Powerwall 2 Design

[mbroowil]

I'm looking to install solar panels for a few reasons (in order): increased self-reliance, environmental, new electronic gadget.

I'm a Tesla and Tesla PowerWall fan, so I asked for the Powerwall 2 by name.

The rest of the system being suggested is:

• (9), (14), or (20) 'Solaria 360' panels (depending on how many roof regions I want to use... each region has slightly worse geometry that the previous)
• (1) SolarEdge SE6000H Inverter
• (1) Powerwall 2

I used 322 KWH of electricity last month in my house according to my utility bill.

My concern is that with a single Powerwall 2, it won't be the whole house backup generator I really want. I'm not really concerned with the length of backup, what I really want is to not notice the 1 second to 1 hour outages (once a month?). If I'm concerned it will be a longer outage, I can ration my usage accordingly (turn a bunch of things off). Under normal conditions, I'd like everything to be backed up. The more I read makes it look like I'm going to have to pick and choose circuits to backup. It also looks like sometimes some of the solar panels skip the battery and wired to grid only?

Given my priorities (short-duration whole-home backup...) am I going to need more than one powerwall?
Can the powerwalls be hung on the wall together (I only have enough length for one, but plenty of depth if they could be two deep)? Others users with similar needs seem to think I'll hit a current limit with one and even with two should be installing starter softeners on my AC units.

Also, I've read that the model Y has the hardware built-in to support vehicle to grid if Tesla chooses to support it. The model Y will be my next car and I would love VTG fuctionality. Is there anything in the solar and battery installation that would be needed to support VTG if Tesla enables it someday?

I don't know enough to ask smart questions to the solar install team about their design. Does anyone have any advice for me about battery quantity, V2G, or panels connected before/after inverter/batter?

Thanks,
Mike

 

[jjrandorin]

I'm looking to install solar panels for a few reasons (in order): increased self-reliance, environmental, new electronic gadget.

I'm a Tesla and Tesla PowerWall fan, so I asked for the Powerwall 2 by name.

The rest of the system being suggested is:

• (9), (14), or (20) 'Solaria 360' panels (depending on how many roof regions I want to use... each region has slightly worse geometry that the previous)
• (1) SolarEdge SE6000H Inverter
• (1) Powerwall 2

I used 322 KWH of electricity last month in my house according to my utility bill.

My concern is that with a single Powerwall 2, it won't be the whole house backup generator I really want. I'm not really concerned with the length of backup, what I really want is to not notice the 1 second to 1 hour outages (once a month?). If I'm concerned it will be a longer outage, I can ration my usage accordingly (turn a bunch of things off). Under normal conditions, I'd like everything to be backed up. The more I read makes it look like I'm going to have to pick and choose circuits to backup. It also looks like sometimes some of the solar panels skip the battery and wired to grid only?

Given my priorities (short-duration whole-home backup...) am I going to need more than one powerwall?
Can the powerwalls be hung on the wall together (I only have enough length for one, but plenty of depth if they could be two deep)? Others users with similar needs seem to think I'll hit a current limit with one and even with two should be installing starter softeners on my AC units.

Also, I've read that the model Y has the hardware built-in to support vehicle to grid if Tesla chooses to support it. The model Y will be my next car and I would love VTG fuctionality. Is there anything in the solar and battery installation that would be needed to support VTG if Tesla enables it someday?

I don't know enough to ask smart questions to the solar install team about their design. Does anyone have any advice for me about battery quantity, V2G, or panels connected before/after inverter/batter?

Thanks,
Mike

What did you use last "year" for electricity, a full 12 month period? Looking at a month isnt really going to help you... especially when you start talking about months where electricity usage is usually lower (march / april / may) for most people in most places.

 

[wjgjr]

I can help answer some of these items....

https://www.tesla.com/sites/default/files/pdfs/powerwall/Powerwall 2_AC_Datasheet_en_northamerica.pdf - this lists the specs for the powerwall. Of note is the 30A limit for one powerwall. If you have one or more circuits over this limit, you could not do a whole-home backup solution with one powerwall. However, if your concern is only for outages of 1h or less, it might be reasonable to conclude that things on the higher-amp circuits (that might include things like AC/heater, or an electric stove/oven) are not necessary for 1h outages. Then, you would mainly need to note the discharge limits and determine if those would be of concern (since you cannot discharge the full powerwall in 1 hour.)

