xw 6048 battery bank ah size, kWh production

I had one good month of production 50+ kWh per day and then production dropped off to about 25 kWh per day.

My system: 2 xw 6048, 4 - xw mppt60 a charge controllers, 48 volt 220 ah battery array (4 - 12 volt agm batteries), 45 - 230 watt sharp modules.

I'm trying to maximize sell kWh, my grid support volts are set at 51.5 volts.

Charging is set to 2 stage, no float

Does anyone have any suggestions why my production is so low?

I relied on the guy who sold me the equipment to size my battery array, is my battery array too small - how do you properly size a battery array?

Or is there some other setting that is affecting kWh production

Comments

  • RCinFLARCinFLA Solar Expert Posts: 1,351 ✭✭✭
    Re: xw 6048 battery bank ah size, kWh production

    Xantrex is recommending a 400 AH battery size for a single XW6048 if you want to sell.

    The manuals say 100 AH minimum for an XW4048 but that seems just for using as just an inverter. This may be where the installer figured the 200 AH for two units.

    The battery provides the short term voltage anchor. The XW will 'wiggle' the push and pull currents from the battery and the battery impedance must be low enough to keep the battery voltage swing from getting too wild.

    You may also damage the batteries with such a small AH setup and large PV array. With 10 kW of PV panels I am somewhat surprised you have done as well as you have. Have you been getting any error messages?

    You might have fried the batteries but you should check the voltage range they swing over and do a load test on them of say, 50 amps. (about 2500 watt load on inverter with no solar assisting).

    Then there is always the possiblity of an assault by pigeons on your PV panels to explain the power drop.
  • Solar GuppySolar Guppy Solar Expert Posts: 1,963 ✭✭✭
    Re: xw 6048 battery bank ah size, kWh production

    ( same as in other thread )

    For 10kw+ of panels , you need at minimum 5X the battery's you have now

    With 225ah , you might get 30 minutes before you melt the plates in the battery's.

    I have 660ah for my single XW-6048.
  • RCinFLARCinFLA Solar Expert Posts: 1,351 ✭✭✭
    Re: xw 6048 battery bank ah size, kWh production

    This may help explain the stress on the batteries.

    PV panels have to have a even constant DC current pull to get maximum power out and allow an MPP algorythm to work. The CC high frequency switcher pushes near pure DC current at the battery node.

    A single phase inverter hooked to AC mains has a DC current profile at the battery node that looks like a full wave rectified sinewave (120 Hz rate current pulses). If you are pushing 6 kW's, the inverter current draw profile is about 160 amps peak to valley of ripple current at 120 Hz. The batteries are providing the 'filter capacitor' to supply these high peak currents.

    Ramming 220 AH batteries with this much ripple current is going to fry them out pretty quickly.

    There is also requirement for the inverter to test the grid periodically. It does this by bucking the grid periodically to test if grid is there and valid. This also puts high current spikes to batteries.

    You could put about a 4 Farad, 75 wvdc cap across the battery to supply the ripple current. Yes, that was Farads. (just a joke, don't do it) ;)
  • Wildwood NJ ToddWildwood NJ Todd Registered Users Posts: 5
    Re: xw 6048 battery bank ah size, kWh production

    Thanks for the good info. I wish Xantrex had this type of sizing information readily available.

    No error messages that don't self correct (just momentary stuff when I reboot etc.)

    I'll try the 2500 watt load - at 220 AH times 48 volts (10,560 watt hours.) If the batteries aren't already fried, I should get about 4 hours of run time before my voltage drops to whatever discharge level Deka bases their AH reading on.

    I guess I'll plan on at least an additional 220 AH.

    The last time I disconected the cable from the battery terminal to correct a wiring issue, I got quite a large spark when I touched the cable lug to the terminal. The breakers were off on the inverter, so I thought it was odd that I got this spark - does this indicate anything to you?

