Conext XW+ Grid Support Voltage Questions

ewb

In the XW+, the Grid Support and Grid Support Voltage (GSV) settings seem to serve several purposes. One of those is to enable the use of excess power from an external DC charger to help power locally connected loads on ACout or even to sell back to the grid (if enabled).

I am mostly interested in the situation where the charger is a Conext MPPT-80-600 or 60-150 and Enhanced Grid Support is enabled by setting GSV to a high value above the charge controllers equalization voltage (eg: 64 volts), and grid selling is disabled.

Question 1: Does this function work if the grid is down (eg: AC1 is not qualified)?

Question 2:  If so, does it also work if a generator is running and qualified on AC2 (possibly with generator support enabled)?

Question 3: In these cases does a charge controller (eg: MPPT-80-600) modulate the PV power to match demand changes on ACout since it cannot sell excess power? Is that mediated by the DC bus voltage or by Xanbus commands?

Question 4: If Grid support is not enabled, would an MPPT-80-600 likewise modulate the DC power to maintain the absorption voltage or the float voltage (eliminating excess power)?

I have not been able to find answers to these questions in the manuals or online.  My apologies if this has been addressed before. I do not own any Schneider equipment, but am considering installing an XW+ and an MPPT 80-600 and just want to understand how they work.

WaterWheel

First let me say that while I have a 6848 and 80-600 I do not sell to the grid or use a generator so my answers may not be the most knowledgeable but since you don't seem to have any other replies I'll take a run at this.      I do use the grid support feature to protect my batteries from overly draining.

First why do you want to set the Grid Support voltage above the controllers 64V?        Just disable grid selling, enable grid support, and set the grid support voltage somewhere around 48.5v to allow the grid to add some power only when your batteries get below the set voltage.
I set my grid support voltage at 49.0v and if my batteries drop below about 73% the grid automatically steps in and covers most of my loads protecting my batteries.

When using grid support the 6848 will always draw about 80 watts of energy from the grid.      It does this so it can sync it's AC cycle to the Grid AC which is required if the grid suddenly needs to supply a lot of power to your system.      So you're probably going to be buying about 25 cents worth of electricity per day on most days.       But that allows you to automatically use grid power when you have a few no sun days and the batteries get low.  
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1.      Assuming no AC2 input when the grid is down the inverter simply keeps drawing on the batteries until the battery voltage drops below the Low Battery Cut Out setting which I set at 47.3v (about 30% SOC).      When we lose the grid we usually don't notice unless I look at the meters.      It's a very smooth transition between battery and grid power. 

2.      If I understand your question correctly the answer is yes.

3 and 4.     Your charge controller is always adjusting it's output voltage/amperage in conjunction with the DC voltage and where it is in the charge cycle.       When the panels are making more power than the charge controller needs the controller doesn't accept the extra power and the panels burn off the extra power as heat.       

ewb

WaterWheel, thank you very much for the response. Since I don't actually have one of these units, it is great to hear about actual experience and compare it with what I have learned by reading manuals and other online postings.

To answer your question, the owner's manual, and some other app. notes from Schneider explain that setting the GSV above the equalization voltage of a Xanbus connected Conext charge controller (such as the 80-600) enables a featured called Enhanced Grid Support in which the XW+ (with recent firmware at least) will "track" the charging cycle of the CC, using Xanbus communications, and after bulk is complete (eg: during absorption and float) will pull excess PV power off the DC bus to power loads, or to sell (if that is enabled). The advantage (per the manual) seems to be that the batteries will actually reach the full absorb voltage which they apparently will not using the non-Enhanced Grid Support mode that would be necessary with any non-Conext charge controller or other DC source. I just interpret this to mean that the xanbus communications allows the process of grabbing excess DC power to be more precise than it would be with another brand of CC, and perhaps to begin during absorption rather than having to wait for float.  The manual also says that if you don't use Enhanced Grid Support, that you should periodically make sure the batteries receive a full absorption cycle (perhaps at night using grid power, or with generator power).

It is also necessary (per the manual) to set the CC to 3-stage charging, and the XW+ to 2-stage No Float for this to work correctly.

