Battery Bank Configuration for a 48VDC, 2430 AH bank

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Comments

  • Tmp4000Tmp4000 Registered Users Posts: 34 ✭✭
    edited June 2017 #32
    Estragon said:
    The gear apparently produces roughly 15,000 btu, which has to be moved from inside the enclosure to outside. There will be a point at which reducing the size of the enclosure is counterproductive, depending on the delta from ambient to conditioned space, the r-value of the insulation, and convective vs conductive heating, etc.

    Still, 4500w seems like a lot of juice for a remote atmospheric monitoring application, and reducing that would change the air conditioning load as well.. Seems to me there may be ways of rethinking the loads before thinking too hard about accomodating them.
    That is correct:  15,000 Btu/h combined heat that will have to be removed (equipment heat and heat due to weather from outside).

    I am thinking that maybe we could have two solar systems:  one powering the air conditioning (say ~2000W inverter) and the other will power the instrumentation/computer equipment (~5000W inverter). So have two inverters and two battery banks. 

    Unfortunately the sensor instrumentation needs a little lee-way:  the expected range of operation is 3400W with no add-ons (GPS, etc...)....up to 4300W with extra add-ons to support different science sorty. So yeah, maybe on a Monday it will only draw 3400W, but then on Wednesday it might draw 4000W and then on Friday it might draw 4300W. So we go with the highest expected power draw. It all depends on the request from the science folks and what configuration of the sensors they want to use. If they want everything, then 4300W it is.

    And then it might happen that the science package won't be used for a week.... it's is impossible to say what the schedule will look like.

    So we go with the highest expected power draw:  4300W


  • mvasmvas Registered Users Posts: 384 ✭✭✭
    edited June 2017 #33
    Tmp4000 said:

    Is 10,300W of power not enough in 7 hours to recharge 3504AH battery bank ?

    During the day the Solar Panels must run all of the loads and recharge the deeply discharged battery bank back to 100% SOC,
    specifically when yesterday was a CLOUDY DAY = 0 PV watts.
    After a very cloudy day, it may take two days or three days

    sanity checks ...

    Solar Panel Array
    =============
    136 KWH Generated daily = 72 panels x 315 watts x 6 hours
    137 KWH Consumed daily = 5,700 watts x 24 hours 
    Better, but the PV watts are still too low for the daily load + previous cloudy day
    How are you converting ( 5.7 - 6 kWh/m^2 ) to ( 7 Solar Hours ) in your formulas ?
    Do you need to derate the PV watts for HEAT?
    Are you assuming that Lead Acid Batteries are 100% efficient?  ( approx 85% - 90% ? )
    PV watts generated needs to be greater than Daily Loads, otherwise the battery bank can never "catch-up"
    Yesterday was cloudy ( PV = 0 Watts ) and you discharged your battery bank more than normal.
    So, today the PV array needs to generate = ( Today's Loads / 0.85 ) + Yesterday's shortage 
    You cannot leave the battery bank is PSOC state forever.
    * If Solar Panels are rated at 125% of ( Daily Loads / 0.85 ) then battery bank "catches-up" in four days.
    * If Solar Panels are rated at 133% of ( Daily Loads / 0.85 ) then battery bank "catches-up" in three days.
    * If Solar Panels are rated at 150% of ( Daily Loads / 0.85 ) then battery bank "catches-up" in two days.
    Be conservative with estimated PV generation.

    Inverter
    =======
    Will the 7,000 Watt inverter support 4,300 watts of equipment and then start a 1,400 Watt  A/C Compressor ?
    What is the surge rating of the A/C unit?
    Is the A/C an "inverter" style?
    The Inverter will shutdown due to low battery voltage, will all of your equipment auto-magic-ally restart upon next sunrise ?

    Battery Bank 
    ==========
    168 KWH Battery Capacity    = 7,008 AH x 48 Volts  x 50% DOD
    136 KWH Power Consumed  = 5,700 Watts x 24 Hours on battery
    OK
    How many years do you need / expect the battery bank to last ?
    Can you support Flooded Lead Acid or will you be using Sealed AGM batteries ?
    There is a Lifeline AGM that can last approx 3 Years at Daily 50% DOD, another 5 years pro-rated.

    Charge Controller
    ==============
    Have you verified the PV Array will not exceed Max Volts ?
    Have you verified the PV Array will not exceeded Max Amps ?
  • Tmp4000Tmp4000 Registered Users Posts: 34 ✭✭
    edited June 2017 #34
    mvas said:
    Tmp4000 said:

    Is 10,300W of power not enough in 7 hours to recharge 3504AH battery bank ?

