Considering a Powerwall 2 - I had some questions:

[pgrovetom1]

I'm in the process of having Tesla quote me a Powerwall 2 setup and I had some questions for other PW2 users.

My arrangement suggests I need 3 PW2's mounted on a pedestal/frame near my main service entrance which is located about 50 feet from my home. My primary purpose is to provide emergency backup plus prepare for the new TOU tariff by PG&E which shifts the peak toward the evening and away from the optimum solar production time. I currently am on the PG&E E6 tariff and have about 15KW+ of solar which is slightly above my usage. I have 3 separate solar systems, 2 each SMA 7000US's with each producing about 5.5KW and another based on 17 Enphase M215 micro-inverters which produces about 4KW.

Each PW2 will serve one solar system. The PW2 and the solar system ( of 3) will have its own sub-panel. These will be combined to serve my 2 home sub-panels of 100A and 200A. My well water pump, my irrigation water pump, and my pool 100A panel will not be backed up and remain on my existing 200A service panel. The Tesla gateway will isolate ( disconnect) between that main 200A not backed up panel and the 3 PW2/solar panels and the 100A and 200A home sub-panels.

I will need a ground mounted frame to hold the PW2's and various panels and the disconnect switches for my solar systems. Tesla sent me specs for this frame and its a bit ridiculous in its details. Does anyone know if the frame with concrete, posts etc.. specs are rigid as it looks like gross overkill and could be expensive? If Tesla specifies it in a rigid way, I know my county building department will demand it be perfect. I fear the simple frame could blow the budget plus it must be done in a tight location and it might not be practical to meet the details of their specs. Does anyone know how rigid this is? Since the PW2's would be stacked and their weight on an existing concrete pad, the frame itself would not carry much weight. Any thoughts here?

Are there any online tools that provide any kind of modeling for PW2's, solar and usage power and flows?

If I have 3 PW2's then there is 40.5 KWh of backup power when the grid is down. Each is capable of 5KW or 15KW of total power during backup. If a water pump turns on during backup, it draws significant startup power/current. Do the 3 PW2's load share all the power drain equally while in backup. This would suggest that all loads combined while on backup must not exceed 15KW but it doesn't really matter where the load exists on any of the sub-panels. Is this true?

What happens if by chance the PW2's are overloaded during backup - load exceeds 15KW. Do they shut down nicely? If the load is removed, will they come back on? Can they be restarted manually? How is this done?

If in backup, the 40.5KWh is reached, do they shut down cleanly? Then when the sun comes up and solar begins charging the PW2's, how do they restart? How is all this managed? Automatically? Manually? Could someone explain how all the various cases work and how much is automatic and how much is manual?

Will backup work if the internet is out? Can things like restart be done without the internet? besides the nice data collection and app features, do things basically work for backup when the internet is down? I suspect most peoples internet is dependent on local power and therefore is lost during a major outage or emergency like an earthquake or fire.

thanks

 

[woferry]

I'm sure others will chime-in also and likely have more experience with some of the specifics below, here are my comments based on what I've seen/heard. Sorry for the big post, but there's a lot to respond to here.

My arrangement suggests I need 3 PW2's mounted on a pedestal/frame near my main service entrance which is located about 50 feet from my home. My primary purpose is to provide emergency backup plus prepare for the new TOU tariff by PG&E which shifts the peak toward the evening and away from the optimum solar production time. I currently am on the PG&E E6 tariff and have about 15KW+ of solar which is slightly above my usage. I have 3 separate solar systems, 2 each SMA 7000US's with each producing about 5.5KW and another based on 17 Enphase M215 micro-inverters which produces about 4KW.

Good with you so far, though you mention 15kW is slightly above your usage, any idea what your daily usage (or production) is in terms of kWh?

Each PW2 will serve one solar system.

And then I lose you here. This isn't really how it works, unless you're saying you're going to get 3 separate Gateways in addition to 3 Powerwall 2's. Are all of the house loads behind one service meter, or are there multiple service inputs? If the loads are split then I could see how separate systems would be needed, if PG&E connects in one place then I'd expect a more traditional system with one Gateway and 3 PW2's, where they really act more like a single battery pack 3x the size of one PW2 (with 3x the inverter capability for charging/discharging), not one-per-solar system.