At this time I am not very interested in improving my self-consumption. I have a decent enough feed-in tariff (but not true net metering) to make this equipment completely unjustifiable for that purpose. I plan for it to be a back-up system. It will just sit there keeping the batteries ready to go until an outage occurs. More below.

What you are describing is basically the non-enhanced mode. Perhaps that is just fine or even better than enhanced mode in practice - I don't know but I'm glad to get your input.

Another question that comes to my mind is what happens with Load Shaving if you try to use it in conjunction with Enhanced Grid Support. Since Load Shaving occurs only when the battery voltage is below the GSV setting and presumably there is no excess DC voltage available, it seems like Load Shaving would always be trying to be active with GSV set to 64 or 65 volts.  I have not seen an explanation. I don't plan on enabling load shaving since it would be useless during an outage, but I'd still like to know the answer to this question.

Anyway, my primary concern arises from this feature being called "grid support." which could imply that it does not work unless there is a grid qualified on AC1. That seems ridiculous since anyone with solar would want to be able to use any excess PV power to run their loads particularly during a longer outage, but I'd just like to be sure that it does actually work when the grid is not available.

My thought is that this will be a backup system only until such time as LFP batteries like Simpliphi or Discovery become affordable (ha!). I don't really want to cycle lead-acid batteries daily. Instead I want to deeply discharge them (down to 20 or 30%) on the rare occasions that I need to. My plan is to use around 800 AH of AGMs at 48 volts. Sure such a deep discharge will limit lifetime, but that is what I expect the batteries to do for me for a few years. Obviously they will then need a full charge from the grid or from solar after the outage is over. Yes I understand the danger of operating them in PSOC mode during an outage but that also seems unavoidable. I would have a generator to try to limit that problem. Basically LA batteries seem to be non-ideal for anything.

Dave Angelini

With 13 posts under your belt here it is a pretty big gulp to say LA batteries a non-ideal for anything. The world has run on them a long time and will continue to. I have some good long stories about LFP failing with clients from the brands you sight, but no time for that.

WaterWheel

ewb said:

To answer your question, the owner's manual, and some other app. notes from Schneider explain that setting the GSV above the equalization voltage of a Xanbus connected Conext charge controller (such as the 80-600) enables a featured called Enhanced Grid Support in which the XW+ (with recent firmware at least) will "track" the charging cycle of the CC, using Xanbus communications, and after bulk is complete (eg: during absorption and float) will pull excess PV power off the DC bus to power loads, or to sell (if that is enabled). The advantage (per the manual) seems to be that the batteries will actually reach the full absorb voltage which they apparently will not using the non-Enhanced Grid Support mode that would be necessary with any non-Conext charge controller or other DC source. I just interpret this to mean that the xanbus communications allows the process of grabbing excess DC power to be more precise than it would be with another brand of CC, and perhaps to begin during absorption rather than having to wait for float.  The manual also says that if you don't use Enhanced Grid Support, that you should periodically make sure the batteries receive a full absorption cycle (perhaps at night using grid power, or with generator power).

Considering that cycling through LA or AGM batteries loses about 10% of the energy for most people using the solar power directly to the inverter is a better choice than using grid power while the controller is in bulk.     I understand that in your case you are willing to forgo this economic and energy savings.     Most people simply limit using high draw devises like the clothes washer until after lunch to help the batteries get well into absorb but I've found that on most sunny days it really doesn't make much of a difference.

I plan for it to be a back-up system. It will just sit there keeping the batteries ready to go until an outage occurs.

AGM and LA batteries will last longer if you cycle them below 80% SOC at least every few weeks.      It minimizes stratification of the electrolyte.

What you are describing is basically the non-enhanced mode. Perhaps that is just fine or even better than enhanced mode in practice - I don't know but I'm glad to get your input.

With enough panels and good solar exposure most people don't seem to have too much trouble getting fully charged batteries several days a week assuming the system is well designed to match the loads without using "enhanced mode".     Proper charging voltage, time, and battery bank size programming of the charge controller seems more important with Schneider equipment.      I don't know about other brands of charge controllers.
While I'm sure "enhanced mode" has its place I don't know if it's much of an improvement for a well designed and programmed system.