    During the day the Solar Panels must run all of the loads and recharge the deeply discharged battery bank back to 100% SOC,
    specifically when yesterday was a CLOUDY DAY = 0 PV watts.
    After a very cloudy day, it may take two days or three days

    sanity checks ...

    Solar Panel Array
    =============
    136 KWH Generated daily = 72 panels x 315 watts x 6 hours
    137 KWH Consumed daily = 5,700 watts x 24 hours 
    Better, but the PV watts are still to low for the daily load + previous cloudy day
    How are you converting ( 5.7 - 6 kWh/m^2 ) to ( 7 Solar Hours ) ?
    Do you need to derate the PV watts for HEAT?
    Are you assuming that Lead Acid Batteries are 100% efficient?  ( approx 85% - 90% ? )
    PV watts generated needs to be greater than Daily Loads, otherwise battery bank can never "catch-up"
    Yesterday was cloudy ( PV = 0 Watts ) and you discharged your battery bank more than normal.
    So, today the PV array needs to generate = Today's Loads / 0.85 + Yesterday's shortage 
    You cannot leave the battery bank is PSOC state forever.
    If Solar Panels are rated at 125% of ( Daily Loads / 0.85 ) then you "catch-up" in four days.
    If Solar Panels are rated at 133% of ( Daily Loads / 0.85 ) then you "catch-up" in three days.
    If Solar Panels are rated at 150% of ( Daily Loads / 0.85 ) then you "catch-up" in two days.

    Inverter
    =======
    Will the 7,000 Watt inverter support 4,300 watts of equipment and then start a 1,400 Watt  A/C Compressor ?
    What is the surge rating of the A/C unit?
    Is the A/C an "inverter" style?
    The Inverter will shutdown due to low battery voltage, will all of your equipment auto-magic-ally restart upon next sunrise ?

    Battery Bank 
    ==========
    168 KWH Battery Capacity    = 7,008 AH x 48 Volts  x 50% DOD
    136 KWH Power Consumed  = 5,700 Watts x 24 Hours on battery
    OK
    How many years do you need / expect the battery bank to last ?
    Can you support Flooded Lead Acid or are will you be using Sealed AGM batteries ?

    Charge Controller
    ==============
    Have you verified you will not exceed Max Volts ?
    Have you verified you will not exceeded Max Amps ?
    Okay...I see your point. How about now:  please verify the following:

    ======================================
    Cooling System:  1400W assume 2000W
    ======================================
    Daily cooling energy needed:

    (2000W*24)=48,000Wh

    Use a 315W panel, that has a NOCT rating of 226W. Assume 1000 Wh/m^2 equals to ONE SOLAR HOUR --> 6 solar peak hours

    # of panels needed:  48,000W/(226W*6)=35.4 -> 36 panels

    According to MidNite Classic 200 Controller online sizing tool, I can configure these 36 panels as follows:

    1 Controller for every 12 panel:  4 panels in series to make a string, then three such strings in parallel.
    1 Controller for every 12 panel:  4 panels in series to make a string, then three such strings in parallel.
    1 Controller for every 12 panel:  4 panels in series to make a string, then three such strings in parallel.
    ================================
    3 Controller for 36 panels. 

    Battery bank needed for ONE DAY of autonomy:

    1400W/(0.92*0.93) =1637 W needed (where 0.92 and 0.93 are efficiencies of inverter/cabling)
    1637W*24 = 39270Wh

    Use a 48VDC bank:

    39270Wh/48V = 818Ah of bank.  Apply Dod=50%

    818Ah/0.5=1637 Ah of battery bank needed


    ====================================
    Sensor Instrumentation:
    ====================================
    4300W * 24h = 103200Wh per day

    # of panels needed (@315W, but using 226W)
    103200Wh/(226W*6h)=76.1 -> 77 -> go with 80

    7 charge controllers:  MidNite Classic 200

    1 Controller for every 12 panel:  4 panels in series to make a string, then three such strings in parallel.
    1 Controller for every 12 panel:  4 panels in series to make a string, then three such strings in parallel.
    1 Controller for every 12 panel:  4 panels in series to make a string, then three such strings in parallel.
    1 Controller for every 12 panel:  4 panels in series to make a string, then three such strings in parallel.
    1 Controller for every 12 panel:  4 panels in series to make a string, then three such strings in parallel.
    1 Controller for every 12 panel:  4 panels in series to make a string, then three such strings in parallel.
    1 controller for 8 panels:  4 panels in series to make string, then 2 such strings in parallel

