AC coupling my Outback Skybox to a Solaredge inverter

Ampster

Renewable Energy Hobbyist
I have had an Outback Skybox for several years but recently decided to finally rewire my GT Inverter to take advantage of the new battery pack I recently installed. Details of that build are here.

My GT system is a 3.8 kW Solaredge inverter with 19 Hanwha cells for a total DC capacity of 5.7kW. It is on a NEM 2.0 aggreement with PG&E. What NEM 2.0 means is that I am charged Non Bypassable Charges (NBCs) for every kWh that I am using the grid. It adds about $0.01 to 0.015 the the applicable TOU rate. I think last year I paid less than a $100 in NBCs last year, in addition to fixed month Minimum Delivery Charges (MDCs). I can go into details about my rate structure if anybody is interested.

One of my long term goals has been to be self sufficient in terms of Energy as far as practical with two EVs. For that reason and to increase my backup capacity I upgraded my pack. After doing that I was finally ready to swing the GT inverter over to my critical loads panel that is controlled by the transfer switch in my Skybox. The other motivation was that during fire season in Northern California we have Public Safety Power Shutoffs. (PSPS) I was able to limp through them last year but my old Frankenpack of Nissan Leaf Modules was barely able to make it through the night and the only solar I had connected to the Skybox was some west facing used Sunpower panels and they didn't even start producing until afternoon. So now with a 28 kWh pack of 28 kWh of thirty two LF280 cells I wanted to get the full benefit of AC coupling my GT inverter so I could charge from the sun in the morning and use some of that solar to charge my EVs during the afternoons.

A few days ago I completed the rewiring of the GT inverter and now it runs through the Skybox. I have several modes on the Skybox and the one I chose to use was Self Consumption because it charges the batteries and covers the loads as its first priority then sells any excess to the grid. The Skybox has a coulomb counter so I can describe things in terms of percentage of SOC. By morning the pack is down to about 70% of SOC and begins charging by 9AM ramping up the Amperage to about 40 Amps by 10:30 to 11:00 AM. Usually it is done my 1:00 PM. The last hour is in the ramp down of current in the Constant Voltage stage so it begins sell to the grid. What I like about the Skybox is that I can set the maximum kW that I sell to the grid. That is important because my NEM agreement limits me to 4.8 kWs so that is the setting on my Skybox.

It will take me a year to see the financial impact of all of this and I did not do it with a particular payback in mind. Part of that is because I have two EVs that I can charge with any excess solar or by using the credits I have built up in my NEM arrangement with PG&E
 

GXMnow

Photon Sorcerer
I am looking forward to your report on how that works out. Your setup is a bit different from mine, but we are both trying to get a very similar end result. Is your Solar Edge Rule 21 or HECO compliant? If not, I think you need to limit it to 5,000 watts max on the AC couple to the SkyBox. It can take something like 7,000 watts if it is Rule 21 with the Frequency/Watt curtailment.

Even with our Net Metering 2.0 agreements, it still works out better to self consume as much as possible. And having the battery backup in an emergency is an added bonus.
 

Ampster

Renewable Energy Hobbyist
My Solaredge inverter is Cal Rule 21 compliant. I previously had coupled 4 Enphase IQ7 micros and I watched them modulate. That was with the Enphase Envoy and under an earlier configuration of the Skybox where my sell to grid was much lower.
 

newbostonconst

Solar Addict
Nice over view and system.

I am currently running 24 Panel with Enphase inverters (7.3Kw) on the grid side, 12 panels with 3 APsystems 4-channel QS-1 inverters (3.7Kw) on the critical loads panel AC coupled for solar.

280ah 17 cells battery bank 5 amp active cell balancer.

GS4048 Outback Hybrid inverter using the AC coupling.

Thursday I lost the GS4048 for the second time with a control board failure. Very frustrated without Outback. Then Sat we had power outage and with lots of money spent didn't have a backup power source. We rarely have power outages. But of course when we do....no backup....

Anyway, Ampster, I thought you had a GS8048? Is that right? If so why did you change?
 