Anyway, my primary concern arises from this feature being called "grid support." which could imply that it does not work unless there is a grid qualified on AC1. That seems ridiculous since anyone with solar would want to be able to use any excess PV power to run their loads particularly during a longer outage, but I'd just like to be sure that it does actually work when the grid is not available.

Grid support will always try to use the solar/battery energy 1st and pull from the grid (AC1) as a backup.      Assuming your battery voltage is above the LBCO level the inverter will power the loads with the grid up or not.

My thought is that this will be a backup system only until such time as LFP batteries like Simpliphi or Discovery become affordable (ha!). I don't really want to cycle lead-acid batteries daily. Instead I want to deeply discharge them (down to 20 or 30%) on the rare occasions that I need to. My plan is to use around 800 AH of AGMs at 48 volts. Sure such a deep discharge will limit lifetime, but that is what I expect the batteries to do for me for a few years. Obviously they will then need a full charge from the grid or from solar after the outage is over. Yes I understand the danger of operating them in PSOC mode during an outage but that also seems unavoidable. I would have a generator to try to limit that problem. Basically LA batteries seem to be non-ideal for anything.

Different people have different opinions on battery types.      But if you don't occasionally cycle those AGM batteries I suspect you will be disappointed when they die an early death.

Have you actually looked at your loads in an effort to see what size battery bank you'll need to support them?
12 kwh/day or 22 kwh/day.      How much do you actually use?     What is your defining load?     

mike95490

I'm not able to follow your stated conditions.   Are you on grid and not wanting to sell ?   Off-grid and want generator support ?

The XW has 2 interlocking transfer switches, the generator cannot sell to the grid.

The XW can assist a small generator with a large load, by using the batteries.  If you have sunlight at the time, your load is running off the sun, not the stored battery power, unless some local floor contractor alligator clips his 3HP floor sander into the main panel and you wonder why your batteries are going down !!

I am off grid and cannot help with selling to grid issues.

ewb

Thanks Waterwheel, more good information. Exercise the batteries every few weeks.

What I really wanted to know though was simply whether the XW+ feature called "grid support" works when the grid is down?

I am asking this mostly because on the surface it seems simple: Of course you can't "support the grid" when it is down! And maybe that is right. Maybe grid support is all about maximizing the DC harvest to sell to the grid?  In that case my question becomes whether the charge controller during absorb and float will modulate the PV operating point to maintain the absorb voltage or the float voltage (if it can), even while the inverter is siphoning off what it needs to run the loads?  And maybe this just works automatically without "grid support" at all?

During bulk charging, I am assuming that the CC will operate the PV array at MPP and the batteries will absorb all the current that is available after the XW siphons off what it needs to run the loads (if the voltage is above LBCO). I assume that it makes no sense to sell to the grid during bulk. I also am assuming a reasonable PV to battery ratio.  Maybe I assume wrong?

Is there any use case for enabling grid support without enabling sell?

So, I am simply asking how this equipment works before I buy it (or something else). I'm not real satisfied with someone saying basically "yes, it works." Any bozo marketer can say that. I want to know *how* it works and of course what doesn't work mostly to get past the marketing hype.

Waterwheel, you asked about my loads. Yes, I have spent a lot of time understanding my loads. I am on grid so this applies mostly to a blackout scenario although I have also done this work to try and reduce my utility draw. My power currently costs $32/month + 16.3 cents/kWH and I am paid 12.2 cents for power that I export from my PV system. Relatively expensive, but nothing like some other places. I have a consumer grade Efergy true power monitor. It reports true power, not apparent power. Seems to be reasonably accurate but is certainly not revenue grade. It has a single channel. I move the current sensors around to monitor different things at different times including the whole house.

My loads consist of a long term average of 15 kWH/day, excluding heat and A/C. I could reduce that to under 10 kWH during a grid outage, maybe to 6 or less if I'm desperate.  I am all electric (except for a wood stove).  My major loads are all 240V and consist of a Mitsubishi multi-split heat pump, a heat-pump water heater, a Grundfos well water pump and the usual range and dryer and 120V fridge.  Lighting is hardly an issue - all LED.  I have put my monitor on most of these items, and I have a spreadsheet with their typical usage and apparent maximum power.  I don't have the equipment to measure inrush. The Grundfos is *supposed* to be of the soft start variety. We have been in this house for almost 2 years. We built it new.

