Xantrex 6048: semi grid-tie question

Dusty
Dusty Solar Expert Posts: 271 ✭✭✭
I just ordered a Xantrex 6048 (hasn't arrived yet) from this forum's sponsor, and I have a question about its configuration which I can't seem to find an answer in the downloaded installation or operations manual.

I do not intend to sell power back to the utility in the near future, but I do intend to connect my main power panel to the inverter's grid input connection via a Midnight Solar XW E-panel.

I currently have 6 Grape Solar 185-watt panels wired into 3 parallel pairs. Once the 6048 is wired up, they will feed a Xantrex MPPT-60 controller into two (later 3) parallel banks of 4, 12V 55AH AGM batteries.

I know that I don't have much battery capacity. I plan to add a third bank of batteries, but due to weight/storage restrictions, I need to keep the batteries small enough to move without the need for mechanical assistance.

The connection from my main panel to the inverter's grid input will be via a 240v, 60-amp breaker through 6/3 AWG cable.

Hopefully, that's enough background. My question is;

Is there a way to configure the Xantrex 6048 to run off stored battery power during the night until a preset DOD (say, 40%) is reached, and then the inverter switches automatically to grid power to run the house circuits BUT STILL allows the MPPT-60 to charge the batteries the next day? I'd like to rely on the PV array to recharge the batteries but not discharge the batteries any lower than a preset (safe) amount during the night.

I hope what I'm trying to do makes sense. Since I will not be able to sell back excess power to the utility, I'd like to minimize as much as possible what I take from the grid. With my current configuration, I am able to run my refrigerator during the day off a smaller inverter, and when I get home from work, the batteries are fully charged. When the sun goes down, I run my laptop and various lighting, but at night I have to plug the refrigerator back into a wall outlet so I don't risk over-discharging the batteries. The next morning, I plug the refrigerator back in to the inverter (the only load during the day), and when I get home, the batteries are recharged--even with the refrigerator load on the inverter.

If I knew that the 6048 could be configured to switch to utility power during the night when the battery bank reaches 60% state of charge, I could leave the refrigerator plugged in all night and let the solar panels recharge the batteries during the day. I just don't want the grid to recharge the batteries, since that will waste the excess output of the solar panels during the day.
XW6048, 3.4KW PV, Grid-Tied, always tweaking.

Comments

  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: Xantrex 6048: semi grid-tie question

    I have a battery question... In general, we have recommended here basically 100 AH of 48 volt battery bank per 1kW of inverter/solar panel capacity. At 110 to 165 AH battery bank--That really limits you to 1.65 kW of "useful" solar/inverter loading (~3.3kW of surge load). Will that be OK with you?

    The problems can include batteries going outside of ~42-72 volt battery bus voltage range (inverter/charge controller faults--not damage but error codes and possible reset required) and (possible) damage to battery bank if power limits are exceeded (AGM's are very good at sourcing current--so they probably will not be damaged by inverter surge current).

    What is your reason for running from batteries at night? In general, if you have grid power, your utility costs will be less than replacing a battery bank.

    Does your locality support net metered (Grid Tied) power?

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: Xantrex 6048: semi grid-tie question

    I think you're going to be disappointed with that set-up, particularly the battery bank (especially if you add a third parallel string).

    What Bill was referring to is the need for the Xantrex to have a minimum 100 Amp hours per kW inverter capacity to deal with the AC ripple. As it is you won't be able to backfeed the grid because the thing will just keep generating errors and cutting in and out (crude way of explaining it).

    Your 110 Amp hour battery bank is going to provide about 2.4 kW hours AC @ 50% DOD. That should run a refrigerator for two days without charging. So I wouldn't worry about the bank dropping to 60% overnight and needing the grid to recharge it if all your running is the 'frige. You should be able to program the XW to a low Voltage shutdown that is roughly 60% SOC if you want to. One of the XW guys would know for sure. But I don't see the point in doing so.

    Your panels at six time 185 Watts is 1110 Watts, which should support 178 Amp hours @ 48 Volts. Plenty for recharging that battery bank but not enough to make good use of the XW's 6 kW capacity in a sell-back situation.

