Trying to understand Off-Grid vs On-Grid, PV and battery Backup

[TurbineTester]

I'm wanting to greatly reduce my grid power bill and be able to supply as much as possible from ~16kw of roof mounted panels. I'd like any excess power generated stored in batteries for use at night or when the PV is too low to compensate for big loads like AC/Dryer/Water Heater. When either the batteries need to be charged or the PV array cannot supply enough power I'd like to use the grid to power my home and charge the batteries. I was thinking i would do this with a bank of eg4 batteries, a couple of eg4 inverters for split phase output and a some kind of smart controller to automatically supplement battery/PV power with grid power. The EG4 6.5KW inverters support grid input, and I have no interest in net metering, but my grid is typically very reliable and i know we won't be able to get all of our power from solar. I also do not want to install a "critical load panel". According to this resource https://diysolarforum.com/resources/grounding-and-bonding-for-mpp-lv6548-and-eg4-6500ex-48.275/ this at least seems possible using the above equipment. I was hoping for a dual inverter setup with grid input, battery backup and automatic switching with no net metering. In otherwords maximizing the PV and batteries as much as possible before utilizing the grid. I see several options with these inverters using grid power, but all of them have a critical load panel. So is there a way to get grid power to supplement PV/battery without a critical loan panel using the EG4 6.5KW inverters?

 

[timselectric]

If you have enough inverting power for the whole house, you don't need a critical loads panel. You can just feed the whole thing. The EG4 inverters are off grid inverters. So, there's no possibility for exporting to the grid. They only have a grid connection for backup.

 

[timselectric]

Standard setup is in this order.
Meter
Service panel
Inverters
Loads panel
All circuits are fed from the loads panel

 

[TurbineTester]

Standard setup is in this order.
Meter
Service panel
Inverters
Loads panel
All circuits are fed from the loads panel

Gotcha here so a service panel would do what? Connect the grid input to my home directly to the inverters, so wire from meter to the service panel, out to the inverters, and inverters directly to the Loads Panel. So my only concern is that the EG4 has an AC output limit of 60A, so assuming 60Ax2 in split phase configuration =120A. I'm not sure what my actual max amperage use case in my house. So i guess my first question is what happens if i need 150A of power and the inverters can't deliver?

 

[timselectric]

Then, your system will shutdown and leave you without power. Until you restart it.

 

[TurbineTester]

Then, your system will shutdown and leave you without power. Until you restart it.

So then that's not really what i'm looking for it to do, i want it to supplement the inverter power with grid power. How do i solve that problem?

 

[timselectric]

If you overload the inverter, it shuts down.
You can add more inverting power. Or split part of your circuits into a critical loads panel. In other words, keep some circuits in the service panel.

 

[timselectric]

You could also manage your loads, so that you don't overload the inverters.

 

[DThames]

 

[John Frum]

I think what you are looking for is called "grid-tie net zero".

 

[schmism]

Then, your system will shutdown and leave you without power. Until you restart it.

Mine have a setting to restart on overload. The thinking is that most things will set to off state when they power back on. aka the microwave just doesnt come back on, the washing machine just doesn't come back on etc. This allows the lights/fridge to be back up in about 10 sec and then you can figure out what you overloaded.

 

[timselectric]

Mine have a setting to restart on overload. The thinking is that most things will set to off state when they power back on. aka the microwave just doesnt come back on, the washing machine just doesn't come back on etc. This allows the lights/fridge to be back up in about 10 sec and then you can figure out what you overloaded.

Yes, mine is set for the same thing. But, I know what my loads are. I'm not familiar with theirs.
So, I don't usually recommend that. Because what is causing the overload could be something that starts right back up. And then the cycle continues.

 

[adamantium]

So then that's not really what i'm looking for it to do, i want it to supplement the inverter power with grid power. How do i solve that problem?

