1 kw solar panels

oadkinsoadkins Registered Users Posts: 17 ✭✭
I am new to solar and the forum and I would like to know approximately how many amp hour of battery bank can be maintained with 1kw of solar panels. Am near st johns az off grid and will add to system as I go. Thank You

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  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: 1 kw solar panels
    oadkins wrote: »
    I am new to solar and the forum and I would like to know approximately how many amp hour of battery bank can be maintained with 1kw of solar panels. Am near st johns az off grid and will add to system as I go. Thank You

    Welcome to the forum.

    There is a missing factor of system Voltage here, but I can give you approximations for the three standard system Voltages. They work out to about the same amount of stored power.

    A 1kW array using an MPPT type charge controller under typical conditions will put out approximately the following peak currents:

    12 Volt system; 64 Amps
    24 Volt system; 32 Amps
    48 Volt system; 16 Amps

    Using the 10% rule-of-thumb you multiple that current by 10 to get the approximate Amp hour capacity at the Voltage. In other words 640 Amp hours 12 Volts, et cetera.

    There are a number of mitigating factors such as a certain range of tolerance to peak charge rate and how the system is used.
  • PhotowhitPhotowhit Solar Expert Posts: 4,912 ✭✭✭✭
    Re: 1 kw solar panels

    In sunny AZ, you can likely get away with a bit larger battery bank, one of many mitigating factors!

    With a 1000 watt array likely you will want to look at a 24 volt system, unless you have many 12 volt loads.

    All things start with loads, so it would be easier to understand what you need if we started there. It tends to be difficult to 'Grow' a system, if you intend on a larger system, I would say 24 volt is nearly a must. You typically don't want to add new batteries to old, you will also want to pick a charge controller and combiner box with room to add panels. Possible looking at your future needs when picking an inverter...
    Home system 4000 watt (Evergreen) array standing, with 2 Midnite Classic Lites,  Midnite E-panel, Prosine 1800 and Exeltech 1100, 660 ah 24v ForkLift battery. Off grid for @16 of last 17 years. Assorted other systems, and to many panels in the closet to not do more...lol
  • oadkinsoadkins Registered Users Posts: 17 ✭✭
    Re: 1 kw solar panels

    Thank You for the answers. I will probably start with a 12 volt system and will learn on this system , then move it to barn and workshop and put a larger system in for house. oadkins thanks to all.
  • BB.BB. Super Moderators, Administrators Posts: 29,218 admin
    Re: 1 kw solar panels

    Just to give you some numbers to hang your hat on...

    I like to start with the battery as the "heart" of your system. Generally 5% to 13% rate of charge from your solar array to the battery bank is a good range. If the system is used lightly (weekends, summer evenings, etc.), then 5% rate of charge can work. If the system is used heavily, then you should be looking at a 10-13% or so rate of charge (less baby sitting of loads vs sun, quicker to recharge next sunny day, etc.).

    So, for a 10% rate of charge with 1,000 watts of panels using other rules of thumbs:
    • 1,000 Watt array * 0.77 panel+controller derating * 1/0.10 rate of charge * 1/14.5 volt battery charging = 531 AH @ 12 volt battery bank

    Of course, if you chose a 24 volt battery bank, you would have ~266 AH @ 24 volt battery bank. Same energy storage, roughly the same costs, just at 24 volt DC (and 1/2 the current) as 12 volt bank.

    Now, what does that give you... If you assume 2 days of "no sun" and 50% maximum discharge, then your 120 VAC storage would be:
    • 531 AH * 12 volts * 0.85 inverter eff * 1/2 days of storage * 0.50 maximum discharge = 1,354 Watt*Hours = 1.35 kWH per day nominal 120 VAC energy per day available from battery bank

    How big of AC inverter... Roughly, C/8 would be a good nominal maximum continuous discharge rage. And C/2.5 would be the recommended maximum surge current (starting well pump, etc.)--This is for a flooded cell battery, but is also very conservative for AGM batteries too. And a "good inverter" can usually surge around 2x its maximum continuous load. So:
    • 531 AH * 12 volts * 0.85 inverter eff * 1/8 hour discharge = 677 Watt "nominal maximum" inverter
    • 531 AH * 12 volts * 0.85 inverter eff * 1/2.5 hour discharge * 1/2 surge derating = 1,083 Watt "nominal maximum useful" inverter

    And how much energy from the solar panels can you get... In much of the US, we get about a minimum of 4 hours of "noon time equivalent sun" per day for ~9 months of the year...
    • 1,000 Watt array * 0.52 end to end AC system efficiency * 4 hours of sun per day minimum for nine months of year = 2,080 WH per day ~ 2.1 kWH per day minimum

    Now, look at your loads. Do you need 12 VDC or 24 VDC? Do you need AC power, and if so, how much (Kill-a-Watt type energy meter). Does it look like the above system will meet your needs?

    Will you need a backup genset + AC charger?

    A Honda eu2000i will run a 45 amp or so 12 volt AC Iota charger (22.5 amp or so at 24 VDC battery bank). If you assume a 10% or 20% rate of charge, then:
    • 45 amp * 1/0.10 rate of charge = 450 AH @ 12 volt battery bank
    • 45 amp * 1/0.20 rate of charge = 225 AH @ 12 volt battery bank

    It would be a bit small for a 531 AH battery bank--But if you do not need to use a generator very much and can live with longer generator run time, when needed (typically dark winter days), I probably would still start with the eu2000i and a 45 amp Iota charger.

