12v and 24v panel

shella
shella Registered Users Posts: 23
hello
can anyone tell me what the difference between a 12v solar panel and a 24 v solar panel
«1

Comments

  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: 12v and 24v panel

    Yes indeed. :D

    They are "nominal" Voltage ratings for panels: a "12 Volt" panel is meant to work with a 12 Volt battery system, and a "24 Volt" panel with a 24 Volt system utilizing a PWM type charge controller. As such, the panel Voltage at maximum power (Vmp) is in a range suitable for "direct connection" to the battery. For 12 Volt systems this is 17 to 18 Volts, for 24 Volt systems it is 2X that.

    Unfortunately there are panels label as 12 or 24 which are not suitable. Some "12 Volt" panels have a Vmp of 16, which can lead to not having enough Voltage to actually charge the battery once the panel gets hot (reduces output Voltage) and also has to overcome wiring resistance (hence the need for Vmp several Volts above the actual charging point). Many "24 Volt" panels have unsuitable Vmp because they are actually designed for grid-tie systems which have a different goal (string panels in series to come up with a high Voltage array for a GT inverter; no batteries involved). These "oddball" Vmp panels can be used with battery systems, but you either have to buy a (more expensive) MPPT type controller or lose a significant amount of power.
  • shella
    shella Registered Users Posts: 23
    Re: 12v and 24v panel
    Yes indeed. :D

    They are "nominal" Voltage ratings for panels: a "12 Volt" panel is meant to work with a 12 Volt battery system, and a "24 Volt" panel with a 24 Volt system utilizing a PWM type charge controller. As such, the panel Voltage at maximum power (Vmp) is in a range suitable for "direct connection" to the battery. For 12 Volt systems this is 17 to 18 Volts, for 24 Volt systems it is 2X that.

    Unfortunately there are panels label as 12 or 24 which are not suitable. Some "12 Volt" panels have a Vmp of 16, which can lead to not having enough Voltage to actually charge the battery once the panel gets hot (reduces output Voltage) and also has to overcome wiring resistance (hence the need for Vmp several Volts above the actual charging point). Many "24 Volt" panels have unsuitable Vmp because they are actually designed for grid-tie systems which have a different goal (string panels in series to come up with a high Voltage array for a GT inverter; no batteries involved). These "oddball" Vmp panels can be used with battery systems, but you either have to buy a (more expensive) MPPT type controller or lose a significant amount of power.

    so how do you know what type of solar panel you are buying. i mean how can i tell if a solar panel is truly 12 or 24v and how can i tell a solar panel is not for a grid tyed only system
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: 12v and 24v panel
    shella wrote: »
    so how do you know what type of solar panel you are buying. i mean how can i tell if a solar panel is truly 12 or 24v and how can i tell a solar panel is not for a grid tyed only system

    Very good question.
    Get the full specifications for the panel: Voc, Vmp, Imp, and Isc.
    If they can't/won't supply that, don't buy it.

    The 12/24 issue is mainly one of the Vmp. Many of the grid-tie panels have a Vmp of about 30 and are promoted as "24 Volt panels". But since a 24 Volt battery system charges at 28.8 Volts (+/-) 30 Volts isn't enough to do the job. When panels get hot (as they do) the Voltage goes down. More Voltage is lost in the wiring. So by the time you get to the battery that 30 Vmp can be less than the charging Voltage: no current flows, no charging occurs. A "real" 24 Volt panel will have a Vmp of 35 to 36.

    Beware also of high Voltage panels; there are some with Vmp around 60 which can only be used with MPPT controllers on battery systems.
  • inetdog
    inetdog Solar Expert Posts: 3,123 ✭✭✭✭
    Re: 12v and 24v panel
    Very good question.
    More Voltage is lost in the wiring. So by the time you get to the battery that 30 Vmp can be less than the charging Voltage: no current flows,

    Strictly speaking, voltage is only lost in the wiring when current is flowing. So the temperature factor could prevent charging completely while the wire resistance will only reduce the amount of current available for charging. Both are bad and both are reasons for needing a higher Vmp from the panels.
    You can reduce the wiring losses by using better terminals and larger, shorter wires. You cannot do much about the temperature factor.
    SMA SB 3000, old BP panels.
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: 12v and 24v panel
    inetdog wrote: »
    Strictly speaking, voltage is only lost in the wiring when current is flowing. So the temperature factor could prevent charging completely while the wire resistance will only reduce the amount of current available for charging. Both are bad and both are reasons for needing a higher Vmp from the panels.
    You can reduce the wiring losses by using better terminals and larger, shorter wires. You cannot do much about the temperature factor.

    Strictly speaking, photovoltic panels are a current source and allow the Voltage to go to whatever point. As such they always put out current, so the Voltage drop is always a factor and a concern.
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: 12v and 24v panel

    Vmp=Voltage Maximum Power
    Voc=Voltage Open Circuit (no current flowing)
    Imp=Voltage Maximum Power
    Isc=Short Circuit Current (if a panel's wiring got shorted

    For the most part, we are looking at Voc-cold (very cold panels output higher voltage--need to make sure solar charge controller can handle the maximum input voltage).

    Vmp needs to be a few volts higher than battery charging voltage... Panels as they get hot, have Vmp fall. So Vmp~17.5 to 18.5 volts is "optimum" for use with "simple" PWM charge controllers.

    If Vmp is >> Vbatt-charging, then you need a MPPT type charge controller (seriously more expensive) to use the panel Vmp*Imp "efficiently" (it is easy to lose 1/2 of the efficiency or more with wrong Vmp to battery bank voltage selection).

    Imp determines the current "rating" of the charge controller used... Isc is used to size the wiring/fuse/breaker to protect the solar panels in larger configurations to insure no overheating of wiring during normal operation or if there is a short circuit somewhere.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • vtmaps
    vtmaps Solar Expert Posts: 3,741 ✭✭✭✭
    Re: 12v and 24v panel

    Shella,
    depending on what you want to do with your solar power system, you may not need to think too much about all the info you have been provided. There are a number of factors that may mean you should be using an MPPT controller.

    If you use an MPPT controller you don't have to worry about whether they are "real" 12 or 24 volt panels. Just buy the cheapest panels (which are often not "real" 12 or 24 volt).
    If you use an MPPT controller you will simplify wiring and fusing at the combiner box (saves money). Depending on the size of your system you may not even need a combiner.
    If you use an MPPT controller you will get more usable power from any panels of any voltage.
    If you use an MPPT controller you can use thinner wire (saves money) between the combiner and the controller.

    --vtMaps
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
  • shella
    shella Registered Users Posts: 23
    Re: 12v and 24v panel

    hi
    this is great info
    i like to know as much as ik believe if you only know some info (like just learning about 12v systems only) you are heading for a big disapointment jmho.
    so on a 12v system could i get the panels that say 24v and mppt controller would that work and what of the higher imp is that a typo or i havent understood its the same as vmp ?
    so how would i wire the panels does the same rules apply
  • vtmaps
    vtmaps Solar Expert Posts: 3,741 ✭✭✭✭
    Re: 12v and 24v panel
    shella wrote: »
    so how would i wire the panels does the same rules apply

    First, does it make sense to use an MPPT controller? MPPT controllers cost more. In a small system it often doesn't pay to spend the extra on MPPT.

    For example, MPPT controllers can simplify the wiring and fusing of a combiner. If your system is only 1 or 2 panels, you may not even have a combiner, so no gain there by using MPPT.

    I assume your system is small because you ask about a 12 volt system. How small?

    --vtMaps
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: 12v and 24v panel
    shella wrote: »
    hi
    this is great info
    i like to know as much as ik believe if you only know some info (like just learning about 12v systems only) you are heading for a big disapointment jmho.
    so on a 12v system could i get the panels that say 24v and mppt controller would that work and what of the higher imp is that a typo or i havent understood its the same as vmp ?
    so how would i wire the panels does the same rules apply

    Basic difference between a PWM type controller and an MPPT type:
    The PWM will pass the current rating of the panel only, with the Voltage at the battery level. Any extra Voltage (and thus power) above that is lost.
    The MPPT will convert the input Watts to output Watts, switching higher input Voltage and converting it to greater output current at the battery level.

    If the panel is designed for the system Voltage and all other factors are equal (no long wire lengths or cold temperatures) there really is not much difference between the two controllers.
    The MPPT type will show better performance when you need to "down convert" high Voltage panels (with a PWM controller the difference between the panel "ideal" and the panel "actual" Vmp is power lost). This is useful for adapting "odd" panels to battery systems. It is also useful for overcoming the extra resistance in long wire runs from panels to controller (higher Voltage array = less power loss from Voltage drop in the wiring). This is actually the main benefit of MPPT controllers. The "cold temperature" advantage (cold panels output higher than rated Voltage) is not available to everyone, and can cause headaches for those who can use it (Voc also increases and may exceed the controller's input maximum).

    It is easier to understand this with a specific scenario, rather than in generalized terms.

    Let's say you want to run panels with a Vmp of 30 and a Imp of 7.8 on a 12 Volt system (235 Watts). The "ideal" Vmp for 12 Volt systems is about 17.5. On a PWM controller these panels would yield 7.8 Amps @ system Voltage or about 112 Watts each or about 47% of the rated output. The Wattage missing is due to the batteries pulling the Voltage of the panel down to their level. Using an MPPT type controller you would see about 77% of the panel power actually reaching the batteries because it can turn the difference between 17.5 "ideal" Vmp and 20 "real" Vmp into current. In fact you might see 15 Amps @ 12 Volts or 180 Watts. The actual output from an MPPT controller is less predictable, as it will select what it feels is the best "loading" to achieve maximum charge current for the prevalent conditions.
  • inetdog
    inetdog Solar Expert Posts: 3,123 ✭✭✭✭
    Re: 12v and 24v panel
    shella wrote: »
    ... and what of the higher imp is that a typo or i havent understood its the same as vmp ?

    In case this has not been cleared up for you yet, here are the four main parameters of a panel:

    Voc (open circuit voltage) is the voltage that you would measure with no load on the panels. It does not vary strongly with the amount of light hitting the panels.
    Isc (short circuit current) is the current that the panel can send through a short circuit. It is the maximum current that the panel can produce and is roughly proportional to the amount of light hitting the panel.
    Those are the easy ones.
    Vmp (maximum power voltage). Since the power from a panel is volts times amps, clearly at Voc and no current you get no power. At Isc and no voltage you also get no power. Somewhere in between those two is the maximum power point (MPP) where the product of the two is as large as possible.
    For an ideal battery that will be at exactly 1/2 of Voc and 1/2 of Isc. But for a solar panel instead of a battery, it is reached closer to Voc and also fairly close to Isc.
    Vmp is that voltage, at the sweet spot.
    Imp (maximum power current) is the current measurement at exactly the same operating point.
    So the highest power you get from the panel (at the standard light conditions) will be Vmp time Imp.

    A controller which tracks the MPP (MPPTracking or MPPT) keeps adjusting the load it puts on the panel to keep the panel working at the current value of Vmp, which will vary with temperature, etc. and at the constantly changing Imp which depends on the incoming sunlight.
    SMA SB 3000, old BP panels.
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: 12v and 24v panel

    Another analogy... A single speed bike vs the automatic transmission in a car...

    The single speed bike is very efficient when operated when geared to the average speed (up hills, vs flat road, etc.)... PWM controller. Matched solar panels (Vmp~17.5 volts to "12 volt" battery).

