Adding storage to my Enphase system

SolarPrep

Solar Enthusiast
Joined
Jul 15, 2021
Messages
197
It seemed I got more information on how Sunny Island worked in the 2000's, more theory, diagrams, and explanation.
It works very well for what it does, pass-through from grid and interacting with with AC coupled Sunny Boys off-grid. Some things like load-shed relay are needed and addressed deep in the manual, but conspicuously absent from the system block diagram, which would be the easiest way for people to see and understand.
Sunny Island has been used for load shaving and grid support, but maybe only with custom communications, and in an R&D environment. I haven't seen anything indicating SMA supports that application.
Now, SMA seems to focus on decentralized control and having customers sell power into the spot market. More internet-connected boxes and communications with GT PV inverters. That may be where the grid and net-metering is headed, but it isn't what most of us do.
If you are doing an off-grid or grid-backup system, the basic block diagram is shown in their data sheet, and there are relays available for some functions.
Of course, lithium battery support is officially a number of commercial products. And we know REC is available for DIY.
Hedges: I think we are going to buy Sunny Island. Just one, and use with an autotransformer. I want our basic system to heavily focus on battery backup, and try to get to the point where we can run at night on batteries, and recharge the next day. I did think about adding a grid tied portion too, and use Sunny Boy for that. Trying to avoid roof mounted panels.

From what GXMnow has stated about the XWPro being able to do in off grid mode, it does seem like that would be a good option for us too. Maybe even the Conext SW.
 

SolarPrep

Solar Enthusiast
Joined
Jul 15, 2021
Messages
197
I’m still deciding. Right now it’s between the Outback Radian and XW Pro. The XW hits the sweet spot with surge and right in the middle of both Raidians (4048, 8048). I will only be DC coupled and never sell back to grid, only use grid as backup when solar can’t charge. Just concerned about the support levels and software for XW based on a lot of threads in here but I know it’s mainly AC couples items.
Chris: I'm of the same mind about the power level you mention. That also works for the SMA Sunny Island, which is a great piece of gear,and can be had for about the same amount as the XW. But, the SMA stuff uses some wonky accessories, and they are really costly.

I wish someone would chime in with a direct comparison of the XWPRO and the SW from Schneider; like what each one is best suited for.
 

Hedges

I See Electromagnetic Fields!
Joined
Mar 28, 2020
Messages
9,072
Stacking XW Pro 6848's

Here is a link to the “multi-unit design guide”
I was going to stack more XW Pro 6848’s until I read this guide.
The 60A relay is a limitation, and their suggested solution is ugly.


"Because of these 60 A rated relays, the current flowing through the AC1 and AC2 ports of the XW Pro is limited accordingly. When several units are placed in parallel and operating in AC pass-through mode, they will all be connected to the same AC source and share a fairly even amount of current to the load. However, when the AC source is disqualified, it is not possible to ensure that every relay will open at the exact same time (see Figure 7 on page 23). The last relay to open will have to handle the total overall load current. In addition, when qualifying, the first relay to close will have to handle the total system current. As a result, when using the internal transfer relays to switch the AC sources, a maximum of 60 A of loads can be connected to the AC Out port of the inverter. For systems with loads larger than 60 A, it is necessary to use an external contactor for switching the AC Source."

What Sunny Island will do is invert power from batteries to limit AC input current. When reconnecting to AC input, it first increases frequency to knock AC coupled sources (Sunny Boy) offline, then synchronizes frequency to AC input, then closes relays. (I don't know if it adjusts AC output voltage to match input before closing relay, or remains a nominal 120V.) It can have 4 in parallel at 120V, or 2s2p for 120/240V split-phase.

Obviously relays could handle 2x or much more current briefly. That's what starting surge of a motor is like. I would think the two Sunny Islands in parallel close at the same time but not at all sure. One phase (of 120/240V split phase, or 120/208Y three phase) can close while another doesn't, and it will make the missing phases.)
 