The PW2 and the solar system ( of 3) will have its own sub-panel. These will be combined to serve my 2 home sub-panels of 100A and 200A. My well water pump, my irrigation water pump, and my pool 100A panel will not be backed up and remain on my existing 200A service panel.

A sketch would go a long way to explain this better, but I think I get it.

The Tesla gateway will isolate ( disconnect) between that main 200A not backed up panel and the 3 PW2/solar panels and the 100A and 200A home sub-panels.

Okay, this sounds like a more traditional system, but seems to conflict with what was said before.

I will need a ground mounted frame to hold the PW2's and various panels and the disconnect switches for my solar systems. Tesla sent me specs for this frame and its a bit ridiculous in its details. Does anyone know if the frame with concrete, posts etc.. specs are rigid as it looks like gross overkill and could be expensive? If Tesla specifies it in a rigid way, I know my county building department will demand it be perfect. I fear the simple frame could blow the budget plus it must be done in a tight location and it might not be practical to meet the details of their specs. Does anyone know how rigid this is? Since the PW2's would be stacked and their weight on an existing concrete pad, the frame itself would not carry much weight. Any thoughts here?

I can't offer much help on this. I know when I discussed my system I was ordering 1 PW but ensuring I could add a second one later. A single PW can be hung off a structure (assuming nothing else forbids it like local code), but if more than one is going to be "stacked" (front-to-back is the only way they stack) then they have to sit on a platform. So I'd discussed adding a concrete pad with my site surveyor, but ultimately found enough wall space to mount two independent PW2's, so I have one now with the second spot waiting for one to be installed sometime later. I did recently see a picture of 2 PW2's with seemingly no structure (see here, note that it all seems to be sitting on a plastic pallet, though you can't see what's in the middle), but not sure if that was a special-case given the circumstances.

Are there any online tools that provide any kind of modeling for PW2's, solar and usage power and flows?

I'm not aware of any. Self-powered is pretty simple, but the Advanced modes are much more complex. The Gateway gets 3 current inputs: What's going to/from the grid, what's coming from the solar, and what's going to/from the Powerwalls (which it also controls). The home loads are deduced by what the 3 above sensors don't see (i.e. if the solar is producing more than is going to the grid or the PWs, the rest must be going to the home). In Self-powered I think the PW is basically set to zero-out the grid reading, both for charging and discharging. I.e. whatever solar is producing that would have gone to the grid, goes to the PWs instead (up to the charging limit of 5kW/PW, and until the PWs are full of course. The max charging rate does drop as the PWs near full-charge). Similarly if the house starts to draw fro the grid, the PWs will discharge to make up for that grid consumption, up to the discharge limit of 5kW/PW continuous (7kW/PW peak for a few seconds) or until the PWs hit their Reserve. The Advanced modes also take into account peak/off-peak/shoulder energy periods and past usage to try to be smarter about when to charge/discharge, with different goals in mind.

If I have 3 PW2's then there is 40.5 KWh of backup power when the grid is down. Each is capable of 5KW or 15KW of total power during backup. If a water pump turns on during backup, it draws significant startup power/current. Do the 3 PW2's load share all the power drain equally while in backup. This would suggest that all loads combined while on backup must not exceed 15KW but it doesn't really matter where the load exists on any of the sub-panels. Is this true?

40.5 kWh is the maximum, but there's a Reserve that generally speaking you don't want to set below 20% (more on that below). So it's really more like 32.4 kWh. 3 PW2's can output up to 15kW continuously or 21kW peak as I mentioned above. But you said above that your well water pump would not be backed-up. If that's true then the pump simply won't have any power during backup, so there's no concern there (except that you don't have a pump). The only circuits that get backed-up are the ones connected between the Gateway and the PW's, anything on the grid-side of the Gateway will lose power during an outage. You can either put those loads in your grid-side monitoring loop or not, if you include those loads then during PW discharge with the grid up the PW will try to power those non-backed-up loads as well (which drains your battery faster but reduces grid consumption), or you can make it so that these loads are not seen by the Gateway, and they will always draw direct from the grid.

