Help picking inverter

rp3703
rp3703 Registered Users Posts: 129 ✭✭

So here is my situation. I am putting together a off-grid solar system that will be used at our cabin in Ontario Canada that we visit from June at the earliest through August at the latest but we are usually only there during the month of July. We will have loads of up to 15 charging cell phones, 10 LED lights, a Shurflo pressure pump and a cheap 18-22 cu ft. refrigerator. Here are my load calculations:

15 cell phones x 120 volts x .08 amps = 144 Watts x 1.5 hours a day = 216 WH/Day

10 lights x 120 volts x .075 amps = 90 Watts x 2 hours a day = 180 WH/Day

1 pump x 12 volts x 7 amps = 84 Watts x 3.5 hours a day = 294 WH/Day

Refrigerator load is based on well above average 450 kWh energy star rating divided by 365 = 1700 WH/Day

Total load= 2390 WH/Day (2096 AC, 294 DC)

2096(AC @ 24V) x .04 = 83.84 x 2 = 167.68 x 2 = 335.36AH

294(DC @12V) x .08 = 23.52 x 2 = 47.04 x 2 = 94.08AH

Total AH storage for 2 days autonomy = 429.44AH

Here is my required panel array calculations:

429.44 AH x 29 = 12,453.76 x 1.3 = 16,189.89 x .1 = 1618.99 Watts Max

2390 WH/Day x 1.92(1 / .52) = 4588.8 x .23(1 / average hours of sunlight) = 1055.42 Watt Minimum

I have already purchased six 310 watt panels that I got a deal on for $108 a piece:

4 x 310 = 1240

5 x 310 = 1550

I plan to try using just 4 panels but will add a fifth one if necessary. Eight 6V 215AH Deka batteries wired series parallel will cover our power storage and I'm thinking about going with a Midnite classic 150 SL just in case we actually need to use the fifth panel. Now here is where I need help. I need to pick out an inverter that will handle running a refrigerator without overloading when the compressor fires up. At the same time, I don't want to get too powerful an inverter that the inverter itself drains the batteries prematurely. The best I could do as far as finding amp specs on the size refrigerators I’m looking at was a Frigidaire that stated 720 watts but I’m guessing it’s probably safer to go with 1000 watts just incase. I have read varying advice on what to use as a multiplier to figure surge from 4-5 times continuous which would put surge at 4000 - 5000 watts. Does this sound about right to you guys? Any idea what I should be looking at as far as specs go on such an inverter? Am I correct in assuming that I do not need a charging inverter?

1860 W (6) Rensola JC310M, Classic 150, 430AH@24V (8) Deka DSGC15 FLA's, Victron Phoenix Multi 24/2500 Inverter
Powering-20.5 CuFt. Fridge, 1 HP Submersible water pump, UV, Washing Machine, Gas Dryer, Gas Stove, Lights and Receptacles
Off Grid Cottage on lake in Northern Ontario 46˚N 

Comments

  • 706jim
    706jim Solar Expert Posts: 514 ✭✭✭✭
    Are you considering a pure sine wave inverter? I'm hoping to be able to run a fridge from my old Trace 1500 watt inverter. Surge load is the least of my concerns as this transformer based unit can provide 4400 watts for up to a minute and I can't see any decent fridge taking THAT much to start. My concern is whether or not the fridge motherboard will be happy with modified sine power. As for a charging inverter, you probably don't need it looking at your loads, but they are nice to have.
    Island cottage solar system with 2500 watts of panels, 1kw facing southeast 1.3kw facing southwest 170watt ancient Arco's facing south. All panels in parallel for a 24 volt system. Trace DR1524 MSW inverter, Outback Flexmax 80 MPPT charge controller 8 Trojan L16's. Insignia 11.5 cubic foot electric fridge. My 30th year.
  • westbranch
    westbranch Solar Expert Posts: 5,183 ✭✭✭✭
    edited May 2017 #3
    Well I can confirm that a brand new Frigidaire model FFTR1521R* can run on a (cheap) Eliminator TSW 12 V 1000W inverter from Canadian Tire...  I helped a friend get his hooked up at his cabin yestrday.  No idea of additional ''head space'' he had left in that unit for additional power.  We will see how it performs over the summer.
    ADD;  there was one short squawck on startup but only once... rates out at 720W running
     
    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
  • rp3703
    rp3703 Registered Users Posts: 129 ✭✭
    I would probably choose pure sine vs modified only due to increased efficiency but I have no idea how much less efficient modified is vs pure.
    1860 W (6) Rensola JC310M, Classic 150, 430AH@24V (8) Deka DSGC15 FLA's, Victron Phoenix Multi 24/2500 Inverter
    Powering-20.5 CuFt. Fridge, 1 HP Submersible water pump, UV, Washing Machine, Gas Dryer, Gas Stove, Lights and Receptacles
    Off Grid Cottage on lake in Northern Ontario 46˚N 
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    MSW inverters tend to be more efficient than TSW inverters.

    However, many loads (induction motors, many electronic power supplies, transformers) tend to be less efficient on MSW inverters (more waste heat in motors, power supplies, and transformers because of higher harmonic energy in MSW inverter outputs). The waste heat can cause early life failure in some devices (and sometimes annoying buzzes too).

    Probably the old rule that ~80% of the stuff works fine on MSW, and 10% will fail an early death. How to know the difference--Not always easy to tell.

    Older devices (brushed/universal AC/DC motors for tools, kitchen appliances, filament light bulbs, etc.) did not really care MSW vs TSW wave-forms.

    Newer stuff (electronics, battery chargers for cell phones, power tools, CFL+LED lightning ballasts, laptop power supplies, plug in transformers for small devices, etc.) and Energy Star rated electric refrigerators that are are now efficient enough to run off on an off grid solar power system (and cheap solar panels+chargers+inverters) tend to be more picky about the "quality" of AC power. How to pick an inverter:

    https://lib.store.yahoo.net/lib/wind-sun/Pump-Inverter.pdf

    -Bill


    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • Estragon
    Estragon Registered Users Posts: 4,496 ✭✭✭✭✭
    If the fridge uses 1700wh/day, and the rating is based on ~1/3 duty cycle it's ~200w running, so surge around 1000w?
    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
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    My cheap fridge and freezer use around 120 to 100 watts with the compressor running.

    It may take around 600 watts peak to run the defrost heater.

    - Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • westbranch
    westbranch Solar Expert Posts: 5,183 ✭✭✭✭
    He will be back next weekend as he did not have time to do much more than move the 560Ahr AGMs into his crawl space, set up the rack, wiggle them into place  and do the connections before his promise to the wife came into play .... be home for dinner!!... He did have the fridge on overnight on his old bank but he is new to his MN KIDS and learning how to read the output...  Obviously Frigidaire has some new technology for the start-up on their fridges.

    more as it comes


     
    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