10.78kW Enphase system and XW6048

RK_Solar_HopefulRK_Solar_Hopeful Solar Expert Posts: 69 ✭✭✭✭
I am interested in AC-coupling the XW6048 with 44 - M215 Enphase micro inverters using 245W pv panels. I have read the frequency shift for the XW6048 occurs in -0.4Hz/s increments. That seems too large and would likely cause too many (all) of the M215 inverters to drop off line at one time. Causing all of the inverters to cycle on - off at the same time.

Has anyone performed any testing in this area?
Is it possible to adjust the -0.4Hz/s to a smaller value? Perhaps -0.1Hz/s or -0.05Hz/s?

The goal is to have the grid tied M215 inverters (producing about 40amps) feed through the XW6048 until there is a loss of power. Then the XW6048 would go off grid, produce 240VAC/60Hz, the M215s would sync up with the XW6048, battery voltage would go up, XW6048 would quickly reduce frequency causing the M215s to sequentially drop off due to out of spec power.

Or should I look at another solution? A data center UPS...
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Comments

  • RCinFLARCinFLA Solar Expert Posts: 1,397 ✭✭✭✭
    Re: 10.78kW Enphase system and XW6048

    What frequency shift are you referring too?

    When grid is present it is lock to grid.

    When grid is not present it is clock master and does not shift frequency unless GT PV power has nowhere to go and XW must cause GT inverter(s) to shut down.

    If GT PV power back flow exceeds XW power capability during off grid situation the inverter will shut down.
  • RK_Solar_HopefulRK_Solar_Hopeful Solar Expert Posts: 69 ✭✭✭✭
    Re: 10.78kW Enphase system and XW6048
    RCinFLA wrote: »
    What frequency shift are you referring too?

    When grid is present it is lock to grid.

    When grid is not present it is clock master and does not shift frequency unless GT PV power has nowhere to go and XW must cause GT inverter(s) to shut down.

    If GT PV power back flow exceeds XW power capability during off grid situation the inverter will shut down.

    From Xantrex AC-Coupling app note (976-0240-01-01 rev-a)

    AC Coupling Module with Line Frequency Variation Pattern starts on pg 5 of attached pdf

    The transfer switch between AC1 & AC2 can handle 60 amps. So it appears that while grid tied there is no issue.

    What I hope to find out is if someone else has installed GT PV panels greater than 6kW and what their results were.
  • Dr. StrangeloveDr. Strangelove Solar Expert Posts: 49
    Re: 10.78kW Enphase system and XW6048

    I have been considering a similar design as you. It is not clear to me that the 60 Amp relays in the XW hybrid line are 60 Amp/hot, thus good for 14kW total?

    However, I get the impression that the "frequency shift power control" for AC coupling in the Xantrex hybrids was an after-thought add-on that is tested only with their GT inverters (now called Conext), in a on/off mode of operation. Other manufacturers, eg. SMA, scale the frequency shift to power cut-back relationship, and shift frequency in a reverse direction to nullify the longer term drift. I thought that I read somewhere that it is a European standard but I can't seem to find the reference.

    AC coupling, in general, appears to also be a "me too" afterthought in light of the fact that the XW line has no problem controlling power to the DC batteries when drawing on AC1 or AC2, but can not guarantee proper charging in an AC coupled, off-grid configuration without killing the other source (GT inverter), and running off batteries until they must be charged again. Why not simply stop charging, go to float, and allow the GT inverter to supply power with the inverter in a "mini-grid support" mode? Other manufacturers such as SMA seem to have designed-in this feature, thought they fall short in terms of an integrated grid-tied/mini-grid fall-back solution.

    It's just my impression that Schneider bought Xantrex to fill a perceived hole in their spectrum of products. In the interim, they have fully off-shored the manufacturing to China, and appear to have abandoned any further firmware development, to increase profit. From the latest issue of SolarPro magazine, Schneider has a whopping 0.8% of the in-process single phase string inverter market as of mid-May, while their deployed base is 7.1% of the market. So the trend appears quite negative. Given the remarkable manufacturer support reported here, I'm not surprised.