During an outage: there is no hope of running the heat pump off of batteries. It is certainly a defining load in the winter, using 50% to 80% of all our electricity. I have a wood stove as a backup. I also would not even try to use it as an air conditioner if the power was out. Otherwise I hope to be able to run the heat pump water heater during an outage. It draws surprisingly little - 400 to 600 watts, but for quite a long time. I'd probably turn it on if batteries were charged and the sun was shining.  What I really need of course is to run the water pump and ideally our electric tea kettle (1200 watts for 3 minutes). I would generally not try to run the clothes washer or dryer off of batteries. Maybe I'd be able to run the smallest stove burner. Otherwise I'd use the camp stove outside. No gourmet meals during an outage (that's what restaurants are for - if they have power .  I believe that a small generator will also be necessary. I very much believe in "generator support," and hope it really works (another issue).

The major unknowable:  how long will the power be out?

I have 12 kW of PV on the roof. My site is excellent. Works very well until the power fails of course. Only about half of this will go into a charge controller via a PV "transfer switch". Normally I'll just run my efficient SMA inverters. I'm toying with feeding some of the rest of the PV into an XW+ using AC coupling (during an outage only), but that is another can of worms. The main reason would be to power some heavier loads with direct sunshine. Or I could pony up for another CC. Later.

I am in rural northern New England (USA). I have seen periods of no sun for 8 or 9 days in a row in the winter, but that is surprisingly rare. PV can be iced over for days (I bought a 30 foot long roof rake this year:). Electric heating dominates everything in the winter even though this house is fairly efficient (R40, R60, etc.). PV can't keep up - too little sun. It reverses in the summer with PV dominating and building a surplus, but without true net metering, the surplus is not large enough to get through the whole winter. That is a pretty minor gripe though, I'm happy with all this. The issue really is the power lines running through the forest. We've experienced one week-long outage with a relatively minor storm last year.  If a bigger storm takes out most of NH, Maine and Vermont one can anticipate being out for a lot longer than a week.

WaterWheel

The 6848 inverter will power your home when the grid is down seamlessly.      Two years ago while I was in Mexico the grid went down here for 6 days.      My adult son never even noticed until day 3 when a neighbor asked to borrow a generator.    (neighbors homes are far away so he didn't notice that their homes were dark)

Is there any use case for enabling grid support without enabling sell?
Yes.     I use grid support to protect my batteries but because of changes in what the utility is willing me to pay combined with higher meter fees I do not sell back to the grid.

So, I am simply asking how this equipment works before I buy it (or something else). I'm not real satisfied with someone saying basically "yes, it works." Any bozo marketer can say that. I want to know *how* it works and of course what doesn't work mostly to get past the marketing hype.
After 4 years I am happy with my Schneider equipment.      Like anything it takes a little hands on learning to figure it all out.

Having 12,000 watts in panels gives you all sorts of options.       We have 6000 watts in panels and the 6848 pulls from the grid about 1 day a month to supplement the battery power.      Before we added 2 small wall mount propane heaters the 6848 was pulling from the grid more often in the winter because we use a 2 head mini-split occasionally for heat.     Normally we use wood heat but those propane heaters are so easy we're doing less burning now days.

a thought...
When people see my panels they often ask about emergency power for when the grid goes down.      For occasional emergency power I suggest that they consider a whole house generator; something you may also want to consider.      For the $3000 that inverter is going to cost you can buy the generator.       Wiring costs are probably less with the generator.      Rent a 250 gallon propane tank ($48/year) and you'll have a lot more stored energy than the expensive battery bank will hold.      

ewb

Mike,

Thanks very much for your response. It sounds like PV can support the loads when the XW+ is supporting the generator. I think I see why and how this would work.

I'll try to clarify my situation, plan and ideas:

 I am on grid. I have 12.6kW PV and 3 SMA Sunnyboy inverters. I sell back to the grid at about 75% of retail, but possibly declining. I want to add battery based backup. I want to be able to use my PV to power some of my loads and charge my batteries when the sun is shining during an outage. I expect to need a small generator also because here in northern New England USA, sunshine can be scarce in the winter.