    An MPPT controller is sort of the automatic transmission... The vehicle speed is the "battery bank", and the engine/gas peddle is the solar array. The transmission "shifts" to convert the high speed/low torque of the engine to the low speed/high torque at the wheels. The automatic shifting to match the available engine speed to the current vehicle speed/wind loading/grade/etc... MPPT controller from Vmp~17.5 volts to Vmp~100 volts or more (or less), depending on controller.

    Note that the typical MPPT controller has limits... Maximum input voltage/current. The input voltage always needs to be a volt or so higher than output voltage to the battery (the typical buck converter used in MPPT controllers can only "down convert" from high voltage/low current to low voltage/high current--there are other types--but that is for another discussion).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • shella
    shella Registered Users Posts: 23
    Re: 12v and 24v panel

    thanks to you all for your replys
    ok i am trying to digest this info
    i have been reading that if you have a hotch botch of solar panels the mppt would be the way to go
    i still having trouble understanding the voc vmp and such will have to divert my attentions to these
    i knew i would have trouble with the maths lol
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: 12v and 24v panel
    shella wrote: »
    thanks to you all for your replys
    ok i am trying to digest this info
    i have been reading that if you have a hotch botch of solar panels the mppt would be the way to go
    i still having trouble understanding the voc vmp and such will have to divert my attentions to these
    i knew i would have trouble with the maths lol

    If you have a "hotch botch" or "hodge podge" :D of solar panels an MPPT type controller will not necessarily help.
    For parallel connections, the Vmp of the panels needs to be close, preferably within 5% to 10%. The greater the difference the greater the power loss.
    For serial connections it's the Imp that matters, same rule-of-thumb. In a series string of panels the current will be reduced to the lowest Imp in the string. No controller can make up for these differences.

    We actually have a glossary that may help you understand all the terms used here on the forum: http://forum.solar-electric.com/showthread.php?6136-Glossary

    Everybody has trouble with the math, especially as there's quite a lot of it!
  • shella
    shella Registered Users Posts: 23
    Re: 12v and 24v panel
    If you have a "hotch botch" or "hodge podge" :D of solar panels an MPPT type controller will not necessarily help.
    For parallel connections, the Vmp of the panels needs to be close, preferably within 5% to 10%. The greater the difference the greater the power loss.
    For serial connections it's the Imp that matters, same rule-of-thumb. In a series string of panels the current will be reduced to the lowest Imp in the string. No controller can make up for these differences.

    We actually have a glossary that may help you understand all the terms used here on the forum: http://forum.solar-electric.com/showthread.php?6136-Glossary

    Everybody has trouble with the math, especially as there's quite a lot of it!

    thank you lol
    i will be reading that now
  • afadh
    afadh Registered Users Posts: 1
    Hello all..need some help..can u all guys tell me this panel is 12v @ 24v rating..thanks in advance.
  • westbranch
    westbranch Solar Expert Posts: 5,183 ✭✭✭✭
    It fits the definition of a 12 volt panel where you need a Vmp of ~ 17V to 18V to properly charge a 12 v  battery
     
    KID #51B  4s 140W to 24V 900Ah C&D AGM
    CL#29032 FW 2126/ 2073/ 2133 175A E-Panel WBjr, 3 x 4s 140W to 24V 900Ah C&D AGM 
    Cotek ST1500W 24V Inverter,OmniCharge 3024,
    2 x Cisco WRT54GL i/c DD-WRT Rtr & Bridge,
    Eu3/2/1000i Gens, 1680W & E-Panel/WBjr to come, CL #647 asleep
    West Chilcotin, BC, Canada
  • Photowhit
    Photowhit Solar Expert Posts: 6,002 ✭✭✭✭✭
    afadh said:
    Hello all..need some help..can u all guys tell me this panel is 12v @ 24v rating..thanks in advance.



    This would be one of those panels designed for a grid tied system, that's not to say it can't be used in a battery based system, only that you will lose some of the power (wattage) if you use it with the inexpensive PWM charge controllers. If you assume 100% transition, the 180watts at 23.7 vmp will charging a 12 volt battery at 14.4 volts will use about 14.4/23.7= 60.7% of the energy available, while a 17.5v would use about 14.4/17.5=82%.