Ampster

Renewable Energy Hobbyist
Anyway, Ampster, I thought you had a GS8048? Is that right? If so why did you change?
Three years ago I had a Radian GS4048. I moved and sold that system. Later after installed solar in my new home I bought the Skybox. I did have to swap out the inverter portion when a firmware upgrade bricked the system. I have been happy with Ouback service.
 

newbostonconst

Solar Addict
Yes, their service support is good, just frustrated this is the second time.....both failures happened in pass through mode(grid connected) with batteries all charged....so like no load.

Thanks, was just wondering why you didn't still have the GS4048 and didn't buy the unit again. Thought you might of had problems.
 

taxil

New Member
@Ampster Could you explain what would happen if I AC coupled my 10.5kW LG panels powered by Enphase IQ7+ microinverters to the Skybox? Would anything over 5kW get clipped?
 

Archetype-IS

Solar Enthusiast
@Ampster Could you explain what would happen if I AC coupled my 10.5kW LG panels powered by Enphase IQ7+ microinverters to the Skybox? Would anything over 5kW get clipped?

Don't think it is wise to go over what the technical doc stated per below for outback Skybox AC Coupling. Maybe if you can branch out the Enphase IQ7+ into two groups? One under 5KW for the AC Coupling side to the Skybox and the other 5.5KW to the grid-tie like how it is now. If you split it up, you will need two ENVOYs to monitor the consumption? I am not sure, because the CTs are per breakers. Maybe not, because the ENVOY will see IQ7+s since it all needs the grid frequency lock. But once your AC Coupling and grid down, the ENVOY might not be online depending on where you have it.

If you split into two branches, will that void your warranty per the permits?

@Ampster 's setup is within spec of the Skybox on the Grid Tie side. DC Coupling side will power the load regardless if the GT Micro works or not. Best of both worlds.




Compatibility
o The SkyBox supports GD inverters up to 7.6 kW, provided the GD inverter is UL1741SA-listed and programmed for HECO Rule 14 or CA Rule 21 with export ramping.
o The SkyBox supports GD inverters up to 5 kW if not programmed for HECO Rule 14 or CA Rule 21.
o When grid-connected, the SkyBox follows the grid voltage and frequency. The GD inverter takes the same power through the SkyBox's transfer circuit, meaning it is still fully compliant to UL1741SA or any other requirement.
o AC coupling may be used in conjunction with the Time of Use function.

Restrictions
o The GD inverter must be connected on the SkyBox LOAD terminals. This function will not work if it is connected to either of the other sets of AC terminals (GRID or GEN).
o This application is for a single SkyBox. Stacked SkyBoxes cannot perform AC coupling at this time
 

solardad

Solar Addict
I have had an Outback Skybox for several years but recently decided to finally rewire my GT Inverter to take advantage of the new battery pack I recently installed. Details of that build are here.

My GT system is a 3.8 kW Solaredge inverter with 19 Hanwha cells for a total DC capacity of 5.7kW. It is on a NEM 2.0 aggreement with PG&E. What NEM 2.0 means is that I am charged Non Bypassable Charges (NBCs) for every kWh that I am using the grid. It adds about $0.01 to 0.015 the the applicable TOU rate. I think last year I paid less than a $100 in NBCs last year, in addition to fixed month Minimum Delivery Charges (MDCs). I can go into details about my rate structure if anybody is interested.

One of my long term goals has been to be self sufficient in terms of Energy as far as practical with two EVs. For that reason and to increase my backup capacity I upgraded my pack. After doing that I was finally ready to swing the GT inverter over to my critical loads panel that is controlled by the transfer switch in my Skybox. The other motivation was that during fire season in Northern California we have Public Safety Power Shutoffs. (PSPS) I was able to limp through them last year but my old Frankenpack of Nissan Leaf Modules was barely able to make it through the night and the only solar I had connected to the Skybox was some west facing used Sunpower panels and they didn't even start producing until afternoon. So now with a 28 kWh pack of 28 kWh of thirty two LF280 cells I wanted to get the full benefit of AC coupling my GT inverter so I could charge from the sun in the morning and use some of that solar to charge my EVs during the afternoons.

