Enter Zipcode

Results 1 to 7 of 7

Thread: Calculation of battery back up for Solar PV Power Plant

  1. #1
    Junior Member
    Join Date
    Dec 2011
    Posts
    8

    Default Calculation of battery back up for Solar PV Power Plant

    Hi,
    Can anyone pls help me to calculate the battery sizing. I have gone through various websites and have found different formulae and not able to decide which formula is effective. pls suggest a effective formula for battery sizing and also how to decide the system voltage.

    The following are the formulae i have come across and i would appreciate it if anyone can verify them

    Total KWhr load = Total No. of Load*Wattage of each unit*total No. of working hours


    Solar PV Module Capacity = (Total KWhr Load)/4 Considering insolation to be 4 hours

    Inverter Capacity = Solar PV Module Capacity

    Effective Load = (Total KWhr Load)/(Inverter Efficiency)

    Ampere hours per day = (Effective Load)/(System Voltage)

    Total Battery Bank Capacity = ((Total Module Capacity)*(No. of backup hours))/((System Voltage)*(Inverter Efficiency)*(Battery deep discharge))


    Thank you,
    Regards
    Seshadri.A.V
    Last edited by seshu; 02-01-2012 at 05:00 AM. Reason: to eloborate the query

  2. #2
    Solar Fanatic
    Join Date
    Feb 2010
    Posts
    13,165

    Default

    It is real easy. First decide on how many days of reserve you want. Minimum is 5 days which gives you 2.5 real days before you hit the 50% DOD mark. So let's say you use 1 Kwh/day, that means you need 5 days x 1 Kwh = 5 Kwh total capacity.

    All you do now to find the amp hours is factor out the battery voltage gives you Wh / volts = AH. So lets say you want a 12 volt battery system. 5Kwh / 12 volts = 417 AH.
    MSEE, PE

  3. #3
    Junior Member
    Join Date
    Dec 2011
    Posts
    8

    Default

    Quote Originally Posted by Sunking View Post
    It is real easy. First decide on how many days of reserve you want. Minimum is 5 days which gives you 2.5 real days before you hit the 50% DOD mark. So let's say you use 1 Kwh/day, that means you need 5 days x 1 Kwh = 5 Kwh total capacity.

    All you do now to find the amp hours is factor out the battery voltage gives you Wh / volts = AH. So lets say you want a 12 volt battery system. 5Kwh / 12 volts = 417 AH.
    Thank you Sunking, could you please tell me what are the factors that are to be taken into consideration to choose the system voltage i.e the input voltage to the inverter from the battery bank. Also i would appreciate it if you could tell me if the formulae i used for the design is correct or not.

    Thanks in advance
    Regards
    Seshadri A V

  4. #4
    Moderator
    Join Date
    Jul 2009
    Posts
    9,145

    Default

    Total KWhr load - a useful number can only be obtained by measuring each individual device over a couple of days.

    Solar PV Module Capacity = (Total KWhr Load)/4 - a meaningless number really - the 4 hours is a number grabbed out of the air and is possibly right for some location somewhere

    Inverter Capacity = Solar PV Module Capacity - roughly though the module capacity can often be slightly higher than the inverter rating - the efficiency of the panels etc is in the 77% range
    Effective Load = (Total KWhr Load)/(Inverter Efficiency) - a made up number by someone - the inverter efficiency (MPPT) is in the 93% to 97% range - for quality units - no name junk from China or elsewhere is most likely far lower

    Ampere hours per day = (Effective Load)/(System Voltage) - there is the effective load word again?

    Total Battery Bank Capacity = ((Total Module Capacity)*(No. of backup hours))/((System Voltage)*(Inverter Efficiency)*(Battery deep discharge)) - salesman's smoke?

  5. #5
    Junior Member
    Join Date
    Dec 2011
    Posts
    8

    Default

    Quote Originally Posted by russ View Post
    Total KWhr load - a useful number can only be obtained by measuring each individual device over a couple of days.

    Solar PV Module Capacity = (Total KWhr Load)/4 - a meaningless number really - the 4 hours is a number grabbed out of the air and is possibly right for some location somewhere

    Inverter Capacity = Solar PV Module Capacity - roughly though the module capacity can often be slightly higher than the inverter rating - the efficiency of the panels etc is in the 77% range
    Effective Load = (Total KWhr Load)/(Inverter Efficiency) - a made up number by someone - the inverter efficiency (MPPT) is in the 93% to 97% range - for quality units - no name junk from China or elsewhere is most likely far lower

    Ampere hours per day = (Effective Load)/(System Voltage) - there is the effective load word again?

    Total Battery Bank Capacity = ((Total Module Capacity)*(No. of backup hours))/((System Voltage)*(Inverter Efficiency)*(Battery deep discharge)) - salesman's smoke?
    Thank you Russ for your valuable reply, I understand that most of the calculations seem to be traditional assumptions in sizing of a solar power plant, I would appreciate it if you could guide me through the proper standard calculations that are required. I have been having a tough time since every person or every source I find to learn these calculations have a different approach.

    Thank You in advance
    Regards
    Seshadri A V

  6. #6
    Moderator
    Join Date
    May 2009
    Location
    off grid retirement in Northern Calif
    Posts
    7,466

    Default

    what are the factors that are to be taken into consideration to choose the system voltage


    1) for every 1KW of load, add 12V to the battery system:
    800W could work on 12V
    1200w should have 24V
    2300w should have 36V - but no gear exists so use 48V
    2300w & greater = 48V

    2) increase voltage to meet your wattage demand with a single string of batteries. Adding batteries in parallel is possible, but can lead to more troubles than a proper single string.
    Since the dawn of time it has been mankind's dream to blot out the sun.
    Montgomery Burns

    "Always listen to experts. They'll tell you what can't be done and why. Then do it."

    spreadsheet based voltage drop calculator:
    http://www.solar-guppy.com/download/...calculator.zip
    http://www.solarpaneltalk.com/showth...oss-calculator

    http://www.mike-burgess.org/PVinfo_2.html

    solar: http://tinyurl.com/LMR-Solar
    gen: http://tinyurl.com/LMR-Lister ,
    battery lugs http://tinyurl.com/LMR-BigLug
    Setting up batteries http://tinyurl.com/LMR-NiFe

    gear :
    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 || || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

  7. #7
    Junior Member
    Join Date
    Dec 2011
    Posts
    8

    Default

    Quote Originally Posted by Mike90250 View Post

    1) for every 1KW of load, add 12V to the battery system:
    800W could work on 12V
    1200w should have 24V
    2300w should have 36V - but no gear exists so use 48V
    2300w & greater = 48V

    2) increase voltage to meet your wattage demand with a single string of batteries. Adding batteries in parallel is possible, but can lead to more troubles than a proper single string.
    Thank You Mike your post was of great help.

Tags for this Thread

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •