"Zeroing" household consumption using an XW Pro?

[wschwa]

Hey All,

I currently have a grid-connected PV system with APSystems DS3 inverters. I'm interested in adding batteries primarily to save on TOU rates, but secondarily to provide backup power for some critical loads. The goals for my battery system are:
1. Offset peak electricity usage by discharging the batteries to supply my local loads (load both "downstream" in a critical loads panel, and "upstream" in my main panel, assuming the grid is operating normally).
a. When my PV system is meeting the demand/exceeding the demand and exporting power to the grid, the batteries would not discharge.
b. When I'm a net consumer from the grid (PV not meeting/exceeding demand), discharge the batteries to approximately offset whatever power I'm currently using.
2. Provide backup power to a critical loads panel in case of a grid outage, ideally with AC coupling my existing APSystems PV setup.

I've identified the Conext XW Pro 6.8kW as a possible solution to meet these needs, but even after reading all installation/configuration/whitepapers I could find on it, I'm unclear if it will actually meet my needs. Considering the architecture outlined in the figure below (with appropriate current monitoring in the main panel provided probably by a WattNode):

Can I configure the XW Pro to try to "zero" the power input from the grid during peak hours, by using the batteries to backfeed power to AC1 (obviously only in cases where the grid is operational, since backfeeding AC1 would not be allowable if the grid was down)?

If this is not possible, is anyone aware of an inverter/charger that might meet my needs? I think some of the newer EG4 stuff would probably work, but I'd like to not have to buy something with solar input, if possible, since I have no use for a DC string inverter function.

Thanks for any and all advice!



EDIT: To better clarify my concerns, I can't tell from the documentation whether it's even possible to backfeed AC power sourced from the batteries in this configuration. If it is possible, it's not clear if there's any way to regulate the inverter so that the backfed current is approximately matched to the grid demand (note that in this application, error in matching the grid demand exactly is acceptable - I can backfeed or import from the grid a lttle bit. I'm just trying to minimize my peak time usage).

 

[blerpaderpa]

Take a look at the Schneider Backup Control Switch- it has a Wattnode integrated and a 200A contactor and is about 5-600 at NAZ. Integrates directly with the XW Pro. I have a very similar setup as yours- for me, I have an existing Ac Coupled microcontroller PV system on an outdoor meter/main panel, and I'm going to 'zero-out' my inside house panel (200A panel that has the 99% of the house usage) using the Schneider BCS and a single XW Pro. I will basically be taking the feeder from the house panel and redirecting it to the BCS- this allows the BCS to disconnect the house panel from the grid in a grid-down scenario (off grid mode), but more importantly, it allows the XW to backfeed the house panel while the grid is up and 'zero-out' the usage that is happening in the house panel.

The downside 1 to this method is you can't utilize AC coupled PV in the 'zero-export' panel as the XW can't frequency shift/regulate AC coupled solar while the grid is up, and you will therefore have inadvertent export on the line side of the BCS. My plan to resolve this is to add an automatic transfer switch that basically disconnects the PV from the outside meter/main panel when the grid is down and connects it to the house panel and vice versa when the power comes back on.

Downside 2 is you likely need to have an additional interconnect agreement with your POCO as the BCS route means your system runs in parallel with the grid rather than via transfer switch.

I found this document to be helpful: https://solar.se.com/eu/wp-content/...l-Limiting-Solution-Guide-990-91371_rev-A.pdf Note that the term 'ac-coupled' is nowhere to be found in the document.

 

[GXMnow]

I started with a very similar setup. I have an Enphase grid tied system and an XW-Pro to time shift the energy.

The main problem is that the XW-Pro does not know how to charge from excess AC coupled power. I tried all kinds of settings and talked with Schneider tech support and they said I was right, it doesn't have coding to "smart charge" from AC coupled solar. I spent a year manually starting a charge cycle each day. I ended up adding a PLC (programmable logic controller) that reads the power values from the XW-Pro and commands it to charge when their is extra solar power coming in and then adjusts the charge current to zero out the export to the grid until the batteries are full. Once the batteries are full, the extra solar will still export to grid. You can't stop that from happening.

Since I have the PLC, I also programmed it to do zero export using the XW-Pro to power my home overnight from the batteries. It works very well. The "Watt-Node" will do that side. The Schneider BCS has a Watt Node in it and it costs the same as just buying a Watt Node. With my PLC I am using a pair of cheap Amazon power meters to monitor the load in my home. It basically does the same thing.

 

[BKY2003]

The EG4 hybrids will definitely do all the things you are asking. Probably a lot easier to setup also, but I am not totally confident in the longevity vs the XW6848 pro.