A few days ago I completed the rewiring of the GT inverter and now it runs through the Skybox. I have several modes on the Skybox and the one I chose to use was Self Consumption because it charges the batteries and covers the loads as its first priority then sells any excess to the grid. The Skybox has a coulomb counter so I can describe things in terms of percentage of SOC. By morning the pack is down to about 70% of SOC and begins charging by 9AM ramping up the Amperage to about 40 Amps by 10:30 to 11:00 AM. Usually it is done my 1:00 PM. The last hour is in the ramp down of current in the Constant Voltage stage so it begins sell to the grid. What I like about the Skybox is that I can set the maximum kW that I sell to the grid. That is important because my NEM agreement limits me to 4.8 kWs so that is the setting on my Skybox.

It will take me a year to see the financial impact of all of this and I did not do it with a particular payback in mind. Part of that is because I have two EVs that I can charge with any excess solar or by using the credits I have built up in my NEM arrangement with PG&E

@Ampster Excellent idea! Do you still receive the credit from the utility or did you have to bypass the net meter meter for the AC couple? Here is a YTuber that did something very similar with a Sol-Ark and was able to retain the credit even though the excess energy not used at 'point in time' by the house is now charging his batteries vs. being sent out to the grid.

 

GXMnow

Photon Sorcerer
I don't have my Schneider running yet as it just arrived today, but I have done a bit of study on AC coupling.

I agree to not go over what the inverter says it can take. Not only could it be unstable, it could cause damage, or even a fire. The power needs to be able to go somewhere, and if the internal components can't take more than 7.6 KW, don't do it. The Enphase micros can be set to Rule 21 with Frequency Watt, I was able to adjust my grid profile on the local network from the Enphase installer toolkit on my iPhone.

When you add a hybrid inverter between the Enphase micros and the grid, the extra power not used by your loads is going to first charge the battery. This will not be credited to you as you are not exporting that power. This is fine as you can now use that power later for free instead of selling it to the utility and buying it at a higher price later. If your battery bank reaches full charge and the hybrid inverter has to stop putting the power in the battery, any more excess your solar panels generate will then go through to the grid and export, and you will then get credit for that power, just as you did before with just the microinverters.

Depending on your hybrid inverter, there are a few other things that can happen. They all can push battery power to the essential loads panel and run those loads without pulling from the grid, or using some grid power and some battery, it all depends on the settings and available modes. This can also add power to the solar in some cases, if you have a heavy load for a short time, but most of the time, the battery power will be used when the sun is down. Some hybrid systems can also export power out the grid input from the battery. I will use this function because I want to use the stored power to help run my A/C which is still on the main panel, not in the essential loads. The plan is not to export, but only reduce grid current needed to power my heavy loads in the main panel. My XW-Pro can also export as it is Rule-21 compliant. My NEM 2.0 agreement allows me to export up to 16 amps at 240, up to a total of 900 KwH per month. One odd rule here in Cali, You can only export solar or other renewable generated power. You are not supposed to store grid power and sell it back.
 

Ampster

Renewable Energy Hobbyist
@Ampster Excellent idea! Do you still receive the credit from the utility or did you have to bypass the net meter meter for the AC couple?
I did not change anything about my NEM agreement because I am still using the Inverter described in my agreement. The fact that its output is now m monitored by the Skybox should not affect the NEM agreement. Under that agreement I am permited to add 1 kW and that is what I have done by limiting the total kW output to 4.8 kW.
 

Ampster

Renewable Energy Hobbyist
@Ampster Could you explain what would happen if I AC coupled my 10.5kW LG panels powered by Enphase IQ7+ microinverters to the Skybox? Would anything over 5kW get clipped?
I would not recomend that because you would be exceeding the 7.6 limit of the Skybox. If it did clip it would be a waste of capacity, much like throwing away 2.4 kW of inverters. You would be much better separating that much capacity and leaving it connected to the grid. Then the other 7.6 kW of micros would be working through the Skybox and continue to work when the grid is down. The 2.4 kW would not work when the grid is down.
.
 

newbostonconst

Solar Addict
I haven't researched the Skybox wiring but on the Outback GX4048 when the grid is up the power follows straight through a relay closure in the GS4048 to the critical loads panel. I added 2.4k of APsystems inverters to the critical loads panel. So when grid is up the solar power flows backward through the GS4048 box to grid and I get net metering credit. When grid is down the 2.4k solar in the critical loads panel charges the batteries.