    Experts, please correct me if I'm wrong, but these are my impressions after poring over all the available Schneider documentation and fora posts.
  • RK_Solar_HopefulRK_Solar_Hopeful Solar Expert Posts: 69 ✭✭✭✭
    Re: 10.78kW Enphase system and XW6048

    I sent out some emails. Hopefully someone will be able to point me in the right direction.

    While I'm waiting please double check some math for me.

    The forums suggest 100 amp/hr for each kW of inverter capacity.
    -XW6048 is 6kW at 48VDC
    -So I should have 6x100 amp/hr at 48VDC=28800W/hrs of capacity
    -About $10K worth of batteries, equipment & delivery

    1. Am I doing my math correctly? That seems like a very large battery setup.
    2. Is a battery system this size needed for an AC-coupled system?
    3. Should I abandon all hope of trying to make the idea work?
  • nielniel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: 10.78kW Enphase system and XW6048

    i'm not following why you need to feed the enphase system through the xantrex inverter. the enphase system would automatically disconnect from the grid if the utility power disappears and enphase inverters are parasitic in nature in that they can't produce without seeing the grid there and is called anti-islanding.

    if the inverter is for backup power then the power being fed to the grid by the enphase pv system would then feed the loads in the house first and that includes the charger on the inverter so this is technically still part of the solar setup, but just done separately. if those enphase inverters are used to lock onto the ac output of the xantrex inverter you could run into some problems there and is a form of a backfed system. i'm not an expert in that area, but there are some here that are familiar with backfed arrangements.

    as to the battery capacity the 100ah/kw may or may not be the case as it really depends on how much power you use over the course of a day without utility power and if it needs to go beyond a day. with the battery power determined by the loads you must now be cautious not to let the batteries go below 50% or risk depleting some of their lifespan so the batteries, once the loads are determined, should be doubled from there. solar guppy has stated a very minimal start point of 100a for the battery bank and that is used for selling to the grid without much need for backup and 6kw would certainly not be handled by a battery bank that low in capacity.

    as a rough guess take your total wh/day used by your household loads that the xantrex inverter would cover and multiply that by 2 and divide that by the nominal battery voltage (48v) to arrive at a good rough estimate for the battery bank capacity. sometimes this needs readjusted for high surges or longer time periods needing to be covered. the 6kw capacity of the inverter is not to be viewed as a consistent power draw even though it can handle it, but more as a maximum for odd times that that much could operate at one time and is not the norm. drawing 6kw consistently over 24hrs would be a very high draw of power as we are talking 144kwh per day!!!
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: 10.78kW Enphase system and XW6048
    I sent out some emails. Hopefully someone will be able to point me in the right direction.

    While I'm waiting please double check some math for me.

    The forums suggest 100 amp/hr for each kW of inverter capacity.
    -XW6048 is 6kW at 48VDC
    -So I should have 6x100 amp/hr at 48VDC=28800W/hrs of capacity
    -About $10K worth of batteries, equipment & delivery

    1. Am I doing my math correctly? That seems like a very large battery setup.
    2. Is a battery system this size needed for an AC-coupled system?
    3. Should I abandon all hope of trying to make the idea work?

    XW6048 should have at least a 600 Amp hour battery bank. At 50% DOD that would be 14400 Watt hours (approx.)
    I don't know where you're buying your batteries, but it shouldn't be $10,000 for that bank. One example: sixteen Crown 395 Amp hour 6 Volt batteries http://www.solar-electric.com/cr395amdecyb.html @ $304 each = $4864 - about half your estimate, not including the taxes and shipping et cetera. Trojan 325 Amp hour 6 Volts about $7 cheaper each. Shop around.

    If you intend to use the XW as a "synch base" for the Enphase units and thus increase your over-all capacity be prepared for headaches.
  • RK_Solar_HopefulRK_Solar_Hopeful Solar Expert Posts: 69 ✭✭✭✭
    Re: 10.78kW Enphase system and XW6048
    niel wrote: »
    i'm not following why you need to feed the enphase system through the xantrex inverter. the enphase system would automatically disconnect from the grid if the utility power disappears and enphase inverters are parasitic in nature in that they can't produce without seeing the grid there and is called anti-islanding.