Hedges

I See Electromagnetic Fields!
Joined
Mar 28, 2020
Messages
9,072
But, the SMA stuff uses some wonky accessories, and they are really costly.

Which are the wonky and costly accessories you're referring to?

There are a variety of communication boards and boxes, depending on what it needs to talk to.
The transformer unit for Sunny Island, another for Sunny Boy Storage, and multi-cluster box or the higher priced accessories. Enough so that I'd buy two Sunny Island before getting their transformer for it. But surplus transformers can be had. I bought a 9kVA one that came from a UPS. Of course, there are some voltage tolerance issues with auto-transformers, all the more so when used for bidirectional power.
 

GXMnow

Photon Sorcerer
Joined
Jul 17, 2020
Messages
1,463
The 60A relay is a limitation, and their suggested solution is ugly.
How much power do you figure you need?

The one odd thought that I had, if I truly needed more power than that, would be to have a separate backup loads panel on the third XW-Pro. This way, the first pair stacks and can run up to 60 amps. That's 14,400 watts, a little more than the continuous rating of the two inverters. And a second panel for another 6,800 watts, breakered at 30 amps. Even my central air conditioning will have no problem starting on the stacked pair. Probably won't even need a soft starter. With soft start, one unit might start it. While the 3 units are on grid, they will stay in sync, but during a grid outage, I would have to look into how things tie together to see if they will follow a master clock, or if the third unit would free run. Since it is a separate panel, it would not be a problem if the 60 Hz waves drifted out of sync. When the grid comes back, they will pull back into sync before it closes the transfer relay. I watched that happen on my single unit. When it is flashing during qualifying, the output wave just slips phase until it lines up.

The external transfer contactor is a bit of a convoluted setup, but it will work for stacking more units where you need a lot of power to a single load. The only place I see my split setup being a bit of a pain is where you have loads that share a neutral from the existing wiring. Any loads sharing a neutral need to come from the same inverter, or stacked pair with tied/synced outputs.

My hope is that a UL listed battery option will become available before my contract is out, and I can have my system inspected and signed off by the city. Then I can shift it to true zero export and lose NEM completely.
 

pvdude

Solar Addict
Joined
Feb 8, 2021
Messages
262
The big power problem to solve is starting the heat pump.
It’s hot here 9 months of the year.

LRA for the compressor is 132A, so stacking a second WX Pro is probably not going start the compressor.
(Although it will be fun to try - the massive copper transformer in the XW Pro can sustain a large instantaneous spike)

Typical running load for the house AFTER the compressor starts and the blower is running is 3-4kw.

I only have 445Ah of batteries (FLA), so not enough for running the AC all night.
However, the heat pump cycles much less after dark, so that would be another experiment to try.

No problems replacing the old batteries w/ new larger batteries, if needed, now that I know the
convoluted path to the Miami Rolls battery dealer.

Although I can run the Diesel genset (90A of 240v), hoping to avoid that unless emergency conditions
(days of dark before/during/after hurricane)

Will expand the existing PV to about 8700 watts if the ships ever get off-loaded @ the LA port.

Weekend load includes the water heater and dryer (laundry day), so 12-14kw peaks for a short time.
I have a Hyper Engineering Sure Start that I was hoping to install this Winter to reduce the compressor LRA.
But I might try a Micro-Air EasyStart instead.

So with two stacked XW Pro’s, and a reduced compressor LRA, there would be enough power available to both run the AC and handle the weekend laundry loads.

The solar electronics and PV are in a separate building from the house, 200 ft. Away, so I am limited on how things can be split up, unless I want to bury more conduit and run more large power cables & install more switchgear.

