add'l panels based on charge rate and batteries

ldiorio
ldiorio Solar Expert Posts: 47 ✭✭
just installed a 6 panel 48 volt interactive system with 8 415 Fullriver AGMs
have been looking thru many posts and found one that Coot provided a formula to determine array size

i worked thru the formula and it resulted in a req of 3368 watts for .13 chrge rate
i have 6 255watt panels which deliver 1530 watts

so if i understand this right i am deficent by 6 more panels

trying to learn as much as i can as i operate the system

have not let the batteries so far get below 70% SOC
have the ACIN connect at 47.2 volts if it reaches that level but hasent yet --will put more of load on the system this week
have a ref/freezer/well pump//dishwasher//boiler//and a few plug ckts for lights and TV
stove is propane
i know i could just keep all on the grid and have the batteries float ( and maybe discharge the batteries once a month) --but want to see how the system will handle the critical loads







Comments

  • vtmaps
    vtmaps Solar Expert Posts: 3,741 ✭✭✭✭
    ldiorio wrote: »
    just installed a 6 panel 48 volt interactive system with 8 415 Fullriver AGMs
    have been looking thru many posts and found one that Coot provided a formula to determine array size

    i worked thru the formula and it resulted in a req of 3368 watts for .13 chrge rate
    i have 6 255watt panels which deliver 1530 watts

    so if i understand this right i am deficent by 6 more panels

    Rule of thumb: Charge rates in MOST systems should be 5% to 13%. That is a rule of thumb... what your charge rate should be in your system in your climate with your loads is yet to be determined. You may, or may not be deficient in your number of panels.
    ldiorio wrote: »
    have not let the batteries so far get below 70% SOC
    Why do you think you know the SOC of your batteries? It's not easy to know that in an AGM battery.

    --vtMaps
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
  • ldiorio
    ldiorio Solar Expert Posts: 47 ✭✭
    tks VT
    i have a whizbang--yesterday it showed 75%---the Magnum remote showed 49.2V and i measured the batteries with a meter and they indicated 49.4V
    i have the VDC connect set to 47.1(ACIN) with LBCO set at 46.2 based on some info from prior post

    this morning whizbank indictes 88%SOC --magnum shows 51.6V and batteries measure 51.5V

    cant seem to coorlate the whizbank SOC with Battery voltage--dont know how accurate the Whizbank is
    prob should get a Battery monitor to more accurately show battery SOC

    If i had a Battery monitor i could use SOC to regulate the battery levels and not voltage???

    thoughts--i live in Rhode Island

    Lou
  • vtmaps
    vtmaps Solar Expert Posts: 3,741 ✭✭✭✭
    ldiorio wrote: »
    cant seem to coorlate the whizbank SOC with Battery voltage--dont know how accurate the Whizbank is
    prob should get a Battery monitor to more accurately show battery SOC

    If i had a Battery monitor i could use SOC to regulate the battery levels and not voltage???

    You cannot judge the SOC by measuring voltage in a dynamic system. If you disconnect the batteries for a few hours and then measure their voltage you can make an estimate of their SOC.

    As far as trusting the WhizBangJr... The WhizBangJr is a shunt based battery monitor.

    Battery monitors are often compared to the gas gauge in your car, but that is not a good analogy.

    The gas gauge in your car actually measures the level of gas in your tank. A battery monitor doesn't measure the level of anything. It is more like the odometer in your car. The odometer counts miles and the battery monitor counts ampHours.

    Suppose you have a car that gets about 25 mpg and has a 15 gallon gas tank. Suppose also that your gas gauge does not work. What do you do? You use your odometer. For example: After a fill up you drive 150 miles and you expect that you have used 6 gallons and have 9 gallons remaining in your tank.

    If you fill up the tank again you can, as above, use your odometer to estimate your gallons remaining.

    But what if you do not completely fill your tank. For example, starting from a full tank you drive 150 miles and then you add 3 gallons to your tank and then drive 100 miles and then add 4 gallons to your tank and drive 150 miles and then add 5 gallons to your tank and drive 100 miles. At this point you estimate that you have 7 gallons remaining in your tank, but that estimate is not too accurate because your mileage is not ever exactly 25 mpg. The only time you know exactly how much gas is in your tank is when you have just filled it up (or when you run out of gas).

    So it is with your battery monitor. The only time it is exactly accurate is when you fully charge your batteries and reset the battery monitor to read 100% full. It can be very accurate counting the amphours in and out of the battery, but it can only estimate the state of charge based on your assumptions of the battery capacity and of the battery efficiency. It can read 100% (by counting amphours into the battery) before the battery is fully charged.

    Some battery monitors reset to 100% SOC only when certain criteria are met. I believe the WhizBangJr resets when the controller goes to float. Of course, that doesn't mean the batteries are charged... it just means the controller went to float. If the controller goes to float before the batteries are fully charged, then the monitor is wrong.

    Bottom line: the longer its been since a complete charge, the less you can trust your battery monitor. And you can't trust it at all if its not set up correctly. That said, battery monitors are valuable tools in estimating your SOC, but you have to understand their limitations.