If you go with 2 powerwalls, you may well still need to install a sure/soft start device on your AC - I know we did, with 2 powerwalls, as the LRA number for our AC is 72.2 amps. We were also able to stack our powerwalls so it only takes up the width of one on our wall. I believe they will stack like 6, though I have also heard that sometimes local codes may come into play, so it is worth checking, but it is supported by Tesla anyway.

 

[gpez]

I'm looking to install solar panels for a few reasons (in order): increased self-reliance, environmental, new electronic gadget.

I'm a Tesla and Tesla PowerWall fan, so I asked for the Powerwall 2 by name.

The rest of the system being suggested is:

• (9), (14), or (20) 'Solaria 360' panels (depending on how many roof regions I want to use... each region has slightly worse geometry that the previous)
• (1) SolarEdge SE6000H Inverter
• (1) Powerwall 2

I used 322 KWH of electricity last month in my house according to my utility bill.

My concern is that with a single Powerwall 2, it won't be the whole house backup generator I really want. I'm not really concerned with the length of backup, what I really want is to not notice the 1 second to 1 hour outages (once a month?). If I'm concerned it will be a longer outage, I can ration my usage accordingly (turn a bunch of things off). Under normal conditions, I'd like everything to be backed up. The more I read makes it look like I'm going to have to pick and choose circuits to backup. It also looks like sometimes some of the solar panels skip the battery and wired to grid only?

Given my priorities (short-duration whole-home backup...) am I going to need more than one powerwall?
Can the powerwalls be hung on the wall together (I only have enough length for one, but plenty of depth if they could be two deep)? Others users with similar needs seem to think I'll hit a current limit with one and even with two should be installing starter softeners on my AC units.

Also, I've read that the model Y has the hardware built-in to support vehicle to grid if Tesla chooses to support it. The model Y will be my next car and I would love VTG fuctionality. Is there anything in the solar and battery installation that would be needed to support VTG if Tesla enables it someday?

I don't know enough to ask smart questions to the solar install team about their design. Does anyone have any advice for me about battery quantity, V2G, or panels connected before/after inverter/batter?

Thanks,
Mike

Hi @mbroowil, welcome!

If you're looking at the Powerwall for backup only scenarios you need to consider a couple of things which you've already noted:

1) The maximum wattage your appliances can draw at any given moment during an outage. Each Powerwall can provide 5kw of power continuously and surge up to 7kw for 10 seconds. @wjgjr noted this as the 30a limit of each Powerwall which translates to if you have any single 240v circuit over 30a you won't be able to back it up with a single Powerwall. This means if you have high wattage loads (dryer, ac, stove, oven, etc) or a combination of multiple things together that combined may be too large for a single Powerwall you can choose to either not back those up or get additional Powerwalls. AC units are notoriously difficult to back up due to their very high surge demand which is why you see soft starts required, though surge is only half of the consideration because of #2...

2) The total power consumption over your backup period. Each Powerwall has 13.5kwh of usable energy. To determine how long your Powerwall will last during an outage simply divide your consumption during that time in to 13.5kwh. Again AC is the toughest here as a 3 ton, 3 star rated (2.7 EER) AC will draw 4kW continuously which means a single Powerwall will only run it for about 3 hours - yikes. If you have a smaller or more efficient AC unit and are only looking at riding through <1 hour outages maybe one Powerwall will be fine.

 

[gpez]

FWIW I should add that I have a single Powerwall and is only for backup purposes. The dryer, oven, A/C, and EV charging plug are all excluded from the backed up loads panel.

 

[GenSao]

Mbroowil,

Welcome to the TMC. Enjoy your stay...

Get 3-5 quotes. Size your solar system to 90% to 100% of your annual usage. Most cost effective to build as big as you can now. Although they can have hit-or-miss in customer service, consider contacting Tesla directly for a price quote. You'll find pricing directly with Tesla very compelling.

One Powerwall is typically enough to run the lights, the 120 V plugs, and related small appliances. Two or more are required for 240 V appliances such as AC and an electric oven. Check out "What does Powerwall Backup" for more information. Check the Locked Rotor Amp rating (LRA) for your AC on how many Powerwalls are needed. I went with two Powerwalls to ensure our AC can run on backup power.

Powerwalls can not be hung on the wall stacked (front to back). They can sit on the floor stacked (front to back) or hung next to each other on the wall (side by side). I am not sure top to bottom (with clearances) is possible.

