how to connect the pv panel and what is the size ?

Amna97Amna97 Registered Users Posts: 2
in my system there are two pump and each pump has a voltage about 220v and 300w , so what is the size of invertor, pv panel I need it in the system ?? 


  • mcgivormcgivor Solar Expert Posts: 3,817 ✭✭✭✭✭✭
    The inverter needs to be large enough to not only run the pumps but also large enough to absorb the inrush current during starting. If both pumps are to be run  at the same time, staging the starts so they don't start together can allow for a smaller inverter, however not all inverters are created equal, cheap not good, good not cheap. Around the 1500 to 2000W should work, pure sine wave would be the best, modified sine wave are hard on motors and are best avoided.

    As far as PV is concerned, details on when and how long they need to operate, as well as location, would be required, there are systems designed to work strictly off solar without batteries, but when using existing pumps, batteries are likely a requirement, as well as a means to charge them. More details including pump specifications are needed to even provide a rough calculation.
    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.
  • Amna97Amna97 Registered Users Posts: 2
    Iam going to use the Pv for 5 hours in the day so how can I know the size of pv , invertor, convertor ( DC - DC) ?? and charge buttery 
  • BB.BB. Super Moderators, Administrators Posts: 31,688 admin
    Amna, I am still not sure we have enough information... But I will give it a shot to show you how we size a system (paper designs are cheap--Do a few of them before you pay hard earned monies for your hardware).

    Say you want to run 2x pumps @ 300 Watts each, for 5 hours per day. Using our typical rules of thumb for a reasonable cost effective and reliable off grid power system (full time off grid), the system may look like this--Assuming 2 days of battery storage (no sun) and 50% maximum battery discharge (for longer battery life). Guessing a minimum of 24 VDC battery bus, flooded cell lead acid batteries (cheap(er) and fairly easy to monitor and forgiving):
    • 2x 300 Watt pumps * 5 hours per day = 3,000 Watt*Hours per day (enough to run a small/very efficient off grid home)
    • 3,000 WH per day * 1/0.85 AC inverter eff * 1/24 volts * 2 days of storage * 1/0.50 maximum discharge = 588 AH @ 24 volt battery bank

    That would be (one example) 4x 6 volt @ 200 AH "golf cart" batteries in series (for 25 volts) and 3 parallel strings (for 600 AH @ 24 volt battery bank). Or 12 golf cart type batteries. It is good to start with less expensive batteries as many of us have "killed" our first battery bank pretty quickly (mistakes, not paying attention, etc.).

    Now to charge the battery bank, we do two calculations. One sizing the array to give 5% to 13% or so rate of charge. The other based on hours of sun per day for your region and your daily loads. First, sizing for charging.

    5% is good for a weekend/summer seasonal system. 10%+ rate of charge is better for full time off grid system:

    • 600 AH battery bank * 29 volts charging * 1/0.77 panels+charge controller deratings * 0.05 rate of charge = 1,130 Watt array minimum
    • 600 AH battery bank * 29 volts charging * 1/0.77 panels+charge controller deratings * 0.10 rate of charge = 2,250 Watt array nominal
    • 600 AH battery bank * 29 volts charging * 1/0.77 panels+charge controller deratings * 0.13 rate of charge = 2,938 Watt array "typical cost effective maximum" array
    And then there is sizing the array based on hours of sun by day (seasonal) and the location of the system. Lets use a fixed array in Sharjah, UAE:

    Average Solar Insolation figures

    Measured in kWh/m2/day onto a solar panel set at a 65° angle from vertial:
    (For best year-round performance)
    Jan Feb Mar Apr May Jun
    Jul Aug Sep Oct Nov Dec
    A very sunny region of the world, assume you need water pumping pretty much all year round (maybe you can cut back by 30-40% in "winter" months--Pick December with 4.93 hours of sun for "break even" month (cut back on pumping or start a generator in bad weather):
    • 3,000 WH per day * 1/0.52 off grid end to end system eff * 1/4.93 hours of sun (Dec) = 1,170 Watt array minimum (Dec)
    So, somewhere between a 1,170 Watt and a 2,250 Watt array should do nicely.

    A 24 volt @ 600 AH flooded cell lead acid battery bank will run a 1,500-3,000 Watt 24 volt AC inverter pretty nicely. I would suggest you keep the AC inverter only big enough to run your loads (start your pumps). Too large of AC inverter will waste energy just being turned on (no AC loads)... Ideally, you would only want the inverter to run with the pumps are needed--A larger inverter can draw (waste) 20-40+ watts just being turned on with no loads (tare loading).

    Anyway--A quick paper design. Just a starting point. Please feel free to ask questions and correct my guesses.

    Note that there are other ways of pumping water... A common method is to get a DC compatible water pump that can connect directly to a solar array. It will only pump water during the day (if that is good enough for you)--Pump to a cistern/storage pond, etc. Solar Powered DC pump motors are not cheap--But saving the costs and maintenance of battery bank+AC inverter+checking that all is OK/adding water--Solar only pumping can be a huge improvement over battery based AC pumping.

    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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