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Second powerwall, what do I need?
#11
(03-28-2020, 06:59 PM)drspeakman Wrote:
(03-05-2020, 04:06 PM)OffGridInTheCity Wrote: As @Korishan said, have to have 'synced' inverters to share the AC power produced by the individual units.    Magnum and Outback inverters are a couple of commonly known inverters that can do this.  

I use AIMS inverters due to price / output, but they cannot sync/share their output.  The 2 separate AIMS pull from a single battery bank with each inverter's output going to its own (seperate) distribution panel and powers different circuits.  


There's kind of a spectrum of price vs output range vs modular-sharing for AC pure sine wave inverters.   
* AIMS makes 12,000watt inverters (as shown above) with relatively lower price but they don't cooperate - so its 2 seperate 12,000watts rather than shared 24,000watts which is not efficient in handling peak loads as each inverter has to handle its own circuits and can't share excess capacity.
* Magnum makes inverters that can 'share/cooperate' but they are only 4,000watts each to a max of 2 or 3  - e.g. 8,000 or 12,000watts max   
* You can buy 24,000watt (and higher) single unit inverters but the price and shear weight *really* goes up when you get into that range of power.       
Second powerwall constructed and hung into place.  Now, to make the final decision on the inverter situation.  I have really been looking hard at just getting a single AIMS 12,000 watt inverter, and let it charge and discharge the battery pack as a single 48 volt pack, very cheap grid power at night, and during day with nine 280watt solar panels with a PCM 60X charger) connecting both powerwalls together in parallel, total of 24 kWh to power a single loads panel.  I would just ditch the Schneider unit, maybe sell on eBay to recover some of the costs.  It would just seem simpler this way.  The AIMS unit is $3541 on Amazon Prime, a little more than twice what I paid for the 4,000 watt Schneider unit 2 years ago, but it is really 3 times the output.  Warranty is only 2 years, and although usually don't go for extended warrarties, it is only $76 for 4 years.  Probably worth the peace of mind.

The Schneider unit was very difficult to wire, unless you have tiny hands.  It looks like the AIMS is much easier.  Has that been your experience?
No problems wiring the AIMS.  The conduit was the difficulty...  1st one was EMT but wised up on 2nd one and used flexible armour Smile My 1st AIMS has been in service about a 1.5yrs now - on/off each day with an average run time of 10hrs/day. The 2nd AIMS is just a month old but it did survive a 94a (20,000w 'ish) surge when my old AC compressor motor locked. So far so good - 11,432kwh produced to date.

They are HEAVY though - 174lbs. I contacted AIMS and they said it OK for them to 'lay flat' (as you see in the picture). Had to use block and tackle to get the top one stacked on the rack.

@LithiumSolar bought a used/2nd-hand 10K one and was successful ordering / replacing internal boards to revive it. So presumably there are repair options. He also did a youtube review of his showing much detail: https://youtu.be/tr4cyr2gqqo The 10K and 12K are pretty much identical except 12K is full ETL.
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#12
(03-28-2020, 08:58 PM)OffGridInTheCity Wrote:
(03-28-2020, 06:59 PM)drspeakman Wrote:
(03-05-2020, 04:06 PM)OffGridInTheCity Wrote: As @Korishan said, have to have 'synced' inverters to share the AC power produced by the individual units.    Magnum and Outback inverters are a couple of commonly known inverters that can do this.  

I use AIMS inverters due to price / output, but they cannot sync/share their output.  The 2 separate AIMS pull from a single battery bank with each inverter's output going to its own (seperate) distribution panel and powers different circuits.  