V2G with the Model Y is still up in the air. It is possible the cybertruck and newer vehicles would have this feature instead. If it was to be supported, I would imagine you would want at least two Powerwalls so that you can connect a 240 V circuit to the backup panel.

The wall connector's 60 A circuit draws a lot of power when charging an EV. Typically it is placed outside of the backup panel. In the event of a power outage, the car would not drain your Powerwall dry. Fortunately there is a recent software fix. At least install a 240 V, 40 A NEMA-14-50 to your backup panel to charge your EV if the grid is down.

 

[jrweiss98020]

Be aware that if you do not have a Powerwall with its "Gateway" that automatically disconnects your house from the grid when it detects an outage, you CANNOT use solar power during a grid outage. This is to protect workers who are restoring the grid from electrocution from stray power inputs from your solar panels. AFAIK, electric codes in all areas are similar in this regard.

Another consideration is the Tesla requirement (as stated by my installer) that you have 1 Powerwall for each 7.6 KW AC rating of solar production. For example, my 9.045 KW (27 x 335 W panels with Enphase IQ7+ Microinverters) system yields a peak output of of 7.965 KW AC (27 x 295 VA) or 7.83 KW (27 x 290 VA) max continuous. Since it is over 7.6 KW, Tesla requires a minimum of 2 Powerwalls so they can absorb any peak influx during switchovers.

Your 20 x 360 W panels will be under the threshold for 2 Powerwalls, so you COULD install a single PW. However, you might be best served to back up the whole house instead of a subpanel with "essential loads". Two PWs can back up an entire 200 Amp main panel. That way YOU can control what you use your electricity for during a grid outage. Even a single AC unit, electric oven or dryer (or charging an EV) could put your intermittent loads above the 5 KW max for a single PW, but 2 PWs would cover you in most reasonable cases (e.g., 1 AC unit + an oven).

And yes, you can stack up to 3 PWs in front of each other when on the floor next to a wall.

 

[SoundDaTrumpet]

@mbroowil

The rest of the system being suggested is:

• (9), (14), or (20) 'Solaria 360' panels (depending on how many roof regions I want to use... each region has slightly worse geometry that the previous)
• (1) SolarEdge SE6000H Inverter
• (1) Powerwall 2

I used 322 KWH of electricity last month in my house according to my utility bill.

Based upon the 9 panels above I can deduce your annual usage to be on the single PW end. I would not be surprised that the influence is based upon other PW owners needing to fulfill some incentive requirements from their state. Heavily biased forum is upon sizing to the size of your array. In California SGIP, solar-connected residential users must discharge and fill-up the PW 52 times minimum per year for 5 years, or else they forfeit ~$2000-5000 for each PW they bought. Installers are afraid to recommend too much storage, and are conservative in their estimates.

My concern is that with a single Powerwall 2, it won't be the whole house backup generator I really want. I'm not really concerned with the length of backup, what I really want is to not notice the 1 second to 1 hour outages (once a month?). If I'm concerned it will be a longer outage, I can ration my usage accordingly (turn a bunch of things off). Under normal conditions, I'd like everything to be backed up. The more I read makes it look like I'm going to have to pick and choose circuits to backup. It also looks like sometimes some of the solar panels skip the battery and wired to grid only?

You obvious need at least two PW. My pair only backups the house subpanel and garage subpanel. It's everything minus EV and A/C.

Given my priorities (short-duration whole-home backup...) am I going to need more than one powerwall?

Yes. If duration isn't a priority you can look at other options like the LG Chem, Sonnen, etc. Tesla PW boasts a lot of energy storage compared to their peers.

Can the powerwalls be hung on the wall together (I only have enough length for one, but plenty of depth if they could be two deep)?

3 stacked on floor is commonplace. I have seen 4 but didn't ask what wire was in the 1" conduit.

Others users with similar needs seem to think I'll hit a current limit with one and even with two should be installing starter softeners on my AC units.

Get 3 PW and it won't be a question. Soft starters need scroll compressors. I have two A/C units and they drain the batteries quick. A/C configured to work only when grid is up, and PW system monitors the power and offsets the load. Good way to avoid peak electric rates.

Also, I've read that the model Y has the hardware built-in to support vehicle to grid if Tesla chooses to support it. The model Y will be my next car and I would love VTG fuctionality. Is there anything in the solar and battery installation that would be needed to support VTG if Tesla enables it someday?