So probably going w/ simple first.
Second XW Pro sounds like a fun project!
Will need to replace the existing Schneider Mini-PDU with the big PDU.
I planned for the wall space expansion before installing this system, so not a big deal to switch PDU’s

Already have the bracket in place for the second XW Pro.

newinverterinstalledjune152021 copy.jpg



I’m not sure I understand the difference in power available between a single XW Pro 6848 and two, stacked.
The data sheet for a single XW Pro 6848 120/240v says:
Continuous output power =6800 W
Overload 30 minutes =8500 W
Overload 60 seconds =12000 W
Maximum output current 60 seconds 52A (240v)

I can't find a similar description in this doc, so as to compare single & two stacked power ratings:

info on the top of page 27, for two stacked XW Pro 6848 120/240:
Continuous kVA = 13.6
Peak kVA = 14.4

So if I convert kVA to watts @ unity PF, it looks like I can really work the 60A relay pretty hard.
Possibly I should invest in a box of spare relays;)
 
Last edited:

SolarPrep

Solar Enthusiast
Joined
Jul 15, 2021
Messages
197
Which are the wonky and costly accessories you're referring to?

There are a variety of communication boards and boxes, depending on what it needs to talk to.
The transformer unit for Sunny Island, another for Sunny Boy Storage, and multi-cluster box or the higher priced accessories. Enough so that I'd buy two Sunny Island before getting their transformer for it. But surplus transformers can be had. I bought a 9kVA one that came from a UPS. Of course, there are some voltage tolerance issues with auto-transformers, all the more so when used for bidirectional power.
Hedges: Already have an autotransformer. I cannot afford the backup system from SMA, so that is out of the question. Sunny Boy Storage is interesting, but would likely need two.
 

Hedges

I See Electromagnetic Fields!
Joined
Mar 28, 2020
Messages
9,072
So far I think only a single Sunny Boy Storage works in an off-grid or backup setup, not multiple ones. And it requires an expensive 400V battery. And an external "Automatic Backup Unit", which contains relay + transformer. Also weak surge current.

Backup system from SMA? They used to offer a box with transformer for one Sunny Island. But a second Sunny Island isn't much more expensive. Two Sunny Islands will provide a 120/240V 56A pass-thru (50A from battery) "backup" system resembling a UPS.
One Sunny Island and a transformer will pass through 56A at 120V and feed 120/240V on loads side.
 

pvdude

Solar Addict
Joined
Feb 8, 2021
Messages
262
Getting started on upgrade planning. (Stacking a second XW Pro 6848)
According to page 31 in “XW Pro Multi-unit Power System”, it is possible to obtain 17kVA (peak),
if I use an external contactor.


Can anyone explain why the diagram shows a connection between the Neutral and L1?
(I am guessing it is an error in the schematic.)

schneider_relay_contactor_schematic.png
 

400bird

Solar Enthusiast
Joined
May 23, 2020
Messages
380
Wow, quite the system, a second 6848. Sounds good.

I don't think that is a (edit) connection short from L1 to N

It looks to me like you have the middle red arrow as the L1 source.
That goes to A1 on the contactor to power the coil (the load on this small part of the circuit)
A2 and further through the diagram is the low side switched portion of the circuit.
So, A2 on th contactor is connected to N (to complete the circuit and energize the contactor) through the solid state relay.
To form the complete circuit it needs to connect to Neutral.
 

pvdude

Solar Addict
Joined
Feb 8, 2021
Messages
262
Thanks, that helps!
I have figured out from looking @ other Schneider contactor and SS relay docs that the rectangle outline in the circuits could be a resistor.
Or it could just represent a more complex circuit inside the SSR.
I can see how that could limit the current.

Regardless, I shall “Stand Well Back” when I turn it on (hoping for Jan-Feb-2022)

 

400bird

Solar Enthusiast
Joined
May 23, 2020
Messages
380
Glad to help, in the case of a contactor or relay that would be an electro magnetic coil, the one that is going to close the contacts.

It doesn't show the resistance of the coil. But, I'd wager around 120 ohms or more. It doesn't take much current to close a contactor.

For the SSR, it's probably just draw for consistency.
 

GXMnow

Photon Sorcerer
Joined
Jul 17, 2020
Messages
1,463
I was out of touch for a few days, just got back.