There's kind of a spectrum of price vs output range vs modular-sharing for AC pure sine wave inverters.   
* AIMS makes 12,000watt inverters (as shown above) with relatively lower price but they don't cooperate - so its 2 seperate 12,000watts rather than shared 24,000watts which is not efficient in handling peak loads as each inverter has to handle its own circuits and can't share excess capacity.
* Magnum makes inverters that can 'share/cooperate' but they are only 4,000watts each to a max of 2 or 3  - e.g. 8,000 or 12,000watts max   
* You can buy 24,000watt (and higher) single unit inverters but the price and shear weight *really* goes up when you get into that range of power.       
Second powerwall constructed and hung into place.  Now, to make the final decision on the inverter situation.  I have really been looking hard at just getting a single AIMS 12,000 watt inverter, and let it charge and discharge the battery pack as a single 48 volt pack, very cheap grid power at night, and during day with nine 280watt solar panels with a PCM 60X charger) connecting both powerwalls together in parallel, total of 24 kWh to power a single loads panel.  I would just ditch the Schneider unit, maybe sell on eBay to recover some of the costs.  It would just seem simpler this way.  The AIMS unit is $3541 on Amazon Prime, a little more than twice what I paid for the 4,000 watt Schneider unit 2 years ago, but it is really 3 times the output.  Warranty is only 2 years, and although usually don't go for extended warrarties, it is only $76 for 4 years.  Probably worth the peace of mind.

The Schneider unit was very difficult to wire, unless you have tiny hands.  It looks like the AIMS is much easier.  Has that been your experience?
No problems wiring the AIMS.  The conduit was the difficulty...  1st one was EMT but wised up on 2nd one and used flexible armour Smile    My 1st AIMS has been in service about a 1.5yrs now - on/off each day with an average run time of 10hrs/day.    The 2nd AIMS is just a month old but it did survive a 94a (20,000w 'ish) surge when my old AC compressor motor locked.    So far so good - 11,432kwh produced to date.

They are HEAVY though - 174lbs.  I contacted AIMS and they said it OK for them to 'lay flat' (as you see in the picture).  Had to use block and tackle to get the top one stacked on the rack.

@LithiumSolar bought a used/2nd-hand 10K one and was successful ordering / replacing internal boards to revive it.  So presumably there are repair options.  He also did a youtube review of his showing much detail: https://youtu.be/tr4cyr2gqqo    The 10K and 12K are pretty much identical except 12K is full ETL.
The one thing I see missing in this unit is a connection for your solar DC input to charge the batteries.  I guess this needs to be a separate connection from your solar charger (PCM 60X in my setup) to the battery bank.  I do not have enough solar to totally charge, so I use inexpensive grid power at night.  I would need it to invert 24/7 to run my loads panels.  Am I missing anything here?  My Schneider unit works fine, just not big enough, and it understands the solar charger that is connected to it.
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#13
(03-30-2020, 12:59 AM)drspeakman Wrote: The one thing I see missing in this unit is a connection for your solar DC input to charge the batteries.  I guess this needs to be a separate connection from your solar charger (PCM 60X in my setup) to the battery bank.  
Yes - you would direct your PCM 60x to charge the battery bank.   The AIMS has an AC input option that can charge the batteries as well.  They can both charge the batteries independent of each other.   However, I don't use AIMS to charge my batteries as that's not efficient - I use automatic transfer switches instead....

(03-30-2020, 12:59 AM)drspeakman Wrote: I do not have enough solar to totally charge, so I use inexpensive grid power at night.  I would need it to invert 24/7 to run my loads panels.  Am I missing anything here?  My Schneider unit works fine, just not big enough, and it understands the solar charger that is connected to it.
My PV power goes thru the Charge Controllers to charge the battery bank.  When the battery charges 'a bit' (e.g. reaches 52v) I turn the inverter on.  This triggers the ATS to take power from the inverter instead of the grid.  When the PV power runs out and the battery hits the cutt-off voltage (49.5v) the inverter turns off and the ATS switches back to grid.

If I'm understanding your comment above - I don't see the point of using 'grid' to charge the batteries to just turn around and run the inverter to create AC.  Instead, I just connect the grid directly (via the ATS) to the AC load and avoid the 15-20% power loss incurred by directing grid -> battery -> inverter -> AC load. 

