Panel/inverter efficiency

hemmjohemmjo Solar Expert Posts: 90 ✭✭
We have a system installed that has been working very well for almost a year. It has 4 SolarWorld 275 mono panels in 2 strings of 2. The CC is Classic 150. The batteries are 4-InterState GC2-XHD-UT 6-Volt 2 x 12v strings. The SOC is typically about 70% each morning before the sun starts recharging.

As I mentioned in another thread, we are installing a similar system in another building. In reading the many posts trying to learn more, I have come across the topic of loss of efficiency in converting the high panel voltage to the lower battery voltage. In our first system the nominal panel voltage is 72, the battery voltage is 12.

The new system will have the same components. Would it be a good idea to bring the power in from the panels in at 36 v instead of 72? The distance from the panels to the CC is short, maybe 15 feet.

Thanks,

John
Two systems in the Dominican Republic  http://villagemountainmission.org/
installed Feb 2014 at 19.796189° -70.893594°, Classic 150 + WBJR, KISAE SW1210, MN Battery Monitor, IOTA DLS 55/IQ4,  4- Solar World 275w, 4-6v x 225ah Trace Batteries
installed Feb 2015 at 19.795733° -70.893372°, same components  as above
Honda PowerMate PC0497000, 7000/8750w generator - powers the well and chargers maybe once a week






Comments

  • gww1gww1 Solar Expert Posts: 963 ✭✭
    Re: Panel/inverter efficiency

    I believe so, Outback, either in the manual or somewhere on their site has an actual chart for the fm charge controllers. If I remember correctly it wasn't that much differance but when counting watts why not get the best you can. You will probly still decide on wire size and with 12 volts I don't know if that will add up to anything or not at 15'. The 1% or so you gain will last for ever.

    gww
  • westbranchwestbranch Solar Expert Posts: 5,183 ✭✭✭✭
    Re: Panel/inverter efficiency

    John are you planning to use the same wire? if so there would be some additional loss but you can check it out with a voltage loss calculator, and use a larger wire if the losses are too high. At 15 feet I dot think it will be too great.
    see post #1 here http://forum.solar-electric.com/showthread.php?29-voltage-drop-calculator/page8&highlight=voltage+loss+calculator


    What wire sizes do you have?
     
    KID #51B  4s 140W to 24V 900Ah C&D AGM
    CL#29032 FW 2126/ 2073/ 2133 175A E-Panel WBjr, 3 x 4s 140W to 24V 900Ah C&D AGM 
    Cotek ST1500W 24V Inverter,OmniCharge 3024,
    2 x Cisco WRT54GL i/c DD-WRT Rtr & Bridge,
    Eu3/2/1000i Gens, 1680W & E-Panel/WBjr to come, CL #647 asleep
    West Chilcotin, BC, Canada
  • Mountain DonMountain Don Solar Expert Posts: 494 ✭✭✭
    Re: Panel/inverter efficiency

    Depends.
    If the wire length can benefit from the higher voltage with smaller gauge wires that cost less, that is one thing.
    If the system (with high voltage PV) still gets the batteries into float every normal day, why worry too much?

    Just my way of looking at the details.
    Northern NM, 624 watts PV, The Kid CC, GC-2 batteries @ 24 VDC, Outback VFX3524M
  • hemmjohemmjo Solar Expert Posts: 90 ✭✭
    Re: Panel/inverter efficiency

    On the system that is already installed, we are using 30 Foot MC4 Solarline 2, Extender Cables. They are cut into two pieces, to get male and female ends for the panel connections, and to run the 10-15 feet to the inside combiner box. So there are 2 pairs of RHW-2/RHH 10 ga wires running inside. I just put the combiner inside since it is so close and it does not have to be waterproof.

    If there is not that much difference in the efficiency I will just install the new system the same way. It would cost us $90.00 extra to run 2 more pairs of wires through larger conduit inside to 2 more breakers in the combiner box. I was just wondering if the benefit justifies the extra expense.

    I am actually not certain if it gets into float most days. I do think it does. I have not been there that much when it is in operation. I got it all installed and running about a week before I left last March. I was there again for 4 weeks in July. It was working ok then. I am anxious get back down next month to see what the logs look like for the last 6 months. I am a little concerned about the batteries. The staff we have there full time are great, actually awesome, but their skills are humanitarian in nature, teaching, nursing, not electrical/mechanical/solar/technical etc. They are learning, but it is a lot to grasp when it is totally out of their background.

    Thanks,

    John
    Two systems in the Dominican Republic  http://villagemountainmission.org/
    installed Feb 2014 at 19.796189° -70.893594°, Classic 150 + WBJR, KISAE SW1210, MN Battery Monitor, IOTA DLS 55/IQ4,  4- Solar World 275w, 4-6v x 225ah Trace Batteries
    installed Feb 2015 at 19.795733° -70.893372°, same components  as above
    Honda PowerMate PC0497000, 7000/8750w generator - powers the well and chargers maybe once a week






  • BB.BB. Super Moderators, Administrators Posts: 32,008 admin
    Re: Panel/inverter efficiency

    It should work fine. Do you have heavy enough cable on the combiner box output to handle the additional panels/current?