    Battery bank needed for ONE DAY of autonomy:

    4300W/0.92/0.93 =5026 W needed (where 0.92 and 0.93 are efficiencies of inverter/cabling)
    5026W*24 = 120624Wh

    Use a 48VDC bank:

    120624Wh/48V = 2513Ah of bank.  Apply Dod=50%

    2513Ah/0.5=5026 Ah of battery bank needed
    ======================================================================

    TOTAL # of panels in system:  36 + 80 = 116
    TOTAL # of charge controllers: 7 + 3 = 10

    Questions:

    1. Which batteries would work for this case ? What would be the best way to configure them ?
    2. Any better charge controllers besides the MidNite 200 for these scenarios ?


  • mcgivormcgivor Solar Expert Posts: 3,854 ✭✭✭✭✭✭
    edited June 2017 #35
    Question 2 
    You might want to consider high voltage passively cooled. No fans to fail.Fewer controllers.
    https://www.solar-electric.com/xaxwmp80amp6.html
    https://www.solar-electric.com/morningstar-ts-mppt-600v-48-solar-charge-controller.html
    1500W, 6× Schutten 250W Poly panels , Schneider MPPT 60 150 CC, Schneider SW 2524 inverter, 400Ah LFP 24V nominal battery with Battery Bodyguard BMS 
    Second system 1890W  3 × 300W No name brand poly, 3×330 Sunsolar Poly panels, Morningstar TS 60 PWM controller, no name 2000W inverter 400Ah LFP 24V nominal battery with Daly BMS, used for water pumping and day time air conditioning.  
    5Kw Yanmar clone single cylinder air cooled diesel generator for rare emergency charging and welding.
  • PhotowhitPhotowhit Solar Expert Posts: 5,657 ✭✭✭✭✭
    I've done my bit and haven't seen any answers, So let me ask a couple direct questions.

    What happens on the cloudy day and system fails? All of your calculations are based on perfect weather. The reason for over sized batteries with days of autonomy has to do with this. I don't knw anywhere that has perfect weather every day. Assuming the inverter restarts once a reasonable DC voltage is 'seen'. Will your data systems restart? Will the computers reboot and reconnect? Since the room will become a oven, will they be okay until the room is cooled, assuming the air conditioning restarts.

    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.
  • Tmp4000Tmp4000 Registered Users Posts: 34 ✭✭
    We cannot have everything. So when the clouds set in and the system dies down...we will just wait until the Sun starts to shine. I have explained to our team that they will NOT get 24/7 operation of the instrumentation. They are fine with that. They can put up with one or two days of downtime. 

    Historically speaking, this remote location has Sun everyday, with 12 hours of *some* sunlight. In fact, it is the best place to have a solar pv installation...so I am told. When a thunderstorm moves in, it moves out. 
  • BB.BB. Super Moderators, Administrators Posts: 32,018 admin
    Depending on where your system will be installed--PV Watts can give you a "typical" day for 365 days a year... You can run that through a spread sheet and see how well your proposed system design will work on "real" hourly solar data (or do a statistical evaluation of x Standard Deviations from median/average/whatever you like).

    You have to be a bit careful about what data column you use and the "fudge factors" you may have entered (you do not want to double derate your numbers).