I think what this latest discussion is highlighting
- off-grid, grid-tie, hybrid  - e.g. how you consume the AC power.   
-  There are distinct 'components' - PV Input, Charge Controller, Battery, Inverter, and ATS.   These can be combined or not - which affect the system design.    
- Goals.   Mine is: "Consume 100% of PV power produced in my off-grid system and let the grid take over once PV power is used.".   

I'm assuming you're are off-grid and (similar to my own goals) you want to consume all of your PV power - which lead me to the comments above.
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#14
(03-30-2020, 05:45 AM)OffGridInTheCity Wrote:
(03-30-2020, 12:59 AM)drspeakman Wrote: The one thing I see missing in this unit is a connection for your solar DC input to charge the batteries.  I guess this needs to be a separate connection from your solar charger (PCM 60X in my setup) to the battery bank.  
Yes - you would direct your PCM 60x to charge the battery bank.   The AIMS has an AC input option that can charge the batteries as well.  They can both charge the batteries independent of each other.   However, I don't use AIMS to charge my batteries as that's not efficient - I use automatic transfer switches instead....

(03-30-2020, 12:59 AM)drspeakman Wrote: I do not have enough solar to totally charge, so I use inexpensive grid power at night.  I would need it to invert 24/7 to run my loads panels.  Am I missing anything here?  My Schneider unit works fine, just not big enough, and it understands the solar charger that is connected to it.
My PV power goes thru the Charge Controllers to charge the battery bank.  When the battery charges 'a bit' (e.g. reaches 52v) I turn the inverter on.  This triggers the ATS to take power from the inverter instead of the grid.  When the PV power runs out and the battery hits the cutt-off voltage (49.5v) the inverter turns off and the ATS switches back to grid.

If I'm understanding your comment above - I don't see the point of using 'grid' to charge the batteries to just turn around and run the inverter to create AC.  Instead, I just connect the grid directly (via the ATS) to the AC load and avoid the 15-20% power loss incurred by directing grid -> battery -> inverter -> AC load. 

I think what this latest discussion is highlighting
- off-grid, grid-tie, hybrid  - e.g. how you consume the AC power.   
-  There are distinct 'components' - PV Input, Charge Controller, Battery, Inverter, and ATS.   These can be combined or not - which affect the system design.    
- Goals.   Mine is: "Consume 100% of PV power produced in my off-grid system and let the grid take over once PV power is used.".   

I'm assuming you're are off-grid and (similar to my own goals) you want to consume all of your PV power - which lead me to the comments above.
The ATS is the piece I am missing.  My current Schneider inverter/charger essentially does this automatically.  It is programmed to charge the batteries from the grid when low, essentially using this option only after 11 pm and before 7 am each morning, to take advantage of $0.15 per kWh grid energy, then I discharge all of that all day, and use whatever PV can do to keep up the battery charge, and with my current load panel, it never runs out. I am not using the grid during the day for this load panel, so all is coming from the battery bank...for the loads I currently have.  But I have a LOT more loads to add, and that is why I have added my second powerwall of 12 kWh. The remainder of my system is a lot more PV using two SolarEdge StoreEdge inverters, but no battery connection is possible for my DIY powerwalls, only Tesla or LG.  The excess PV energy is lost, goes back to the grid without reimbursement unfortunately.

At night, my Schneider unit charges the batteries, and acts as an ATS to power the loads from the grid, at least that is my understanding.  If it isn't doing it efficiently, I wouldn't know it.  I do know it is dirt cheap electricity from 11 am to 7 am.

Is the ATS automatic?  A=automatic?  I am interested in exactly the same goal as you, but I do not want to be watching the SOC and having to flip switches.  I want it to be fully automatic.  Set and forget.  If getting an ATS and using this AIMS inverter, could accomplish my goals of having a larger system with bigger capability.

If you can direct me to some place where I can get more information about ATS, and where to purchase, that would be great.  