To do what you want to do, you must first be connected to the grid. Second you need an inverter that has a large pass-through such as 200A and frequency shifting capability. Third you need to connect a PV inverter to the load side (output side) of the inverter. This inverter supplies the power from the panels to the loads. Now with that configuration, the solar panels will feed all the power they can to the loads. If there is not enough power from the PV panels then the rest will be supplemented by the grid automatically. If there is too much power from the solar panels then the primary inverter will charge any batteries you have, or if they are already fully charged, will allow the power to flow back through to the grid. If the grid goes down, then the primary inverter will lock out the grid pass-through and generate its own grid for the loads from the battery and the PV inverter will continue to supply all that it has to feed the loads. If there is insufficient power from the PV panels then the inverter will supplement power from the batteries. If there is too much power from the PV panels then the primary inverter will frequency shift the PV inverter to decrease its output. You can also then configure the primary inverter to use battery power before it uses the grid. This means that the inverter will all the battery power it has at night before it supplements with the grid.

The connections would be from your service entrance to your primary inverter input. Then your primary inverter output would go to your existing load panel. Then your PV inverter input would connect to your PV panels and its output would also connect to your existing load panel. Two inverts are then connected to your existing load panel, and one has input from the grid and battery and one has input from the PV panels.

That meets your goal.

There are other ways to configure it as well that eliminate the need for the PV inverter. If the primary inverter supports connection from PV panels then you just connect them to the primary inverter instead of the load panel and let it manage the power sources from PV, battery, and grid. The primary inverter will have options to control when to use grid and battery.

Take a look at the new LuxPower and GSL 12k inverters. They do all of this I believe. In addition a single inverter would do the job. It accepts up to 18kW of PV input and generates 12kW of output. So unless you think you are going to need more than that a single inverter will suffice.

New Lux Power LXP-LB-US 12k / GSL-H-12KLV-US with 200A AC Passthrough Current (US Market)

I was notified yesterday that GSL will be releasing their new 12K hybrid split-phase inverter with 200A AC passthrough for the US market. Production will be limited in September but will ramp up through October and November. Significant features to note: 12kW EPS output (surge: 14k 10 mins...

diysolarforum.com

 

[timselectric]

To do what you want to do, you must first be connected to the grid. Second you need an inverter that has a large pass-through such as 200A and frequency shifting capability. Third you need to connect a PV inverter to the load side (output side) of the inverter. This inverter supplies the power from the panels to the loads. Now with that configuration, the solar panels will feed all the power they can to the loads. If there is not enough power from the PV panels then the rest will be supplemented by the grid automatically. If there is too much power from the solar panels then the primary inverter will charge any batteries you have, or if they are already fully charged, will allow the power to flow back through to the grid. If the grid goes down, then the primary inverter will lock out the grid pass-through and generate its own grid for the loads from the battery and the PV inverter will continue to supply all that it has to feed the loads. If there is insufficient power from the PV panels then the inverter will supplement power from the batteries. If there is too much power from the PV panels then the primary inverter will frequency shift the PV inverter to decrease its output. You can also then configure the primary inverter to use battery power before it uses the grid. This means that the inverter will all the battery power it has at night before it supplements with the grid.

The connections would be from your service entrance to your primary inverter input. Then your primary inverter output would go to your existing load panel. Then your PV inverter input would connect to your PV panels and its output would also connect to your existing load panel. Two inverts are then connected to your existing load panel, and one has input from the grid and battery and one has input from the PV panels.

That meets your goal.

There are other ways to configure it as well that eliminate the need for the PV inverter. If the primary inverter supports connection from PV panels then you just connect them to the primary inverter instead of the load panel and let it manage the power sources from PV, battery, and grid. The primary inverter will have options to control when to use grid and battery.

Take a look at the new LuxPower and GSL 12k inverters. They do all of this I believe. In addition a single inverter would do the job. It accepts up to 18kW of PV input and generates 12kW of output. So unless you think you are going to need more than that a single inverter will suffice.