    if the inverter is for backup power then the power being fed to the grid by the enphase pv system would then feed the loads in the house first and that includes the charger on the inverter so this is technically still part of the solar setup, but just done separately. if those enphase inverters are used to lock onto the ac output of the xantrex inverter you could run into some problems there and is a form of a backfed system. i'm not an expert in that area, but there are some here that are familiar with backfed arrangements.

    as to the battery capacity the 100ah/kw may or may not be the case as it really depends on how much power you use over the course of a day without utility power and if it needs to go beyond a day. with the battery power determined by the loads you must now be cautious not to let the batteries go below 50% or risk depleting some of their lifespan so the batteries, once the loads are determined, should be doubled from there. solar guppy has stated a very minimal start point of 100a for the battery bank and that is used for selling to the grid without much need for backup and 6kw would certainly not be handled by a battery bank that low in capacity.

    as a rough guess take your total wh/day used by your household loads that the xantrex inverter would cover and multiply that by 2 and divide that by the nominal battery voltage (48v) to arrive at a good rough estimate for the battery bank capacity. sometimes this needs readjusted for high surges or longer time periods needing to be covered. the 6kw capacity of the inverter is not to be viewed as a consistent power draw even though it can handle it, but more as a maximum for odd times that that much could operate at one time and is not the norm. drawing 6kw consistently over 24hrs would be a very high draw of power as we are talking 144kwh per day!!!

    This project started life as a grid tied micro system to maximize production. The 10.78kW size was chosen as that uses almost all of my south facing roof, saving a section for solar HW. I'll use the term UPS, came into play because my wife asked if we could keep the panels on during the day. So I'm not really looking for a battery backup system as such, more something to make the panels work during the day if the power goes out.

    I saw the XW6048 mentioned on the forums (I've been reading for while) and it seems like a prefect fit for keeping the panels on. Should I consider a smaller inverter?

    So what am I trying to do? I want to install the 10.78kW micro inverter system such that I can expand it later with a UPS to keep the lights on during the day and maybe later add batteries for complete backup. The primary goal is maximizing daytime harvest. Secondary goal is to install the system to make it easy to expand in the future.

    I have another idea that involves an electric car...
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: 10.78kW Enphase system and XW6048

    Okay, first flaw:
    maybe later add batteries for complete backup.

    XW6048 doesn't run without batteries.

    Second flaw: the Enphase units want to put out all the power they can harvest from the panels. If there aren't sufficient loads, where does it go? Unlike back-feeding the grid, a battery-based inverter such as the XW doesn't have an endless capacity for swallowing surplus Watts. Not sure about the XW specifically, but off-grid inverters will take back-feed - and charge the batteries with them. To a point. When that point is reached and the loads are satisfied ... you've got 10 kW that wants to go somewhere. Juggling that against the actual power needs and trying to keep your Enphase units running could become quite a circus.

    Third flaw: I'm pretty sure this would not come under the definition of prescribed use of either the Enphase of Xantrex equipment. Instant warranty void.

    If you had a central GT inverter with high Voltage array you could make use of one of the new (and expensive) Xantrex high Voltage charge controllers to maintain some back-up battery for an XW from the same GT array. Of course the XW can back-feed the grid itself too.

    Or you can do a lot of extra wiring and make it possible to switch your panels from feeding the Enphase units individually to feeding a charge controller (or two or three) collectively to keep up some back-up batteries.

    On the whole, and just my opinion, seems like a lot of hassle and expense any way you slice it for very little gain. Cheaper to buy a back-up gen for when the power goes down. Works in all weather too.
  • RK_Solar_HopefulRK_Solar_Hopeful Solar Expert Posts: 69 ✭✭✭✭
    Re: 10.78kW Enphase system and XW6048
    Okay, first flaw: XW6048 doesn't run without batteries.

    Second flaw: the Enphase units want to put out all the power they can harvest from the panels. If there aren't sufficient loads, where does it go? Unlike back-feeding the grid, a battery-based inverter such as the XW doesn't have an endless capacity for swallowing surplus Watts. Not sure about the XW specifically, but off-grid inverters will take back-feed - and charge the batteries with them. To a point. When that point is reached and the loads are satisfied ... you've got 10 kW that wants to go somewhere. Juggling that against the actual power needs and trying to keep your Enphase units running could become quite a circus.