I am also looking at the Outback Radian 8 kW hybrid inverter, and from the looks of it, no ATS is required.  It has a gridzero setting which is exactly our goal here.  Biggest drawback is price per kWh of the inverter.  $3700 for the 8kWh Radian, or $3600 for the 12 kWh AIMS + whatever an ATS costs.
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#15
(03-30-2020, 12:43 PM)drspeakman Wrote: If you can direct me to some place where I can get more information about ATS, and where to purchase, that would be great.  

I am also looking at the Outback Radian 8 kW hybrid inverter, and from the looks of it, no ATS is required.  It has a gridzero setting which is exactly our goal here.  Biggest drawback is price per kWh of the inverter.  $3700 for the 8kWh Radian, or $3600 for the 12 kWh AIMS + whatever an ATS costs.
Cool, I think the discussion is at least resulting in a sharing of ideas.  I'm just not familiar with Schneider so I may be talking 'past you' rather than helping. So me just share that in my case - I designed around off-grid + ATS (automatic transfer switch) as the heart of my power consumption and I agree 100% - its all automatic!  I don't have to touch a thing.  In fact its cool because all I have to do work on things is turn off the inverter and grid automatically takes over - so I don't have to do anything to shut-down/work on solar subsystem. However - there are some things to consider:

* Motor surge -  Some on this thread warn about ATS motor surge due to the sine wave not being synchronized when inverter switches to grid and vice versa.   I handle this by a surge protected ATS and have been running 1.5years with several ATS(s) and over 1,000 switch-overs (twice a day) to date with no problems.  I power the full range of household stuff including 2 x refrigerators (full size Frigidaire type), furnace fan, tools, hybrid hot water heater, portable heat-pump unit, microwave, AC compressor (in past), whole-house heatpump (currently),   etc.    I personally don't believe this is a problem for residential level motors. 
* Switch-over gap - I use APC UPSs to bridge the switch-over gap for computers/TV/Coffee-pot with clock etc so they don't falter or shut-off or reset.   
* Production<=Consumption -  I recently added an additional 21 panels and this has pushed my spring time power production so high - I had to add extra battery to be able to consume 100% of PV power produced right now.     In other words, when you don't sell back to the grid you have to use it or loose it and that takes  planning. 

This all works for me, but I don't want to push you to go this way necessarily as there are OTHER solutions out there and I'm not by any means an overall expert.   Maybe more folks can weigh in here to give you additional options.     

If you decide to follow the route I'm using - I'm happy to share all details Smile
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#16
(03-30-2020, 03:16 PM)OffGridInTheCity Wrote:
(03-30-2020, 12:43 PM)drspeakman Wrote: If you can direct me to some place where I can get more information about ATS, and where to purchase, that would be great.  

I am also looking at the Outback Radian 8 kW hybrid inverter, and from the looks of it, no ATS is required.  It has a gridzero setting which is exactly our goal here.  Biggest drawback is price per kWh of the inverter.  $3700 for the 8kWh Radian, or $3600 for the 12 kWh AIMS + whatever an ATS costs.
Cool, I think the discussion is at least resulting in a sharing of ideas.  I'm just not familiar with Schneider so I may be talking 'past you' rather than helping.  So me just share that in my case - I designed around off-grid + ATS (automatic transfer switch) as the heart of my power consumption and I agree 100% - its all automatic!  I don't have to touch a thing.  In fact its cool because all I have to do work on things is turn off the inverter and grid automatically takes over - so I don't have to do anything to shut-down/work on solar subsystem.  However - there are some things to consider:

* Motor surge -  Some on this thread warn about ATS motor surge due to the sine wave not being synchronized when inverter switches to grid and vice versa.   I handle this by a surge protected ATS and have been running 1.5years with several ATS(s) and over 1,000 switch-overs (twice a day) to date with no problems.  I power the full range of household stuff including 2 x refrigerators (full size Frigidaire type), furnace fan, tools, hybrid hot water heater, portable heat-pump unit, microwave, AC compressor (in past), whole-house heatpump (currently),   etc.    I personally don't believe this is a problem for residential level motors. 
* Switch-over gap - I use APC UPSs to bridge the switch-over gap for computers/TV/Coffee-pot with clock etc so they don't falter or shut-off or reset.   
* Production<=Consumption -  I recently added an additional 21 panels and this has pushed my spring time power production so high - I had to add extra battery to be able to consume 100% of PV power produced right now.     In other words, when you don't sell back to the grid you have to use it or loose it and that takes  planning. 