If you exceed the PW inverter capability while the grid is up, then the rest simply comes from the grid. If this happens while the grid is down then as I understand it the PWs will shut down, and I believe you need to flip the switches on the units to restart them. I've never done this myself, so I can't say this for certain. But yes, your backed-up loads cannot exceed the 21kW peak / 15kW continuous draw when the PWs are the only power source. During the day if the solar is producing then you can power higher loads I believe, but the solar inverters will be stopped/restarted depending on battery capacity, so if the load surges at the wrong time the solar may not be there to help. And of course if it's early/late in the day and the solar can't cover the extra load then you'll still overload the PWs.

What happens if by chance the PW2's are overloaded during backup - load exceeds 15KW. Do they shut down nicely? If the load is removed, will they come back on? Can they be restarted manually? How is this done?

In this case I think the little On/Off switches on the PW's themselves are all that need to be toggled, but again I have no direct experience with this.

If in backup, the 40.5KWh is reached, do they shut down cleanly? Then when the sun comes up and solar begins charging the PW2's, how do they restart? How is all this managed? Automatically? Manually? Could someone explain how all the various cases work and how much is automatic and how much is manual?

"Cleanly" means the power stops, just like an outage. As I understand it if you want the PW2s to get the solar back up and running in the morning you need to keep the Reserve at 20% or above, if they shut down at a lower battery percentage then they don't come back on their own. I don't totally understand how this works, I guess the Gateway keeps itself powered (not sure how) and knows when daylight rolls around to try applying power to get the solar synchronized and running again. Of course if your house surges when the power suddenly comes back (ACs try to turn on, etc) then it may not be able to sustain the power for the ~5 minutes required for the solar to start producing again. Based on this forum it sounds like some have been successful with this, but others haven't been. My PW capacity / house consumption is enough that I haven't fully-discharged it overnight yet, so it hasn't been a concern for me.

Will backup work if the internet is out? Can things like restart be done without the internet? besides the nice data collection and app features, do things basically work for backup when the internet is down? I suspect most peoples internet is dependent on local power and therefore is lost during a major outage or emergency like an earthquake or fire.

The Gateway supports up to 3 connections, wired ethernet, WiFi and cellular (3G with the current Gateway used in the US). While you should always try to provide ethernet if possible or WiFi otherwise, it's connected so long as at least one of those three is good. As far as I know (haven't had to test this yet, thankfully) it does not need to be constantly-connected, but it sounded like it does expect to 'phone home' every few days or something. So I don't think any short-term outage is in danger of the Gateway/PWs not working. If it goes more than a few days without at least the 3G connection I'm not sure just what happens, hopefully they'd have cellular restored faster than that.

One thing to consider is that you really only need your PWs to be able to keep the house powered when the solar isn't running. Though that does assume that once the solar starts producing there will be enough excess to recharge the PWs for the next evening, so if the house consumes everything the solar produces then you're going to end up starting off from a worse place each evening, or potentially not charging the PWs at all.

And when you say 15kW, is that really the peak combined solar output? It sounds like your two 7000 inverters are oversized for the panels they're on, were you planning on adding more panels later or something? Since the 3 PWs max-charge rate is 15kW, if the inverters can ever output more than 15kW you might be forced to put one of the solar inverters on the grid side of the Gateway, which means it would be lost production during an outage. My house is set up this way, since I have two 5200W inverters but only one PW2, so one inverter is on the backup side and the other on the grid side of the Gateway. If/when I get the second PW then the second inverter should be able to flip sides, and I'd have extra charging capability during an outage.

 

[Dan123]

I'm in the process of having Tesla quote me a Powerwall 2 setup and I had some questions for other PW2 users.

My arrangement suggests I need 3 PW2's mounted on a pedestal/frame near my main service entrance which is located about 50 feet from my home. My primary purpose is to provide emergency backup plus prepare for the new TOU tariff by PG&E which shifts the peak toward the evening and away from the optimum solar production time. I currently am on the PG&E E6 tariff and have about 15KW+ of solar which is slightly above my usage. I have 3 separate solar systems, 2 each SMA 7000US's with each producing about 5.5KW and another based on 17 Enphase M215 micro-inverters which produces about 4KW.

Each PW2 will serve one solar system. The PW2 and the solar system ( of 3) will have its own sub-panel. These will be combined to serve my 2 home sub-panels of 100A and 200A. My well water pump, my irrigation water pump, and my pool 100A panel will not be backed up and remain on my existing 200A service panel. The Tesla gateway will isolate ( disconnect) between that main 200A not backed up panel and the 3 PW2/solar panels and the 100A and 200A home sub-panels.

