Best options for getting battery backup ASAP (probably DIY) while planning on solar panels professionally installed in 1-2 years

[aunsafe2015]

Increasingly frequent power outages have led me to decide that I need a backup power solution ASAP even though I won't be able to have solar panels installed for another year or two. I'd like to choose batteries + inverter now that will be usable with a future 11-12 kW professionally installed solar array a year or two down the road. I'm trying to understand my options for doing that. As I understand it (and my understanding may well be wrong or very limited), the below would be some of the most common options. Any suggestions which is best, and whether or not there are other options I should be considering? Thanks for any input! BTW, portability is NOT a concern.

1) A critical loads subpanel + inverter + batteries. This requires a full blown subpanel where the individual critical circuit home runs are moved from the main electrical panel to the subpanel. To accommodate an 11-12 kW solar array in the future I'm probably looking at something like the Sol-Ark 8K or 12K. Has the advantage of potentially being automatic transfer to batteries, like a UPS. Apparent disadvantage is that if inverter goes down, the critical loads subpanel presumably goes down with it, even if grid power is working fine.

2) Same as above but instead of doing a critical loads subpanel, just do an interlock kit with a 30-amp inlet for battery output from the inverter during power outages connected to the interlock breaker. Advantage is that it's an easier install with no subpanel and all panel circuits potentially available for battery backup. Disadvantage is that I'd have to manually do the switchover to battery power during grid outages.

3) On Reddit, one guy did a Reliance Controls manual transfer switch, but kept his inverter+batteries plugged into the MTS power inlet 24/7, and left the MTS breakers in "generator" mode with the inverter in "pass-through" mode. Apparently he did 24/7 pass-through power from the inverter to the MTS, such that if there were a power outage, the inverter automatically switched from passing-through grid power to using the batteries to power the MTS. So it was a manual transfer switch that was effectively operating as an automatic transfer switch. Sounded like an interesting option because a full blown separate subpanel is not required, you get automatic transfer during power outages, but you could also get power to the circuits in the MTS directly from the main panel (rather than passing-through the inverter) if your inverter went down. No idea if this is a common solution or not but it sounded interesting.

4) Something like an EcoFlow Smart Home Panel + Ecoflow Delta Pro batteries. The problem I see with this one is that I don't think it's really compatible with my plan for 11-12 kW of solar panels in the future.

 

[FilterGuy]

Increasingly frequent power outages have led me to decide that I need a backup power solution ASAP even though I won't be able to have solar panels installed for another year or two. I'd like to choose batteries + inverter now that will be usable with a future 11-12 kW professionally installed solar array a year or two down the road. I'm trying to understand my options for doing that. As I understand it (and my understanding may well be wrong or very limited), the below would be some of the most common options. Any suggestions which is best, and whether or not there are other options I should be considering? Thanks for any input! BTW, portability is NOT a concern.

1) A critical loads subpanel + inverter + batteries. This requires a full blown subpanel where the individual critical circuit home runs are moved from the main electrical panel to the subpanel. To accommodate an 11-12 kW solar array in the future I'm probably looking at something like the Sol-Ark 8K or 12K. Has the advantage of potentially being automatic transfer to batteries, like a UPS. Apparent disadvantage is that if inverter goes down, the critical loads subpanel presumably goes down with it, even if grid power is working fine.

2) Same as above but instead of doing a critical loads subpanel, just do an interlock kit with a 30-amp inlet for battery output from the inverter during power outages connected to the interlock breaker. Advantage is that it's an easier install with no subpanel and all panel circuits potentially available for battery backup. Disadvantage is that I'd have to manually do the switchover to battery power during grid outages.

3) On Reddit, one guy did a Reliance Controls manual transfer switch, but kept his inverter+batteries plugged into the MTS power inlet 24/7, and left the MTS breakers in "generator" mode with the inverter in "pass-through" mode. Apparently he did 24/7 pass-through power from the inverter to the MTS, such that if there were a power outage, the inverter automatically switched from passing-through grid power to using the batteries to power the MTS. So it was a manual transfer switch that was effectively operating as an automatic transfer switch. Sounded like an interesting option because a full blown separate subpanel is not required, you get automatic transfer during power outages, but you could also get power to the circuits in the MTS directly from the main panel (rather than passing-through the inverter) if your inverter went down. No idea if this is a common solution or not but it sounded interesting.

4) Something like an EcoFlow Smart Home Panel + Ecoflow Delta Pro batteries. The problem I see with this one is that I don't think it's really compatible with my plan for 11-12 kW of solar panels in the future.

I'll talk about the options out of order.