They would have to release a wall mounted charge unit for this. There's no way the this can be relied on via car software to protect linemen trying to restore power during an outage. That said, do a 100A 3 gauge wire to your Tesla Wall Connector with 1" conduit.

I don't know enough to ask smart questions to the solar install team about their design. Does anyone have any advice for me about battery quantity, V2G, or panels connected before/after inverter/batter?

Thanks,
Mike

I really like the LG Chem. Outside of limited capacity, the cost is narrower between Tesla and LG Chem now that Tesla PW prices have significantly increased for hardware and the installation cost. Which company will have a brighter future? is a question.

 

[mbroowil]

What did you use last "year" for electricity, a full 12 month period? Looking at a month isnt really going to help you... especially when you start talking about months where electricity usage is usually lower (march / april / may) for most people in most places.

It's a new house (new construction) that we just moved into, so I don't have anything more than one full month of usage history. Thanks for such a quick reply!

 

[mbroowil]

I can help answer some of these items....

https://www.tesla.com/sites/default/files/pdfs/powerwall/Powerwall 2_AC_Datasheet_en_northamerica.pdf - this lists the specs for the powerwall. Of note is the 30A limit for one powerwall. If you have one or more circuits over this limit, you could not do a whole-home backup solution with one powerwall. However, if your concern is only for outages of 1h or less, it might be reasonable to conclude that things on the higher-amp circuits (that might include things like AC/heater, or an electric stove/oven) are not necessary for 1h outages. Then, you would mainly need to note the discharge limits and determine if those would be of concern (since you cannot discharge the full powerwall in 1 hour.)

If you go with 2 powerwalls, you may well still need to install a sure/soft start device on your AC - I know we did, with 2 powerwalls, as the LRA number for our AC is 72.2 amps. We were also able to stack our powerwalls so it only takes up the width of one on our wall. I believe they will stack like 6, though I have also heard that sometimes local codes may come into play, so it is worth checking, but it is supported by Tesla anyway.

Thanks!

 

[mbroowil]

Hi @mbroowil, welcome!

If you're looking at the Powerwall for backup only scenarios you need to consider a couple of things which you've already noted:

1) The maximum wattage your appliances can draw at any given moment during an outage. Each Powerwall can provide 5kw of power continuously and surge up to 7kw for 10 seconds. @wjgjr noted this as the 30a limit of each Powerwall which translates to if you have any single 240v circuit over 30a you won't be able to back it up with a single Powerwall. This means if you have high wattage loads (dryer, ac, stove, oven, etc) or a combination of multiple things together that combined may be too large for a single Powerwall you can choose to either not back those up or get additional Powerwalls. AC units are notoriously difficult to back up due to their very high surge demand which is why you see soft starts required, though surge is only half of the consideration because of #2...

2) The total power consumption over your backup period. Each Powerwall has 13.5kwh of usable energy. To determine how long your Powerwall will last during an outage simply divide your consumption during that time in to 13.5kwh. Again AC is the toughest here as a 3 ton, 3 star rated (2.7 EER) AC will draw 4kW continuously which means a single Powerwall will only run it for about 3 hours - yikes. If you have a smaller or more efficient AC unit and are only looking at riding through <1 hour outages maybe one Powerwall will be fine.

Really helpful, thanks!

I hadn't even thought about 110 vs 220. Is a second powerwall needed for anything that is on a 220 plug (putting aside current and depletion rate for a second)? (I don't even know if I have anything on a 220 plug... I assume my washer/dryer (even though dryer is gas)... but I'll take a look tonight)

Thanks again!

 

[mbroowil]

FWIW I should add that I have a single Powerwall and is only for backup purposes. The dryer, oven, A/C, and EV charging plug are all excluded from the backed up loads panel.

I think that makes a ton of sense and is probably better scaled for my solar collection, but the existing electrical panel is BRAND NEW and there's something in me that thinks it's less wasteful to backup the whole thing and then selectively turn off equipment in an outage. But dryer, oven, A/C, and future EV are exactly the things I would think I would also exclude if I'm on go with one powerwall.

Thanks!

 

[mbroowil]

Mbroowil,

Welcome to the TMC. Enjoy your stay...

Get 3-5 quotes. Size your solar system to 90% to 100% of your annual usage. Most cost effective to build as big as you can now. Although they can have hit-or-miss in customer service, consider contacting Tesla directly for a price quote. You'll find pricing directly with Tesla very compelling.