I will need a ground mounted frame to hold the PW2's and various panels and the disconnect switches for my solar systems. Tesla sent me specs for this frame and its a bit ridiculous in its details. Does anyone know if the frame with concrete, posts etc.. specs are rigid as it looks like gross overkill and could be expensive? If Tesla specifies it in a rigid way, I know my county building department will demand it be perfect. I fear the simple frame could blow the budget plus it must be done in a tight location and it might not be practical to meet the details of their specs. Does anyone know how rigid this is? Since the PW2's would be stacked and their weight on an existing concrete pad, the frame itself would not carry much weight. Any thoughts here?

Are there any online tools that provide any kind of modeling for PW2's, solar and usage power and flows?

If I have 3 PW2's then there is 40.5 KWh of backup power when the grid is down. Each is capable of 5KW or 15KW of total power during backup. If a water pump turns on during backup, it draws significant startup power/current. Do the 3 PW2's load share all the power drain equally while in backup. This would suggest that all loads combined while on backup must not exceed 15KW but it doesn't really matter where the load exists on any of the sub-panels. Is this true?

What happens if by chance the PW2's are overloaded during backup - load exceeds 15KW. Do they shut down nicely? If the load is removed, will they come back on? Can they be restarted manually? How is this done?

If in backup, the 40.5KWh is reached, do they shut down cleanly? Then when the sun comes up and solar begins charging the PW2's, how do they restart? How is all this managed? Automatically? Manually? Could someone explain how all the various cases work and how much is automatic and how much is manual?

Will backup work if the internet is out? Can things like restart be done without the internet? besides the nice data collection and app features, do things basically work for backup when the internet is down? I suspect most peoples internet is dependent on local power and therefore is lost during a major outage or emergency like an earthquake or fire.

thanks

First, I am not really sure why each solar system is on a separate subpanel with a separate powerwall. It seems like you should be able to combine all 3 solar systems and the 3 powerwalls into one subpanel, and then feed your main panel.

Powerwalls are syncronized, so they will supply power together. They can supply up to 7kw each for up to 10 seconds, so 3 of them will give you 21 kw. During the day, you will also have solar production, so you will be able to start anything.

If you exceed their capacity, they abruptly shut down. Then they try to restart - I don't know how long the wait is. It may depend on the state of charge of the batteries and the time of day. I think it may be 5 minutes or so if they shut down because of an overload.



Backup will work if the internet is down. In the backup mode, they will shut down somewhere around 10% (it is a combination of the state of charge and load that triggers the shutdown. I think at low state of charge they restart automatically in the morning, or in 30 minutes. The problem is that if those loads are still connected, after the Powerwall restarts, the loads will try to draw power again (before the solar kicks in). So to restart the Powerwall at low state-of-charge you may need to disconnect all of your breakers (except for solar), wait until the Powerwall and solar comes back, and then start slowing flipping on circuit breakers. You can manually restart the Powerwalls using switches and breakers. I heard that if it gets really low, then you have to jump start it with a 9 volt battery.

 

[pgrovetom1]

First, I am not really sure why each solar system is on a separate subpanel with a separate powerwall. It seems like you should be able to combine all 3 solar systems and the 3 powerwalls into one subpanel, and then feed your main panel.

This is how Tesla proposed arranging them. They said in order to meet the 120% current rule per panel, my 3 solar systems plus 3 PW2's current design limit would exceed the 120% current for a single 200A panel. So they proposed pairing 1 solar system with 1 PW2 combined into one 100A panel. Then these 3 panels would be combined into a single 200A sub-panel, on the home side of the gateway with my existing 200A panel with my non-backed up circuits including the irrigation pump, well pump and pool circuit operating directly out of my main panel. So they are all combined but to meet the 120% rule, they could not all be combined in a single 200A - or so they said. The combined maximum current for 3 PW2's and my 3 solar systems plus all my backed up loads greatly exceeds the 200A x 12% = >240A. So by pre-combining the pairs of solar system plus a PW2 into their own 200A sub-panels they are able to meet the limit.

Powerwalls are syncronized, so they will supply power together. They can supply up to 7kw each for up to 10 seconds, so 3 of them will give you 21 kw. During the day, you will also have solar production, so you will be able to start anything.