Option 4 should be considered a quick but short-term solution. You are correct that the solar generators available today will not accommodate a large array like you are considering in the future.

Option 1 and option 2 come down to a personal choice, You seem to have the pro's and con's pretty well understood.

Option 3 is good, but...... Depending on what inverter you are looking at you may have to make some hard choices.
The Reliance Multi-circuit transfer switch does not switch the neutral power line. This by itself is not a problem. However, this ends up requiring what I call a common neutral arrangement on the inverter (The input neutral and output neutral end up being the same circuit). Most of the higher-end inverters not only can handle this but the neutrals are permanently wired together internally. (They are always common-neutral)

However, the manufacturers and distributors of many of the value-priced inverters from MPP, Growatt, and EG4 say common neutral configurations are dangerous and don't do it. Meanwhile, there are many reports of it working just fine. Furthermore, I have looked at it closely and can not see why it would be dangerous. Your timing is good because I have been discussing this just today over on this thread:

EDITED TITLE: Why not common Neutral? What is dangerous about it?

As many of you know, The value-priced inverter manufacturers provide horrible documentation so I have been on a mission to understand the grounding and bonding of the popular value-priced inverters. Edit: Corrected Ground to Neutral. As part of this, the question of 'common Neutral' has come up...

diysolarforum.com

 

[wattmatters]

I have option 3. You can read about my progression towards that on my linked thread:

Backup down under

Greetings from down under. I live in a home near the small town of Bellingen, in northern NSW, Australia. Glorious country: That's our home at left centre, and obscured by the tree and slightly off the left of the image is a secondary dwelling where my Mum lives. 12 acres, behind our home (to...

diysolarforum.com

In essence I have a regular grid-tied inverter/PV system and an off-grid inverter. The off-grid inverter has it's own small PV array plus of course the battery.

Mine is set up such that the off-grid inverter feeds a small distribution panel. That supplies two circuits, one for a couple of dedicated off-grid GPOs (office/pool pump area), the other is connected to the input of the manual transfer switch in the main circuit board.

The transfer switch is now left set to the "generator" supply position.

There are some circuits which are excluded from being supplied power via the off-grid/generator side of the transfer switch. These circuits are grid power only circuits and operate normally from grid power while the rest are powered via the off-grid system via the transfer switch. These grid-only circuits include the oven, the ducted aircon system, one other large aircon system, hot water, the pool pump GPO circuit and importantly, the circuit dedicated to supply AC power to the off-grid inverter.

That last one is important because when operating the off-grid inverter in Utility First mode (pass thru of grid power), you do not want the inverter to be feeding power back to itself.

In this way all the "essential" circuits will be automatically backed up by the off-grid inverter. in the event of a grid outage then either the system is already running from the battery, or if it is passing through grid power then the off-grid inverter's internal ATS switches over instantly to run from the battery (and off-grid solar PV). Grid-only circuits are not backed-up during outages.

My off-grid inverter is programmed to operate in one of two modes:
- Utility First, which is typically during the daytime when there is sufficient power from my grid-tied PV system to cover all consumption. Meanwhile the smaller off-grid PV array recharges the battery. If needed, I can supplement battery charging from the grid supply, which I only do if there is sufficient excess available and the small off-grid system won't have enough capacity on that day (I have Home Assistant automations looking after that).
- SBU mode, which is typically the night-time mode. The home is powered by the battery (and any solar PV from the off-grid array if it is still light).

It works well but there are a few things to note:
- none of the energy consumption for the grid-only circuits can ever be supplied by the battery. That means all my ducted AC consumption at night time is still imported from the grid (in the day my grid-tied PV generally covers it). Same for the other circuits.
- there are some efficiency losses when passing grid power through the off-grid inverter to power loads, so expect the actual loads placed on the grid power supply to be a little higher in this mode of operation than had they be powering the loads directly

What solution you go with really depends on what your objectives are.

There are of course other options with professionally installed battery systems (e.g. Tesla Powerwall 2) which do most of what you want, just very very expensive.

Mine is a bit complicated by a few other factors, not least of which my home is 3-phase supply and there are two outbuildings services with 3-phase supply. In effect the transfer switch on the generator side connects all the essential circuits to become a single phase supply.

 

[aunsafe2015]

I'll talk about the options out of order.

Option 4 should be considered a quick but short-term solution. You are correct that the solar generators available today will not accommodate a large array like you are considering in the future.

Option 1 and option 2 come down to a personal choice, You seem to have the pro's and con's pretty well understood.