    If you can't expand both the array and the battery bank then in my opinion you've spent a lot of money on what is too large an inverter for your use.

    Why you are doing this is a whole 'nother question, as the utility power is almost certainly far cheaper than the solar.

    P.S.: If this were an Outback you could program the LVD to something ridiculously high that represents the approximate 60% SOC (like 48.8 Volts) and set the AC charge current to zero. Then you'd use the auto gen start to throw a relay to connect the AC. It would take over the loads and the charge setting would prevent it being used for recharging the batteries. Perhaps the Xantrex has similar ability (maybe better, as they have more complex AC handling). But again I don't see the point in doing this.
  • ggunn
    ggunn Solar Expert Posts: 1,973 ✭✭✭
    Re: Xantrex 6048: semi grid-tie question
    Dusty wrote: »
    I just ordered a Xantrex 6048 (hasn't arrived yet) from this forum's sponsor, and I have a question about its configuration which I can't seem to find an answer in the downloaded installation or operations manual...
    I think I understand what you are going for, but it seems to me that unless the production from your PV system is significantly more than your usage on a typical day, all you will be doing is exercising your batteries unnecessarily and wearing them out sooner.
  • Dusty
    Dusty Solar Expert Posts: 271 ✭✭✭
    Re: Xantrex 6048: semi grid-tie question
    BB. wrote: »
    I have a battery question... In general, we have recommended here basically 100 AH of 48 volt battery bank per 1kW of inverter/solar panel capacity. At 110 to 165 AH battery bank--That really limits you to 1.65 kW of "useful" solar/inverter loading (~3.3kW of surge load). Will that be OK with you?

    The problems can include batteries going outside of ~42-72 volt battery bus voltage range (inverter/charge controller faults--not damage but error codes and possible reset required) and (possible) damage to battery bank if power limits are exceeded (AGM's are very good at sourcing current--so they probably will not be damaged by inverter surge current).

    What is your reason for running from batteries at night? In general, if you have grid power, your utility costs will be less than replacing a battery bank.

    Does your locality support net metered (Grid Tied) power?

    -Bill

    My local utility does support net metering, and I will upgrade to that capability in the future. I only have about 1/2 acre and wish to keep the PV array off my roof, so I currently have a ground mount and intend to install a pole mount to eventually have 8-10 185watt panels.

    I started this project out of curiosity, and as I learn, the system capability expands. I knew that I didn't want to keep upgrading my inverter and controller hardware, so a good inverter and controller right off the bat made sense.

    If I understand your question of "3.3kw loading," I am okay with that for now. Your question about running the batteries at night caught me off guard--as well as the comment about utility power being cheaper than replacing battery banks. Newbie here! :o) Because I started this out as a fun project with no need to live "off grid," it's become a mission to see just how low I can get my monthly electric bill. Through all the great tips on the sponsor's website, I've reduced my electrical demand by almost 50%, but I'm still averaging about 20kwh per day. I had hoped that by running as many loads as possible through the PV during the day and battery at night, I'd be able to cut my utility cost even further. It's true that for now the cost of battery replacement will exceed the utility savings realized. It was my understanding (probably incorrectly) that once the batteries were purchased, they'd last about the same length of time kept constantly topped off or cycled to around 40% DOD. So to me it made sense to use them at night until they reached 40% DOD before taking power from the utility again and allow the PV arrays to top the batteries off again the next day.

    I just didn't want to have to disconnect loads from the inverter each evening when the sun went down--leaving the batteries topped off overnight. But your point is well taken....once I have more of my house circuits tied to the inverter, I won't have to worry about wasted harvest during the day. Currently I'm only using a small inverter in one room of the house since it's not tied in to my main panel yet, so it's frustrating to come home after work and see that I'm not harvesting the maximum power possible from the PVs.
    XW6048, 3.4KW PV, Grid-Tied, always tweaking.
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: Xantrex 6048: semi grid-tie question

    What is the cycle life of your batteries to 40% DOD? ... for example, here is a charge for a "generic flooded cell battery:

    Deep Cycle Battery FAQ

    cyclelife2.gif

    So--In this case, an 60% deep cycle will give about 800 cycles... OR:

