power loss of 24 volt panel connected to 12 volt battery??

rvravi
rvravi Registered Users Posts: 3
in Solar Beginners Corner #1
hi guys and gals, new here and new to solar. just wondering if a 190 watt solar panel connected via 30A mppt controller to 12 volt battery would loose power or not. of course panel output is affected by angle of elevation and temperature and amount of sunlight.

for the sake of this discussion, I am assuming everything at its optimum so the panel is producing 190 watts.


Solar panel ratings:

Vmax -1000vdc
Pmax -190Watts
Isc -5.62A
Voc -45.3V
Imp -5.27A
Vmp -36.05A

tracer mppt controller 2210RN - 97% conversion

as to what i understand about power is that:

P = V x I
189.98 = 36.05 x 5.27 ... approx 190W

@97% conversion : 184watts usable (sticking to whole numbers for easier calculations)

assuming charging voltage being 14 volts, with 184 watts power

power entering mppt controller- 190 watts, at 36.05 volts

conservation of energy:

Power in = power lost in conversion + power out
190 = 6 watts + 184 watts

Now the question is :

Will the output Amps be 13 Amps at 14volts charging, as

P = V x I
182 =14 x 13 (say 2 watts got lost in the wires) for the sake of my whole numbers.

now if this were to happen, it would be wonders
if not , then where does the rest of the energy go or what kinda energy production and loss is going on


i asked this question here because i have not seen any decent answer upon googling for it.


please enlighten me with your knowledge and experience
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Comments

  • NorthGuy
    NorthGuy Solar Expert Posts: 1,913 ✭✭
    #2
    Re: power loss of 24 volt panel connected to 12 volt battery??

    That is all correct given that your panels are in optimum conditions: About 0C ambient temperature, exactly perpendicular to the sun and good atmospheric conditions.
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  • vtmaps
    vtmaps Solar Expert Posts: 3,741 ✭✭✭✭
    #3
    Re: power loss of 24 volt panel connected to 12 volt battery??
    rvravi wrote: »
    P = V x I
    182 =14 x 13 (say 2 watts got lost in the wires) for the sake of my whole numbers.

    now if this were to happen, it would be wonders
    if not , then where does the rest of the energy go or what kinda energy production and loss is going on

    Welcome to the forum.

    Your thinking is on the right track, but maybe your efficiency numbers are a bit optimistic. As for where the missing energy goes, it makes heat in the wires and in the controller.

    --vtMaps
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #4
    Re: power loss of 24 volt panel connected to 12 volt battery??

    Expect to see closer to 12 Amps peak power.

    This will be worse if more is lost in wiring (undersized, long run) or panel temperature is higher (decreases panel Voltage).

    Do not expect to see maximum current all the time or even if it is potentially available.
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,642 admin
    #5
    Re: power loss of 24 volt panel connected to 12 volt battery??

    You typical maximum current (unless you have below freezing temperatures) will be:
    • 190 watts * 0.77 panel+controller derating * 1/14.5 volts battery charging = 10.1 amps

    Note if the battery is significantly discharged, your battery maybe 13.0 to 13.5 volts at the beginning of the charging cycle:
    • 190 watts * 0.77 panel+controller derating * 1/13.0 volts battery charging = 11.3 amps

    Roughly, the panel will operate at 81% to 85% of name plate power and the control will be at ~95% efficiency (0.81*0.95=0.77 overall efficiency).

    You can calculate the power from a solar panel (as temperature rises, Vmp falls and Imp--very slightly--rises). For example, assuming a ~-0.4% drop in power per degree C and some nominal temperatures (note that cell temperature rise can be as high as +35C on wind-less days and panel mounted tight to roof--no air circulation):
    • Power(15C)=Vmp*(1+Temp-cell-coeff(Tcell-Tamb)) = 190 Watts * (1+ (-0.004 per C)(15Cambient+20Crise-25Cstc)) = 182.4 Watt Panel output power

    And 0.95 Eff:
    • 182.4 watt panel output * 0.95 typical controller efficiency (and wiring losses, dust on panel) = 173.28 Watts to battery
    • 173 Watts to battery * 1/13.5 volts charging = 12.84 Amps

    The range from 10.1 to 12.84 amps to battery depends on how clear the sky is, altitude of installation, humidity/dust/smoke in air, time of day, seasonal location of sun, tracking vs fixed array, etc...

    We try to be conservative--If you use the 0.77 derating, it will be pretty close for most people. If you have snow on the ground (or refection from lakes/sand/etc., you can get some very surprisingly high numbers in winter)--But that is not common for most installations.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • rvravi
    rvravi Registered Users Posts: 3
    #6
    Re: power loss of 24 volt panel connected to 12 volt battery??

    thank you so much guys. at least now i know that m thinking in the right direction , i understand that "ideal condition "never exists. its such a relief to know that there is no hidden electrical engineering glitch or some rocket science type of stuff to chew on the power produced by the panels. at least i know now as to what type of figures to see on the watt meter receiving input from the mppt controller. VERY BIG THANK YOU to ALL of you.
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  • rvravi
    rvravi Registered Users Posts: 3
    #7
    Re: power loss of 24 volt panel connected to 12 volt battery??

    this is really interesting. the empirical formula that has brought up the factor of 0.77 is so much work cut short and calculations made so easy. thanks
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  • Photowhit
    Photowhit Solar Expert Posts: 6,006 ✭✭✭✭✭
    #8
    Re: power loss of 24 volt panel connected to 12 volt battery??

    You might look to see if there are Normal Operating Cell Temperature (NOCT) values for your panels in the spec sheet or on the back of the panels. These values will give a more realistic idea of what you panel will produce.
    Home system 4000 watt (Evergreen) array standing, with 2 Midnite Classic Lites,  Midnite E-panel, Magnum MS4024, Prosine 1800(now backup) and Exeltech 1100(former backup...lol), 660 ah 24v Forklift battery(now 10 years old). Off grid for 20 years (if I include 8 months on a bicycle).
    - Assorted other systems, pieces and to many panels in the closet to not do more projects.
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