    -Bill
    "PVWatts: Hourly PV Performance Data"<br>"Requested Location:","palu indonesia"<br>"Location:","SINGAPORE, SINGAPORE"<br>"Lat (deg N):","1.37"<br>"Long (deg E):","103.98"<br>"Elev (m):","16"<br>"DC System Size (kW):","10"<br>"Module Type:","Standard"<br>"Array Type:","Fixed (open rack)"<br>"Array Tilt (deg):","0"<br>"Array Azimuth (deg):","180"<br>"System Losses:","14"<br>"Invert Efficiency:","96"<br>"DC to AC Size Ratio:","1.1"<br>"Average Cost of Electricity Purchased from Utility ($/kWh):","No utility data available"<br>"Capacity Factor (%)","14.4"	<br><br>"Month","Day","Hour","Beam Irradiance (W/m^2)","Diffuse Irradiance (W/m^2)","Ambient Temperature (C)","Wind Speed (m/s)","Plane of Array Irradiance (W/m^2)","Cell Temperature (C)","DC Array Output (W)","AC System Output 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"0","25.7","2.7","0","25.7","0","0"<br>"1","4","4","0","0","25.6","1.5","0","25.6","0","0"<br>"1","4","5","0","0","25.5","2.4","0","25.5","0","0"<br>"1","4","6","0","0","25.5","3.2","0","25.5","0","0"<br>"1","4","7","0","6","25.4","4.1","6","24.233","51.786","0"<br>"1","4","8","0","94","26.6","4.3","94","27.371","799.392","728.27"<br>"1","4","9","78","222","27.7","4.4","262.841","32.18","2168.42","2065.751"<br>"1","4","10","163","347","28.9","4.6","461.116","37.607","3718.85","3572.742"<br>"1","4","11","120","470","29.2","5.5","569.406","39.342","4564.001","4390.764"<br><br>


    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • LumisolLumisol Registered Users Posts: 374 ✭✭✭
    Exactly. Decide what is needed, not what is wanted, and go from that point.
  • EstragonEstragon Registered Users Posts: 4,495 ✭✭✭✭✭
    How accessible is the site? Can you get heavy equipment in? This could be a factor in battery choice.
    Off-grid.  
    Main daytime system ~4kw panels into 2xMNClassic150 370ah 48v bank 2xOutback 3548 inverter 120v + 240v autotransformer
    Night system ~1kw panels into 1xMNClassic150 700ah 12v bank morningstar 300w inverter
  • Dave AngeliniDave Angelini Solar Expert Posts: 6,033 ✭✭✭✭✭
    I was involved in a few of these very large projects. Yours would be the largest! The only way to do this was with shipping containers.
    They were pre-built, insulated and shipped in, duty paid, all of the gear in the containers tested. The ground crew built a series of roofs to keep the sun off and mount the solar.

    You may need a helicopter.  Your budget is insanely low!

    I would go thru all of the posts here and make a list with the answers and re-post it here. It might help you !
    "we go where power lines don't" Sierra Mountains near Mariposa/Yosemite CA
     http://members.sti.net/offgridsolar/
    E-mail [email protected]

  • Tmp4000Tmp4000 Registered Users Posts: 34 ✭✭
    edited June 2017 #42
    We will most likely use ship freight/containers.

    So I have newly revised numbers. Here is the current plan:

    Two solar systems:  one will power the air conditioning system...and the other will power the science package. The solar panels will be 315W, at actual peak NOCT of 228W. Peak solar hours is 6 hours.

    This will reduce the need for a vast number of charge controllers and battery banks in one system.

    Air Conditioning
    ===============
    Power needed: 1400W. (two window air conditioners). A/C will be on non-stop 24/7. Will need 28 panels. Battery bank will have DoD=0.70, 1 day autonomy. Eff of converter=0.92, -> 1268 Ah --> 61 kWh battery bank needed

    Science package
    ================
    Power needed:  3400W. Will be on 15 hours during the night. If possible...if not...every other day...Will need 60 panels. Battery bank will have Dod=0.50, 1 day autonomy --> 2358 Ah --> 113.2 kWh battery bank needed.

    Inverter eff = 0.92, controller eff ~ 0.90, 

    Is my math sound ? Does anyone have any recommendation on charge controllers and battery banks? I saw the one mentioned before (Morningstar 60-600V) and it only allows max 12 panels in series. The MidNite 200 also only allows 12 panels. I have trouble finding a charge controller for large number of panels connected......

  • mcgivormcgivor Solar Expert Posts: 3,854 ✭✭✭✭✭✭
    @Tmp4000 said
     Is my math sound ? Does anyone have any recommendation on charge controllers and battery banks? I saw the one mentioned before (Morningstar 60-600V) and it only allows max 12 panels in series. The MidNite 200 also only allows 12 panels. I have trouble finding a charge controller for large number of panels connected......