This all works for me, but I don't want to push you to go this way necessarily as there are OTHER solutions out there and I'm not by any means an overall expert.   Maybe more folks can weigh in here to give you additional options.     

If you decide to follow the route I'm using - I'm happy to share all details Smile
Would love to hear the details.  Your method is using what I believe is a simple inverter, not all the bells and whistles of these more expensive hybrid inverters that have other things built in (Outback Radian, Schneider Conext).  And using the ATS sounds awesome.  Currently, the way my electrician has wired it, when I need to work on my inverter (so far, no issues) or battery pack (yes, have had some low functioning packs over the last 2 years that I have rebuilt), the power to all of my loads goes OFF.  So, I have to be ready to do things quickly to make the family happy with my "science project".  And what if I am away on vacation...I want my electrician to arrange this differently, but unfortunately, he really doesn't know that much about solar, and nobody in my area DOES at this point.  I am in need of a redesign.  So, I am reaching out to anyone who can lay out the different possible designs and ways to do this right now, hoping someone else can chime in and describe in detail how they have done it.  Certainly, I am not the only newbie here that would like to know.  And certainly there are those DIYers that have done this more than once, and learned better ways of doing things.  And, what about ATS's, where to read about and purchase?

I need to train my electrician.  He helped me with my solar panels, and install of solar battery charger, and all inverters.  He does great work and is anxious to learn.
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#17
>Your method is using what I believe is a simple inverter, not all the bells and whistles....
Yes.    The Midnite Classic controllers (that I use) have an "AUX1" feature which allows control of external devices. This is used to turn the AIMS on at 52v and off at 49.5v  (or whatever you set) thru the remote LCD port - e.g. wires 3 and 5 of simple RJ45 (internet) wire.

If you look at my build thread - https://secondlifestorage.com/showthread.php?tid=8514    The 4th post shows a Progressive Dynamics 240v@50a ATS in combination with a Pro-Tran 10-circuit Manual Transfer switch and discussion to answer @cowpen.     The main panel 240v@50a circuit breakers provide the shore power side of the ATS and the AIMS 12,000w  (e.g. 240v@50a) powers the generator side of the ATS.

> Its automatic....
Its simple - when the Inverter is on, the ATS takes it's power from the inverter.  When the inverter is off, the ATS takes power from the grid... e.g. standard grid operation.  So all you have to do to work on your solar system is make sure the inverter is off and it reverts to grid power.   

The main panel ATS I'm using  is Progressive Dynamics PD52DCSV Transfer Switch Surge Protected  https://www.amazon.com/gp/product/B0136U...UTF8&psc=1  - ETL certified.     You can go cheaper if you skip the 100a surge protection.   The "DCSV" is DC relay coil instead of AC which is quieter.   There is a low hum as this is a mechanical relay system and the coil hums a bit - so best its positioned in garage or someplace where a low hum won't bother you.      There are some other automatic transfer switches - such as "Generac 100-Amp Outdoor Automatic Transfer Switch w/ 16-Circuit Load Center" -  https://www.ebay.com/itm/Generac-100-Amp...Sw-A1dRMyv  but I'm not sure they are good at twice daily switch-overs and more expensive.  Your electrician may have an opinion. 