    Third flaw: I'm pretty sure this would not come under the definition of prescribed use of either the Enphase of Xantrex equipment. Instant warranty void.

    If you had a central GT inverter with high Voltage array you could make use of one of the new (and expensive) Xantrex high Voltage charge controllers to maintain some back-up battery for an XW from the same GT array. Of course the XW can back-feed the grid itself too.

    Or you can do a lot of extra wiring and make it possible to switch your panels from feeding the Enphase units individually to feeding a charge controller (or two or three) collectively to keep up some back-up batteries.

    On the whole, and just my opinion, seems like a lot of hassle and expense any way you slice it for very little gain. Cheaper to buy a back-up gen for when the power goes down. Works in all weather too.

    Flaw 1: Please remember how the project got started. I was thinking of using something like 2 - 120VAC, stacked for 240VAC, computer UPS units (with small batteries) to give the Enphase units something to sync with. I am trying to get an effective, low cost method of "turning on" the GT inverters in the event of a daytime power outage. The XW6048 seems like it would fit very well, especially since when AC-coupled it doesn't have do anything with the AC, it just passes it through a relay. I was planning to use a small battery setup, but it would need to be big enough to be effective.

    Flaw 2: The reading I've done indicates using AC-coupled GT inverters, string or micro, will work. The trouble is they seem to ALL turn on or off at the same time. So an inverter with batteries would be necessary during the 5 minute anti-islanding safety time out. Maybe if I bring the AC strings individually to the panel and give each it's own breaker... Requires more thought.

    Flaw 3: This is the real reason for making the system easy to expand after initial installation. Most electronic components fail either: less than 1 year or very late in life cycle. I am willing to "risk it" AFTER a year or two of proven GT service. Xantrex specifically supports AC-coupling, please check the pdf attached to message #3, ac-coupling-app-note(976-0240-01-01_rev-a).pdf.

    I am considering something like the Xantrex XW - solar charge controller XWMPPT80-600 for a central inverter. I have a 360VDC, 24kW/hr battery being delivered in 2 weeks. Does anyone know if the XWMPPT80-600 has integral current limiting for use on a battery? It would be an explosively energetic event if not. On paper it looks like a good fit.

    The extra wiring idea to another charge controller is something I'll need to think about. It would work...

    Most likely I would buy the bigger batteries prior to pursuing the engine generator route.
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: 10.78kW Enphase system and XW6048

    SunnyIsland might be a better choice. Expensive, though.

    I'd rather got the impression the high Voltage Xantrex controller took a 600 Volt input for output to standard battery bank Voltage (i.e. 48 VDC), not 360 VDC.

    But what do I know? I'm just a half-wit. :roll:
  • RK_Solar_HopefulRK_Solar_Hopeful Solar Expert Posts: 69 ✭✭✭✭
    Re: 10.78kW Enphase system and XW6048

    I looked at the Sunny Island, briefly. The XW6048 seems almost perfect in comparison:
    XW6048
    +120/240 Split phase
    +6kW & 12kW for 15sec
    +28W idle
    -FS -.4Hz/s
    +$3300
    +built-in xfer relay

    Sunny Island
    -Buy 2 to get 240VAC
    -5kW & 12kW for 3sec
    -2 x 25W = 50W idle!
    +FS appears to be user adjustable!!
    -2 x $3,974.11 = $7,948.22
    -have to add external xfer relay

    Except for the fixed Frequency Shift, the XW6048 is the clear winner.

    What do the 2 Sunny Islands need for minimum effective battery size? Can I make up the difference in cost do to smaller battery capacity?

    It is very possible I read the XWMPPT80-600 data sheet wrong. I attached the pdf for you to check. My wife has accused me of reading things the way I want them to read several (ok many) times.

    I sincerely doubt anyone who is a moderator is anything less than full of wittiness!
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: 10.78kW Enphase system and XW6048

    The two forum members who know the XW system best would be Solar Guppy and XWguy (who works for Schneider-Xantrex).