One Powerwall is typically enough to run the lights, the 120 V plugs, and related small appliances. Two or more are required for 240 V appliances such as AC and an electric oven. Check out "What does Powerwall Backup" for more information. Check the Locked Rotor Amp rating (LRA) for your AC on how many Powerwalls are needed. I went with two Powerwalls to ensure our AC can run on backup power.

Powerwalls can not be hung on the wall stacked (front to back). They can sit on the floor stacked (front to back) or hung next to each other on the wall (side by side). I am not sure top to bottom (with clearances) is possible.

V2G with the Model Y is still up in the air. It is possible the cybertruck and newer vehicles would have this feature instead. If it was to be supported, I would imagine you would want at least two Powerwalls so that you can connect a 240 V circuit to the backup panel.

The wall connector's 60 A circuit draws a lot of power when charging an EV. Typically it is placed outside of the backup panel. In the event of a power outage, the car would not drain your Powerwall dry. Fortunately there is a recent software fix. At least install a 240 V, 40 A NEMA-14-50 to your backup panel to charge your EV if the grid is down.

Wow. Thanks for the answers, there's a lot of info there.

I'm a borderline Tesla fan-boy and I love the idea of a single brand solution, but the one (and only one) company I've reached out to seems to be open listing to my aesthetic concerns. For me to get the green light from my wife, form trumps function. I can't have conduit outside of the house or exposed framing. I have the preconception that Tesla's loose national network of installers might be less custom than other shops? Maybe I just need to see who they put me in touch with locally to make the determination.

That "What does Powerwall Backup" link is great.

I wonder if the powerwalls are sitting on the floor if I could put other equipment (inverter, gateway?, or subpanels) above the powerwalls?

Thanks again!

 

[mbroowil]

Be aware that if you do not have a Powerwall with its "Gateway" that automatically disconnects your house from the grid when it detects an outage, you CANNOT use solar power during a grid outage. This is to protect workers who are restoring the grid from electrocution from stray power inputs from your solar panels. AFAIK, electric codes in all areas are similar in this regard.

Another consideration is the Tesla requirement (as stated by my installer) that you have 1 Powerwall for each 7.6 KW AC rating of solar production. For example, my 9.045 KW (27 x 335 W panels with Enphase IQ7+ Microinverters) system yields a peak output of of 7.965 KW AC (27 x 295 VA) or 7.83 KW (27 x 290 VA) max continuous. Since it is over 7.6 KW, Tesla requires a minimum of 2 Powerwalls so they can absorb any peak influx during switchovers.

Your 20 x 360 W panels will be under the threshold for 2 Powerwalls, so you COULD install a single PW. However, you might be best served to back up the whole house instead of a subpanel with "essential loads". Two PWs can back up an entire 200 Amp main panel. That way YOU can control what you use your electricity for during a grid outage. Even a single AC unit, electric oven or dryer (or charging an EV) could put your intermittent loads above the 5 KW max for a single PW, but 2 PWs would cover you in most reasonable cases (e.g., 1 AC unit + an oven).

And yes, you can stack up to 3 PWs in front of each other when on the floor next to a wall.

The powerwall "gateway" seems like a huge tip! It would be super disappointing during an outage not to be able to partially charge via my panels. Is the Powerwall Gateway the same as an inverter? Does it replace the SE 6000H the potential installer has suggested? This seems like a really big deal.

I do have a brand new 200 Amp main panel and I do like the simplicity of imagining the battery between the grid and my whole panel.

Regarding the floor stacked PWs... I've seen photos of them with just ONE wiring harness coming out of them (like they are internally connected). Are there words I can say to the installers to request that?

Thanks!

 

[mbroowil]

@mbroowil
Based upon the 9 panels above I can deduce your annual usage to be on the single PW end. I would not be surprised that the influence is based upon other PW owners needing to fulfill some incentive requirements from their state. Heavily biased forum is upon sizing to the size of your array. In California SGIP, solar-connected residential users must discharge and fill-up the PW 52 times minimum per year for 5 years, or else they forfeit ~$2000-5000 for each PW they bought. Installers are afraid to recommend too much storage, and are conservative in their estimates.

You obvious need at least two PW. My pair only backups the house subpanel and garage subpanel. It's everything minus EV and A/C.