    --vtMaps

    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
  • ldiorio
    ldiorio Solar Expert Posts: 47 ✭✭
    tks VT ---after reading your post -i dont feel confident using SOC levels
    so risky to use SOC in general when determining when to start a generator or switch to ACIN(grid) when the batteries get to the 50% level--can i assume its better to use voltage settings to regulate charging of the my AGM batteries which i am doing now --the battery manufacture said 46.2 volts is 50%SOC for my batteries --i think am safer to go with that ??(as i said earlier LBCO set at 46.2 and VDC connect to ACIN set at 47.1(gen/grid)
    might still consider getting one to experiment with-i see you have a trimetric would you recommend that brand
    i have a magnum inverter/midnight epanel and classic 150 CC

    the battery manufacture gave me ranges for Float(8-24hrs) Absorb(1-4 hrs) but no specific number for my situation--could you give me some guidence on that

    thanks VT

    ps any more thought on more panels(4:15 Sunday just went into Float mode)
  • new2PV
    new2PV Solar Expert Posts: 305 ✭✭
    This is right from the fullriver manual for all there agm batteries. The recommended bulk current for your battery would be 20% and MAX 35% of the AH rating in your case 83-145 amps. I would see the max output spec on the CC and take that current rating and subtract 125% to get the max panel amps. Attachment not found.
    XW6848 inverter with 2 X mppt 60 150 CC , with Canadian solar 260Watt panels 2 x 3.5 kw array
  • ldiorio
    ldiorio Solar Expert Posts: 47 ✭✭
    my CC is Classic 150 with amp capacity of 96Amps--could you go thru the math using the 150%
    tks
  • new2PV
    new2PV Solar Expert Posts: 305 ✭✭
    XW6848 inverter with 2 X mppt 60 150 CC , with Canadian solar 260Watt panels 2 x 3.5 kw array
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    You mean:

    96 amps * 1.25 NEC derating = 120 Amp minimum wiring+circuit breaker rating from controller to battery bank?

    Or are you asking about something else (like if you have ABC @ 12 volt battery bank, how large of solar array)?

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • ldiorio
    ldiorio Solar Expert Posts: 47 ✭✭
    have a 48v system with 415AH--6 255 panels
    should i add 6 more panels
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Just going through some rules of thumbs:
    • 415 AH * 58 volts charging * 1/0.77 panel+controller derating * 0.05 rate of charge = 1,563 Watt array minimum (emergency, weekend, seasonal use)
    • 1,563 Watt / 255 watt panels = 6 panels minimum
    • 415 AH * 58 volts charging * 1/0.77 panel+controller derating * 0.10 rate of charge = 3,136 Watt array nominal (typical full time minimum array)
    • 3,136 Watt / 255 watt panels = 12 panels nominal
    • 415 AH * 58 volts charging * 1/0.77 panel+controller derating * 0.13 rate of charge = 4,064 Watt array typical "cost effective maximum"
    • 4,064 Watt / 255 watt panels = 16 panels "cost effective maximum"
    Then there is sizing the array on your loads. Using solarelectrichandbook, we see:

    Pawtucket
    Average Solar Insolation figures


    Measured in kWh/m2/day onto a solar panel set at a 48° angle from vertical:
    (For best year-round performance)

    Jan
    Feb
    Mar
    Apr
    May
    Jun


    3.33
    3.97
    4.61
    4.67
    4.93
    5.04


    Jul
    Aug
    Sep
    Oct
    Nov
    Dec


    5.04
    5.01
    4.76
    4.31
    3.24
    2.98


    A 12 panel array will produce (toss bottom three months as needing a genset/alternate power):
    • 12 * 255 watt panels * 0.52 off grid system eff * 3.97 hours of sun (February long term average per day) = 6,317 Watt*Hours per day (Feb).
    If you cycle the battery bank down 25% depth of discharge per day, you bank should supply around:
    • 415 AH * 48 volts battery bank * 0.85 inverter eff * 0.25 discharge of battery bank = 4,233 Watt*Hours per very dark day/over night power usage
    Personally, I would suggest your base loads (refrigerator, lights, computer, cell phone charging, etc.) be around 65 to 75% of the "predicted output" maximum.. On days where you get average or more than average sun, then run the vacuum cleaner, washing machine, cook bread/crook pot, run well pump to refill cistern, etc.
    • 6,317 WH per day Feb * 0.65 base load = 4,106 WH per Feb day base load
    • 6,317 WH per day Feb * 0.75 base load = 4,738 WH per Feb day base load (should be 0.75, not 0.65)
    So--That is the basics... What are your loads like? What size solar array do you think you need?