    The 600v controller will allow a larger array, total wattage, consider the Midnite 200V 80 A vs  Schneider 600V 80A,
    the 600V unit has a 3 times the capacity, rough calculation,  of course using each manufacturers string calculator would be a more accurate means of calculating the allowable number of the panels you have selected. 
    1500W, 6× Schutten 250W Poly panels , Schneider MPPT 60 150 CC, Schneider SW 2524 inverter, 400Ah LFP 24V nominal battery with Battery Bodyguard BMS 
    Second system 1890W  3 × 300W No name brand poly, 3×330 Sunsolar Poly panels, Morningstar TS 60 PWM controller, no name 2000W inverter 400Ah LFP 24V nominal battery with Daly BMS, used for water pumping and day time air conditioning.  
    5Kw Yanmar clone single cylinder air cooled diesel generator for rare emergency charging and welding.
  • Tmp4000Tmp4000 Registered Users Posts: 34 ✭✭
    mcgivor said:
    @Tmp4000 said
     Is my math sound ? Does anyone have any recommendation on charge controllers and battery banks? I saw the one mentioned before (Morningstar 60-600V) and it only allows max 12 panels in series. The MidNite 200 also only allows 12 panels. I have trouble finding a charge controller for large number of panels connected......

    The 600v controller will allow a larger array, total wattage, consider the Midnite 200V 80 A vs  Schneider 600V 80A,
    the 600V unit has a 3 times the capacity, rough calculation,  of course using each manufacturers string calculator would be a more accurate means of calculating the allowable number of the panels you have selected. 
    According to Morningstar's Tristar string calculator, when I input my solar panel, it says max # of panels is 12.
  • EstragonEstragon Registered Users Posts: 4,495 ✭✭✭✭✭
    Maybe I'm missing a zero somewhere, but it seems to me a 600v 60a charge controller should be able to handle 600 x 60 = 36000w input. 36000w / 315 = 114 panels.

    There are lots of reasons why you might not want to do such a thing, but I don't grok the 12 panel limit in the calculator.
    Off-grid.  
    Main daytime system ~4kw panels into 2xMNClassic150 370ah 48v bank 2xOutback 3548 inverter 120v + 240v autotransformer
    Night system ~1kw panels into 1xMNClassic150 700ah 12v bank morningstar 300w inverter
  • mcgivormcgivor Solar Expert Posts: 3,854 ✭✭✭✭✭✭
    Estragon said:
    Maybe I'm missing a zero somewhere, but it seems to me a 600v 60a charge controller should be able to handle 600 x 60 = 36000w input. 36000w / 315 = 114 panels.

    There are lots of reasons why you might not want to do such a thing, but I don't grok the 12 panel limit in the calculator.

    @Estragon You fell into the same trap as I did, the capacity of the controller is governed by the charge current and battery voltage, the 600V is the maximum input voltage, which it would down convert to the nominal battery voltage, the only advantage of using 600V would be to reduce conductor size over longer destance, probably not a requirement in this case. My apologies to @Tmp4000 for the mistake, seemed logical at first but further thinking revealed my error in thinking.
    1500W, 6× Schutten 250W Poly panels , Schneider MPPT 60 150 CC, Schneider SW 2524 inverter, 400Ah LFP 24V nominal battery with Battery Bodyguard BMS 
    Second system 1890W  3 × 300W No name brand poly, 3×330 Sunsolar Poly panels, Morningstar TS 60 PWM controller, no name 2000W inverter 400Ah LFP 24V nominal battery with Daly BMS, used for water pumping and day time air conditioning.  
    5Kw Yanmar clone single cylinder air cooled diesel generator for rare emergency charging and welding.
  • BB.BB. Super Moderators, Administrators Posts: 32,018 admin
    edited June 2017 #47
    60 amps × 59 volts charging × 1/0.77 panel+controller derating = 4,597 Watts STC of panels max recommended (max cost effective array)

    Output current self limiting for MPPT charge controller

    - Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • Tmp4000Tmp4000 Registered Users Posts: 34 ✭✭
    edited June 2017 #48
    BB. said:
    60 amps × 59 volts charging × 1/0.77 panel+controller derating = 4,597 Watts STC of panels max recommended (max cost effective array)

    Output current self limiting for MPPT charge controller

    - Bill

    This whole charging process does not seem to make logical sense to me.

    Let's say that I have the following:
    • 6 hours of peak Sun
    • 48,784 Wh per day, which is about 1016 Ah consumption per day
    • battery at dod=70% = 1451 Ah bank at 48V
    • solar panel is rated 228W @ NOCT
    So if I have a 1451AH battery bank, I would have to pump 1016AH back into it (48,784Wh) during the 6 hours that the Sun shines. So that means that during the 6 hour Solar window, I need

    47,784Wh/(228*6) = 35 panels, which is 7980W

    ============================================================

    BUT, according to some information on this forum, actually what happens is that you need

    1451AH * 0.13 * 58V / 0.90 = 12,156W,  which is  54 panels
    ==============================================================

    You get different answers......This does not make much sense to me.....


