Pro/Cons to running a DIY battery bank via whole house switch?

[Bear22]

Morning Peeps,

After doing the research with mainstream solar backup solutions (Enphase, Tesla, etc.) I've come to these conclusions: The "mainstream solution" batteries are too costly, the installer costs are shady, and there's too many pitfalls with respect to warranty reliance.

I am now scratching the surface with researching DIY means in terms of building my own battery backup: So, looking at other more viable (realistic) means for battery storage/backup through a whole house generator transfer switch.

Looking for some decent threads/advice for building such a system.

Thanks in advance!
G

 

[TomC4306]

What is your roundabout budget? $10,000 or $40,000.

 

[Bear22]

What is your roundabout budget? $10,000 or $40,000.

Ideally, less than $10K (SHTF battery back up). The amount isn't so important (to me), as is the value/cost index and more importantly: the ability to fix/replace something when component XYZ goes awry.

My personal grail is getting power from my grid-tied system (Enphase) to the wall socket in a black out situation in order to charge a DIY battery bank, that in turn can power certain circuits (main panel) from a whole house switch.

 

[Casteil]

What is your roundabout budget? $10,000 or $40,000.

^^ we need to know a little more about your budget and anticipated consumption to provide you with suitable recommendations.

Some other questions that'll help people advise you:

1. Do you know how much your house uses on average in a given day? ...how many total kWh in a year?
2. Do you intend to grid-tie this system?
3. Whole house switch essentially dictates the need for a huge battery/inverter bank (for things like central AC, electric stove, etc)... have you considered a smaller 6-10 circuit transfer switch that'll allow you to select which circuits to run off your battery/inverter system? (you can do ~$2k on the low end, but whole house is likely going to run at least $15k

 

[Casteil]

Ideally, less than $10K (SHTF battery back up). The amount isn't so important (to me), as is the value/cost index and more importantly: the ability to fix/replace something when component XYZ goes awry.

My personal grail is getting power from my grid-tied system (Enphase) to the wall socket in a black out situation in order to charge a DIY battery bank, that in turn can power certain circuits (main panel) from a whole house switch.

Ah, in that case I'd probably recommend LifePower4 battery(ies?) and an inexpensive off-grid hybrid inverter (or a separate charge controller + inverter setup for replacement/repair reasons). I just received a Growatt SPF 3000TL + LifePower4 recently and so far I'm pretty impressed with them.

If you don't need split-phase 240V AC, that'll help keep your system costs down. That said, you could still do split-phase AC with 2x LifePower4 and 2x 120V inverters (that support paralleling) or 1x 240V inverter for <$10k.

Edit: Well, reconsidering around your "repairability" aspect, LifePower4+Hybrid Inverter's probably not the way to go, and I'm not one to give advice on DIY batteries so that's about all I have to contribute here

 

[Bear22]

Ah, in that case I'd probably recommend LifePower4 battery(ies?) and an inexpensive off-grid hybrid inverter (or a separate charge controller + inverter setup for replacement/repair reasons). I just received a Growatt SPF 3000TL + LifePower4 recently and so far I'm pretty impressed with them.

If you don't need split-phase 240V AC, that'll help keep your system costs down. That said, you could still do split-phase AC with 2x LifePower4 and 2x 120V inverters (that support paralleling) or 1x 240V inverter for <$10k.

Edit: Well, reconsidering around your "repairability" aspect, LifePower4+Hybrid Inverter's probably not the way to go, and I'm not one to give advice on DIY batteries so that's about all I have to contribute here

I've done a little research into LifePower.

Now, the harder nut to crack are idea(s) for getting the power (from my rooftop array) to the battery bank for charging purposes.

 

[Casteil]

I've done a little research into LifePower.

Now, the harder nut to crack are idea(s) for getting the power (from my rooftop array) to the battery bank for charging purposes.

Indeed.. as I understand it, microinverters need to "see" the grid so you wouldn't be able to just use a manual transfer switch to pump their power into your 'off grid' inverter rather than your main panel & the grid.

 

[zanydroid]

This is a theoretically solved problem. You can AC couple to a grid forming hybrid transformer. In the SLD I've seen the other inverters are connected on the critical loads side, not the utility side (well, you can connect them on both, there's reasons to do that, but if you want it to work with grid down you need to put the AC couple in the right place.) The grid forming hybrid will then create a grid that will defeat the anti-islanding algorithm on the microinverters (basically by counteracting the power variations that the inverters inject into their output).