    800 cycles / 365 days per year = 2.2 year life

    I am not sure--But I think that AGM's may have a shorter cycle life than a flooded cell deep cycle battery (especially forklift/traction motor types which can have upwards of 20 year life--with the downsides of adding water, clean up, less efficient than AGM, etc.).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • Dusty
    Dusty Solar Expert Posts: 271 ✭✭✭
    Re: Xantrex 6048: semi grid-tie question

    Oh, I misunderstood Bill. I thought he meant that I needed that much PV output to support the battery bank, not that I needed that much to support the output of the inverter. Now I understand! At this time I do not intend to sell back to the grid, because I am not making enough excess to make it worthwhile. I'll never have a net-zero house. I just thought that as long as I can take some circuits off the grid (and balance that load to my daily possible harvest), I could reduce my daily utility consumption.

    However, the whole reason I'm doing this is just to enjoy learning how to do it.

    Thanks for the information on setting up the Outback. Perhaps I can set something up like that on the Xantrex. I read that a shunt is included in the Midnight Solar E-panel, but I had already set up a shunt for a Xantrex battery gauge to closer monitor the baterry bank's health.
    I think you're going to be disappointed with that set-up, particularly the battery bank (especially if you add a third parallel string).

    What Bill was referring to is the need for the Xantrex to have a minimum 100 Amp hours per kW inverter capacity to deal with the AC ripple. As it is you won't be able to backfeed the grid because the thing will just keep generating errors and cutting in and out (crude way of explaining it).

    Your 110 Amp hour battery bank is going to provide about 2.4 kW hours AC @ 50% DOD. That should run a refrigerator for two days without charging. So I wouldn't worry about the bank dropping to 60% overnight and needing the grid to recharge it if all your running is the 'frige. You should be able to program the XW to a low Voltage shutdown that is roughly 60% SOC if you want to. One of the XW guys would know for sure. But I don't see the point in doing so.

    Your panels at six time 185 Watts is 1110 Watts, which should support 178 Amp hours @ 48 Volts. Plenty for recharging that battery bank but not enough to make good use of the XW's 6 kW capacity in a sell-back situation.

    If you can't expand both the array and the battery bank then in my opinion you've spent a lot of money on what is too large an inverter for your use.

    Why you are doing this is a whole 'nother question, as the utility power is almost certainly far cheaper than the solar.

    P.S.: If this were an Outback you could program the LVD to something ridiculously high that represents the approximate 60% SOC (like 48.8 Volts) and set the AC charge current to zero. Then you'd use the auto gen start to throw a relay to connect the AC. It would take over the loads and the charge setting would prevent it being used for recharging the batteries. Perhaps the Xantrex has similar ability (maybe better, as they have more complex AC handling). But again I don't see the point in doing this.
    XW6048, 3.4KW PV, Grid-Tied, always tweaking.
  • Dusty
    Dusty Solar Expert Posts: 271 ✭✭✭
    Re: Xantrex 6048: semi grid-tie question

    Wow. I could have sworn I read in one of the Home Power magazines that it's not good for the batteries to discharge to only 10% DOD. But this charge doesn't reflect that at all. Thanks for sharing!
    BB. wrote: »
    What is the cycle life of your batteries to 40% DOD? ... for example, here is a charge for a "generic flooded cell battery:

    Deep Cycle Battery FAQ

    cyclelife2.gif

    So--In this case, an 60% deep cycle will give about 800 cycles... OR:

    800 cycles / 365 days per year = 2.2 year life

    I am not sure--But I think that AGM's may have a shorter cycle life than a flooded cell deep cycle battery (especially forklift/traction motor types which can have upwards of 20 year life--with the downsides of adding water, clean up, less efficient than AGM, etc.).

    -Bill
    XW6048, 3.4KW PV, Grid-Tied, always tweaking.
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: Xantrex 6048: semi grid-tie question

    No, you are correct... Lead Acid batteries do like to cycle. Keeping them in float (for emergency use) has its own issues too.

    More or less, if you cycle an average of 25% per day (and recharge the next day)--Is usually a good operating plan.