    If I used 48,784Wh from the battery, shouldn't I put back 48,784 Wh ? 





  • mcgivormcgivor Solar Expert Posts: 3,854 ✭✭✭✭✭✭
    edited June 2017 #49
    Using the linked calculator, below  and the information supplied in the example above, the result was 35 panels. Note, the results are a minimum estimate based in the information entered, not 100% accurate, you may want to include a safety margin to ensure there is always a surplus of supply over demand.

    https://www.wholesalesolar.com/solar-information/start-here/offgrid-calculator
    1500W, 6× Schutten 250W Poly panels , Schneider MPPT 60 150 CC, Schneider SW 2524 inverter, 400Ah LFP 24V nominal battery with Battery Bodyguard BMS 
    Second system 1890W  3 × 300W No name brand poly, 3×330 Sunsolar Poly panels, Morningstar TS 60 PWM controller, no name 2000W inverter 400Ah LFP 24V nominal battery with Daly BMS, used for water pumping and day time air conditioning.  
    5Kw Yanmar clone single cylinder air cooled diesel generator for rare emergency charging and welding.
  • BB.BB. Super Moderators, Administrators Posts: 32,018 admin
    There are two different calculations for sizing the solar array... This calculation:
    • 47,784Wh/(228*6) = 35 panels, which is 7980W
    ...is based on the load and hours of sun per day. For sunny areas (more hours of sun), you need fewer panels (obviously).

    The second:
    • 1451AH * 0.13 * 58V / 0.90 = 12,156W,  which is  54 panels
    Is based on the size of the battery bank (AH @ xy volts). For flooded cell lead acid batteries, typically you want a minimum of 5% rate of charge for several reasons.

    One is that you need ~5% rate of charge to properly equalize the battery bank (controlled over charging to bring up weak cells by forcing current through the full cells, plus to generate hydrogen and oxygen gases to mix the electrolyte--particularly important with tall cased flooded cell batteries).

    A second reason is that you want to recharge the battery bank fairly quickly--You do not want two days of bad weather to take many days (or longer) to recharge the battery bank prior to the next few days of bad weather.

    Other reasons... 10% rate minimum rate of charge is minimum recommended by some flooded cell battery manufacturers. Also, if you have day time random loads, that "extra" charging current lets you both run some loads during the day and recharge the battery bank >5% rate of charge--without getting specific about the loads being run. In your case, you know the daytime loads, and therefore we can calculate them and "add" them to the base array separately.

    And, roughly 13% rate of charge is the maximum current you want to recharge a flooded cell lead acid battery bank at without worrying about over heating and thermal runaway. Basically, as the battery gets hot, the charging voltage requirement drops. And a non-temperature corrected charge controller may see that as additional loads (rather than as a hot battery) and jack up the charging current... Battery gets hotter, charging voltage drops, more current, and eventually you have an overheated battery (or worse). Most of the good solar battery chargers have remote temperature sensors available as an option so the charge controller can drop the charging voltage as the batteries get hot (or in sub freezing weather, the controller needs higher charging voltage for quick/proper lead acid battery charging).

    Lastly, over ~13% rate of charge, for most people running homes and cabins off grid--A higher rate of charge generally is not needed--The battery bank will usually be in float by or before noon with a very large solar array (unless they have large daytime loads such as irrigation, business needing computers/air conditioning at home, etc.).

    We try to get people to have "balanced" system designs. And avoid the old solutions--Such has a huge battery bank to "increase system power". Not very common now, but in the "olden days" when panels were $10+ per Watt (and not sub $1 per Watt like today)--Many folks were told, if they did not have enough power, they should add more batteries. Which then usually left them with a very large battery bank that was still not getting properly charged.

    Since you probably will be going with LiFePO4 batteries (or even AGM), and you know your power usage, and are in an extremely sunny region of the world (with little marine layer/cloud cover?), many of the rules of thumbs we use to quickly size a system for a "generic" cabin or home are not as important. We just use the "real numbers" instead. LiFePO4 batteries do not need a minimum rate of charge, and LFPO+AGM batteries do not need equalization--Those minimum charging numbers are not a "requirement".

    However, in general, since solar panels are cheaper (these days) than battery banks, and batteries improperly charged/maintained/over discharged can have very short lives--I still tend to suggest that the arrays be sized on the larger side to give you some headroom.