    The SunnyIsland has a minimum 100 Amp hour battery - up to 10,000! In my opinion it's better able to handle the back-feed from GTI's. The downside vs. the Xantrex is less power ... and the price always makes me cringe.
  • RK_Solar_HopefulRK_Solar_Hopeful Solar Expert Posts: 69 ✭✭✭✭
    Re: 10.78kW Enphase system and XW6048

    I posted something on the Solar Guppy website. I'll look up XWguy and send him a message.

    Is the SI 100 amp/hr requirement the same as the XW6048, 100amp/hr per kW, 500amp/hr x 48VDC? Or can I get by with a smaller battery 100amp/hr x 48VDC?
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: 10.78kW Enphase system and XW6048

    I'm pretty sure the XW's requirement of 100 Amp hours per kW is for when it's used as a GT inverter, not for when it's strictly off-grid. The SunnyIsland doesn't indicate any such need; just 100 to 10,000 Amp hours.

    10,000 Amp hours @ 48 Volts: 240,000 Watt hours! ;)
  • Solar GuppySolar Guppy Solar Expert Posts: 1,973 ✭✭✭
    Re: 10.78kW Enphase system and XW6048

    the 100ah per kw is my rule of thumb, and its significantly LOWER than what would be required to have the inverter run as an off grid unit.

    Do the math, the XW-6048 is 6kw inverter, at its rated load would be pulling close to 150 amps from a battery bank. At C20 draw it would require a 3000 ah battery bank, selling the same 6kw to the grid, same AC ripple with a 600ah bank is a 5X increase on the battery's compared to what a properly sized off grid system would have.

    The 100ah/kw is the minimum needed to get the battery's from being physically torn apart or burned up from the AC current ripple. This is a BATTERY issue, it has nothing to do with what manufacture of inverter you select.
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: 10.78kW Enphase system and XW6048

    Thanks for that, SG!

    I'm the first to admit I'm out of my element with the grid-tie stuff; just trying to help where I can.
    We tend to approach off-grid systems from quite a different direction, so all the battery bank/inverter size relationships tend to take care of themselves, as it were.

    So how viable is this idea of back-feeding or "boosting" the XW with 10 kW of Enphase units?
  • RCinFLARCinFLA Solar Expert Posts: 1,397 ✭✭✭✭
    Re: 10.78kW Enphase system and XW6048
    I sent out some emails. Hopefully someone will be able to point me in the right direction.

    While I'm waiting please double check some math for me.

    The forums suggest 100 amp/hr for each kW of inverter capacity.
    -XW6048 is 6kW at 48VDC
    -So I should have 6x100 amp/hr at 48VDC=28800W/hrs of capacity
    -About $10K worth of batteries, equipment & delivery

    1. Am I doing my math correctly? That seems like a very large battery setup.
    2. Is a battery system this size needed for an AC-coupled system?
    3. Should I abandon all hope of trying to make the idea work?

    This applies to a PV charge controller fed to battery line. Feeding PV DC power through charge controller to battery line puts large ripple current on battery as the inverter is pushing a single phase AC output which has a sine squared power profile (120 Hz power pulses).

    For a GT inverter AC coupled, the battery capacity only applies to absorbing maximum back feed power from GT inverter. Worse case would be no grid present, no output AC loads, and maximum PV generation. In this case all the PV power would be pushed to batteries.

    XW will take whatever you backfeed it up to point where XW inverter power capability is exceeded. At this point inverter will shutdown with overload condition, causing everything to shutdown. There is no charge current regulation as with grid powered charging and your batteries must be large enough to take the XW inverter maximum of about 100 amps of DC charging current if the ACout coupled PV power is pushing 6kW's back to inverter. This assumes battery voltage has not reached regulation voltage (absorb level) which will cause the inverter to do a frequency shift to shed GT inverters.