Option 3 is good, but...... Depending on what inverter you are looking at you may have to make some hard choices.
The Reliance Multi-circuit transfer switch does not switch the neutral power line. This by itself is not a problem. However, this ends up requiring what I call a common neutral arrangement on the inverter (The input neutral and output neutral end up being the same circuit). Most of the higher-end inverters not only can handle this but the neutrals are permanently wired together internally. (They are always common-neutral)

However, the manufacturers and distributors of many of the value-priced inverters from MPP, Growatt, and EG4 say common neutral configurations are dangerous and don't do it. Meanwhile, there are many reports of it working just fine. Furthermore, I have looked at it closely and can not see why it would be dangerous. Your timing is good because I have been discussing this just today over on this thread:

EDITED TITLE: Why not common Neutral? What is dangerous about it?

As many of you know, The value-priced inverter manufacturers provide horrible documentation so I have been on a mission to understand the grounding and bonding of the popular value-priced inverters. Edit: Corrected Ground to Neutral. As part of this, the question of 'common Neutral' has come up...

diysolarforum.com

Thanks for the response. I read your linked post about common neutrals and, to be honest, most of it was a bit above my head. As to option (3), if I purchase one of the higher end inverters with the neutrals that are permanently wired together internally, is there any danger or NEC violation with option (3)? Or is it simply a matter of selecting an inverter that officially supports it? BTW, do you know off the top of your head if Sol-Ark inverters have the neutrals permanently wired together internally?

One last question about option (3). Do you know if, with the right inverter, this option would support scheduling for time-of-use grid pricing? I.e., setting the inverter to switch to battery power during peak hours, and using pass-through during off-peak hours?

Thanks so much for your help.

 

[aunsafe2015]

I have option 3. You can read about my progression towards that on my linked thread:

Backup down under

Greetings from down under. I live in a home near the small town of Bellingen, in northern NSW, Australia. Glorious country: That's our home at left centre, and obscured by the tree and slightly off the left of the image is a secondary dwelling where my Mum lives. 12 acres, behind our home (to...

diysolarforum.com

In essence I have a regular grid-tied inverter/PV system and an off-grid inverter. The off-grid inverter has it's own small PV array plus of course the battery.

Mine is set up such that the off-grid inverter feeds a small distribution panel. That supplies two circuits, one for a couple of dedicated off-grid GPOs (office/pool pump area), the other is connected to the input of the manual transfer switch in the main circuit board.

The transfer switch is now left set to the "generator" supply position.

There are some circuits which are excluded from being supplied power via the off-grid/generator side of the transfer switch. These circuits are grid power only circuits and operate normally from grid power while the rest are powered via the off-grid system via the transfer switch. These grid-only circuits include the oven, the ducted aircon system, one other large aircon system, hot water, the pool pump GPO circuit and importantly, the circuit dedicated to supply AC power to the off-grid inverter.

That last one is important because when operating the off-grid inverter in Utility First mode (pass thru of grid power), you do not want the inverter to be feeding power back to itself.

In this way all the "essential" circuits will be automatically backed up by the off-grid inverter. in the event of a grid outage then either the system is already running from the battery, or if it is passing through grid power then the off-grid inverter's internal ATS switches over instantly to run from the battery (and off-grid solar PV). Grid-only circuits are not backed-up during outages.

My off-grid inverter is programmed to operate in one of two modes:
- Utility First, which is typically during the daytime when there is sufficient power from my grid-tied PV system to cover all consumption. Meanwhile the smaller off-grid PV array recharges the battery. If needed, I can supplement battery charging from the grid supply, which I only do if there is sufficient excess available and the small off-grid system won't have enough capacity on that day (I have Home Assistant automations looking after that).
- SBU mode, which is typically the night-time mode. The home is powered by the battery (and any solar PV from the off-grid array if it is still light).

It works well but there are a few things to note:
- none of the energy consumption for the grid-only circuits can ever be supplied by the battery. That means all my ducted AC consumption at night time is still imported from the grid (in the day my grid-tied PV generally covers it). Same for the other circuits.
- there are some efficiency losses when passing grid power through the off-grid inverter to power loads, so expect the actual loads placed on the grid power supply to be a little higher in this mode of operation than had they be powering the loads directly

What solution you go with really depends on what your objectives are.

There are of course other options with professionally installed battery systems (e.g. Tesla Powerwall 2) which do most of what you want, just very very expensive.

Mine is a bit complicated by a few other factors, not least of which my home is 3-phase supply and there are two outbuildings services with 3-phase supply. In effect the transfer switch on the generator side connects all the essential circuits to become a single phase supply.

Very helpful. Thank you! One quick follow up question: When there's a grid outage and your off-grid inverter switches from pass-through mode to battery mode, how fast is the changeover? And is the changeover speed dictated solely by the inverter? Or does the manual transfer switch have some impact on how fast the changeover occurs?

