New system what should I get?

jedjed Registered Users Posts: 4
I’m hoping to hear from anybody I want to go to a 3.5kw system. Is it best to buy a package? Or separate? Where’s the best and cheapest place to go? I’m going off grid and will need to run a water system off it. What voltage should I go 12? 24? 48? Hanjs


  • mike95490mike95490 Solar Expert Posts: 7,364 ✭✭✭✭
    What are the specific loads you need to run (water pump model, HP, voltage, amps.....)
    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

    gen: ,

  • BB.BB. Super Moderators Posts: 26,976 admin
    There is the peak load (like 3.5 kWatts for a ~1.5 HP well pump). And there is how many hours per day it will pump (like 1,500 watts * 4 hours per day = 6,000 WH per day).

    There are also different ways to design a water system... Pump with a "slow" solar pump (~900 Watts, for 6 hours per day) to a cistern, then use a 12 or 24 VDC RV type pump for pressurization (solar pumps tend to be expense, but "kind" to off grid power systems. Standard 240 VAC well pumps tend to be much cheaper, but require a much larger off grid power system to run the high power pump for a minute at a time to pressurize a water tank+air bladder, or other less expensive pumps like jet pump or similar.

    Others have used a genset with large AC well pump to fill a large cistern once a week, and an RV DC pressure pump with a very small solar power system.

    Before you buy any equipment, doing several paper designs may save you some money and frustration.

    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • jedjed Registered Users Posts: 4
    Thanks the idea of Gen to fill a tank sound the way to go. How about the off grid system??
  • BB.BB. Super Moderators Posts: 26,976 admin
    There are relatively inexpensive RV pumps (good for cabin or small home). They run from 12 or 24 volts:

    Set up a pressure tank (if you want a smoother, quieter flow, and to reduce pump cycling). Then you are left with the question of how much water... For example a 100 gallons per day per person, 2x people would be 200 gallons per day (domestic use). At ~3 gallons per minute, that would be roughly 67 minutes per day run time or 1.1 hours per day at 10 amps or 11 amp*hours per day.

    Get two 6 volt * 200 AH batteries (golf cart) in series for a 12 volt @ 200 AH. Run the battery bank to a maximum of 50% discharge or 100AH / 10 amp ~ 10 hours of pumping... More than enough to pump water for over a week without sun (100 AH capacity / 11 AH  per day = 9.1 days of pumping from battery).

    Say you are around Bramton Ontario, fixed array:

    Average Solar Insolation figures

    Measured in kWh/m2/day onto a solar panel set at a 46° angle from vertical:
    (For best year-round performance)
    Jan Feb Mar Apr May Jun
    Jul Aug Sep Oct Nov Dec
    Two calculations for solar array, one based on battery bank size (charging rates), the other based on hours of sun per day.

    For battery charging, 5% to 13% rate of charge is recommended... 5% can work for weekend/summer cabin use. 10%+ for full time off grid usage:
    • 200 AH * 14.5 volts charging * 1/0.77 solar panel * 0.05 rate of charge = 188 Watt array minimum
    • 200 AH * 14.5 volts charging * 1/0.77 solar panel * 0.10 rate of charge = 377 Watt array nominal
    • 200 AH * 14.5 volts charging * 1/0.77 solar panel * 0.13 rate of charge = 490 Watt array typical cost effective maximum

    And based on loads and hours of sun per day. Say you do not go (very often) in deep winter, so Feb at 3.50 hours of sun per day as "break even" month:

    • 11 AH * 12 volts = 132 WH per day pumping
    • 132 WH per day * 1/0.61 DC system solar eff * 1/3.50 hours of sun per day (Feb) = 62 Watt minimum array
    Now, if you really do not need this large of system/battery bank (weekend/summer cabin), you could go down to ~44 AH @ 12 volt smaller battery bank (2 days of storage and 50% maximum discharge ~ 4x daily load).

    Or keep the larger system, and use it for lighting, cell phone charging, running a laptop computer, etc... Using the golf cart batteries at "nominal" capacity:
    • 200 AH * 1/2 days of use * 0.50 max discharge = 50 AH per day total available "average" energy

    And, if you want to use 50 AH per day during Feb:

    • 50 AH * 14.5 volts charging * 1/0.61 DC system eff * 1/3.5 hours of sun (Feb) = 340 Watt array (Feb break even)

    Works out pretty closely to 377 Watt array for full time off grid energy usage for 9 months out of the year. And if you use the genset to pumping to cistern, you can pull some energy out to recharge your battery bank during bad weather/deep winter (if needed).

    Say you can pump 10 gallons per minute into your tank with a genset and well pump. 200 gallons per day * 7 days = 1,400 gallons. 1,400 gallons / 10 gpm = 140 minutes or 2 hours 20 minutes per week.

    For the RV water pump, try not to "lift" much height on suction side (with inlet screen, if needed). Water pump outside tank below water level is more efficient and less problems. With any pumping system, plan for water leaks. You don't want leaks to flood a basement, short out your pumps/electrical, or if tank overfills (failed tank valve/float).

    Anyway--Some suggestions of how to look at the issues. How much water, pumping 1x per week or once for 2 day weekend plus a few weeks of every other day pumping for summer. Your choices.

    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • MichaelKMichaelK Registered Users Posts: 63 ✭✭
    In my own case, I purchased Renogy's 3600watt cabin kit, but added another 3 panels to bring the total wattage up to 4500.  I do have to be careful to point my panels to different directions to prevent the batteries from over-amperage.  Coupled to a XW6848 inverter and eight L-16 batteries, the system can power my 1.5hp well pump 6-8 hours a day.  It's working well.

    You need to give more details if you have them; the ones Mike mentioned.
    15 Renogy 300w panels,  Midnight 200 CC, 8 Trojan L16 batteries, Schneider XW6848 NA inverter, AC-Delco 6000w gen.
  • EstragonEstragon Registered Users Posts: 1,723 ✭✭✭✭
    A kit could work, but many such kits I've seen appear to be assembled to meet a price point for advertising purposes and tend to be not well balanced for most applications. They may also tempt buyers to skip the important planning steps (understanding load requirements and trade-offs etc).
    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
  • MrM1MrM1 Registered Users Posts: 12 ✭✭
    edited January 12 #8
    How much do you want to spend?   And (as mentioned) what are your loads in daily Watt hours?
    REC TwinPeak 2 285W 3S-3P 2.6kW-STC 1.9kW-NMOT Array / MN Solar Classic 150 / Conext SW 4024 Inverter latest firmware
    Trojan L16H-AC 435Ah bank 4S connected to Inverter with 10' of 4/0 cable / 24 volt system / Grid-Assist Off-Grid / Need 3200Whs Daily
    System Pics and Discussion
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