://tinyurl.com/LMR-Solar
    gen: http://tinyurl.com/LMR-Lister ,

  • Dave AngeliniDave Angelini Solar Expert Posts: 5,082 ✭✭✭✭✭
    mike95490 wrote: »
    Well, then you are all set. The Morningstar View SW will let you tweak the settings beyond what the dip switch can select.


    And when the user adds more solar it is really easy to change wiring at the array with a 600 volt controller. With low voltage controllers adding solar will just add more current and a higher percentage of loss on long distance runs. The high voltage wiring is simple with most applications just needing a junction box at the array and a disconnect outside the house/garage.
    "we go where power lines don't" Sierra Mountains near Mariposa/Yosemite CA
     http://members.sti.net/offgridsolar/
    E-mail [email protected]

  • mjp24cohomjp24coho Solar Expert Posts: 104 ✭✭✭
    But isn't the Morningstar limited at 3200W? If I wanted a total array of 10-12k watts, wouldn't I need 3-4 of these? Also, what are the monitoring capabilities of the Morningstar? I really like the real-time data I get from my Midnite CCs.
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