The solar inverters shut down when they see no grid power. So if the PW2's shut down due to running out of charge, what brings the solar inverters back online. If the gateway disconnects the backup side from the main panel and their is no grid power, the backup side will shut down when the PW2's run out of charge. Then when the sun comes out in the morning, the solar inverters will not come back on unless they see AC power on the home side of the gateway. If the PW2's are shut down, where will the AC power come from to "fool" the solar inverters into believing there is grid power. The solar inverters will not come on because they are UL 1741 compliant and have no way of knowing they are inside the gateway. The gateway must turn and provide "seed" AC when they believe the solar inverters have panel power and can provide both home power and charging power. Do you know what I mean? It sounds a bit like a catch 22.

If you exceed their capacity, they abruptly shut down. Then they try to restart - I don't know how long the wait is. It may depend on the state of charge of the batteries and the time of day. I think it may be 5 minutes or so if they shut down because of an overload.

Do they just keep trying every 'N' minutes until it works? If the PW2's went down at midnight and the solar inverters began seeing enough solar power to charge the PW2's at 10AM, would they keep trying to restart for 10 hours until it all came back up due to the solar power? It sounds clumsy.

Backup will work if the internet is down. In the backup mode, they will shut down somewhere around 10% (it is a combination of the state of charge and load that triggers the shutdown. I think at low state of charge they restart automatically in the morning, or in 30 minutes. The problem is that if those loads are still connected, after the Powerwall restarts, the loads will try to draw power again (before the solar kicks in). So to restart the Powerwall at low state-of-charge you may need to disconnect all of your breakers (except for solar), wait until the Powerwall and solar comes back, and then start slowing flipping on circuit breakers. You can manually restart the Powerwalls using switches and breakers. I heard that if it gets really low, then you have to jump start it with a 9 volt battery.

This is what I feared. The solar won't just "come back on" because of UL 1741 requirement to stay off till the grid AC returns. Which it won't because the gateway has disconnected the grid. Only the gateway or a PW2 can provide the AC to fool the solar inverters into restart. It must be the gateway because one piece of equipment must provide reference AC 60Hz for the 3 PW2's and the 3 solar inverters which must be fooled into thinking the grid is on due the UL 1741 requirements. The actual 60Hz and 120/240V must also be sourced as a reference such that the 3 PW2's and 3 solar inverters are voltage plus phase and frequency synchronized during operation. So the gateway must be the master reference. So it must decide when it thinks solar power is available and provide 240V 60Hz to get the solar inverters started and then the PW2's see that and come on.

 

[pgrovetom1]

I'm sure others will chime-in also and likely have more experience with some of the specifics below, here are my comments based on what I've seen/heard. Sorry for the big post, but there's a lot to respond to here.

Good with you so far, though you mention 15kW is slightly above your usage, any idea what your daily usage (or production) is in terms of kWh?

And then I lose you here. This isn't really how it works, unless you're saying you're going to get 3 separate Gateways in addition to 3 Powerwall 2's. Are all of the house loads behind one service meter, or are there multiple service inputs? If the loads are split then I could see how separate systems would be needed, if PG&E connects in one place then I'd expect a more traditional system with one Gateway and 3 PW2's, where they really act more like a single battery pack 3x the size of one PW2 (with 3x the inverter capability for charging/discharging), not one-per-solar system.

A sketch would go a long way to explain this better, but I think I get it.

Okay, this sounds like a more traditional system, but seems to conflict with what was said before.

I can't offer much help on this. I know when I discussed my system I was ordering 1 PW but ensuring I could add a second one later. A single PW can be hung off a structure (assuming nothing else forbids it like local code), but if more than one is going to be "stacked" (front-to-back is the only way they stack) then they have to sit on a platform. So I'd discussed adding a concrete pad with my site surveyor, but ultimately found enough wall space to mount two independent PW2's, so I have one now with the second spot waiting for one to be installed sometime later. I did recently see a picture of 2 PW2's with seemingly no structure (see here, note that it all seems to be sitting on a plastic pallet, though you can't see what's in the middle), but not sure if that was a special-case given the circumstances.