New Lux Power LXP-LB-US 12k / GSL-H-12KLV-US with 200A AC Passthrough Current (US Market)

I was notified yesterday that GSL will be releasing their new 12K hybrid split-phase inverter with 200A AC passthrough for the US market. Production will be limited in September but will ramp up through October and November. Significant features to note: 12kW EPS output (surge: 14k 10 mins...

diysolarforum.com

He doesn't want to export anything to the grid. Only use grid if solar production is low. And 200A is probably twice what he needs. A simple off grid inverter is all that he wants. I would recommend any AIO's that are stackable.

 

[adamantium]

He doesn't want to export anything to the grid. Only use grid if solar production is low. And 200A is probably twice what he needs. A simple off grid inverter is all that he wants. I would recommend any AIO's that are stackable.

Wrong! How does he supplement his inverter power with the grid if he is off grid? A simple off grid inverter means you are off grid. You don't need to use 200A to use an inverter that has a 200A pass-through. Show me an inverter with something more than 60 and less than 200A that will do the job. And finally your recommendation to use a stackable AIO when you just recommended an off-grid inverter is contradictory in both off-grid-ness and the amount of power you think he needs. All he needs is a single inverter with a 200A passthrough so that he doesn't have any chance of it limiting his ability to get the power he needs for his AC without having to install a secondary loads panel.

 

[timselectric]

Wrong! How does he supplement his inverter power with the grid if he is off grid? A simple off grid inverter means you are off grid. You don't need to use 200A to use an inverter that has a 200A pass-through. Show me an inverter with something more than 60 and less than 200A that will do the job. And finally your recommendation to use a stackable AIO when you just recommended an off-grid inverter is contradictory in both off-grid-ness and the amount of power you think he needs. All he needs is a single inverter with a 200A passthrough so that he doesn't have any chance of it limiting his ability to get the power he needs for his AC without having to install a secondary loads panel.

Most AIO's are off grid inverters. Only a few are capable of grid tie. He doesn't need grid tied, because he has no need for exporting power to the grid.
Many off grid AIO's are stackable. (Growatt, MPP, EG4, just to name a few) off grid AIO's usually have an AC in connection. This can be fed by grid or generator. This is used to supplement or take over for low solar production.

 

[OffGridInTheCity]

I'm off-grid (with grid assist). I use automatic ATSs to feed power to my home circuits. When solar is enough to turn on the inverters, the ATSs sense the inverter power on the generator leg and automatically switch to that source. When the solar/batteries are used up for the day and the inverter turns off, the ATSs automatically switch back to grid. I put a MTS at the main panel ATS so I can choose individual circuits / control the over the overall load by just flipping switches between GEN and LINE.


The only issue with this is that I have to UPS sensitive circuits as the ATSs are mechanically linked relays and not fast enough for computers, Tivo, etc. I use cheaper (but UL listed) ATSs but they're limited to 240v @ 50a so I have several of them. For example, I have one a dedicated one for the whole house heat pump compressor circuit (240v @ 40a).



Overall, I'm powering about 80% of my circuits this way - plenty for a fully functional home with no grid.

 

[adamantium]

Most AIO's are off grid inverters. Only a few are capable of grid tie. He doesn't need grid tied, because he has no need for exporting power to the grid.
Many off grid AIO's are stackable. (Growatt, MPP, EG4, just to name a few) off grid AIO's usually have an AC in connection. This can be fed by grid or generator. This is used to supplement or take over for low solar production.

I understand what you say but I don't agree, so let me explain. First of all who said he needs an AIO inverter? You did. I say he needs a hybrid inverter, and a hybrid inverter is capable of on-grid, off-grid, and grid-tie capabilities. Most brand name full-house inverters are hybrid inverters not AIO inverters. They include but are not limited to Lux Power, GSL Energy, Amensolar, Deye, Sol-Ark, Huayu, Outback, Schneider, Growatt, MPPSolar, SunGoldPower, and more. Grid-tie means you are tied to the grid, and grid interactive means that you can interact with the grid. Neither of those imply that the inverter is PV-only or must unconditionally feed power back to the grid. What you are referring to is a PV inverter and those are grid-tie capable, but that doesn't make everything else not grid-tie capable. So I can say he needs a grid-tie inverter and mean what I mean and not mean what you mean. For example, you can have a grid-tie inverter that has no solar inputs such as the old Schneider XW+ from almost a decade ago. Its not a hybrid, its not a PV inverter, but it is most definitely grid-tied. It has a connection to the grid, a 60A pass-through, and you can choose to charge your batteries with wind power and sell your battery power to the grid if you want to.