    If you will not have days or weeks of daily max loads, and you can reschedule loads to sunny weather--You can get away with a smaller array (and battery bank).

    And if you go with LFPO batteries, they can charge much quicker than lead acid (LA batteries charge very efficiently, like LFPO batteries, from "zero" to ~80% state of charge. Between 80-90%+ state of charge, they are charged at a constant voltage for 2-6 hours, depending on how deeply discharged they were). LFPO batteries do not have this "absorb" state of charging and can take high charging currents to near full.

    Also, as you get into the details--You will have to decide how to run your battery bank. For example, you may choose to run your LFPO battery bank between 20-80% or 20-90% of charge--Many LFPO batteries have a longer cycle life if you avoid getting close to 100% state of charge (lead acid batteries too are just fine charging to 90% SoC except for equalization).

    Also, LFPO batteries can sit for years at 20-80% state of charge (when unused). Lead Acid batteries generally must be stored >75% SoC or they will sulfate (faster).

    I still think counting on 6 hours of sun and your exact load is a bit optimistic... But if your loads are well known, and your weather has few clouds/dust/humidity/etc., plus you have flexibility to delay running during less than ideal weather--Then you may not need or want the extra margin.

    And why I was suggesting using PVWatts and the hourly/daily "average" year results to see how much variability you will have at your site (if there are no stations near your site, PVWatts is going to be making gridded estimates anyway--Perhaps not that helpful in terms of accurate predictions).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • PhotowhitPhotowhit Solar Expert Posts: 5,657 ✭✭✭✭✭
     ============================================================

    BUT, according to some information on this forum, actually what happens is that you need

    1451AH * 0.13 * 58V / 0.90 = 12,156W,  which is  54 panels
    ==============================================================

    You get different answers......This does not make much sense to me.....
    Part of what is going on is you have changed the rules, you don't understand that you have changed the rules yet!

    Flooded lead acid batteries NEED higher voltage to encourage the transfer of current from the array (via Charge Controller) to the battery bank. So a 48 volt battery bank that was nearing full charge, would have a resting voltage of 50 volts but would be charging with a voltage of near 60 volts. It would loos some of the current as heat as well with a transfer of only @80% of the power (wattage)

    A lithium battery bank doesn't require this much difference to allow the transfer of current. A lithium battery bank of 52.8 will only require a bit higher voltage with roughly a 97% transfer of power (wattage). Lithium also have another nice feature for a situation like yours. It can charge at higher rates, up to 50% per hour for some chemistries. Wish I could give more info, but Lithium isn't my "end of the pool"

    You are envisioning a "total loss system" one that shutting down/failure is planned. This is NOT what most people will plan for... If a "typical" off grid system plans to use 4 Kwh's a day, normally minimum available charging on a sunny day would be 2-3x or 8-12 Kwh's a day. The plan being to never run the system 'dry'. For flooded lead acid batteries, maintaining a charged level in the top 20-30% of capacity prolongs battery life. Having lower demands prolongs life and the system cost

    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.
  • EstragonEstragon Registered Users Posts: 4,495 ✭✭✭✭✭
    > @mcgivor said:
    > Estragon said:
    >
    >
    > Maybe I'm missing a zero somewhere, but it seems to me a 600v 60a charge controller should be able to handle 600 x 60 = 36000w input. 36000w / 315 = 114 panels.
    >
    >
    >
    > There are lots of reasons why you might not want to do such a thing, but I don't grok the 12 panel limit in the calculator.
    >
    >
    >
    >
    > @Estragon You fell into the same trap as I did, the capacity of the controller is governed by the charge current and battery voltage, the 600V is the maximum input voltage, which it would down convert to the nominal battery voltage, the only advantage of using 600V would be to reduce conductor size over longer destance, probably not a requirement in this case. My apologies to @Tmp4000 for the mistake, seemed logical at first but further thinking revealed my error in thinking.