The main panel manual transfer switch is a way to hook the ATS output back into the main panel circuits and at the same time control which circuits are powered by the inverter.  I used the 50a / 10-circuit model https://www.homedepot.com/p/Reliance-Controls-50-Amp-10-Circuit-Manual-Transfer-Switch-A510C/206503336   They make a range of amps and no of circuits.    The Generac (above) is 100a and includes a 'load center' - so its kind of a combination of ATS + manual TS. 


>Sensative circuits
In the house, the computer/tv circuits will need a UPS as the ATS switches back and forth.    

In my case, I went a step further because I had some larger APC UPSs and centralized the UPS capability.   You can see these as 4th picture in the 2nd post of the build thread.  I used a Go Power! TS-30 30 Amp Automatic Transfer Switch(s) https://www.amazon.com/gp/product/B00153...UTF8&psc=1  to power APC 3000va UPS(s).  Each of these 3000va UPSs support a 20a circuit - so I can run my K-Cup to keep the clock correct Smile     As in the main panel setup, the grid provides shore side of ATS and the Inverter the generator side of the ATSs.   The ATSs provide power to the APC UPS.     The output of the UPS is directed thru a subpanel to regular house wiring to 'ups plugs' thru the house - so I have 1 UPS that powers several sockets instead of having multiple UPSs.   But this is just an efficiency measure to combine 8 UPSs into 1 central one.   multiple UPSs are fine but each one draws 40watts of idle power - so 8 * 40w = 320w/hour * 24 = 7.7kwh/day of wasted power.

>Expansion is OK
Finally, this ATS method can expand if you decide to grow down the road. I started with 1 at main panel and 2 of them running the UPS subsystem (powered by the 1st inverter), and then this year added a 2nd inverter and a 2nd ATS to power the Heat Pump and 3rd ATS to power some other stuff since I had extra capacity. Just takes some wiring.
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#18
(03-31-2020, 06:45 PM)OffGridInTheCity Wrote: >Your method is using what I believe is a simple inverter, not all the bells and whistles....
Yes.    The Midnite Classic controllers (that I use) have an "AUX1" feature which allows control of external devices. This is used to turn the AIMS on at 52v and off at 49.5v  (or whatever you set) thru the remote LCD port - e.g. wires 3 and 5 of simple RJ45 (internet) wire.

If you look at my build thread - https://secondlifestorage.com/showthread.php?tid=8514    The 4th post shows a Progressive Dynamics 240v@50a ATS in combination with a Pro-Tran 10-circuit Manual Transfer switch and discussion to answer @cowpen.     The main panel 240v@50a circuit breakers provide the shore power side of the ATS and the AIMS 12,000w  (e.g. 240v@50a) powers the generator side of the ATS.

> Its automatic....
Its simple - when the Inverter is on, the ATS takes it's power from the inverter.  When the inverter is off, the ATS takes power from the grid... e.g. standard grid operation.  So all you have to do to work on your solar system is make sure the inverter is off and it reverts to grid power.   

The main panel ATS I'm using  is Progressive Dynamics PD52DCSV Transfer Switch Surge Protected  https://www.amazon.com/gp/product/B0136U...UTF8&psc=1  - ETL certified.     You can go cheaper if you skip the 100a surge protection.   The "DCSV" is DC relay coil instead of AC which is quieter.   There is a low hum as this is a mechanical relay system and the coil hums a bit - so best its positioned in garage or someplace where a low hum won't bother you.      There are some other automatic transfer switches - such as "Generac 100-Amp Outdoor Automatic Transfer Switch w/ 16-Circuit Load Center" -  https://www.ebay.com/itm/Generac-100-Amp...Sw-A1dRMyv  but I'm not sure they are good at twice daily switch-overs and more expensive.  Your electrician may have an opinion. 

The main panel manual transfer switch is a way to hook the ATS output back into the main panel circuits and at the same time control which circuits are powered by the inverter.  I used the 50a / 10-circuit model https://www.homedepot.com/p/Reliance-Controls-50-Amp-10-Circuit-Manual-Transfer-Switch-A510C/206503336   They make a range of amps and no of circuits.    The Generac (above) is 100a and includes a 'load center' - so its kind of a combination of ATS + manual TS. 