Back to the member's request now. When someone says they want to use the grid to supplement their battery power, they don't mean going off-grid. They mean using the grid to supplement their battery power. The reason is that most people can't afford a battery large enough to store all the power they need to go off grid. If they need 15kW immediately and their batteries are dead or charging, or their battery or inverter can't provide all of the power they need, then what they want is the power to be supplied by the grid automatically and instantaneously through a pass-through without a flicker. No mode changes, no prioritization of loads, no load balancing in advance for on-grid or off-grid use, no limitations in what you can run, no critical loads panel, just additional power from the grid now.

So Let's review what the request was really about.

1. I'm wanting to greatly reduce my grid power bill as much as possible from ~16kw of roof mounted panels.
2. I'd like any excess power generated stored in batteries for use at night or when the PV is too low to compensate for big loads like AC/Dryer/Water Heater.
3. When either the batteries need to be charged or the PV array cannot supply enough power I'd like to use the grid to power my home and charge the batteries.
4. I was thinking i would do this with... and a some kind of smart controller to automatically supplement battery/PV power with grid power. 5. The EG4 6.5KW inverters support grid input, and I have no interest in net metering, but my grid is typically very reliable and i know we won't be able to get all of our power from solar.
6. I also do not want to install a "critical load panel".
7. I was hoping for a dual inverter setup with grid input, battery backup and automatic switching with no net metering. In otherwords maximizing the PV and batteries as much as possible before utilizing the grid. I see several options with these inverters using grid power, but all of them have a critical load panel.
8. So is there a way to get grid power to supplement PV/battery without a critical loan panel using the EG4 6.5KW inverters?

This is obviously not a request for an off-grid solution. The member wants to stay on the grid and simply have the grid supplement his power needs without interruption or hassle when PV and battery cannot do it alone. He specifically asks, "is there a way to get grid power to supplement PV/Battery without a critical load panel?"

The solution I offered previously meets all of his criteria. All hybrids today are stackable. The one I proposed is stackable up to 10 units, but what is he going to do with two inverters? He only has 16kW of power from 6 hours a day at best. If he doesn't use any of it while the sun is shining, a single 12k inverter will drain his battery dry before morning. Two will drain it dry before midnight. Besides he has the grid to supplement any additional power over the 12kW the inverter will provide, which is what he desires. The 200A pass-through isn't more than he needs, its what most hybrid inverters 12k and up are coming with now, and that feature alone addresses his need not to install a critical loads panel. Unless you have a specific reference to an inverter that has a pass-through equal to his current service, then a 200A will suffice. Finally it costs less to buy the 12k (with 18k-PV) inverter I recommended than two of the 6k inverters you recommended, and they aren't nearly as feature rich. Prove otherwise.

 

[Pierre]

I understand what you say but I don't agree, so let me explain. First of all who said he needs an AIO inverter? You did. I say he needs a hybrid inverter, and a hybrid inverter is capable of on-grid, off-grid, and grid-tie capabilities. Most brand name full-house inverters are hybrid inverters not AIO inverters. They include but are not limited to Lux Power, GSL Energy, Amensolar, Deye, Sol-Ark, Huayu, Outback, Schneider, Growatt, MPPSolar, SunGoldPower, and more. Grid-tie means you are tied to the grid, and grid interactive means that you can interact with the grid. Neither of those imply that the inverter is PV-only or must unconditionally feed power back to the grid. What you are referring to is a PV inverter and those are grid-tie capable, but that doesn't make everything else not grid-tie capable. So I can say he needs a grid-tie inverter and mean what I mean and not mean what you mean. For example, you can have a grid-tie inverter that has no solar inputs such as the old Schneider XW+ from almost a decade ago. Its not a hybrid, its not a PV inverter, but it is most definitely grid-tied. It has a connection to the grid, a 60A pass-through, and you can choose to charge your batteries with wind power and sell your battery power to the grid if you want to.

