Need help with my solar puzzle?

windgate32windgate32 Registered Users Posts: 8 ✭✭
Ok, here goes,
Before I get the spanking I rightly deserve let me say I know I have tried to do this as far backwards as possible, but hopefully at this point it is salvageable. This is for an off grid cabin that has access to utility. A very kind fellow helped me out on here when I was already knee deep and helped clear out a couple things, TY btw again. I am going to throw it all on the table and if any of you like a challenge please help lol. My goal is to run a chest freezer,110v, 12v led light system, battery charging of items, cordless drill, batteries etc, some kitchen items, computer and printer including modem, small radio, fans. Most all of this would not be run at the same time. Then as I progress see how much I can and cant use.
The pieces….
(3) Sun hs-180-rl 180 watts, 32.60 Voc, 7.78 Isc, 25.9 Vmp, 6.95 imp
(2) Sun-120wp 120 watts, 21 voc, 8.23 isc, 16.80 vmp, 7.15imp
(1) Delta LA602 DC Lightning arrestor
(1) ETQ Generator 7250-8250 max watts
(2) 10 amp deep cycle charger for 6/12v, of course runs off of 110v.
(1) FM-80 Outback charge controller
and now the wrench in my plans…
(1) Sun SL-2012 Inverter see specs here

The questions….
First and foremost, should I try to return the inverter? May not be possible.
With all the other gear do I need a battery meter/monitor? Or will the fm80 take care of my needs there?
Based on the pv power I have currently, what is the largest battery bank I should use, using T-605 210ah at 20hrs, 105mins at 75amps 6v.
Based upon the pv’s I have, what configuration will be best as well?

I am sure I have forgotten something and will have other questions, ty in advance for any and all advice.

Sincerely, Randy


  • mikeomikeo Solar Expert Posts: 386 ✭✭✭
    Re: Need help with my solar puzzle?
    Based upon the pv’s I have, what configuration will be best as well?
    With your panel count, you can't use all your panels with one FM80 the way I see it. If you had one more 180 watt panel I would wire them this way in series 180+180+120 which would produce 68.6 Vmp at 6.95 Imp (the lowest amp module in the string) or 476 watts. Two of these strings in parallel would be 952 watts. This would work great with you FM80 producing around 69 amps on perfect days at 13.8 volts. With what you have you will need a second controller to use all of the panels. If you can swing another panel based on 69 amps, you could support 690 amps of battery at C10 rate of charge. You are hitting the limit for a 12 volt based system with a single controller with this configuration. You inverter will draw 240 amps at rated power (2000 watts) and draw the battery down to 50% DOD in 1 and 1/2 hours. You could power 1000 watts of load approximately 3 hours, 500 watt load about 6 hours, 250 watt load for 12 hours. Now you need to set down and carefully calculate your loads to see what you can support with this system.
  • nielniel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: Need help with my solar puzzle?

    you need to get a handle on roughly what your loads will be and it is difficult for us to know what the wattages or time factors will be for each load. this will be a term in watt hours and once determined the best battery can be determined as the ah x 12v = wh and rearranging wh/12v = ah. now you'd want to double that ah figure so as to not deplete the batteries below 50% and your battery ah capacity shall always be at least 2x or greater than your load ah totals.

    as to the pvs, they are differing at this point enough to warrant 2 separate controllers. as mikeo pointed out another pv could've worked to your advantage, but it could also have been a 120w pv as you can make a series string of a 180w pv and a 120w pv being the currents are near to each other. that would realize 3 strings totally. now i can't say if the capacity in pv will wind up matching your battery capacity either as you've yet to determine what that battery capacity shall be to match your loads, but it may not matter when you can back it up with a generator.

    i'm not sure why it is you want to return the inverter. only you can determine if it fits your needs or want to return it.

    battery monitors are nice to have, but they aren't mandatory.
  • windgate32windgate32 Registered Users Posts: 8 ✭✭
    Re: Need help with my solar puzzle?

    Ty for the replies!
    OK, no need for the battery monitor, that is a cost savings and is good. 8) Dang, ok being that they must be bought in atleast pairs, i can save and buy3 more 120w, but i want the highest IMP number correct? not watts?
    I did buy the killowatt meter. I used it on my upright freezer, and 2 of my fans, I am going to use it on my computer next.I am not sure how to use the numbers I get from it. I will be buying a newer freezer but lets use this one for now.
    0.51 PF
    60 Hz
    224 VA
    1.84 AMP
    121.7 VOLTS
    64.98 KWH
    RATE OF 0.125

  • BB.BB. Super Moderators, Administrators Posts: 32,997 admin
    Re: Need help with my solar puzzle?
    windgate32 wrote: »
    I did buy the killowatt meter. I used it on my upright freezer, and 2 of my fans, I am going to use it on my computer next.I am not sure how to use the numbers I get from it. I will be buying a newer freezer but lets use this one for now.

