how to calculate power usage for system?

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prince_77
prince_77 Solar Expert Posts: 31 ✭
in Solar Beginners Corner #1
Hello all

i want to know how to calculate usage for my system and im not sure
the issue is this

i have 24V 162aH bank, now i know i can only use 50% because the batteries and deep cycle.

i want to light my garden light + a florecent tube

so i have 6 light 28W + 2X13W florecnt light

for how long cani keep the light on after converting the Voltage for the light and
still keep 50% in the rigt area ?

thank u very much
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  • icarus
    icarus Solar Expert Posts: 5,436 ✭✭✭✭
    #2
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    Re: how to calculate power usage for system?

    24 vdc*162=3888 watt hours divided by 2=1944 WH

    Your liights consume 194 watts ( assuming no inverter loses) 1944/194=~ 10 hours.

    Be advised that I would not routinely draw to 50% if I expect my batteries to last. If those are 120 vac lights , and you hve to power them thorugh an inverter, you should consider inverter losses as well.

    Tony
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  • RCinFLA
    RCinFLA Solar Expert Posts: 1,484 ✭✭✭✭
    #3
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    Re: how to calculate power usage for system?

    6 x 28 watts = 168 watts + 2x 13watts = 194 watts.

    The CFL's likely have a short peaking current profile with a PF yield of about 0.6.

    This will up the peak current on the inverter to about 2.7 amps at 120 vac. The VA will be 323 VA but all of this is not taken from battery. The power for this taken from battery will be about 220 watts depending on inverter power rating and efficiency.

    Another missing piece is what kind of inverter you have and specifically its no load current consumption. Inverters can consume 5 to 50 watts depending on whether it is modified sinewave or true sinewave and its overall size (max power rating).

    Take a mid-range for inverter consumption of 25 watts you would have about 240 watt load x inverter power delivered efficiency of about 0.9 = 265 watts from batteries.

    At 25 vdc average battery voltage you would consume 10.6 amps from battery.

    162 AH * 50% = 81 AH's usuable to 50% SOC.

    81 AH / 10.6 amps = 7.6 hours. About 8 hours.
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  • prince_77
    prince_77 Solar Expert Posts: 31 ✭
    #4
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    Re: how to calculate power usage for system?

    thanks very much for the answer

    my inverter has 90% usage of power and in noload mode its using 1A

    also is there any change between 220V and 110V when using> does 220V is better then 110V when running the light ?
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #5
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    Re: how to calculate power usage for system?
    prince_77 wrote: »
    thanks very much for the answer

    my inverter has 90% usage of power and in noload mode its using 1A

    also is there any change between 220V and 110V when using> does 220V is better then 110V when running the light ?

    Devices are Voltage dependent. If the light is a 110 Volt light and you connect it to 220 Volts it will go "poof!" and no longer will be a light. You have to give them the Voltage they were designed for.
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  • prince_77
    prince_77 Solar Expert Posts: 31 ✭
    #6
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    Re: how to calculate power usage for system?

    Im asking because i have a friend with 220v system in the EU
    is 220v more efficent then 110V in inverters?
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  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    #7
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    Re: how to calculate power usage for system?

    i don't think there would be too much of a difference between the 2 inverters to worry about it. technically the farther out the input/output voltage differentials the less efficient, but it would be a small difference. go with what you need as far as those lines go.

    line losses can be lower at higher voltages and i don't believe you'd have too much to worry about as far as that goes as both are going to be fairly good unless you have great distances to send that power.
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,467 admin
    #8
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    Re: how to calculate power usage for system?

    Probably not much difference 120/230 vac... The bigger issue is voltage drop, both on the DC input (12/24/48) and the output (120/230/etc.).

    The for every doubling of the voltage, current goes down by 1/2 and the allowed voltage drop goes up by 2x--So you can send more power, farther, with less copper.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • icarus
    icarus Solar Expert Posts: 5,436 ✭✭✭✭
    #9
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    Re: how to calculate power usage for system?

    Use what ever voltage is native to your country. If 120 is the standard, use it, if 240 is standard,, use it. The availability of things like bulbs will dictate which is easier to use. In N. America, 240 bulbs are the oddity, 120 are ubiquitious.

    Tony
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,467 admin
    #10
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    Re: how to calculate power usage for system?

    However 240 VAC for well pumps is quite common in North America--And can make wiring much less expensive/easier as it cuts current by 1/2 over 120 VAC pump motors.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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