    This is just an example. You need the somewhat higher voltage for other system losses, in wiring and in the charge controller, as well as having enough higher voltage to equalize the batteries (15-15.8 volts)

    In addition some charge controller will find the higher voltage hard to deal with.

    If you have a large quantity of these panels you could use them with a MPPT type charge controller. more expensive but will use the full value of the energy coming into the charge controller.
    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.
  • littleharbor2
    littleharbor2 Solar Expert Posts: 2,037 ✭✭✭✭✭
    In a nutshell, 12 volt crystalline, poly or mono, have 36 cells which produce about .5 volt each resulting in about 18 volts of usable power. 24 volt modules simply have double, 72 cells and double, 36 average volts. Any other cell count such as the sharp panels here (48) cells are something other than 12  or 24 volts nominal.

    2.1 Kw Suntech 175 mono, Classic 200, Trace SW 4024 ( 15 years old  but brand new out of sealed factory box Jan. 2015), Bogart Tri-metric,  460 Ah. 24 volt LiFePo4 battery bank. Plenty of Baja Sea of Cortez sunshine.

  • Roba
    Roba Registered Users Posts: 7 ✭✭
    Hi?Rober here,please assist.I got this panel and I need the best from it.Is it a 12v or 24v type? And what are the correct type and size of charger controller and battery to use?
  • Roba
    Roba Registered Users Posts: 7 ✭✭
    Hi?Rober here.please assist.is this panel a 12v or a 24v type? And what is the correct combination of the charger controller and battery?(type and size of controller and battery)
  • Photowhit
    Photowhit Solar Expert Posts: 6,002 ✭✭✭✭✭
    Roba said:
    Hi?Rober here.please assist.is this panel a 12v or a 24v type? And what is the correct combination of the charger controller and battery?(type and size of controller and battery)

    Your panel falls into the category with the other ones someone was asking about, so the same information applies;

    This would be one of those panels designed for a grid tied system, that's not to say it can't be used in a battery based system, only that you will lose some of the power (wattage) if you use it with the inexpensive PWM charge controllers. If you assume 100% transition, the 180watts at 23.7 vmp will charging a 12 volt battery at 14.4 volts will use about 14.4/23.7= 60.7% of the energy available, while a 17.5v would use about 14.4/17.5=82%.

    This is just an example. You need the somewhat higher voltage for other system losses, in wiring and in the charge controller, as well as having enough higher voltage to equalize the batteries (15-15.8 volts)

    In addition some charge controller will find the higher voltage hard to deal with.

    If you have a large quantity of these panels you could use them with a MPPT type charge controller. more expensive but will use the full value of the energy coming into the charge controller.

    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.
  • Roba
    Roba Registered Users Posts: 7 ✭✭
    Thankyou for the reply.Again,can I use MPPT charger controller and of how many amps?
  • Photowhit
    Photowhit Solar Expert Posts: 6,002 ✭✭✭✭✭
    Roba said:
    Thankyou for the reply.Again,can I use MPPT charger controller and of how many amps?
    Yes, a MPPT type would be preferred, if you just have the one panel, you would likely be fine with a 20 amp charge controller for a 12 volt system. 
    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.
  • Roba
    Roba Registered Users Posts: 7 ✭✭
    Thank you for the reply.it has helped.let me try. but I hop it is possible if I connect two 12 batteries in series?is it safe?
  • Photowhit
    Photowhit Solar Expert Posts: 6,002 ✭✭✭✭✭
    edited October 2017 #27
    Roba said:
    Thank you for the reply.it has helped.let me try. but I hop it is possible if I connect two 12 batteries in series?is it safe?
    It's safe, if the same size batteries, guess it's safe if they are different size, but just ruin one of them [Moderator -BB. the smaller capacity series capacity battery will discharge first and be ruined by taken to zero charge or "reverse charged"].
    ...but in series this would create a 24 volt battery bank. A single panel won't charge this without a special type of MPPT type charge controller.