My plan is to start with an AGM battery bank. Probably around 800 amp-hours at 48 volts. I expect that alone to cost more than all the electronics that is also required, so this is not an inexpensive project.

Uhm, I read that AGM batteries don't have a stratification issue, do they?

 

Since I can sell efficiently to the grid via my Sunnyboy's which I do not intend to replace, I have no need to sell via the battery inverter.

The weird part: My plan is to rewire 2 (identical) high voltage PV strings to a high voltage charge controller (eg: Conext MPPT 80 600) via effectively a transfer switch so that I can simply "flip a switch" to give my charge controller control over the same PV strings that currently go into a Sunnyboy. I would do this only during a grid outage when the Sunnyboy was off line, and there was enough sunshine to make it worthwhile. It would be manual.

I now think I understand "grid support" on the XW+ thank to Waterwheel's help. Some of what I wrote in my last post was brain dead. I see clearly now that there is a use case for "grid support" with sell turned off.  I now *think* that the XW+ and a charge controller will cooperate during a grid outage to maximize the PV harvest to power loads first and charge batteries second.  I also *think* that this would not require "grid support" to be enabled. I could be wrong though - it is based mostly on my own speculations as to how things should/could work.

I'd like to understand how a generator running on AC2 (with AC1 unqualified, grid down) and DC power from a charge controller interact & cooperate.  I am guessing that "grid support" does not work when the AC input is from AC2. I think I understand "generator support."  I'd hope that it is possible for both the generator (via the XW+) and the charge controller to be charging the battery and supporting the loads simultaneously. Below the generator support level I'd expect that the inverter bridge circuit is busy charging and the generator is powering the loads via the XW+ transfer switch. If the loads increased, I'd hope that the XW+ would back off on the charging current in favor of meeting the demand. If demand exceeded the support level I'd hope that the XW+ would stop charging and start inverting to support the generator, drawing power from the charge controller first, and the batteries second depending on the demand.  Thanks Mike for addressing this situation. I'd like this to work when the PV production was small, but meaningful.  I often have just a kW or 2 coming off the roof when there is cloud cover.

I realize that running a generator at a low load when PV is producing well probably isn't efficient.

I realize this is ridiculously long. My apologies. No-one needs to respond to this of course, but I'd be happy to hear more input particularly of people who run an XW+ and/or a Conext charge controller.

Again let me emphasize: I am a newbie. I do not own an XW+ or any battery inverter. I have no real world experience with this type of equipment or with batteries. I'm simply considering doing something like this and trying to understand what to expect from the equipment and what to not expect and having trouble learning what I want to know from publications that I can find about these products.

Estragon

AGMs don't have stratification issues, and also tend to have lower self-discharge, making them good (but costly) for standby applications.

mike95490

I think I understand "generator support."  I'd hope that it is possible for both the generator (via the XW+) and the charge controller to be charging the battery and supporting the loads simultaneously. Below the generator support level I'd expect that the inverter bridge circuit is busy charging and the generator is powering the loads via the XW+ transfer switch. If the loads increased, I'd hope that the XW+ would back off on the charging current in favor of meeting the demand. If demand exceeded the support level I'd hope that the XW+ would stop charging and start inverting to support the generator, drawing power from the charge controller first, and the batteries second depending on the demand. 

Yep,  I run loads, and charge batteries on the dark days.  I hear the generator lug down, and see the charger has backed off.   When I was using a eu2000, I often had gen support activate, but with my main 3Kw generator. it never does.

WaterWheel

Estragon said:

AGMs don't have stratification issues, and also tend to have lower self-discharge, making them good (but costly) for standby applications.

Thanks Estragon,     I'd forgotten that.

ewb

Thanks Mike, good to know.  Gen support/boosting is a must-have for me. I want to minimize fuel use/dependency.

I can see how configuring a Conext system might be a bit fussy, but I can do fussy if I can eventually get it to work. Hoping to get a decent "theoretical" understanding before spending money or stupidly mis-configuring something.