    I wish it was pigeon crap, but it's good to finally have some direction to try and solve this problem, you've been very helpful.
  • RCinFLARCinFLA Solar Expert Posts: 1,351 ✭✭✭
    Re: xw 6048 battery bank ah size, kWh production
    Thanks for the good info. I wish Xantrex had this type of sizing information readily available.

    No error messages that don't self correct (just momentary stuff when I reboot etc.)

    I'll try the 2500 watt load - at 220 AH times 48 volts (10,560 watt hours.) If the batteries aren't already fried, I should get about 4 hours of run time before my voltage drops to whatever discharge level Deka bases their AH reading on.

    I guess I'll plan on at least an additional 220 AH.

    The last time I disconected the cable from the battery terminal to correct a wiring issue, I got quite a large spark when I touched the cable lug to the terminal. The breakers were off on the inverter, so I thought it was odd that I got this spark - does this indicate anything to you?

    I wish it was pigeon crap, but it's good to finally have some direction to try and solve this problem, you've been very helpful.

    On the load test, don't run the batteries down. Just check the battery voltage to see how much it slumps in voltage under load for just a few seconds of load, like turn on a couple of hair dryers on output of inverter while measuring battery voltage. When battery is subjected to high ripple current for some time it can degrade the effective series resistance of the battery. This means more voltage slump with load current.

    The spark you are seeing when you connect the battery cable to inverter is just the inverter input filter caps charging up from zero to battery voltage. Nothing to be concerned about unless you do it around gas vapors.
  • Solar GuppySolar Guppy Solar Expert Posts: 1,963 ✭✭✭
    Re: xw 6048 battery bank ah size, kWh production
    I guess I'll plan on at least an additional 220 AH

    That won't be enough to function correctly longer term

    A battery run time is based on 20 hour discharge , for your battery's that works out to 540 watt load per hour. As you increase the load, the battery's lose efficiency as the internal resistance creates heat, not delivered energy.

    With a pair of 6kw 100% duty cycle inverters, you will literally melt and possibly cause a explosion with that undersized battery bank if you get a large load on the inverters when there is no AC present, possibly even when connected and in sell mode as the full sell current will be cycling at 120hz, very bad for the battery's best case.

    At a load that is for example 5kw on the battery bank, that's 10X the ah rating of the battery and the efficiency will be less than 50%, meaning, 2.5kw will be heat inside the battery's and depending on the load, it could be a positive feedback and cause a run-away condition in the battery's

    This isn't an inverter manufactures issue, its a system design issue that you have 12kw/24kw peak inverters on battery's spec'ed for a 500 watt load. Battery sizing and selection is the job of the system designer, not the manufacture. There are endless dangers of building whole house power systems, which is what you have

    I'm writing the post intentional strong worded as what you have is exceptionally dangerous. DO NOT RUN THE SYSTEM ANY LONGER until you have corrected the battery capacity issue. Your home and anyone living in it are in danger.

    If you don't want the expense of the correct battery's, sell the XW's and use straight grid tie inverters like the GT series. If you desire the battery advantages, then install a system with at minimum a 1200ah capacity, that's what a system of this sizes requires, its not an option.

    Also, make sure you have the proper fault protection ( fuses or breakers on each battery string ). I am glad you came here for answers and we are able to help.

    This advise comes from someone who was a contract engineer for Xantrex for 5 years and worked on the XW program, please take this seriously

    SG
  • Dr. StrangeloveDr. Strangelove Solar Expert Posts: 49
    Re: xw 6048 battery bank ah size, kWh production

    Guppy, can the XW6048s be programmed to draw off the batteries at a lower than 6kW rate? Using a C/10 rate sized to existing batteries, for example? If the load is too high, can the XW can trigger the AGS to bring up a genset to power the load through AC2?

    Otherwise, XW6048 hybrid charger inverter should be spec'ed to connect to no less than a 1200 Ah or 60kWh battery bank. The documentation's minimum battery size of 100 Ah is outlandish and unjustifiably undersized.