    If you were doing this for emergencies (or a weekend cabin), then cycling to 50% DOD/SOC is OK too... 50-100 cycles a year and a 1,000 cycle life--You are still looking at 10+ year cycle life--And for most batteries, they find other reasons to die long before that (it is usually a race between battery suicide vs being killed by owner's mistakes).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • Dusty
    Dusty Solar Expert Posts: 271 ✭✭✭
    Re: Xantrex 6048: semi grid-tie question

    Thank you for all that great information! Can you please explain why I would be even more disappointed with a third parallel string? Wouldn't that help the inverter support a higher output without the AC ripple?

    I can see changing out my AGMs next time with 6V higher AH cells (but I need to keep them AGM because they are indoors with limited ventilation in my garage), but if I increase the number of PV's past what I can install on a pole mount, I'll be forced to install them on my roof--something I really hesitate to do as I get older.

    Thanks again!
    I think you're going to be disappointed with that set-up, particularly the battery bank (especially if you add a third parallel string).

    What Bill was referring to is the need for the Xantrex to have a minimum 100 Amp hours per kW inverter capacity to deal with the AC ripple. As it is you won't be able to backfeed the grid because the thing will just keep generating errors and cutting in and out (crude way of explaining it).

    Your 110 Amp hour battery bank is going to provide about 2.4 kW hours AC @ 50% DOD. That should run a refrigerator for two days without charging. So I wouldn't worry about the bank dropping to 60% overnight and needing the grid to recharge it if all your running is the 'frige. You should be able to program the XW to a low Voltage shutdown that is roughly 60% SOC if you want to. One of the XW guys would know for sure. But I don't see the point in doing so.

    Your panels at six time 185 Watts is 1110 Watts, which should support 178 Amp hours @ 48 Volts. Plenty for recharging that battery bank but not enough to make good use of the XW's 6 kW capacity in a sell-back situation.

    If you can't expand both the array and the battery bank then in my opinion you've spent a lot of money on what is too large an inverter for your use.

    Why you are doing this is a whole 'nother question, as the utility power is almost certainly far cheaper than the solar.

    P.S.: If this were an Outback you could program the LVD to something ridiculously high that represents the approximate 60% SOC (like 48.8 Volts) and set the AC charge current to zero. Then you'd use the auto gen start to throw a relay to connect the AC. It would take over the loads and the charge setting would prevent it being used for recharging the batteries. Perhaps the Xantrex has similar ability (maybe better, as they have more complex AC handling). But again I don't see the point in doing this.
    XW6048, 3.4KW PV, Grid-Tied, always tweaking.
  • Dusty
    Dusty Solar Expert Posts: 271 ✭✭✭
    Re: Xantrex 6048: semi grid-tie question

    One thing I noticed....when I changed the stage 3 float on the Xantrex MMP-60 to stage 2 (I read somewhere that it was easier on the batteries..now I'm not so sure), I no longer was seeing the power out of the controller increase to match the load on the inverter/batteries. It was only when I went back to Stage 3 that the controller output matched the drain on the batteries.

    I've been very good so far about not dipping below 25% DOD, but that's because everything is shut down when I go to bed, and only the small refrigerator is left on the inventor (only on sunny days) when I head to work.

    I thought I read in the 6048 manual that they recommended at least 100AH of battery capacity for the unit, but I completely missed that it was 100AH per 1K of inverter output!!! Why not just say that the 6048 requires a minimum of 600AH battery capacity?! Man.
    BB. wrote: »
    No, you are correct... Lead Acid batteries do like to cycle. Keeping them in float (for emergency use) has its own issues too.

    More or less, if you cycle an average of 25% per day (and recharge the next day)--Is usually a good operating plan.

    If you were doing this for emergencies (or a weekend cabin), then cycling to 50% DOD/SOC is OK too... 50-100 cycles a year and a 1,000 cycle life--You are still looking at 10+ year cycle life--And for most batteries, they find other reasons to die long before that (it is usually a race between battery suicide vs being killed by owner's mistakes).