Yes. If duration isn't a priority you can look at other options like the LG Chem, Sonnen, etc. Tesla PW boasts a lot of energy storage compared to their peers.
3 stacked on floor is commonplace. I have seen 4 but didn't ask what wire was in the 1" conduit.
Get 3 PW and it won't be a question. Soft starters need scroll compressors. I have two A/C units and they drain the batteries quick. A/C configured to work only when grid is up, and PW system monitors the power and offsets the load. Good way to avoid peak electric rates.

They would have to release a wall mounted charge unit for this. There's no way the this can be relied on via car software to protect linemen trying to restore power during an outage. That said, do a 100A 3 gauge wire to your Tesla Wall Connector with 1" conduit.

I really like the LG Chem. Outside of limited capacity, the cost is narrower between Tesla and LG Chem now that Tesla PW prices have significantly increased for hardware and the installation cost. Which company will have a brighter future? is a question.

Thanks for all of the answers!

I think I'm convinced I want 2 PWs. A 100A 3 gauge wire to my garage with 1" conduit is good advice.

The need/want for a 3rd PW seems to be exclusively for the AC which seems to almost be a software problem. As long as the AC doesn't start on its own during the outage, it seems like I could juggle its usage with just 2 PWs. Like if it was uncomfortably hot before going to bed, I could literally turn off all of the other electronics in the house, start the AC, get past the surge, and then turn a few small essential things on too. Is there any feature on Nest thermostats and PWs that would allow you to effectively switch your thermostats to manual during outages?

Thanks again!

 

[jboy210]

The powerwall "gateway" seems like a huge tip! It would be super disappointing during an outage not to be able to partially charge via my panels. Is the Powerwall Gateway the same as an inverter? Does it replace the SE 6000H the potential installer has suggested? This seems like a really big deal.

I do have a brand new 200 Amp main panel and I do like the simplicity of imagining the battery between the grid and my whole panel.

Regarding the floor stacked PWs... I've seen photos of them with just ONE wiring harness coming out of them (like they are internally connected). Are there words I can say to the installers to request that?

Thanks!

The Gateway is a separate unit from the inverter(s). It's purpose is to an intelligent power router. It constantly monitors the power coming from the inverters (the SE 6000H), grid, and powerwall(s), and you home power needs. Under normal operation It can very quickly detect the grid going away and switch to using powerwalls, solar (if producing), or combination of both.

Using the phone app you can tell the gateway you can control how this occurs. You can set it to prioritize cost savings by using the power in your powerwalls. Or you can tell the gateway you want it to focus on keeping the powerwall charge state above certain levels. Or balance the two. You can even tell it your power plan with the utility has Time of Use and you want it to minimize your use when power is expensive, but using the powerwalls.

In a failure, the gateway will detect the grid going away very quickly and switch to using the powerwalls. And by quickly we mean so fast nothing beeps, clocks do not start flashing, etc. Some computer items may drop off line so people often still use a UPS for home servers and NASes.

Another function is when the grid goes away it isolates your home from the grid and control production of your solar making you home a self-contained power grid. This means when the Powerwalls get filled from the output from the solar it can shutdown the solar. And then when you powerwall drains a bit brings back the solar to refill the powerwall. With this cycling and correctly sized powerwalls and solar people have gone over a month without using power from the grid.

 

[jjrandorin]

The powerwall "gateway" seems like a huge tip! It would be super disappointing during an outage not to be able to partially charge via my panels. Is the Powerwall Gateway the same as an inverter? Does it replace the SE 6000H the potential installer has suggested? This seems like a really big deal.

I do have a brand new 200 Amp main panel and I do like the simplicity of imagining the battery between the grid and my whole panel.

Regarding the floor stacked PWs... I've seen photos of them with just ONE wiring harness coming out of them (like they are internally connected). Are there words I can say to the installers to request that?

Thanks!

The gateway does not replace any inverters. Think of it as the "brain" of the battery system. It handles the switching of the flow of electricity (from / to powerwall(s) from solar, from / to the grid, to the house from solar / grid / powerwall). Powerwalls can be stacked on the floor 2 deep no problem (MUST be on the floor or some other substantial surface they can fully rest on, if stacked). There should not be any "code words" needed to an installer to get them to stack them on the floor. Just tell them you want them "here" stacked 2 deep on the floor.".

 

[gpez]

Really helpful, thanks!