    Andrew
  • Solar GuppySolar Guppy Solar Expert Posts: 1,963 ✭✭✭
    Re: xw 6048 battery bank ah size, kWh production

    These systems should be treated with the same respect as other skilled trades. It is well understood that you need licensed professionals to spec and install heat pumps, furnaces or AC systems. Battery based power centers are just as critical if not more so from the safety prospective.

    Proper designs require 100ah per kw of load for proper operation and its nothing to do with the fact its a Xantrex inverter, any other brands have the same need, its a system design parameter.

    The manufactures manual is not a system design guide but a reference for the specification of the product it represents. This is a primary reason Xantrex sells through certified dealers in my opinion.

    I do agree that having the 100ah in a manual as the listed minimum is misleading, but there are many parameters needed for a safe system, wiring, breakers, conduit, enclosure ect.

    So for a XW-6048 this is 600ah , the 1200 ah is because the poster has a dual XW-6048 installation with the ability to sell up to the inverters rated output with close to 11kw of solar which edge of cloud events will push the inverters to there maximum rated output.

    I do wonder how this is connected to the grid, you can't use a 200 amp panel for this, I suspect its another error in the installation.
  • Wildwood NJ ToddWildwood NJ Todd Registered Users Posts: 5
    Re: xw 6048 battery bank ah size, kWh production

    It's seems the minimum amp hours is quite a touchy subject at Xantrex tech support, because when I called to ask what the minimum Amp Hour requirment for a xw6048 is, the guy would only say that the 100 amp hours listed in the literature was wrong. He said he wasn't allowed to tell me what the minimum AMP hours are. He said it was a very important question but wasn't allowed to answer it.

    The system is connected through a lugged tap at a 400 amp switch at the meter, not through a 200 amp panel.

    You are correct about batteries being a very specific science, and it is very difficult to get information about how to size them properly, and you've really laid it out in a very understandable manner, thanks for that. I appreciate your frank statements.

    My application is primarily for grid tie, with a few devices connected to an emergency only panel. The fridge, a few receptacles for the computer and router, etc. So I'll measure my amps on that emergency panel and make sure my loads match my amp hours (100 ah per kW of load.) I have less than 5 kW connected, so if I change my emergency load breaker to 20 amps out of the inverter, that should prevent me from overloading the batteries. (I checked my existing bank is 245 ah and I'll add another 245 ah for 490 total.)

    If I had properly understood the battery issue, I may have gone with one direct grid tie inverter, and one battery backup, instead of 2 xw6048's.

    Thanks again.
  • BB.BB. Super Moderators, Administrators Posts: 31,443 admin
    Re: xw 6048 battery bank ah size, kWh production

    Yep... The issue is really the ability of the battery to manage the power requirements (and that assumes a typical 6kW inverter can run 12kW surges for very short periods of time).

    AGM's can handle sourcing higher current--but once fully charged--I don't think a small AGM bank can manage absorbing the high currents that these hybrid power systems sometimes demand during normal Grid Tied operations.

    And to add a bit of clarity--I believe Solar Guppy is saying 100 AH minimum per 1kWatt at 48 Volts.... If you a 24 volt battery bank, then it would be 200 AH per 1kW, and at 12 volts it would be 400 AH per 1kW of continuous rated load.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • Solar GuppySolar Guppy Solar Expert Posts: 1,963 ✭✭✭
    Re: xw 6048 battery bank ah size, kWh production
    ... so if I change my emergency load breaker to 20 amps out of the inverter, that should prevent me from overloading the batteries. (I checked my existing bank is 245 ah and I'll add another 245 ah for 490 total.)

    If I had properly understood the battery issue, I may have gone with one direct grid tie inverter, and one battery backup, instead of 2 xw6048's.

    Thanks again.

    No, you have almost 11kw of solar, you need the battery's for this as well, not just running loads when the grid goes down.