You got it right, the rectangle in the contactors is the "coil" or driver circuit in the SSR. The aux output is not powerful enough to engage a 120 amp contactor, so it uses the SSR to drive the contactor coil.

When I looked over the stacking setup for the XW-pro, I agree it seems a bit odd, but I understand what they are doing. The only reason for the external contactor is to make sure there is no chance of only one XW going into bypass and trying to carry more than 60 amps. So it delays the external contactor until both XWs are certain to have closed their internal contactors. Then it closes the external. In a perfect world, the two units should evenly share the load. Since the world is not perfect, there could be a 10% difference under certain circumstances. But once they are inverting, they will adjust and balance and hold very close to matched current. The contactor does not carry any of the output current from the stacked inverters. When running on battery, or even in "Grid Support" mode, the power from the inverter bridge and transformer does connect directly to the output terminals. When the system is off grid or during a power failure, the contactors will all be open.

While on grid, you can set the inverters to provide the portion of power you choose. Grid support is a cool function that will have the inverter sit in standby if your load is under a set current. For example, anything less that 3 amps will just come from the grid, but if it goes higher, the inverter will make up the difference from battery. You can also go the other way. Have the inverter supply all load side current up to a limit. If you exceed that limit, it will take any more needed from the grid input side. Since I am only feeding the grid input side from a 20 amp breaker, it also knows to reduce charging current if I pull too much load on the output side. I saw it almost stop charging when the microwave was running and my girlfriend turned on her 1,500 watt hair dryer. Normally, we don't see this happen during the day, because the solar is AC coupled into the XW inverter output. So the solar powers the loads, and usually is still helping run the charger, but it has been quite cloudy. So the charger alone was trying to take 1,500 watts from the grid. I need to make it a bit more intelligent so it knows to curtail the charge rate when solar production is down. But once I add the DC MPPT solar charging, it won't be an issue any more. 90% of the time, the DC charging will be enough to cover my evening loads without ever needing to kick the XW into charge mode.
 

pvdude

Solar Addict
Joined
Feb 8, 2021
Messages
262
Thanks for the detailed explanation!
I’m excited about this Winter project.
altestore.com gave me a great deal on the second inverter, big PDU, connection kit.
Expect to receive it after 1-1-2022.
Zoro.com sent me a very rare 20% off anything code, so I saved $125 on the contactor.
No one has the solid state relay SSM1A112BD in stock, but that is OK, by the time I need it, some supply place will have one.

Not sure if I need to do the procedure listed in this 2019 doc.


It says:
NOTE: This procedure applies only to Conext XW Pro 6848 inverters with firmware version 1.02 BN005.

So I'm guessing the newer inverter firmware (1.11) I am running may have resolved the issues.

It will be fun to find out if the new configuration will start the heat pump compressor.
I measured 132LRA, which is far more than two stacked 6848 can supply.
However:
The heat pump compressor starts just fine when we are on the Diesel genset, and it maxes out at 87A of 240V.
The breaker for the compressor is 50A, a Square-D QO w/ surge capacity of "ludicrous" amps.

I have a Soft start device for the compressor, but am loathe to install it, as the compressor wiring is complicated.
Thus, the device will only be installed if the stacked inverters can't start the compressor.
 

pvdude

Solar Addict
Joined
Feb 8, 2021
Messages
262
Found the answer to the “Configuration-and-Calibration” question.
Addendum “A” in the April 2021 XW Pro Multi-unit design guide describes the calibration procedure required.
Applies to all firmware versions.
But the utility needed to perform the calibration is not available on the Conext gateway I have
(of course).
Need a PC w/ windoze, and a “Conext™ Configuration Tool - 865-1155-01”, and the related software.


The tool appears to be a USB to XANBUS adapter.
XANBUS being a proprietary architecture, the cost for the tiny plastic adapter is ….WOW
Required to install a multi-unit system.
Possibly I should go into the solar biz here, just to amortize the investment in all this crap.
 
Top