Back to the member's request now. When someone says they want to use the grid to supplement their battery power, they don't mean going off-grid. They mean using the grid to supplement their battery power. The reason is that most people can't afford a battery large enough to store all the power they need to go off grid. If they need 15kW immediately and their batteries are dead or charging, or their battery or inverter can't provide all of the power they need, then what they want is the power to be supplied by the grid automatically and instantaneously through a pass-through without a flicker. No mode changes, no prioritization of loads, no load balancing in advance for on-grid or off-grid use, no limitations in what you can run, no critical loads panel, just additional power from the grid now.

So Let's review what the request was really about.

1. I'm wanting to greatly reduce my grid power bill as much as possible from ~16kw of roof mounted panels.
2. I'd like any excess power generated stored in batteries for use at night or when the PV is too low to compensate for big loads like AC/Dryer/Water Heater.
3. When either the batteries need to be charged or the PV array cannot supply enough power I'd like to use the grid to power my home and charge the batteries.
4. I was thinking i would do this with... and a some kind of smart controller to automatically supplement battery/PV power with grid power. 5. The EG4 6.5KW inverters support grid input, and I have no interest in net metering, but my grid is typically very reliable and i know we won't be able to get all of our power from solar.
6. I also do not want to install a "critical load panel".
7. I was hoping for a dual inverter setup with grid input, battery backup and automatic switching with no net metering. In otherwords maximizing the PV and batteries as much as possible before utilizing the grid. I see several options with these inverters using grid power, but all of them have a critical load panel.
8. So is there a way to get grid power to supplement PV/battery without a critical loan panel using the EG4 6.5KW inverters?

This is obviously not a request for an off-grid solution. The member wants to stay on the grid and simply have the grid supplement his power needs without interruption or hassle when PV and battery cannot do it alone. He specifically asks, "is there a way to get grid power to supplement PV/Battery without a critical load panel?"

The solution I offered previously meets all of his criteria. All hybrids today are stackable. The one I proposed is stackable up to 10 units, but what is he going to do with two inverters? He only has 16kW of power from 6 hours a day at best. If he doesn't use any of it while the sun is shining, a single 12k inverter will drain his battery dry before morning. Two will drain it dry before midnight. Besides he has the grid to supplement any additional power over the 12kW the inverter will provide, which is what he desires. The 200A pass-through isn't more than he needs, its what most hybrid inverters 12k and up are coming with now, and that feature alone addresses his need not to install a critical loads panel. Unless you have a specific reference to an inverter that has a pass-through equal to his current service, then a 200A will suffice. Finally it costs less to buy the 12k (with 18k-PV) inverter I recommended than two of the 6k inverters you recommended, and they aren't nearly as feature rich. Prove otherwise.

Very nice explanation. Lots of misunderstanding about connecting to grid. I see an off grid system as totally isolated from grid i.e. where there is no grid at all. Grid tied to me implies import / export to grid. Grid assist or grid follow to me implies : import from grid with no export e.g. Growatt 5000ES with PV input , battery in / out , grid pass- through etc. No need for critical load panel and uses existing service panel. Simple installation - and KISS comes to mind.

 

[timselectric]

Grid-tie means you are tied to the grid, and grid interactive means that you can interact with the grid.

Grid tied and grid interactive are the same thing.
Grid-tied is a bidirectional connection.
An off grid AIO only connects to the grid as a load.
I can see how this terminology can be confusing. Especially when it gets repeated incorrectly a lot.

I don't recommend expensive equipment with a lot of features that aren't needed. (Depending on specific needs) no point in paying extra for Grid-tied and AC coupling capabilities, if you aren't going to use them.