I'm not aware of any. Self-powered is pretty simple, but the Advanced modes are much more complex. The Gateway gets 3 current inputs: What's going to/from the grid, what's coming from the solar, and what's going to/from the Powerwalls (which it also controls). The home loads are deduced by what the 3 above sensors don't see (i.e. if the solar is producing more than is going to the grid or the PWs, the rest must be going to the home). In Self-powered I think the PW is basically set to zero-out the grid reading, both for charging and discharging. I.e. whatever solar is producing that would have gone to the grid, goes to the PWs instead (up to the charging limit of 5kW/PW, and until the PWs are full of course. The max charging rate does drop as the PWs near full-charge). Similarly if the house starts to draw fro the grid, the PWs will discharge to make up for that grid consumption, up to the discharge limit of 5kW/PW continuous (7kW/PW peak for a few seconds) or until the PWs hit their Reserve. The Advanced modes also take into account peak/off-peak/shoulder energy periods and past usage to try to be smarter about when to charge/discharge, with different goals in mind.

40.5 kWh is the maximum, but there's a Reserve that generally speaking you don't want to set below 20% (more on that below). So it's really more like 32.4 kWh. 3 PW2's can output up to 15kW continuously or 21kW peak as I mentioned above. But you said above that your well water pump would not be backed-up. If that's true then the pump simply won't have any power during backup, so there's no concern there (except that you don't have a pump). The only circuits that get backed-up are the ones connected between the Gateway and the PW's, anything on the grid-side of the Gateway will lose power during an outage. You can either put those loads in your grid-side monitoring loop or not, if you include those loads then during PW discharge with the grid up the PW will try to power those non-backed-up loads as well (which drains your battery faster but reduces grid consumption), or you can make it so that these loads are not seen by the Gateway, and they will always draw direct from the grid.

If you exceed the PW inverter capability while the grid is up, then the rest simply comes from the grid. If this happens while the grid is down then as I understand it the PWs will shut down, and I believe you need to flip the switches on the units to restart them. I've never done this myself, so I can't say this for certain. But yes, your backed-up loads cannot exceed the 21kW peak / 15kW continuous draw when the PWs are the only power source. During the day if the solar is producing then you can power higher loads I believe, but the solar inverters will be stopped/restarted depending on battery capacity, so if the load surges at the wrong time the solar may not be there to help. And of course if it's early/late in the day and the solar can't cover the extra load then you'll still overload the PWs.

In this case I think the little On/Off switches on the PW's themselves are all that need to be toggled, but again I have no direct experience with this.

"Cleanly" means the power stops, just like an outage. As I understand it if you want the PW2s to get the solar back up and running in the morning you need to keep the Reserve at 20% or above, if they shut down at a lower battery percentage then they don't come back on their own. I don't totally understand how this works, I guess the Gateway keeps itself powered (not sure how) and knows when daylight rolls around to try applying power to get the solar synchronized and running again. Of course if your house surges when the power suddenly comes back (ACs try to turn on, etc) then it may not be able to sustain the power for the ~5 minutes required for the solar to start producing again. Based on this forum it sounds like some have been successful with this, but others haven't been. My PW capacity / house consumption is enough that I haven't fully-discharged it overnight yet, so it hasn't been a concern for me.

The Gateway supports up to 3 connections, wired ethernet, WiFi and cellular (3G with the current Gateway used in the US). While you should always try to provide ethernet if possible or WiFi otherwise, it's connected so long as at least one of those three is good. As far as I know (haven't had to test this yet, thankfully) it does not need to be constantly-connected, but it sounded like it does expect to 'phone home' every few days or something. So I don't think any short-term outage is in danger of the Gateway/PWs not working. If it goes more than a few days without at least the 3G connection I'm not sure just what happens, hopefully they'd have cellular restored faster than that.

One thing to consider is that you really only need your PWs to be able to keep the house powered when the solar isn't running. Though that does assume that once the solar starts producing there will be enough excess to recharge the PWs for the next evening, so if the house consumes everything the solar produces then you're going to end up starting off from a worse place each evening, or potentially not charging the PWs at all.

And when you say 15kW, is that really the peak combined solar output? It sounds like your two 7000 inverters are oversized for the panels they're on, were you planning on adding more panels later or something? Since the 3 PWs max-charge rate is 15kW, if the inverters can ever output more than 15kW you might be forced to put one of the solar inverters on the grid side of the Gateway, which means it would be lost production during an outage. My house is set up this way, since I have two 5200W inverters but only one PW2, so one inverter is on the backup side and the other on the grid side of the Gateway. If/when I get the second PW then the second inverter should be able to flip sides, and I'd have extra charging capability during an outage.