 

[blerpaderpa]

I started with a very similar setup. I have an Enphase grid tied system and an XW-Pro to time shift the energy.

The main problem is that the XW-Pro does not know how to charge from excess AC coupled power. I tried all kinds of settings and talked with Schneider tech support and they said I was right, it doesn't have coding to "smart charge" from AC coupled solar. I spent a year manually starting a charge cycle each day. I ended up adding a PLC (programmable logic controller) that reads the power values from the XW-Pro and commands it to charge when their is extra solar power coming in and then adjusts the charge current to zero out the export to the grid until the batteries are full. Once the batteries are full, the extra solar will still export to grid. You can't stop that from happening.

Since I have the PLC, I also programmed it to do zero export using the XW-Pro to power my home overnight from the batteries. It works very well. The "Watt-Node" will do that side. The Schneider BCS has a Watt Node in it and it costs the same as just buying a Watt Node. With my PLC I am using a pair of cheap Amazon power meters to monitor the load in my home. It basically does the same thing.

Schneider did add WattNode CT3 support for AC Coupled solar in the final InsightHome update. I believe @400bird said he had some kind of experience with it doing *something* beyond just monitoring. There's zero documentation from Schneider on what adding CT3 does. I assume it's purely for monitoring, but *shrug*. If you have the AC coupled solar outside the context of the BCS or critical loads panel, I would be very curious if the XW does any additional compensation out of the box with the CT3's on the AC PV circuit.

 

[400bird]

The biggest issue is that the XW won't start a charge cycle on it's own unless the grid goes down or you figure out a way to discharge the battery below the recharge voltage. The XW stops discharging 0.5 volts above the discharge voltage setting.

I'm using a Raspberry Pi and node-red to command the daily charge to start. Home assistant would also work.

In this thread I gave some more details about how the wattnode works. Honestly, I've forgotten more about how it works than I'd like to admit.
If you have specific questions not answered in that thread (or search for other posts by me with h the keyword wattnode) go ahead and ask, I'll try to figure it out/remember.

Post in thread 'Schneider XW Pro- AC Coupled Zero Sell... And BCS vs. Critical Loads Panel?' https://diysolarforum.com/threads/s...s-vs-critical-loads-panel.103692/post-1424052

 

[GXMnow]

Yup. That was the reason I added the PLC in my system. It is doing very similar to what Node Red does on @400bird system. Something external has to tell the XW-Pro to go into charge mode. I proved that a small software change in the Insight (or Gateway) could easily do it as all the data needed is already there. In fact we are just reading Modbus registers in the XW-Pro to decide when to tell it to charge and even to set the charge current to efficiently use the extra AC coupled solar. And Schneider did add this functionality to the SW line and called it "Smart Charge". But they never ported it to the XW line.

 

[wschwa]

Thanks all, this information is immensely helpful. I have home assistant running already so will likely head down that path to manually control charging with excess PV. In my case, I don't mind exporting to the grid (and have a net energy metering agreement in place my utility already), so I'm not looking for perfection on zeroing out my usage.

My XW Pro is being shipped as we speak, so I'll likely circle back as I dive into the setup.

Thanks again!

 

[400bird]

Thanks all, this information is immensely helpful. I have home assistant running already so will likely head down that path to manually control charging with excess PV. In my case, I don't mind exporting to the grid (and have a net energy metering agreement in place my utility already), so I'm not looking for perfection on zeroing out my usage.

My XW Pro is being shipped as we speak, so I'll likely circle back as I dive into the setup.

Thanks again!

If you're already running home assistant, you're probably halfway there. If you don't already have it, get a Modbus add in.

I've got net metering too, when charging from AC coupled PV, I let 100-200 watts flow out to the grid when the sun is up. I fully stop charging em once peak rates hit and let PGE take everything at the highest cost.
When running overnight on battery, it pulls something like 80 watts from the grid all night. 3 years and PGE hasn't said a word.

 

[GXMnow]

I had my XW-Pro exporting about 40 watts all night for a year. So Cal Edison never said anything, but then my power graph from them shifted so that my 40 watts of export was moved to 40 watts of consumption. So they obviously noticed and must have thought there was a metering error. Instead of checking or asking, they just "Fixed" the error by basically increasing my consumption by 80 watts all the time.

Once I saw it, I set the XW-Pro to stop exporting at 6 am before the sun comes up so that my loads in the main panel pull a little grid current before the solar stars producing. 3 days of that and the 80 watt offset went away again. So I just left it pull that little grid power each morning and they seem to be happy and it has been 2 years now with no issues from them.