Theoretically solved means not all hardware will support this, you probably need to understand how it works b/c the really easy turn-key approaches are often single brand / higher end, and there may be interoperability issues. Because the baseline interaction, across brands, between hybrid inverter and other inverters, is UL1741SA frequency shift (for newer inverters) or triggering islanding mode (for old inverters). If you have some understanding of electrical you can see that neither of these are available conveniently when grid is up. Within the same brand or brands that work together, they can interoperate with proprietary or (potentially) SunSpec control registers, which are signaled to the inverters via a radio or PLC data packets.

In your current Enphase hardware, IQ7 and IQ8s will mind meld with the Gateway and the microinverters in their same brand batteries to achieve the above. Using PLC. You are unlikely to be able to get this with different batteries, but since Enphase is the most widespread microinverter brand there are lots of war stories about how to AC couple them.

Connecting to critical loads side also makes charging from excess solar easier. Not all hybrid inverters support remote CTs (IE, these only have internal CTs), which is what you need if you want to use the excess solar from inverters connected on the utility side.

 

[Bear22]

This is a theoretically solved problem. You can AC couple to a grid forming hybrid transformer. In the SLD I've seen the other inverters are connected on the critical loads side, not the utility side (well, you can connect them on both, there's reasons to do that, but if you want it to work with grid down you need to put the AC couple in the right place.) The grid forming hybrid will then create a grid that will defeat the anti-islanding algorithm on the microinverters (basically by counteracting the power variations that the inverters inject into their output).

Theoretically solved means not all hardware will support this, you probably need to understand how it works b/c the really easy turn-key approaches are often single brand / higher end, and there may be interoperability issues. Because the baseline interaction, across brands, between hybrid inverter and other inverters, is UL1741SA frequency shift (for newer inverters) or triggering islanding mode (for old inverters). If you have some understanding of electrical you can see that neither of these are available conveniently when grid is up. Within the same brand or brands that work together, they can interoperate with proprietary or (potentially) SunSpec control registers, which are signaled to the inverters via a radio or PLC data packets.

In your current Enphase hardware, IQ7 and IQ8s will mind meld with the Gateway and the microinverters in their same brand batteries to achieve the above. Using PLC. You are unlikely to be able to get this with different batteries, but since Enphase is the most widespread microinverter brand there are lots of war stories about how to AC couple them.

Connecting to critical loads side also makes charging from excess solar easier. Not all hybrid inverters support remote CTs (IE, these only have internal CTs), which is what you need if you want to use the excess solar from inverters connected on the utility side.

I don't posses the personal vernacular/lexicon of much of what you've said above. Can you provide a real world example of such a system?

 

[zanydroid]

I think most of the jargon I used is industry standard, I believe the only one I mangled is Grid Forming, which means something very different in grid power engineering and will pop up confusing results on Google.

Look at a SolArk installation manual, for the 8k and up specifically. The Single Line Diagram shows all the parts I mentioned.

Also search for AC coupling from Outback or SolArk publications, I learned some of this from a good writeup, I believe from Outback.

Search this forum for external CT and you should find schematics (possibly verbally expressed) comparing internal CT to external CT.

 

[zanydroid]

Better discussion of AC coupling on a SolArk than what I wrote. I don’t think the company provides a good SLD for it.

Please recommend inverter to AC couple with Sol-Ark 12K

I'm considering getting an inverter that I can hook about 4k worth of solar panels to and bring that into my Sol-Ark 12K via AC coupling. I have not studied the AC coupling yet to see what requirements it would mean or place onto an inverter. I just got started in my research on which inverter...

diysolarforum.com

 

[zanydroid]

Now, the harder nut to crack are idea(s) for getting the power (from my rooftop array) to the battery bank for charging purposes.

And to be crystal clear AC coupling is what you need to run off grid with your existing micros. If you can’t get it to work you need to buy new micros or rewire and switch to a hybrid string inverter.

 

[curiouscarbon]

edit: Power Line Communication

PLC = Programmable Logic Controller

a small computer with sensors/data input and relays that can be turned on and off based off of a computer program

 

[zanydroid]

PLC = Programmable Logic Controller

a small computer with sensors/data input and relays that can be turned on and off based off of a computer program

It also means Power Line Communication. I don’t believe I used the logic controller sense in my writeup. Unfortunately both are used in solar so you have to infer from context which meaning is being used.

 

[curiouscarbon]

It also means Power Line Communication. I don’t believe I used the logic controller sense in my writeup. Unfortunately both are used in solar so you have to infer from context which meaning is being used.

gotcha! my mistake

---

Power Line Communication is when data is sent through a cable that is also providing power. often seen in AC, but can also be done with DC

cheers!

 

[Bear22]

Thanks!