My 3 solar systems provide about 14KW maximum on a good day. The 2 SMA 7000's produce about 5500W each at peak sun ( the system is 10 years old) and the string of Enphase inverters produce about 3000W also at peak sun on a summer day. So my solar will not quite reach the 3 PW2's 15KW charge rate, but will come close at 14KW+ on a good day. It sounds pretty clumsy and this is not a "non-stop" or automatic system during a long outage at start and restart. It sounds like its necessary to manage one's loads as carefully as possible and try and not let the PW2's shut down if at all possible. And if they do, it sounds like a manual process of getting the solar inverters to come back on when there is sun and get the PW2's to begin charging during sun hours. It sounds very messy but doable.

 

[wwhitney]

The gateway is just a monitoring point and disconnect relay. The inverters in the Powerwalls are dual mode grid-tie/standalone, and they provide the reference voltage source once the gateway has disconnected the grid. When there are multiple Powerwalls, they are connected via a communications cable so the multiple inverters can sync with each other.

 

[pgrovetom1]

The gateway is just a monitoring point and disconnect relay. The inverters in the Powerwalls are dual mode grid-tie/standalone, and they provide the reference voltage source once the gateway has disconnected the grid. When there are multiple Powerwalls, they are connected via a communications cable so the multiple inverters can sync with each other.

I'm not sure what this means. When there are more than one PW2, one of them must be the voltage and frequency and phase source in something like a master slave arrangement.

The solar inverters slave to PG&E phase, frequency and voltage under normal circumstances. When the utility goes down as when the gateway disconnects, the solar inverters see the AC go away and shut down according to the UL 1741 rules. So its a standoff. The solar inverters need to see a proper AC 60Hz and they begin a restart process that typically takes a few minutes. They would normally phase and frequency and voltage lock to the utility AC.

But if the gateway has disconnected the utility AC, one of the systems, a PW2 or a gateway must create a startup AC with 60Hz phase that the others can lock to. Phase and frequency locking is a negative feedback loop controlled process. If multiple PW2's tried to do some kind of mutual phase and frequency locking, the loop would not be stable. One of them needs to take on the responsibility as a reference source that the others and then the solar inverters can lock onto.

It makes sense that the gateway would somehow be the arbiter or source onto which all the PW2's lock onto. It may only have a simple 60Hz clock with phase that's distributed via the communication cables but that makes it the source. It must work that way. Then each PW2 output voltage is regulated depending on whether its sourcing current or charging. Its actually critical that a PW2 or solar inverter NOT source current until its in near perfect phase lock. If 2 PW2's or a solar inverter tried to source current into another that was out of phase or frequency, it would shut it down or damage the output stage due to over-current.

I'm looking for input on how it all works so I understand the many subtle issues. thanks

 

[reddy]

This is what I feared. The solar won't just "come back on" because of UL 1741 requirement to stay off till the grid AC returns. Which it won't because the gateway has disconnected the grid. Only the gateway or a PW2 can provide the AC to fool the solar inverters into restart. It must be the gateway because one piece of equipment must provide reference AC 60Hz for the 3 PW2's and the 3 solar inverters which must be fooled into thinking the grid is on due the UL 1741 requirements. The actual 60Hz and 120/240V must also be sourced as a reference such that the 3 PW2's and 3 solar inverters are voltage plus phase and frequency synchronized during operation. So the gateway must be the master reference. So it must decide when it thinks solar power is available and provide 240V 60Hz to get the solar inverters started and then the PW2's see that and come on.

This isn’t mine works. I had a 30 hour unexpected outage during a severe windstorm.

When the grid went down, the solar shut down as expected, but then waited 5 minutes and resynched with the Powerwalls. The gateway had isolated me from the grid, and I stayed isolated for over 30 hours.

When the solar was working, as the Powerwalls approached 100% charge, they turned off the inverters again. Once charge fell to 95% , the inverters came back on. There was no need to manually start or stop inverters or the Powerwalls.

I had enough capacity to power the house all night. But if I had exhausted the Powerwalls overnight, I could have turned off the breakers to the house, and manually restarted the Powerwalls and inverters once the sun came up. My installer said I needed 1kw of solar production to keep the system up at the time of a manual restart. I have not done an actual restart, but he showed me the connectors and said Tesla or he could talk through it.