    XW has no way to regulate GT inverter's power output other then to shut them down via a frequency shift that takes GT inverter out of GT frequency spec limits. The SMA products have a coordinated feedback control between Sunnyboy's GT inverter and Sunny Island inverter via a gradual adjustment of Sunny Island inverter frequency output that tells the Sunnyboy GT inverter to gradually backdown on its power output when there is nowhere for the excess PV power to go.
  • ggunnggunn Solar Expert Posts: 1,973 ✭✭✭
    Re: 10.78kW Enphase system and XW6048

    This looks to me like yet another try at finding a way to keep a grid tied PV system genning when the grid goes down without spending money on batteries. It's not just UL1741 anti-islanding that is the problem, it's the fact that solar power goes up and down continuously as clouds pass by, as the sun travels its arc, etc., and it's problematic to power loads with it whose demand patterns do not track the supply pattern. You have to have enough battery capacity to supply a constant power source to your loads, and there is no way around it. When you are operating off grid, you are always running off the batteries and the only function of the PV is to charge the batteries.
  • Dr. StrangeloveDr. Strangelove Solar Expert Posts: 49
    Re: 10.78kW Enphase system and XW6048
    ggunn wrote: »
    This looks to me like yet another try at finding a way to keep a grid tied PV system genning when the grid goes down without spending money on batteries. It's not just UL1741 anti-islanding that is the problem, it's the fact that solar power goes up and down continuously as clouds pass by, as the sun travels its arc, etc., and it's problematic to power loads with it whose demand patterns do not track the supply pattern. You have to have enough battery capacity to supply a constant power source to your loads, and there is no way around it. When you are operating off grid, you are always running off the batteries and the only function of the PV is to charge the batteries.

    I'd say it's not just about batteries, though at 10kW that's about 200A at 50 - 55V for a 2000AH battery at C/10 and 4000AH at C/20, which is a boat load of battery. It's also about the system efficiency of PV to MPPT to DC battery to inverter to AC - about 88% by my calculation.

    I'm considering a system with two 3 - 4kW GT inverters and one MPPT80-600 and XW6048 or XW4048 (and 600 - 800AH of battery). When the grid goes down, and it does here, I don't see what laws of nature require that 6 - 8kW of GT inverter capacity to be thrown away. During the productive daylight hours, the GT inverters should be able to supply the mini-grid while the battery of the hybrid inverter charges or idles at float. There is no compelling reason for the Xantrex limitation of binary states for the hybrid inverter of charge or discharge, and GT inverter full on or shut off, other than internal design or firmware limitations.

    The Schneider schematics of the AC coupled system using a transfer relay to bring the GT inverter inside the mini-grid were inspiring. The SMA schematics of the full time AC coupled design were similarly inspiring. Unfortunately, neither has a complete grid tied AC coupled mini-grid solution. For the OP's Enphase question: if the Enphase micro-inverters truly manage to implement frequency shift power control, then an SMA Sunny Island or two is probably your best bet. Unfortunately, it looks like they are limited to 56A AC pass through (6.7 kW each, 13.4 kW per pair).

    Can anyone confirm that the Xantrex hybrids' internal 60 A transfer relay is 60 A per pole, hence 60 A at 240V, hence 14kW?
  • BB.BB. Super Moderators, Administrators Posts: 32,007 admin
    Re: 10.78kW Enphase system and XW6048

    I believe you are correct about the 60 amperes per pole... The inverter is rated at 12 kW surge--so that would make sense.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • RK_Solar_HopefulRK_Solar_Hopeful Solar Expert Posts: 69 ✭✭✭✭
    Re: 10.78kW Enphase system and XW6048

    I think the light bulb over my head finally flickered on!!

    Does grid tied AC-coupling work? Yes, with some limitations.
    1. The PV panel size has to be within the load capacity of the XW or SI.
    2. Using current technology the micro grid will most likely cycle all inverts on/off at the same time.
    3. Using current technology a relatively large battery pack is still needed for battery longevity.

    SI may work to sequentially cycle off/on the micro inverters but testing is required. Has anyone used a Sunny Island AC-coupled and observed the frequency shift in action?

    I attached a jpg of what I wanted to do with the XW6048, XW MPPT and the 360VDC battery. One of my Engineers called it "mission creep". I guess it is... I'll start with the straight GT micro inverters and continue from there.
  • BB.BB. Super Moderators, Administrators Posts: 32,007 admin
    Re: 10.78kW Enphase system and XW6048

    Yep--pretty much it...

    Question about the battery charger/car connection. You want to charge from your car battery bank using a high voltage DC charge controller?

    Otherwise, just move the solar array to the DC charge controller and skip the whole enphase issue... The XW Hybrid inverter will do GT just fine.