    A 55 amp Iota charger may work--But I would talk with NAWS or ask on the forum if anyone here uses 55 amp 12 volt Iota with their eu2000i.

    The above is just a starting point for a suggested design. Check the above against your needs (and wallet) to see if everything will meet your requirements. If not--Then start adjusting (your loads, your solar hardware). It is cheap and easy to do that now on paper -- Vs later when you have the hardware.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • oadkinsoadkins Registered Users Posts: 17 ✭✭
    Re: 1 kw solar panels

    I have a inteli-power9245c would this work as good as iota. Thank You Oadkins
  • BB.BB. Super Moderators, Administrators Posts: 29,218 admin
    Re: 1 kw solar panels

    Is this the Inteli-power you have?

    http://www.progressivedyn.com/prod_details/rv_conv/rv_converter_pd9245c_2.html

    I am not sure--I did not see any detailed specifications--But since you have one already--Why not try it and see if it works well for you (monitor battery bank voltage/current when charging, check specific gravity of the battery cells with a hydrometer to see that they are being properly charged, etc.).

    Are you going to run this with Utility power or using a generator (brand/model?)?

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • oadkinsoadkins Registered Users Posts: 17 ✭✭
    Re: 1 kw solar panels

    Yes that is the one I have. What makes the Honda eu2000i better than the same size generic gen. Thank You
  • BB.BB. Super Moderators, Administrators Posts: 29,218 admin
    Re: 1 kw solar panels
    oadkins wrote: »
    What makes the Honda eu2000i better than the same size generic gen.

    A standard generator (really a gasoline/fuel combustion engine driving an Alternator) requires the motor+alternator to run at a fixed RPM (3,600 RPM or 1,800 RPM typical for a 60 Hz 120/240 VAC output).

    This type of "genset" is simple, cheap, and pretty reliable. However--It does make it less fuel efficient at less than ~50% of rated capacity. Because the genset needs to turn at a fixed RPM (to maintain 60 Hz)--At less than 50% of rated output, fuel flow (gallons per hour, etc.) remains about the same (down to zero power output).

    The Honda and other "inverter/generators" use a "wild frequency" alternator. Basically, the Engine RPM is no longer fixed at 3,600 RPM, but can go faster or slower--And the Wild AC is sent to an internal AC inverter that converts the variable frequency/voltage to 120 VAC @ 60 Hz power.

    At lower power usage (1/4 power or so), the generator can run much slower, quieter, and more fuel efficiently. At >50% rated power, the advantages of the inverter/generator are not really that much.

    Drawback is that at low RPM (1/4 or less), the genset does not have much "surge capacity" and if you throw a heavy load on the generator, it may take a few seconds to increase engine RPM to support full rated output (they have an "ECO Throttle" switch so you can run the Genset at full RPM for heavy/surging loads.

    The Honda and Yamaha inverter generators tend to be quieter (more baffling) and pretty rugged/reliable units if you change the oil and perform recommended maintenance. There are some folks here that are running the Honda eu2000i generators around 6,000 hours now. >2,000 hours should be pretty common. A lot of the "cheap and noisy" gensets have problems making it past 100-500 hours before something breaks.

    The Honda eu family generators are not really worth rebuilding when they wear out or something major breaks (they are designed to be inexpensive).

    Battery Charging can be very hard on generators... It is pretty easy to load up a genset with a fixed load from the battery charger and run it for 3-8 hours at near rated output (deep discharged large battery bank will draw constant current from AC battery charger for many hours). Most non-commercial generators are designed to run residential loads which tend to be fairly light loads with occasional surge current (starting refrigerator, compressors, well pumps, etc.). Running non-commercial generators at over ~80% of rated output for many hours--They can have cooling/overheating problems in the engine and/or alternator+AC wiring.

    For smaller power needs--The inverter-generators can be more nice and fuel efficient. And many people still have a 5kWatt or larger genset to run the shop loads, well pump, etc. for limited time.

    Running a genset that will go ~4-9+ hours while outputting 400-1,600 Watts (enough to run a home in an emergency, or recharge a smaller battery bank), vs running a 7kWatt genset that will drink around a 1/2 to 1 gallon of fuel per power.

    If you need 3.5 to 7 kWatts of power, then a 7 kW genset may be the solution. But if you only store 10-20 gallons of gasoline for emergency power--The Honda can give you 5-20 days of emergency power. The 7kW will go through that amount of fuel in 1-2 days (then what--Does the local gas station have power? Does it have fuel? Can it get get deliveries, etc.).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • vtmapsvtmaps Solar Expert Posts: 3,738 ✭✭✭✭
    Re: 1 kw solar panels
    oadkins wrote: »
    Thank You for the answers. I will probably start with a 12 volt system and will learn on this system , then move it to barn and workshop and put a larger system in for house.

    A workshop on 12 volts? For the LED lights, I presume. You're not thinking of running power tools on a 12 volt system, are you?

    What inverter are you thinking of for your system?

    --vtMaps
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
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