want to make sure this new system will work ok/batt sizing

kev1n69kev1n69 Registered Users Posts: 19
9 lightway 235 lw235p1650 3series legs connected in parallel
1 midnight solar clasic150
and was thinking of a 12-85-15 forklift battery from gb industrial battery they want $2453
for the battery does that sound like a good price? it is new not rebuilt.
will be running a 3kw modifies sine inverter to start and transferring loads from grid breaker box to the off grid box as needed to reduce the grid usage as much as possible within the limits of the system allowing for best battery life.
in addition to installing this system and getting it functional this spring i also have one of two planned fisher&paykel wind turbines i want to get up and running this summer and long range want to add a gasifier and generator.
i am thinking the solar is not going to be enough for that battery by its self. any constructive critiques?

Comments

  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: want to make sure this new system will work ok/batt sizing

    Welcome to the forum.

    Constructive criticism time.
    How much power are you needing to supply? When you're dealing with battery-based systems it is necessary to know this, otherwise you are just guessing at equipment sizes and have a really good chance of getting it wrong.

    You start with the batteries, not the panels. The batteries supply the power, the panels recharge them.

    Connecting nine solar panel all in parallel on an MPPT controller like the Classic is a mistake; that's high current and low Voltage. You have the ability to handle up to 150 Volts there; use it to good advantage.

    Why would you want a 3kW MSW inverter? Or any MSW inverter for that matter. Pure sine will run anything; MSW is more of a gamble. The price difference is not that significant these days.

    "Reduce the grid usage as much as possible" - why? It is doubtful it will save you any money, even at the worst grid prices.

    I think you should rethink the whole thing. Starting by defining your goals. Knowing exactly why you want to go down this road will go a long way towards defining the system and making sure the money is spent wisely.
  • BB.BB. Super Moderators, Administrators Posts: 29,812 admin
    Re: want to make sure this new system will work ok/batt sizing

    Looks like a 24 volt @ 938 AH battery bank.

    Looking at your system from an Off Grid full time home/cabin point of view based on the battery selected... Does the following make sense/support your loads?

    Normally, with a lead acid battery, we recommend 5% to 13% rate of charge nominal (heavier use/deeper cycling, 10+% rate of charge). For forklift batteries, many vendors recommend 10% rate of charge minimum. That is ~94 amps minimum. About the maximum for a single Midnite Classic 150 MPPT controller on a 24 volt battery bank. Note that above ~600 AH battery bank, you should be seriously looking at the next voltage battery bank (i.e., 48 volt in this case, or 2x 24 volt ~470 AH batteries in series) to keep the wire gauge down and allow you to get more power through your MPPT charge controller.

    Sizing the solar array based on our typical rules of thumbs:
    • 938 AH * 29 volts charging * 1/0.77 panel+controller deratings * 0.05 rate of charge = 1,766 watt array minimum (too small for FL battery?)
    • 938 AH * 29 volts charging * 1/0.77 panel+controller deratings * 0.10 rate of charge = 3,533 watt array nominal
    • 938 AH * 29 volts charging * 1/0.77 panel+controller deratings * 0.13 rate of charge = 4,593 watt array "cost effective" maximum
    9*235 watt panels (?) = 2,115 Watt array -- I would be suggesting almost 2x larger array if you went with the fork lift battery to get 10% minimum rate of charge. Buy the way, if you use significant use during the day (say constant irrigation pumping during spring/summer), then you need to add that to the Base Array output so that you do not "steal" current from the charging battery bank.

    If this is a weekend use home/cabin, then you might get away with your present 2,115 array and keep the battery relatively happy (may need some extra generator run-time to help).

    Next, using 2 days of storage with 50% maximum discharge (for long battery life in daily cycling), the expected AC loads would be around:
    • 938 AH * 24 volts * 0.85 inverter eff * 1/2 days storage * 0.50 max discharge = 4,784 Watt*Hours per day (4.8 kWH per day)
    That is a good sized system--3.3 kWH per day will typically support a modern energy star refrigerator + well pump + lights + radio + TV + Washer + Dryer (propane), etc... A "near normal" off grid experience for a very efficient/conservation minded family.

    Solar panel wise--Fixed array tilted to latitude at Houghton Mi using PV watts:
    Month    Solar Radiation (kWh/m 2/day)
    1      2.56     
    2      3.70     
    3      4.68     
    4      5.72     
    5      5.25     
    6      5.56     
    7      5.58     
    8      5.38     
    9      4.48     
    10      3.20     
    11      2.09     
    12      2.11     
    Year      4.19
    

    There is not a lot of sun there--And you will have to pick your minimum "break even sun" point. For lower US, usually 4 hours of sun would be good for 9+ months of solar power, with winter backup via genset. If I drop the bottom three months, that gives me 3.20 hours minimum (based on "optimum" battery bank usage):
    • 4,784 WH per day * 1/0.52 system eff * 1/3.20 hours of sun per day = 2,875 Watt array "break even" October
    And how much power can you draw from such a battery bank:
    • 938 AH * 24 volts * 0.85 inverter eff * 1/20 nominal discharge rate = 957 Watts AC "nominal" average
    • 938 AH * 24 volts * 0.85 inverter eff * 1/8 nominal discharge rate = 2,392 Watts AC "max continuous" average
    • 938 AH * 24 volts * 0.85 inverter eff * 1/5 nominal discharge rate = 3,827 Watts AC "max short term" average
    • 938 AH * 24 volts * 0.85 inverter eff * 1/2.5 nominal discharge rate = 7,654 Watts AC "max surge"
    So, the AC inverter maximum would be around 3,800 watts (supporting ~2x rated surge output).