    The DC Battery Charge Controller is available in several voltages. Solar array/alternate DC power sources 150 VDC max (typically ~100 Vmp volts max--Midnite Solar "Classic" is available in a bit higher PV voltages) or up to 600 VDC max (Schneider/Xantrex new, very expensive, charge controller).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • RK_Solar_HopefulRK_Solar_Hopeful Solar Expert Posts: 69 ✭✭✭✭
    Re: 10.78kW Enphase system and XW6048
    BB. wrote: »

    Question about the battery charger/car connection. You want to charge from your car battery bank using a high voltage DC charge controller?

    Actually I am looking at how to get the 360VDC from the car to supply the high voltage DC charge controller. The Leaf has it's own 240VAC charger to "fill it up". I am still trying to get around the requirement to have big capacity lead acid batteries. More thought may be needed in this area as well. SLA don't like multiple little cycles all the time, Li-ion batteries do fine with little cycles and don't like deep discharges. Maybe some combination of the 2 types would yield the best performance for dollar. Then come the charge balancing & load balancing headaches...

    This is a good forum. It has a large number of people who have knowledge and experience in what they are talking about.
  • BB.BB. Super Moderators, Administrators Posts: 32,007 admin
    Re: 10.78kW Enphase system and XW6048

    Look and see what you can pull out at 12 or 24 volts--If you assume 20% discharge out of a 24kWH battery bank--that is only 4.8 kWH of power... A 1kW DC to DC (or DC to AC) converter will draw that down in less than 5 hours (power loads, recharge 48 volt battery bank, etc.).

    The Prius (as I understand) will use the traction pack to keep the 12 volt Acc Battery "charged" quite nicely (until traction pack limits kick in).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • jaggedbenjaggedben Solar Expert Posts: 230 ✭✭
    Re: 10.78kW Enphase system and XW6048

    Jumping in a little late here...

    There was a thread on the Enphase forum about this kind of thing. I think Enphase removed it from the viewing public.

    I think you get by now that you need batteries...

    It comes down to whether or not you can program the XW or Sunny Islands to control the Enphases just right in a way that won't blow anything up. There would be two modes in a grid-down situation:

    1) Loads (including battery charging) exceed capacity of Enphases, frequency shifts to in range, Enphases turn on.

    2) Loads (including battery charging) don't exceed capacity of Enphases, frequency shifts out of range, Enphases turn off.

    The XW or SI needs to be able to know, to safe tolerances, whether the current state of things demands (1) or (2) and shift frequency accordingly. Also, there would probably be periods with a lot of switching back and forth, possibly causing problems.

    If you think you can actually do it, I would try with a single Enphase inverter first.

    My understanding is that in the SMA system the SI uses frequency to actually tell the Sunny Boy(s) to vary the power produced to match the loads (including battery charging). That won't work with the Enphases because unlike the Sunny Boy they just aren't programmed to do it. They'd all either be all on if frequency is in range or all off it it isn't.
  • jeffkrusejeffkruse Solar Expert Posts: 205 ✭✭✭
    Re: 10.78kW Enphase system and XW6048
    I think the light bulb over my head finally flickered on!!

    Does grid tied AC-coupling work? Yes, with some limitations.
    1. The PV panel size has to be within the load capacity of the XW or SI.
    2. Using current technology the micro grid will most likely cycle all inverts on/off at the same time.
    3. Using current technology a relatively large battery pack is still needed for battery longevity.

    SI may work to sequentially cycle off/on the micro inverters but testing is required. Has anyone used a Sunny Island AC-coupled and observed the frequency shift in action?

    I attached a jpg of what I wanted to do with the XW6048, XW MPPT and the 360VDC battery. One of my Engineers called it "mission creep". I guess it is... I'll start with the straight GT micro inverters and continue from there.


    Maybe I don't understand what you are trying to do. I don't think you can put AC in to the AC out of the Xantrex. I dont think it works that way. They specifically say not to connect the grid to AC out. :confused:
  • RK_Solar_HopefulRK_Solar_Hopeful Solar Expert Posts: 69 ✭✭✭✭
    Re: 10.78kW Enphase system and XW6048

    From XWguy:

    "I read some of the posts on that thread. I have a couple comments.