I hadn't even thought about 110 vs 220. Is a second powerwall needed for anything that is on a 220 plug (putting aside current and depletion rate for a second)? (I don't even know if I have anything on a 220 plug... I assume my washer/dryer (even though dryer is gas)... but I'll take a look tonight)

Thanks again!

Each Powerwall provides 240v split phase power meaning it has two 120v legs that can combine for 240v, just like standard US residential split phase utility. Your backup panel can have 240v circuits however since generally 240v appliances are high wattage devices one Powerwall likely won't be sufficient which is why some loosely say that if you have 240v appliances you should probably have more than 1 Powerwall (which of course gets misconstrued as each Powerwall can only provide 120v, which is incorrect but I digress...)

The need/want for a 3rd PW seems to be exclusively for the AC which seems to almost be a software problem. As long as the AC doesn't start on its own during the outage, it seems like I could juggle its usage with just 2 PWs. Like if it was uncomfortably hot before going to bed, I could literally turn off all of the other electronics in the house, start the AC, get past the surge, and then turn a few small essential things on too. Is there any feature on Nest thermostats and PWs that would allow you to effectively switch your thermostats to manual during outages?

You'll want to double and triple check your math on this. If your numbers are off and the AC pulls more than 2 Powerwalls can handle you'll trip the whole system, not something you want to happen during a power outage. A 5 ton A/C for a 2,000sqft home with an EER of 13 will pull 4.6kw while running and likely 2-3x that on start up, which without a soft start device would be right at the Powerwalls' max surge capability.

There are likely ways to automate your system to avoid problems however I'm not familiar with a simple way for Nest to be aware of the Powerwall and vice versa so something custom or home automation based is likely needed. If you do end up going with just 2 Powerwalls with your A/C backed up you almost certainly will want to get a soft start for them as well.
​

 

[mbroowil]

Maybe I'm putting too much value on the simplicity (design-wise) of a whole-home backup. Maybe it's easier than I imagine to convert my existing main panel (brand new) to a main panel + essential loads panel. Will a lot of electrical work be 'undone' from my existing main panel if I end up just installing a single PowerWall and need to add an essential loads panel to limit backup to lights and outlets? How hard is the wiring for a partial home backup vs a whole home backup?

My utility also pays 1:1 for supplying the grid so I don't need the battery to time-shift my solar usage....

 

[jjrandorin]

Maybe I'm putting too much value on the simplicity (design-wise) of a whole-home backup. Maybe it's easier than I imagine to convert my existing main panel (brand new) to a main panel + essential loads panel. Will a lot of electrical work be 'undone' from my existing main panel if I end up just installing a single PowerWall and need to add an essential loads panel to limit backup to lights and outlets? How hard is the wiring for a partial home backup vs a whole home backup?

My utility also pays 1:1 for supplying the grid so I don't need the battery to time-shift my solar usage....

I have 2 powerwalls and backed up everything but my tesla wall connector... so I have an "essential loads" panel with every load for my home except for the tesla wall connector in it. I guess it depends on how complex your specific setup is. The essential loads panel goes close to the main panel (in my case, its on the interior of my garage, on the same wall as my main panel, which is on the outside of my garage on the same wall).

These are construction projects, so you need to look at your individual circumstances... but with that being said, when I got my 3 quotes, all three basically planned on setting up an essential loads panel, even though my stated goal was "whole home backup". They just all suggested I leave the tesla wall connector separate (in main panel) and move everything to the backup loads panel.

This boils down to personal preference and how protected from power outages you want to be, and how much you want to "live like normal" vs "go into camping mode".

I wanted the ability to live like normal, even though I would probably curtail usage of some stuff. My wall oven (40amp circuit) is backed up (for example) but in a real outage situation, I would just bake with one of my BBQ grills (I have different types of BBQ grills, natural gas hooked up to the home, komodo style, and pellet style). I wanted to be able to run my AC "a bit" if in an outage situation, but wouldnt run it much.

Basically, experience has taught me, especially with technology based things, one usually doesnt regret buying the higher end / better thing... they regret not spending the money up front because some feature or other is missing.

People usually dont say "wow my TV is too large! I wish I got the smaller one!". If you get two powerwalls, and backup almost everything, nothing says you HAVE to run everything. the difference is your choice, vs one forced on you by grid being down. That is, of course if one is just making a decision based on "how much do I want / need this" and not "this is cost prohibitive, I cant do it".