    And to support a 3,800 Watt inverter, the wiring/breaker/fuse would be:
    • 3,800 * 1/0.85 inverter eff * 1/21 volts batt cutoff * 1.25 NEC derating = 266 Amp Rated branch circuit minimum
    Your thoughts?

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • kev1n69kev1n69 Registered Users Posts: 19
    Re: want to make sure this new system will work ok/batt sizing

    1.the inverter is already owned previously used for emergency back up for long duration outages (rare) but saved 3 full freezers and kept my frig cold for the duration of a 12 hr outage.
    2. the panels are on their way along with racking and the classic 150 per midnights calculator 3 series legs paralleled is acceptable and seems to take advantage of max input voltage.
    3.cariboo you may be correct this may not bee the wisest endeavor in the first place the whole idea is to be independant and long term
    no longer paying the co-op several other reasons figure into this but i see it is time for my tax appointment so got to go for now will be back
  • kev1n69kev1n69 Registered Users Posts: 19
    Re: want to make sure this new system will work ok/batt sizing

    bb thank for the info very informative.

    this is a home not cabin so use at first with this array will be just some of the load for the house.
    lighting is mostly cfl a few (4) led and (4) incandescent, two in chicken coop 60w and one is on a timer daylight only the other 2 are table lamps and will be led soon.
    probably most wall outlets, garage, and security light.at least that will be my starting load. the 2 freezers, one frig ,toaster &toaster oven,and 220v air compressor will all remain on grid along with the 1/2 hp 110vac well pump.
    when the wind mill and then mills get hooked in i hope to be able to add one more of these grid connected units to the inverter load.
    another solar bank and charge controller as money and needs allow
    until the build out gets more substantial i was concerned that i may need a 24v charger grid connected for the days i am not getting enough solar or wind inputs to keep up with charging demand as battery life is the primary concern, and i can always transfer load back to grid if i over estimated initially .
  • waynefromnscanadawaynefromnscanada Solar Expert Posts: 3,009 ✭✭✭✭
    Re: want to make sure this new system will work ok/batt sizing

    Is your goal to save money on electricity? If so, what are you now paying per Kwh, for grid power? This info will help those trying to assist you as to what direction you could take, and the answers may surprise you.
  • mike95490mike95490 Solar Expert Posts: 8,497 ✭✭✭✭✭
    Re: want to make sure this new system will work ok/batt sizing
    grid
    ? you has grid ? so the answer is simply, a generator to handle your most basic loads, and fuel for it for a week.
    For fun, put up a 12v 300w system with a car radio, and a couple 12V powered AA chargers, and a 12-5V usb power port. Now you are set for the long term too, with just a single, $100 battery to maintain.
    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

    solar: http://tinyurl.com/LMR-Solar
    gen: http://tinyurl.com/LMR-Lister ,

  • kev1n69kev1n69 Registered Users Posts: 19
    Re: want to make sure this new system will work ok/batt sizing
    mike95490 wrote: »
    ? you has grid ? so the answer is simply, a generator to handle your most basic loads, and fuel for it for a week.
    For fun, put up a 12v 300w system with a car radio, and a couple 12V powered AA chargers, and a 12-5V usb power port. Now you are set for the long term too, with just a single, $100 battery to maintain.

    hi mike i did the play system years ago it was 2-12v panels on a zomeworks tracking mount with a morningstar sunsaver charge controller, and a air 403 wind turbine (what a p.o.s.) (4) 6v battery bank and a 2kw msw inverter.

    it worked well for lighting and running a few circuits the week link was the wind turbine it kept the bats charged good when the turbine worked( i have good wind resources). but that machine was a bad design in my eyes.
    it would develope static charge on the blades in high wind and when it discharged it would fry the regulator circuit once under warranty then again the next big blow it did the same thing so i gave up on it.
    back then failures went something like this turbine then inverter then turbine then batts not being charged fully due to no turbine, lost one 6v due to cold storage & low charge got the system back up with only two 6v batts replaced inverter with smaller one realized my batt storage in the garage was not going to work out well even though i had built an insulated equipment area 3x3 ft the batteries just could not live their.
    we get 10-30 degrees below 0 some years for a month straight. this winter has been like that with a few warm ups here and their
    with out heat the bats were shot by mid summer and system disconnected for a few years.
    last fall i ran the panels to the house and hooked the system to a single 12v deep cycle batt just for winter emergency back up it works well does not have a daily draw but i also use the bat. for a amature radio power source a 12 volt 300lm light and a 100 watt spotlight for the back yard barn area.
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