    1) The HV-MPPT is for 24 or 48V battery systems. It sounds like you want to hook the PV input port on it up to a 360V battery bank. We do not support that configuration. It is meant for a current limited input source with max Isc of below 35A.
    2) You can't use 10+kw of enphase with a single 6kW XW inv/chg and expect it to back feed the batteries properly.
    3) The AC coupling was only tested with our GT inverters
    4) I'm not sure, but I believe that the enphase inverters do not support being run on a off grid or back up power system. I believe it voids the warranty, but you should check that.
    5) The frequency shift of -0.4hz is not configurable.

    For this type of system, we typically recommend our standard system which is an XW inv/chg paired with one of our MPPT charge controllers. You sacrifice some system efficiency over an AC coupled system, but it is well understood in industry and has many years of proven performance. The system you are proposing sounds like a time consuming effort that could require lots of debugging and potentially not be supported by the various equipment manufacturers.."


    #1 kills the idea of using any battery to feed the hig voltage XW MPPT. Bummer, need a method for current limiting a battery.
    #2 When the light bulb came on I finally accepted the idea that AC-coupling doesn't let me side step the component electrical limits.
    #3 OK. Still hoping to hear from some other adventurous person. Anyone know where I can find a used XW6048 in good condition? I'll try it out and give it back. Of course it is possible I'll cause the magic smoke to come out of it, in that case it probably won't work anymore. I probably shouldn't say that even in jest. I'll be clear, feeding too much power through electrical components WILL cause failure, usually accompanied by noise & smoke.
    #4 The Enphase forum was clear on this, the warranty is voided if you AC-couple the inverter.
    #5 Confirms the XW6048 will cycle all inverters off/on at the same time. The Sunny Island appears to have an adjustable frequency shift. Time to dig into the SI.
  • RK_Solar_HopefulRK_Solar_Hopeful Solar Expert Posts: 69 ✭✭✭✭
    Re: 10.78kW Enphase system and XW6048
    jaggedben wrote: »
    There was a thread on the Enphase forum about this kind of thing. I think Enphase removed it from the viewing public.
    I found the thread you're talking about with a google search. Enphase "archived" the June 2011 thread because AC-coupling is "not supported".
    jaggedben wrote: »
    ... Also, there would probably be periods with a lot of switching back and forth, possibly causing problems.
    Very true. This is the standard AC-coupled micro grid behavior. I'm trying to find an inverter (Sunny Island?) that will allow linearly raising frequency with excess AC-coupled power (load is too small). The idea being that even though the inverters are all set the same, tolerances will cause sequential inverters to go off-line and come back on-line.
    jaggedben wrote: »
    If you think you can actually do it, I would try with a single Enphase inverter first.
    That is a good idea.
  • RK_Solar_HopefulRK_Solar_Hopeful Solar Expert Posts: 69 ✭✭✭✭
    Re: 10.78kW Enphase system and XW6048
    jeffkruse wrote: »
    Maybe I don't understand what you are trying to do. I don't think you can put AC in to the AC out of the Xantrex. I dont think it works that way. They specifically say not to connect the grid to AC out. :confused:

    Please read: http://forum.solar-electric.com/attachment.php?attachmentid=1971&d=1310868880 that is attached to message #3.
  • stephendvstephendv Solar Expert Posts: 1,571 ✭✭
    Re: 10.78kW Enphase system and XW6048
    I'm trying to find an inverter (Sunny Island?) that will allow linearly raising frequency with excess AC-coupled power (load is too small). The idea being that even though the inverters are all set the same, tolerances will cause sequential inverters to go off-line and come back on-line.

    Are you sure about the differences in those tolerances? Isn't it possible to reconfigure the frequency on the enphase units? Maybe it's too late to be asking whether the grid tied's absolutely have to be enphase inverters... The only other micros I know of are:
    http://www.enecsys.com/products/overview.php
    and
    http://www.stecasolar.com/index.php?StecaGrid_300_500_Control_en (although not strictly speaking a micro, it is small :D )

    No idea whether either of these will let you reconfigure the frequency. ...or just use 3 x 3300 Sunnyboy inverters, which will give you 3 different mppt trackers to also help avoid shading problems.
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