The manual says:

The Conext XW+ supports the generator (or other power source connected to the
generator [default AC2] input) when the AC load current drawn from the generator

exceeds the GenSup Amps setting for 1 to 2 seconds.

That seems like a long time. Long enough to stall out an inverter generator?  I assume you'd get a voltage sag at least. I'm not quite sure what this means.  I recently learned from a friend that his Victron Quattro has a feature in addition to its generator support that causes it to support while a generator ramps up. I'd guess that the delay and the hysteresis are to prevent rapid on-off-on-off behavior. I don't know how the Victron deals with that. I'm thinking of a propane converted eu2200 with an autoformer and a simple startup surge limiter. I'd expect my water pump among other things to overload it, but it should handle my base load easily.

So, should AGM's in standby be floated for a long time, or not? Exercised occasionally (monthly)? Or maybe left alone and just given a full charge cycle monthly? Concorde recommends doing a charge cycle every 90 days for batteries in storage, and storage at low temperatures to reduce self discharge. I don't see that they comment on float vs no-float for longevity.

Mike, how do you like those NiFe's?

BB.

What can "kill" AGM batteries in standby use is internal gasing (charging at absorb voltage for many hours when the battery is already full).

AGM batteries normally have an internal catalyst that fails after recombing "a lot" of Hydrogen and Oxygen back into water...

Hydro Caps are an aftermarket catalyst cap, and here is their FAQ that explains about their operation (should be similar to AGM operation):

http://hydrocapcorp.com/contact-us/faq/

1. What warranty is provided for HYDROCAPS? One year on materials and workmanship. Abuse is not covered.
2. How long is a HYDROCAPS life? Operating experience indicates 16,000 to more than 30,000 ampere-hours of battery overcharge. In normal application this should be 5 years. Instances of record show HYDROCAPS operating after more than 10 years.
3. Does catalytic activity deteriorate? Chemical activity after the first 16,000 to 20,000 ampere-hours would normally lose 15% to 20% capacity. To offset a decline and insure proper activity, the reliability factor is 15 to 1. Meaning: The reactive catalyst surface area provided is 15 times the area required for normal activity.

Avoid high(er) voltage float charging for many hours.

And avoid high current "gassing" when charging... The catalysts do get hot (recombining hydrogen and oxygen generates heat)--And can damage/ruin the catalyst.

-Bill

mike95490

AGM will often have 2 uses listed : Cycle Duty and Float Duty
 Float duty has lower voltages for Bulk/Absorb + Float

ewb

Thanks very much,  I've not seen information like this before.   Digging a bit, I found this older article that discusses the problem:

https://www.power-eng.com/articles/print/volume-109/issue-10/field-notes/catalysts-on-vrla-batteries-save-air-force-millions-of-dollars.html

The only thing I don't get here is the talk about caps on AGM batteries. The one's I've seen don't have caps at all. I know they have a relief valve but that's not the same thing.

Bill, I realize you are talking about a catalyst in the sealed assembly added by the manufacturer. I wonder if that is standard now or maybe some have it and some don't.

BB.

VRLA batteries (the general class of sealed lead acid batteries which includes AGMs--I think)--It seems that some do have catalysts and others do not.

https://en.wikipedia.org/wiki/VRLA_battery

If the charging current is too great, electrolysis will occur, decomposing water into hydrogen and oxygen, in addition to the intended conversion of lead sulfate and water into lead dioxide, lead, and sulfuric acid (the reverse of the discharge process). If these gases are allowed to escape, as in a conventional flooded cell, the battery will need to have water (or electrolyte) added from time to time. In contrast, VRLA batteries retain generated gases within the battery as long as the pressure remains within safe levels. Under normal operating conditions the gases can then recombine within the battery itself, sometimes with the help of a catalyst, and no additional electrolyte is needed [4][1]. However, if the pressure exceeds safety limits, safety valves open to allow the excess gases to escape, and in doing so regulate the pressure back to safe levels (hence "valve-regulated" in "VRLA").

When an AGM battery is near full, and gassing (a bit), you can sometimes feel the top of the battery and find a warm spot (where the catalysts are installed--if installed). If the battery is gassing too much, the top of the battery will get too hot.

-Bill