    -Bill
    XW6048, 3.4KW PV, Grid-Tied, always tweaking.
  • ggunn
    ggunn Solar Expert Posts: 1,973 ✭✭✭
    Re: Xantrex 6048: semi grid-tie question
    Dusty wrote: »
    Oh, I misunderstood Bill. I thought he meant that I needed that much PV output to support the battery bank, not that I needed that much to support the output of the inverter. Now I understand! At this time I do not intend to sell back to the grid, because I am not making enough excess to make it worthwhile. I'll never have a net-zero house. I just thought that as long as I can take some circuits off the grid (and balance that load to my daily possible harvest), I could reduce my daily utility consumption.
    I really don't get how running off your batteries at night is going to save you any net draw from the utility if your PV is not producing more than you are using during the day. The energy you use from the batteries at night is going to have to be replaced the next day, and it really doesn't make any difference where it comes from. Either it comes from the grid, or it comes from your PV array, in which case your consumption from the grid goes up by the same amount to compensate for it.

    Here's the way I see it: Draw a ring around your house with an arrow in on one side from the grid and an arrow in from the other side for your PV. If the input from the PV is never big enough to reverse the arrow from the grid, nothing you do inside the circle (where the batteries are) has any effect on the net consumption over time from the grid.
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: Xantrex 6048: semi grid-tie question

    The 100 AH per 1kW of load/charging source (48 volt battery bank) is a rule of thumb that we use here (this forum) based on experiences by some of the posters here (I am no expert-just relating what I have read and my, limited, knowledge).

    It turns out the 100 AH per 1kW of load/source also supports the C/8 (capacity/8 hours to 100% discharge) for maximum continuous loads (and max continuous charging current without thermal control measures), and C/2.5 for maximum surge loads (i.e., starting well pump, etc.)--For a "typical" Flooded Cell Deep Cycle Lead Acid battery bank.

    I have fallen back to using "Rules of Thumb" to size/diagnose systems to address the 90% of the "typical" issues that a "typical" install may run up against. It does save a lot of detailed explanations (and sometimes "hand waving") when we are talking with posters new to the forum. I found that "hitting" folks with all of the details up front tends to get people confused and frustrated. It is easier to get people to understand how their "system works" first--Then we can discuss their specific needs (i.e., water pumping during the daytime vs power to light the house and run the computer at night, etc.).

    Anyway, I am not an expert here (battery or otherwise)--Just trying to give you some information and set you off looking for detailed information specific to your needs (i.e., your AGM specifications vs the generic battery I typed about here).

    Your battery bank should be the first thing to study--It can easily be killed (in months/weeks/or even days) if not properly managed. So:

    Deep Cycle Battery FAQ
    www.batteryfaq.org
    Working Thread for Solar Beginner Post/FAQ (lots of links to FAQ's and DIY projects)

    Also, I would suggest having a cash cushion for your hardware too... More or less, you should plan on new inverter/new charge controller/other electronics after about 10+ years. Besides normal things (electrolytic capacitors drying out, solder break, etc.)--It is very difficult to find people/companies that will repair hardware after 5-10 years, and is difficult to find spare parts (I.C.'s, microprocessors, memory, proms, etc.) for "old" equipment.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: Xantrex 6048: semi grid-tie question

    You may well reduce your utility consumption. You may well reduce the size of your electric bill. But will you actually be saving money? No. That's the sad truth about solar; it's more expensive per kW hour (amortized over the life of the equipment) than grid power.
  • Dusty
    Dusty Solar Expert Posts: 271 ✭✭✭
    Re: Xantrex 6048: semi grid-tie question

    You are 100% correct. My system setup right now (before the 6048 is hooked up) doesn't allow me to harvest (use or store) everything that I can produce during the day. But if I use the batteries at night, then my usage during the day PLUS recharging the batteries does use the entire harvest--so there is a net drop in utility usage. I realize now that once I connect the 6048 to my electrical panel, I will be able to draw sufficient load to maximize the harvest during the day, and once that is accomplished, I will not need to use the batteries at night. So thanks to all of your help (and patience!), my original question becomes mostly irrelevant.