>Sensative circuits
In the house, the computer/tv circuits will need a UPS as the ATS switches back and forth.    

In my case, I went a step further because I had some larger APC UPSs and centralized the UPS capability.   You can see these as 4th picture in the 2nd post of the build thread.  I used a Go Power! TS-30 30 Amp Automatic Transfer Switch(s) https://www.amazon.com/gp/product/B00153...UTF8&psc=1  to power APC 3000va UPS(s).  Each of these 3000va UPSs support a 20a circuit - so I can run my K-Cup to keep the clock correct Smile     As in the main panel setup, the grid provides shore side of ATS and the Inverter the generator side of the ATSs.   The ATSs provide power to the APC UPS.     The output of the UPS is directed thru a subpanel to regular house wiring to 'ups plugs' thru the house - so I have 1 UPS that powers several sockets instead of having multiple UPSs.   But this is just an efficiency measure to combine 8 UPSs into 1 central one.   multiple UPSs are fine but each one draws 40watts of idle power - so 8 * 40w = 320w/hour * 24 = 7.7kwh/day of wasted power.

>Expansion is OK
Finally, this ATS method can expand if you decide to grow down the road.  I started with 1 at main panel and 2 of them running the UPS subsystem (powered by the 1st inverter),  and then this year added a 2nd inverter and a 2nd ATS to power the Heat Pump and 3rd ATS to power some other stuff since I had extra capacity.  Just takes some wiring.
Thanks.  A lot of great information.  I have some simple questions, probably answered somewhere, but unable to find.  

I currently have nine (9) 290 watt panels charging my first 14s100p powerwall (about 12kWh or 220 aH), using a single PCM 60X charger rated up to 3kW, pretty much what my 9 panels could produce at maximum.  I am adding an identical powerwall.  Are these 9 panels enough to charge both powerwalls?  If not, I could repurpose 3,6, or 9 other panels (connected to a SolarEdge inverter without batteries) and connect to a second charger if they are needed, but if not really needed, just continue to charge both packs during the day and top off after 11 pm at night with super off-peak grid power.  This would be a lot simpler, and would eliminate the need for a second charger, rooftop rewiring, additional electrician fees, and possibly a second inverter.

I am currently looking at replacing my Schneider Conext 4048SW with a Schneider 6848XW pro inverter, vs adding a second Schneider Conext 4048 SW and adding some manual and/or automatic transfer switches.  Adding a second Schneider SW would give me more power, and be less expensive.
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#19
>Are these 9 panels enough to charge both powerwalls?  
Its a function of PV input, consumption, and DOD on the battery bank.   These are all variable and unique to your case.

In my case, excluding heat/cool (hi variability in consumption), my base home consumption is a pretty steady 48kwh/day @ 2000w/hr.   Thru 2019, with a 6.8kw PV (24 * 285w panels) and ~16kw/day from the battery bank (e.g. average 40% DOD) the system produced 24.5kwh/day.


If we take your 9panels *280w= 2.5kw PV.  That's 2.5kw/6.8kw = 37% of PV power in my example above.
And note that you have 2 * 12kwh batteries so you 24kwh at 100% DOD.

This leads me to the following though experiement.  (assuming you have similar PV power input weather wise)....
- 9 panels = 24.5kwh * 37% = 9kwh/day  with need for at least 16kwh * 37% = 6kwh/day from your battery bank - e.g. 25% DOD.
- 18 panels = 24.5kwh * 74% = 18kwh/day with a need for at least 16kwh * 74% = 12kwh/day from your battery bank - e.g. 50% DOD.  
Both of these are within range of an OK setup.


Conclusion:
If you have 18kwh/day (or more) consumption then either 9 or 18 panel scenario will work.   If you < 18kwh/day consumption that is closer to 9kwh/day then 9 panels would be more effective as you'll just was PV power if you hook all 18 to the battery bank.
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