The if there isn't enough power being used in a grid down situation in the critical loads panel the GS4048 frequency shifts and shuts down the APsystems inverters. The APsystems inverters do not for me throttle back, they just shut off and 5 minutes later come back on and if there still isn't enough load again they are shut back down again for 5 minutes by the GS4048 and over and over....I choose 2.4K of solar on the critical loads panel because that should be able to charge the batteries and run that panel through the day. If I need more solar then that I can flip two breakers and feed 7.3K of enphase solar inverters to the critical loads panel. I have yet to do this or the need. In the last 4 years we have lost power twice.
 

Ampster

Renewable Energy Hobbyist
@newbostonconst Are your Enphase inverters IQ models? If so they will modulate ( ramp up and down) depending on your loads when the grid is down. That may not be a problem for you but on another forum it was a problem for another poster.
 

GXMnow

Photon Sorcerer
My iQ7's were not set in the correct grid code. I had to load the Rule 21 Frequecy/Watt code with the installer toolbox app.
 

taxil

New Member
I would not recomend that because you would be exceeding the 7.6 limit of the Skybox. If it did clip it would be a waste of capacity, much like throwing away 2.4 kW of inverters. You would be much better separating that much capacity and leaving it connected to the grid. Then the other 7.6 kW of micros would be working through the Skybox and continue to work when the grid is down. The 2.4 kW would not work when the grid is down.
I believe 8.9kw is the maximum output I will see from the Enphase GTI. So at worst 1.3kw will clip. But is it correct to think that since the GTI is connected directly to the critical load panel, and I have say 2kw of continuous critical loads, no power will be clipped?
 

newbostonconst

Solar Addict
@newbostonconst Are your Enphase inverters IQ models? If so they will modulate ( ramp up and down) depending on your loads when the grid is down. That may not be a problem for you but on another forum it was a problem for another poster.
The unit went out in the middle of the night... It was in standby, and the the first time it went out I didn't have any solar on the critical loads side...

I am hearing it is common failure... But on hold now to get a replacement board now and will ask them...

Permanently moving the enphase IQ's over to the critical loads panel is not an easy task.
 

Ampster

Renewable Energy Hobbyist
But is it correct to think that since the GTI is connected directly to the critical load panel, and I have say 2kw of continuous critical loads, no power will be clipped?
I don't know if the issue is clipping. I see the issue as exceeding the manufacture's (Outback) recommendations. If you are looking for advice from someone who has been using Outback products for over 5 years (me) I would suggest you ask Outback that question.

If you would like to know what I would do, then the answer is I would move enough microinverter capacity off the critical loads panel to be within the manufacturers specs.

If the answer is that it is just a clipping issue I would still move that capacity to the main panel because I can't stand the thought of having 1.3 kW of solar panels and micro inverters not outputting because i could not find a better solution. What you are suggesting is not optimum. The risk is that if your batteries are in the low Amp stage of Absorb (constant voltage) and you have a 4kW load that drops there may not be enough buffer because of the time it would take for the frequency control to ramp down the output of the micros. That power is going to go into the Skybox as a spike and whether it kills the Skybox or the batteries or both doesn't matter. It might not happen when on the grid because the grid will absorb it. It most likely could happen when you need the Skybox the most, when the grid is down.
 
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GXMnow

Photon Sorcerer
I believe 8.9kw is the maximum output I will see from the Enphase GTI. So at worst 1.3kw will clip. But is it correct to think that since the GTI is connected directly to the critical load panel, and I have say 2kw of continuous critical loads, no power will be clipped?
There are several problems here. When on grid, any grid tie inverter on the output side will not limit it's power. The grid is supplying 60 hz, and there is no way to command the grid to change frequency to make the inverter reduce it's output. If it can put out 10.5 KW, at some point of full sun that can happen. The wiring, contacter, and terminals in the outback just can't take it. And you can't assume the essential loads will bleed off some of the power. You don't want something catching fire if a switch is turned off. When it is running off grid, the situation could get even worse. Even with frequency/watt control, it expect no more than 7.6 KW and a certain ramp down. If the current comes on too high, it could get unstable and maybe destroy the inverter in a shower of sparks. Don't risk it. 5K of old school inverter, or up to 7.6K if it does Rule 21 Frequency/Watt. They don't put that in the instructions for no reason.
 
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