    So your sizing requirement is the gridtie sell of 11kw = the 1200ah I was recommending.

    Manufactures are not design centers, they sell products not completed systems, that is why you can't get the answers on the batteries, it installation specific. Just like people hire professional for AC/Heat pumps, electricians, plumbers ect, its the same for solar. They have the knowledge you don't, its not the manufactures job to educate the DYI inclined.

    And yes, most go straight grid tie as the battery's required for proper operation are almost the same cost as the solar panels now that there ~1.50 watt

    You need to make a decision, buy the battery's you need or sell off the XW stuff and install a pair of GT inverters. Its about 7K for a pair of GT inverters, likely double that for the battery's you need.

    You can sell the XW inverter and chargers to cover the swap to straight grid tie, you might actually come to with money in your pocket.

    Unless you need whole house backup that with 11kw of solar would make you able to run close in indefentantly without grid power if the need should arise, i would recommend you get the GT equipment.

    Also, battery's are not maintenance free and will need replacement very 5-8 years, another reason few go this route when the grid is available.

    Look on the bright side, you were smart to look for help, it didn't cost anything to get the correct advise and options and you now have the information to complete the project.
  • Solar GuppySolar Guppy Solar Expert Posts: 1,963 ✭✭✭
    Re: xw 6048 battery bank ah size, kWh production
    BB. wrote: »

    And to add a bit of clarity--I believe Solar Guppy is saying 100 AH minimum per 1kWatt at 48 Volts.... If you a 24 volt battery bank, then it would be 200 AH per 1kW, and at 12 volts it would be 400 AH per 1kW of continuous rated load.

    -Bill

    Yes Bill , you need battery's rated about 80% of your inverter load, both calculated in watts, then adjusted for the nominal battery bank voltage, whether its to be in sell mode gridtie or offgrid in the XW's example.

    Most offgrid system design for days of autonomy which will typically be far greater need in capacity than the rule of thumb above. The issue is people are installing hybrid inverters and don't make the autonomy calculation, so as a fall back you need as a minimum, the 80% rule.

    GT installers I have observed don't understand this, I know of one in Florida that was installing 250ah with 5Kw units, I tried to explain the issues but it fell on deaf ears.
  • NickhNickh Registered Users Posts: 1
    Re: xw 6048 battery bank ah size, kWh production

    Hello,
    Dr. Strangelove's question above has recently come up for me too. Can the Xantrex be programmed to start generator if load is above certain level to power through AC2? Thanks for your help,
    Nickh
  • BB.BB. Super Moderators, Administrators Posts: 31,443 admin
    Re: xw 6048 battery bank ah size, kWh production

    You may need to contact xantrex Schneider directly. There are updates to firmware and options that are not documented well to customers.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • RJonesRJones Registered Users Posts: 2
    Re: xw 6048 battery bank ah size, kWh production

    I have my 2ea MPPT60-150's and a MPPT 80-600 all set to 3 stage so that they will continue to charge the batteries instead of converting all the power to heat when the 2nd stage has completed. I only run Generator and 3 XW6048's in 2 stage. However, I cannot sell anymore - I used to.

    Are you fully selling back to the electric company? (a.k.a. Co-Production). If you are then setting all 4 MPPT chargers to 3 stage, might help you. Easily done with a SCP II, the front panel on each, or my favorite: A Scheider Electric Com Box - you can see what is happening in 10 second intervals. Then you can fix what is broke - it works over the xanbus and connects to a router so you see the system on your computer screen. The voltage settings for "selling on the 6048" seem fine.
  • RJonesRJones Registered Users Posts: 2
    Re: xw 6048 battery bank ah size, kWh production
    It's seems the minimum amp hours is quite a touchy subject at Xantrex tech support, because when I called to ask what the minimum Amp Hour requirment for a xw6048 is, the guy would only say that the 100 amp hours listed in the literature was wrong. He said he wasn't allowed to tell me what the minimum AMP hours are. He said it was a very important question but wasn't allowed to answer it.