 

[FilterGuy]

Thanks for the response. I read your linked post about common neutrals and, to be honest, most of it was a bit above my head. As to option (3), if I purchase one of the higher end inverters with the neutrals that are permanently wired together internally, is there any danger or NEC violation with option (3)? Or is it simply a matter of selecting an inverter that officially supports it? BTW, do you know off the top of your head if Sol-Ark inverters have the neutrals permanently wired together internally?

Sol-ark is one of the inverter lines that has the input and output permanently bonded. In fact, when you open the inverter to make the connections, all of the neutrals screw on to a single busbar.

As far as NEC violation, look for one that has UL listing and common neutral and you should be ok..... except in California where there is a state-approved list that the device must be on.

One last question about option (3). Do you know if, with the right inverter, this option would support scheduling for time-of-use grid pricing? I.e., setting the inverter to switch to battery power during peak hours, and using pass-through during off-peak hours?

Yes several inverters support that option now. I believe Sol-ark is one of them.

 

[Danke]

You say down the road you would like the solar professionally installed after already having inverter, batteries, etc. I have most of my own stuff purchased already and called around some companies and electricians for some assistance, but they won’t touch anything unless they do the whole project.

Just something to think about.

 

[wattmatters]

Very helpful. Thank you! One quick follow up question: When there's a grid outage and your off-grid inverter switches from pass-through mode to battery mode, how fast is the changeover?

The transfer time for my inverter is rated at 10 ms in UPS mode (which is what mine operates in) or 20 ms is Appliance mode. IOW it is barely noticeable. I have never measured it, nor do I really need to.

In any case, if you have anything you would consider to be sensitive to such power fluctuations then it should be operating via its own UPS or power supply. I have our computers, the NBN box & wifi router, and video/entertainment equipment all powered via their own UPS units.

That's mostly a hangover from when I used to use a regular fuel generator for backup power. It gave time to ensure those items were covered during the time it took to start the generator and flip the transfer switch.

And is the changeover speed dictated solely by the inverter?

In the instance of an outage, yes. It is automatic.

All the other times it switches modes are controlled by my own automations (or manually if I so choose).

 

[wattmatters]

I read your linked post about common neutrals and, to be honest, most of it was a bit above my head. As to option (3), if I purchase one of the higher end inverters with the neutrals that are permanently wired together internally, is there any danger or NEC violation with option (3)? Or is it simply a matter of selecting an inverter that officially supports it? BTW, do you know off the top of your head if Sol-Ark inverters have the neutrals permanently wired together internally?

Where are you located? I thought it was Australia?

If so then the NEC doesn't apply here. Obviously there will be much commonality in standards but local standards apply.

Also I doubt you can get Sol-Ark units suitable for use here. The newest equivalent inverters here are Deye units designed for Australian set ups.

 

[aunsafe2015]

Sol-ark is one of the inverter lines that has the input and output permanently bonded. In fact, when you open the inverter to make the connections, all of the neutrals screw on to a single busbar.

As far as NEC violation, look for one that has UL listing and common neutral and you should be ok..... except in California where there is a state-approved list that the device must be on.


Yes several inverters support that option now. I believe Sol-ark is one of them.

Cool, thanks again.

 

[aunsafe2015]

You say down the road you would like the solar professionally installed after already having inverter, batteries, etc. I have most of my own stuff purchased already and called around some companies and electricians for some assistance, but they won’t touch anything unless they do the whole project.

Just something to think about.

This thought had crossed my mind and I was also planning on calling around. That's pretty frustrating. What did you end up doing?

 

[aunsafe2015]

Where are you located? I thought it was Australia?

If so then the NEC doesn't apply here. Obviously there will be much commonality in standards but local standards apply.

Also I doubt you can get Sol-Ark units suitable for use here. The newest equivalent inverters here are Deye units designed for Australian set ups.

I'm in the US. PNW listed next to my name refers to Pacific Northwest. Hah... maybe I should be more specific.

 

[wattmatters]

I'm in the US. PNW listed next to my name refers to Pacific Northwest.

Ah. If I click on the location link under your user name it takes me to a business located in western Sydney, NSW Australia.

 

[wattmatters]

But more importantly, you can ignore all I said above about Australian requirements/wiring etc.

 

[aunsafe2015]

Ah. If I click on the location link under your user name it takes me to a business located in western Sydney, NSW Australia.

View attachment 128891

Hah hah, I think it's just doing a generic Google maps search for "PNW" when you click on that, so it brings up whatever is near you.