    4+ kWH per day is a pretty good off grid life style... Very near "normal electric" home -- If you are very conservative in your power usage. No A/C, no large desktop computers left running 24x7, etc... Using natural gas, propane, wood, etc. for heating/hot water/most cooking.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • new2PV
    new2PV Solar Expert Posts: 305 ✭✭
    If it was my setup I would go with a c20 charging rate as manufacturer suggests to use on those batteries. On your current setup I would not hesitate to add 6 more panels.
    XW6848 inverter with 2 X mppt 60 150 CC , with Canadian solar 260Watt panels 2 x 3.5 kw array
  • ldiorio
    ldiorio Solar Expert Posts: 47 ✭✭
    after reading all the post --i agree minium array total of 12 panels

    thanks to all
  • ldiorio
    ldiorio Solar Expert Posts: 47 ✭✭
    is there a timeframe that i should be cycling my batteries from full charge to a 50% discharge then charge to float and full charge--
    once a week once a month etc
    now just letting the system run with average loads--using a 12 ckt manul transfer switch to turn loads on and off to see how the system reacts( could shut off the well pump and /or dehumdifier to run other loads from the transfer switch

    just need some operational input as i continue to learn the system with focus on the batteries
  • vtmaps
    vtmaps Solar Expert Posts: 3,741 ✭✭✭✭
    ldiorio wrote: »
    is there a timeframe that i should be cycling my batteries from full charge to a 50% discharge then charge to float and full charge--
    once a week once a month etc

    A battery has many limits on its life. One limit is Cycle Life. That is the number of cycles the battery can be expected to function. The deeper the discharge on each cycle, the fewer the cycles in that battery's life.

    The next issue is PSOC (partial SOC) operation and how often to charge all the way to 100% SOC. PSOC is very typical of solar batteries. When you (for example) discharge from 100% SOC to 80%, then charge up to 90% SOC , then discharge down to 70% SOC, then charge up to 90% SOC, etc, two things are happening: some sulfate on the plates is not put back into solution and begins to harden, and (in flooded cells) stratification develops. Periodic charging to 100% (may include equalization) drives all sulfate into solution and (in flooded cells) stirs the electrolyte.

    The deeper the discharges, the sooner you should recharge to 100%. In my opinion, if you keep your SOC above 70%, you only need to achieve 100% on a weekly basis. When you discharge to below 60% SOC, you need to charge that battery without delay.

    --vtMaps
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
  • new2PV
    new2PV Solar Expert Posts: 305 ✭✭
    Vtmaps what is your opinion on the manufacturer recommending a c20-35 charge rate for these batteries? Does that not seem high?
    XW6848 inverter with 2 X mppt 60 150 CC , with Canadian solar 260Watt panels 2 x 3.5 kw array
  • vtmaps
    vtmaps Solar Expert Posts: 3,741 ✭✭✭✭
    new2PV wrote: »
    Vtmaps what is your opinion on the manufacturer recommending a c20-35 charge rate for these batteries? Does that not seem high?

    Not high for an AGM battery. AGM batteries tend to have internal resistance lower than flooded batteries and can handle higher currents (charging and discharging) than flooded batteries.

    --vtMaps
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
  • zoneblue
    zoneblue Solar Expert Posts: 1,220 ✭✭✭✭
    Indeed there are particular AGM makers that claim charge rates up to 1C. Its unclear at this point if those sort of charge rates enhance cell life, and my feeling is not. Something in the range 0.1 - 0.25C i feel comfortable with with good AGMs. If they start getting warm, id say youve gone too far.

    VT, nice analogy about coloumb counters!
    1.8kWp CSUN, 10kWh AGM, Midnite Classic 150, Outback VFX3024E,
    http://zoneblue.org/cms/page.php?view=off-grid-solar


  • new2PV
    new2PV Solar Expert Posts: 305 ✭✭
    zoneblue wrote: »
    Indeed there are particular AGM makers that claim charge rates up to 1C. Its unclear at this point if those sort of charge rates enhance cell life, and my feeling is not. Something in the range 0.1 - 0.25C i feel comfortable with with good AGMs. If they start getting warm, id say youve gone too far.

    VT, nice analogy about coloumb counters!

    What is the temp that you would consider too warm?
    XW6848 inverter with 2 X mppt 60 150 CC , with Canadian solar 260Watt panels 2 x 3.5 kw array
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Remember that C/20 is 1/20 = 0.05 = 5% rate of charge.... For a full time off grid system, I would suggest that is not high enough rate of charge to use solar power for recharging (not enough hours of sun in a day)--For a UPS (backup power system) with generator/Utility power, then that is a different system.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • new2PV
    new2PV Solar Expert Posts: 305 ✭✭
    BB. wrote: »
    Remember that C/20 is 1/20 = 0.05 = 5% rate of charge.... For a full time off grid system, I would suggest that is not high enough rate of charge to use solar power for recharging (not enough hours of sun in a day)--For a UPS (backup power system) with generator/Utility power, then that is a different system.

    -Bill

    I just re-looked at the calculations I posted, it seems that they are saying C x 20% not C/20 or am I confused?
    XW6848 inverter with 2 X mppt 60 150 CC , with Canadian solar 260Watt panels 2 x 3.5 kw array
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    I think you are correct... C*0.25 = C/4...

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • zoneblue
    zoneblue Solar Expert Posts: 1,220 ✭✭✭✭
    that C/4 style notation is confusing. The "correct" notation is 0.25C20
    1.8kWp CSUN, 10kWh AGM, Midnite Classic 150, Outback VFX3024E,
    http://zoneblue.org/cms/page.php?view=off-grid-solar