    The system is connected through a lugged tap at a 400 amp switch at the meter, not through a 200 amp panel.

    You are correct about batteries being a very specific science, and it is very difficult to get information about how to size them properly, and you've really laid it out in a very understandable manner, thanks for that. I appreciate your frank statements.

    My application is primarily for grid tie, with a few devices connected to an emergency only panel. The fridge, a few receptacles for the computer and router, etc. So I'll measure my amps on that emergency panel and make sure my loads match my amp hours (100 ah per kW of load.) I have less than 5 kW connected, so if I change my emergency load breaker to 20 amps out of the inverter, that should prevent me from overloading the batteries. (I checked my existing bank is 245 ah and I'll add another 245 ah for 490 total.)

    If I had properly understood the battery issue, I may have gone with one direct grid tie inverter, and one battery backup, instead of 2 xw6048's.

    Thanks again.


    When MPPT60-150's are 2 stage they kick in at a certain voltage and charge through stage 1, then 2, then shutdown until the batteries reach a voltage to restart the process of charging.

    When MPPT60-150's are 3 stage they kick in at first light, go through stage 1, then 2, then 3 or FLOAT - the charger will continue to float the batteries at around 55.7 Volts, however, your XW6048's will sell as long as the batteries are at or above -0.5 VDC of what you have them set at.

    For instance: 6048 set to Sell at 54VDC and floating charges are 55.7VDC - thus the charger never shuts down and the XW6048 will continue to supply all it can to the lug you installer put on the meter.

    You should see improvements in you daily harvest of the sun, if you change Sell: to 54 (or whatever your batteries need, my Gel Cells need 54 for float as per mfr). Set all MPPT charges to 3 stage - this is necessary no matter how many batteries you have, because you are Selling, not off grid Using (my Sell is set to 54 at 0 AMPS to keep my 6048 from back feeding). Keep you chargers running, don't let them shutdown! :)
  • SulfurSulfur Solar Expert Posts: 62 ✭✭
    Re: xw 6048 battery bank ah size, kWh production

    Sunny Island 6048 which is a 6000 watt inverter, also claims 100Ah minimum, so I presume some would say this is also dangerous? Is battery overheating causing fire the risk? Are there other risks too? The SI does monitor battery temp and I believe it can shut down based on this. What are others thoughts on this.
  • BB.BB. Super Moderators, Administrators Posts: 31,443 admin
    Re: xw 6048 battery bank ah size, kWh production

    The thoughts on this forum is that for a 6kWatt AC inverter, you need ~600 AH @ 48 volt minimum. 100 AH @ 48 volts is not going to supply 12 kWatt surge power. For flooded cell batteries rules of thumbs:

    100 AH * 48 Volts * 0.85 inverter eff * 1/8 max recommended continuous discharge rate for flooded cell = 510 Watt max continuous AC power
    100 AH * 48 Volts * 0.85 inverter eff * 1/5 max short term discharge rate for flooded cell = 816 Watt max continuous AC power
    100 AH * 48 Volts * 0.85 inverter eff * 1/2.5 maximum discharge rate for flooded cell = 1,387 Watt maximum surge

    If you respect the above limits for AC output power, then you could run the 6kW inverter on a 100 AH @ 48 volt battery bank...

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: xw 6048 battery bank ah size, kWh production
    Sulfur wrote: »
    Sunny Island 6048 which is a 6000 watt inverter, also claims 100Ah minimum, so I presume some would say this is also dangerous? Is battery overheating causing fire the risk? Are there other risks too? The SI does monitor battery temp and I believe it can shut down based on this. What are others thoughts on this.

    Temperature is not the problem. The charge is regulated so the batteries will not be subjected to excessive Voltage or current (unless you have the parameters wrong). It's filtering the AC ripple. Without sufficient battery capacity the inverter doesn't see "pure DC" but badly filter DC. As a result it will fluctuate in operation.
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