    @mcgivor - yup, long day = brain fart. 60a output, not input. You probably could put 100+ panels on it, but it won't use the power.
    Off-grid.  
    Main daytime system ~4kw panels into 2xMNClassic150 370ah 48v bank 2xOutback 3548 inverter 120v + 240v autotransformer
    Night system ~1kw panels into 1xMNClassic150 700ah 12v bank morningstar 300w inverter
  • Dave AngeliniDave Angelini Solar Expert Posts: 6,033 ✭✭✭✭✭
    It may also not make sense to the OP because he has probably never done a small offgrid application!
    He is jumping into the fire with a huge project with changing variables and large risks for failure. 
    "we go where power lines don't" Sierra Mountains near Mariposa/Yosemite CA
     http://members.sti.net/offgridsolar/
    E-mail [email protected]

  • Tmp4000Tmp4000 Registered Users Posts: 34 ✭✭
    edited June 2017 #54
    It may also not make sense to the OP because he has probably never done a small offgrid application!
    He is jumping into the fire with a huge project with changing variables and large risks for failure. 
    There is no need for such statements.

    I am fully aware that the scope of this electrical system is beyond my team's solar electricity knowledge. That is why we have joined such communities to learn as much as possible in putting together the plan for this project. We are humble and eager to ask questions and learn.

    Belittling me in saying "OP is a fool! HaHa...the whole project will crash and burn...they have no idea what they are doing t!!" is not helping me and in fact reflects poorly on this community.

    We have done small-scale solar projects (a few panels to run airplane warning lights on tower...but not 100 solar panels, 60 batteries multiple charge controllers project).

    In the airplane warning light project, we only used one battery, one controller, and a few panels. Done! It was piece of cake!

    Here, we are dealing with 7-8 charge controllers, 60 batteries, thousands of watts of power...and we are trying to figure out how to make it work for a window of 6 peak sun hours. We are a small science team that are excited about upcoming project in studying the atmosphere. 



  • Dave AngeliniDave Angelini Solar Expert Posts: 6,033 ✭✭✭✭✭
    edited June 2017 #55
    Please do not take it personally!  Just my experience with solar for over 40 years. Good Luck! Yes I can make that statement about failure!

    I still think you should do what I suggested and go through all the posts again and address some of the concerns! Restate the project addressing them.
    You only get meaningful feed back if you put the effort in :)
    "we go where power lines don't" Sierra Mountains near Mariposa/Yosemite CA
     http://members.sti.net/offgridsolar/
    E-mail [email protected]

  • PhotowhitPhotowhit Solar Expert Posts: 5,657 ✭✭✭✭✭
    Tmp4000 said:
    It may also not make sense to the OP because he has probably never done a small offgrid application!
    He is jumping into the fire with a huge project with changing variables and large risks for failure. 
    ....
    Belittling me in saying "OP is a fool! HaHa...the whole project will crash and burn...they have no idea what they are doing t!!" is not helping me and in fact reflects poorly on this community.
    Dave did not call you a "fool". I think he was just referencing the difficulties we are all facing trying to help you out. I think he was more trying to say to us trying to help you out that we are faced with challenges as well. Your parameters are different from an off grid home, pretty much my statement above.

    I rejoined the conversation to ask about the need for data at the worse possible time. If you are "...studying the air/atmosphere..." but willing to have the system go down when you have a cloudy day, Won't you skew the data? Isn't that going to be the most valuable time, to assess change?
    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.
  • LumisolLumisol Registered Users Posts: 374 ✭✭✭
    Tmp4000 said:
    It may also not make sense to the OP because he has probably never done a small offgrid application!
    He is jumping into the fire with a huge project with changing variables and large risks for failure. 
    There is no need for such statements.

    I am fully aware that the scope of this electrical system is beyond my team's solar electricity knowledge. That is why we have joined such communities to learn as much as possible in putting together the plan for this project. We are humble and eager to ask questions and learn.

    Belittling me in saying "OP is a fool! HaHa...the whole project will crash and burn...they have no idea what they are doing t!!" is not helping me and in fact reflects poorly on this community.

    We have done small-scale solar projects (a few panels to run airplane warning lights on tower...but not 100 solar panels, 60 batteries multiple charge controllers project).

    In the airplane warning light project, we only used one battery, one controller, and a few panels. Done! It was piece of cake!

    Here, we are dealing with 7-8 charge controllers, 60 batteries, thousands of watts of power...and we are trying to figure out how to make it work for a window of 6 peak sun hours. We are a small science team that are excited about upcoming project in studying the atmosphere. 



    Don't disparage, just consider the source of the statement and give it the weight it deserves, then continue to research and get this thing built.
    I'd stay away from batteries that require maintenance, even with a self fill system in place, there is a lot that can go wrong with such a low level of maintenance visits. Or consider an on site caretaker to do the daily maintenance tasks.
    Good luck.
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