    The relevant part of my question that remains is: I also wanted to know if I could configure some type of fail-safe in the 6048 to ensure I do not drop the batteries below an acceptable level. And apparently I can by adjusting the low voltage cut-off setting. I would have preferred a setting that allows a specific AH usage to more accurately gauge DOD, but since the 6048 doesn't have a shunt built in, that option doesn't look possible. And the Xantrex Lite battery gauge that I currently have connected won't interface with the 6048 to expand that capability.

    I'm in the Navy and away from home fairly often. If I have several cloudy days, I won't be around to manually switch loads off the inverter, and I don't want the batteries to be too deeply discharged while I'm gone (like my current inverter does). I'd like to ensure that the system kicks over to grid long before that happens. In that situation, using the grid to recharge the batteries would be ok--since I am still maximizing the harvest during the day.

    Thank you, again, for lending me some of your experience! :o)
    ggunn wrote: »
    I really don't get how running off your batteries at night is going to save you any net draw from the utility if your PV is not producing more than you are using during the day. The energy you use from the batteries at night is going to have to be replaced the next day, and it really doesn't make any difference where it comes from. Either it comes from the grid, or it comes from your PV array, in which case your consumption from the grid goes up by the same amount to compensate for it.

    Here's the way I see it: Draw a ring around your house with an arrow in on one side from the grid and an arrow in from the other side for your PV. If the input from the PV is never big enough to reverse the arrow from the grid, nothing you do inside the circle (where the batteries are) has any effect on the net consumption over time from the grid.
    XW6048, 3.4KW PV, Grid-Tied, always tweaking.
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: Xantrex 6048: semi grid-tie question

    In general, it is not very accurate to use battery voltage as your cut-off point... You really want to use a Battery Monitor to estimate the state of charge by measuring the Amp*Hours into/out of the battery bank.

    Be that as it may--You could probably start with a battery cut-off voltage of ~46.0 volts as a start (aka 11.5 volts minimum voltage for a 12 volt bank).

    Others here have actual experience with XW (and other) battery based inverters--You hopefully will get better answers from them.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • Dusty
    Dusty Solar Expert Posts: 271 ✭✭✭
    Re: Xantrex 6048: semi grid-tie question

    Sadly, I realize that, but I've really had a lot of fun with this project. I knew I'd probably never reach "pay back." But a dip in my monthly electric bill is a small (albeit very small) shot in the arm for the $ invested. And I really do enjoy the challenge of figuring all this out!
    You may well reduce your utility consumption. You may well reduce the size of your electric bill. But will you actually be saving money? No. That's the sad truth about solar; it's more expensive per kW hour (amortized over the life of the equipment) than grid power.
    XW6048, 3.4KW PV, Grid-Tied, always tweaking.
  • Dusty
    Dusty Solar Expert Posts: 271 ✭✭✭
    Re: Xantrex 6048: semi grid-tie question

    Thanks Bill, I do use a Xantrex LinkLite battery monitor now, but that won't help me if I'm not home to read it. That's why I was hoping there was something more than just battery voltage set points that I could adjust on the 6048. Thanks again!
    BB. wrote: »
    In general, it is not very accurate to use battery voltage as your cut-off point... You really want to use a Battery Monitor to estimate the state of charge by measuring the Amp*Hours into/out of the battery bank.

    Be that as it may--You could probably start with a battery cut-off voltage of ~46.0 volts as a start (aka 11.5 volts minimum voltage for a 12 volt bank).

    Others here have actual experience with XW (and other) battery based inverters--You hopefully will get better answers from them.

    -Bill
    XW6048, 3.4KW PV, Grid-Tied, always tweaking.
  • jeffkruse
    jeffkruse Solar Expert Posts: 205 ✭✭✭
    Re: Xantrex 6048: semi grid-tie question

    Use the grid support feature and set your min voltage to 48.8 or something like that. Search my threads on this subject, much better than going by my memory now.
  • Dusty
    Dusty Solar Expert Posts: 271 ✭✭✭
    Re: Xantrex 6048: semi grid-tie question

    Will do. Thanks Jeff!
    jeffkruse wrote: »
    Use the grid support feature and set your min voltage to 48.8 or something like that. Search my threads on this subject, much better than going by my memory now.
    XW6048, 3.4KW PV, Grid-Tied, always tweaking.