    Likely you mean in parallel? + to + and - to - ? Which is also safe if the same size batteries. You would end up with a battery bank of double the capacity, but the same voltage.
    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.
  • Roba
    Roba Registered Users Posts: 7 ✭✭
    Thank you.I will try with 12v bat. My Idea was to create more storage to use with a 42" lcd tv monitor.
  • Roba
    Roba Registered Users Posts: 7 ✭✭
    Hello,what battery size and Inverter can I use comfortable with above pv module to operate a 40"Tv (Lcd/led) ?
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    You need to know:
    • Watts of TV (power consumed). Using a Kill-a-Watt or similar meter
    • Watts*Hours per day of TV usage (a Kill-a-Watt meter can give you that measurement too)
    • Where the system will be installed (nearest major city).
    • How the panels will be mounted (tilted to optimize solar harvest).
    • Any trees/shade/power lines/etc. shading panels?
    • How many days of energy storage (for rainy/cloudy weather). Typically, we recommend 2 days of storage and 50% maximum battery discharge (for lead acid type batteries).
    • Do you have any size/weight limitations for battery bank (I.e. in an RV)?
    To give you some idea.... My newish LCD/LED 50" TV uses about 65 Watts when running (seems to use 24 watts "turned off"--I am goin gto have to check that). If you are only going to run the TV for 6 hours per day/evening:
    • 65 Watts * 6 hours * 1/0.85 AC inverter eff * 1/12 volt battery bank * 2 days storage * 1/0.50 maximum discharge = 153 AH @ 12 volt battery bank
    Say you use 2x 6 volt @ 200 AH "golf cart" batteries in series for a 12 volt @ 200 AH battery bank (cheap and pretty rugged lead acid batteries). Recommend 5% to 13% rate of charge for solar... 10%+ for full time usage (every day). The solar array would be roughly:
    • 200 AH battery bank * 14.5 volts charging * 1/0.77 charger+panels derating * 0.05 rate of charge = 188 Watt array minimum (weekend/summer cabin usage)
    • 200 AH battery bank * 14.5 volts charging * 1/0.77 charger+panels derating * 0.10 rate of charge = 377 Watt array nominal
    • 200 AH battery bank * 14.5 volts charging * 1/0.77 charger+panels derating * 0.13 rate of charge = 490 Watt array "cost effective" maximum
    And there is sizing the array based on where you live. Say Nairobi Kenya, fixed array, optimized for sun during bad weather (when you watch the most TV?):
    http://www.solarelectricityhandbook.com/solar-irradiance.html


    Nairobi
    Average Solar Insolation figures

    Measured in kWh/m2/day - a winter setting is not recommended. Instead, the panels should be set at an angle of 89° for best year round performance.
    Jan Feb Mar Apr May Jun
    6.64
     
    6.88
     
    6.42
     
    5.85
     
    5.61
     
    5.46
     
    Jul Aug Sep Oct Nov Dec
    5.54
     
    5.67
     
    6.20
     
    6.06
     
    5.69
     
    6.30
     
    The size of the array to run your TV in June:
    • 65 Watt load * 6 hours per day * 1/0.052 off grid AC system eff * 1/0.75 "bad weather" for a few days * 1/5.46 hours of sun per day = 181 Watt array minimum (June weather)
    So, ~188 Watt array minimum (to keep batteries somewhat happy) to 377 Watt array nominal (10% rate of charge recommended for typical flooded cell lead acid batteries for longer life)--Plus you can run some other loads (some LED lighting, cell phone/laptop charger, etc. during good weather/charging during the day).

    Any questions?

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    edited November 2017 #31
    Ok. TV takes near zero watts turned off. 24 watts was tv rebooting and calling home on the internet when I plugged into a watt meter.

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