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • westbranchwestbranch Solar Expert Posts: 5,183 ✭✭✭✭
    Re: Panel/inverter efficiency

    Since you seem to make ~yearly 'maintenance trips' I would suggest that you get a an MNBCM which will give the staff a heads up - as long as they check it daily - so they can contact you if there is a problem developing. If you go that route you could have them do a daily log of the Charge % numbers and state of longer term charge .. 3 stages over 2 weeks since fully charged, 1 - 2 weeks since fully charged and within the last week... If it gets below say Yellow /60% you know something needs adjustment or turn on the generator... really good IMHO for essentially unattended ( by a trained person) battery based systems...

    All you need to add is a 1 amp car fuse and holder...

    http://www.midnitesolar.com/productPhoto.php?product_ID=444&productCatName=Battery%20Accessories&productCat_ID=39&sortOrder=2&act=pc
     
    KID #51B  4s 140W to 24V 900Ah C&D AGM
    CL#29032 FW 2126/ 2073/ 2133 175A E-Panel WBjr, 3 x 4s 140W to 24V 900Ah C&D AGM 
    Cotek ST1500W 24V Inverter,OmniCharge 3024,
    2 x Cisco WRT54GL i/c DD-WRT Rtr & Bridge,
    Eu3/2/1000i Gens, 1680W & E-Panel/WBjr to come, CL #647 asleep
    West Chilcotin, BC, Canada
  • hemmjohemmjo Solar Expert Posts: 90 ✭✭
    Re: Panel/inverter efficiency

    I have plenty of wire capacity from the combiner to the charge controller. It is only 2 feet between them, I had some #4 so I used that.

    My main concern is still how much efficiency I might gain from wiring the new one this way? Is there anyplace I can find numbers about this?

    I like WB's suggestion to get the MNBCM. I am thinking it might make more sense to spend the extra $'s on a pair of MNBCM's for these two installations?

    John
    Two systems in the Dominican Republic  http://villagemountainmission.org/
    installed Feb 2014 at 19.796189° -70.893594°, Classic 150 + WBJR, KISAE SW1210, MN Battery Monitor, IOTA DLS 55/IQ4,  4- Solar World 275w, 4-6v x 225ah Trace Batteries
    installed Feb 2015 at 19.795733° -70.893372°, same components  as above
    Honda PowerMate PC0497000, 7000/8750w generator - powers the well and chargers maybe once a week






  • westbranchwestbranch Solar Expert Posts: 5,183 ✭✭✭✭
    Re: Panel/inverter efficiency

    Yes!
    it might make more sense to spend the extra $'s on a pair of MNBCM's

    They are very light, so postage would be miniscule if you can get someone to bring them in for you. Assuming you are down there now.

    Here is the NAWS listing.. http://www.solar-electric.com/mnbcm.html


    For wire losses see post #3 for an Excel file, just fill in the wire size and length
     
    KID #51B  4s 140W to 24V 900Ah C&D AGM
    CL#29032 FW 2126/ 2073/ 2133 175A E-Panel WBjr, 3 x 4s 140W to 24V 900Ah C&D AGM 
    Cotek ST1500W 24V Inverter,OmniCharge 3024,
    2 x Cisco WRT54GL i/c DD-WRT Rtr & Bridge,
    Eu3/2/1000i Gens, 1680W & E-Panel/WBjr to come, CL #647 asleep
    West Chilcotin, BC, Canada
  • hemmjohemmjo Solar Expert Posts: 90 ✭✭
    Re: Panel/inverter efficiency

    I am still in the USA. Making final decisions now, I will be there most of March.

    I understand about the wire loses. The efficiency I thought I read about was in the Charge Controller. I understood from what I read that efficiency drops as voltage from the panels increases too far above battery voltage. Maybe I should have asked originally, if you had your choice considering ONLY the controller, not the wiring, would you prefer to send 36 volts or 72 volts to the Classic 150 to charge a 12 volt bank?

    I certainly appreciate all of the time you all spend helping those of us who are trying to learn.

    John
    Two systems in the Dominican Republic  http://villagemountainmission.org/
    installed Feb 2014 at 19.796189° -70.893594°, Classic 150 + WBJR, KISAE SW1210, MN Battery Monitor, IOTA DLS 55/IQ4,  4- Solar World 275w, 4-6v x 225ah Trace Batteries
    installed Feb 2015 at 19.795733° -70.893372°, same components  as above
    Honda PowerMate PC0497000, 7000/8750w generator - powers the well and chargers maybe once a week






  • inetdoginetdog Solar Expert Posts: 3,123 ✭✭✭✭
    Re: Panel/inverter efficiency

    36..............
    SMA SB 3000, old BP panels.
  • westbranchwestbranch Solar Expert Posts: 5,183 ✭✭✭✭
    Re: Panel/inverter efficiency

    Agree....36V....

    The closer the PV voltage is to the battery V the less looses to down conversion, therefore the less heat produced , most important/significant in warmer climates than up here, we're just below freezing right now. Higher V is used when wanting to send PV voltage a long distance, think hundreds of feet...
     
    KID #51B  4s 140W to 24V 900Ah C&D AGM
    CL#29032 FW 2126/ 2073/ 2133 175A E-Panel WBjr, 3 x 4s 140W to 24V 900Ah C&D AGM 
    Cotek ST1500W 24V Inverter,OmniCharge 3024,
    2 x Cisco WRT54GL i/c DD-WRT Rtr & Bridge,
    Eu3/2/1000i Gens, 1680W & E-Panel/WBjr to come, CL #647 asleep
    West Chilcotin, BC, Canada
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