    • 0.51 PF
    Power Factor... For a perfect AC Sine Wave driving a Perfect Resistive load (filament light bulb, electric heater, etc.)--Power Factor = 1.0

    For other devices (motors, electronics, etc.) they appear to take more current than they should. This extra current requires larger wires, generators, inverters, fuses than a pure Wattage calculation would appear to suggest.

    The math:
    • Power = Voltage * Current (sort of true--but for AC power and taking the above into account, the true equation:)
    • Power = Voltage * Current * Power Factor
    • Power = VA * Power Factor
    • Notice that PF ranges from 0.0 to 1.0, and that when PF=1.0, then V*A does equal Watts.
    So, for this example:
    • 60 Hz (line frequency of your power--50Hz is a common standard elsewhere)
    • 224 VA (Volt*Amps--what the wiring/inverter must be sized for)
    • 115WATT (power--what "energy" your battery/PV panels must supply)
    • 1.84 AMP (current at 1201.7 VAC)
    • 121.7 VOLTS (and AC line voltage)
    So the various equations should be:
    • Volt*Amps = VA = 121.7v * 1.84 amps = 223.928 VA
    • VA reading from meter = 224 VA
    • Power = Volts * Current * PF = 121.7v*1.84a*0.51PF= 114.2 Watts
    • Watt reading form meter = 115 watts
    • PF = Watts / VA = 115 watts / 224 VA = 0.513
    So, from the above, you would need to size the wiring/fusing to carry 1.84 amps even though, according to "simple power math:
    • I=P/V=115 watts/121.7 volts = 0.94 amps
    Because of the poor power factor of the motor (typical--nothing is wrong)--You hardware will need to supply almost 2x as much current.

    Battery power wise--however, your freezer is drawing only 115 watts when turned on.

    Now, for your system, we need to know how much power in a 24 hour period your freezer draws... It is on perhaps 50% of the time (115 watts for 30 minutes and 0 watts for 30 minutes)--So the meter will take the Watts*Time to figure out how much energy you use in a day:
    • 64.98 KWH
    • 558 HRS ELAPSED
    It gave the number in kWH (kilo-watt-hours). Kilo simply means 1,000x... So:
    • 64.98 kWH = 64,980 Watt*Hours for the time period measured.
    Your time period was 558 hours. The average watt load is:
    • 64,980 Watt*Hours / 558 hours = 116.45 watts
    A little odd--It appears that your freezer is running about 100% of the time... This may be normal, your 115 watt load does not take into account defrost heaters (if this is a frost free freezer). Also may be very hot weather, freezer control set to maximum cooing, dirty condenser coils, blocked air flow inside or outside freezer, low freon levels, mechanical problems, etc.). Check what its predicted energy usage is. You may find it online.

    Anyhow... Your 1 day (24 hour) power usage is:
    • 116.45 watts * 24 hours = 2795 WH per day = 2.795 kWH per day
    And your 1 year rating:
    • 2.795 kWH per day * 365.25 days per year = 1,021 kWH per year
    That is a bit on the high side--You should be able to find a model that is closer to 400-500 kWH per year (guessing) that would meet your needs (and save 1/2 of the energy usage--always critical for solar PV systems).

    Take a look through the Energy Star website. I find, in my weather, that my refrigerator and freezer use a bit less than the rated power usage.

    And I assume you programmed in $0.125 per kWH as your electric rate:
    • RATE OF 0.125
    • 1,021 kWH per year * $0.125 per kWH = $127.625 per year electric cost
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • nielniel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: Need help with my solar puzzle?

    good that you have a meter. you can use that to get a handle on what the kwh per day will look like for each item you wish to power. when you know all of the requirements per day then it can be worked backwards for pv requirements.

    as to the pvs being in pairs none of us said that exactly. i said 3 180w pvs and 3 120w pvs is workable with 3 not being an even number pairs are associated with so more than 1 120w pv won't apply in my example. mikeo's example does not work out to having 1 180w pv to a 120w pv so it really is not pairing that is the right wording here. my example would however mean a series pairing of a 120w pv per 180w pv.

    do not jump on the extra pvs just yet. work out your loads first and we'll figure for your batteries so put extra pvs, or the subject of the pvs, on the backburner until we address this first.
  • windgate32windgate32 Registered Users Posts: 8 ✭✭
    Re: Need help with my solar puzzle?

    TY for all the info. I am still trying to absorb it. 8) The freezer, yes is a frost free and, unfortunately is in our garage here in TX. I am sure that explains why it is running all the time. I really did not know this until now, so it is actually something I can fix and try to save some energy there. I am currently running the killowatt on my computer set up and I will experiment with the kitchen appliances and the tool, phone ipod chargers next. Thank you again for all the help and as soon as I get some more data I will be back. The money saved from the battery monitor and extra panel can be used for the batteries.

    Sincerely, Randy :D
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