 

[power.saver]

Tesla has worked all this out. The GW controls the PW voltage and frequency, so they are always in sync with each other. The GW will also shift the frequency when reconnecting to the grid, so the PW is in phase before the contactor closes. The only thing you need to worry about is not running them down overnight and having to do a manual restart, which is a complicated procedure. Just set your reserve high enough to get you through the night, and cut unnecessary loads during a power outage. As @reddy said above, it is a fully automatic system.

 

[reddy]

I'm looking for input on how it all works so I understand the many subtle issues. thanks

Here is the day I lost power from the grid at about 3 pm. This is the solar production graph. You can see the system cycling on and off until sundown.

 

[reddy]

Here is the Powerwall output after losing grid power at 3pm. From 6pm on we were on Powerwall only. Power wasn’t restored until 9pm the next day.

 

[wwhitney]

I currently am on the PG&E E6 tariff and have about 15KW+ of solar which is slightly above my usage. I have 3 separate solar systems, 2 each SMA 7000US's with each producing about 5.5KW and another based on 17 Enphase M215 micro-inverters which produces about 4KW.

Each PW2 will serve one solar system. The PW2 and the solar system ( of 3) will have its own sub-panel.

That description sounds like a weird layout to me. The following schematic would work:

Service Disconnect
|
Panel(s) with Non-Backedup Loads
|
200A Feeder
|
Backup Gateway -- Generation Panel
|
First Panel with Backed up Loads and with 200A main breaker
|
Other Panels with Backed up Loads

The Generation Panel could be a 200A panel with (3) 30A breakers for the Powerwalls, (1) 20A breaker for the (17) Enphase M215s, and (2) 40A breakers for the (2) SMA 7000US inverters.

Cheers, Wayne

 

[wwhitney]

I'm not sure what this means. When there are more than one PW2, one of them must be the voltage and frequency and phase source in something like a master slave arrangement.

Yes, I agree, but I think the only role the Backup Gateway plays in that is perhaps in determining which one is master and which ones are slaves (or maybe that's statically determined at the time of installation). I think the master Powerwall is generating the reference voltage source. But I may have it wrong, please let me know if you find a specific reference to the contrary.

Cheers, Wayne

 

[Ulmo]

I'm in the process of having Tesla quote me a Powerwall 2 setup and I had some questions for other PW2 users.

My arrangement suggests I need 3 PW2's mounted on a pedestal/frame near my main service entrance which is located about 50 feet from my home. My primary purpose is to provide emergency backup plus prepare for the new TOU tariff by PG&E which shifts the peak toward the evening and away from the optimum solar production time. I currently am on the PG&E E6 tariff and have about 15KW+ of solar which is slightly above my usage. I have 3 separate solar systems, 2 each SMA 7000US's with each producing about 5.5KW and another based on 17 Enphase M215 micro-inverters which produces about 4KW.

Each PW2 will serve one solar system. The PW2 and the solar system ( of 3) will have its own sub-panel. These will be combined to serve my 2 home sub-panels of 100A and 200A. My well water pump, my irrigation water pump, and my pool 100A panel will not be backed up and remain on my existing 200A service panel. The Tesla gateway will isolate ( disconnect) between that main 200A not backed up panel and the 3 PW2/solar panels and the 100A and 200A home sub-panels.

I will need a ground mounted frame to hold the PW2's and various panels and the disconnect switches for my solar systems. Tesla sent me specs for this frame and its a bit ridiculous in its details. Does anyone know if the frame with concrete, posts etc.. specs are rigid as it looks like gross overkill and could be expensive? If Tesla specifies it in a rigid way, I know my county building department will demand it be perfect. I fear the simple frame could blow the budget plus it must be done in a tight location and it might not be practical to meet the details of their specs. Does anyone know how rigid this is? Since the PW2's would be stacked and their weight on an existing concrete pad, the frame itself would not carry much weight. Any thoughts here?

Are there any online tools that provide any kind of modeling for PW2's, solar and usage power and flows?

If I have 3 PW2's then there is 40.5 KWh of backup power when the grid is down. Each is capable of 5KW or 15KW of total power during backup. If a water pump turns on during backup, it draws significant startup power/current. Do the 3 PW2's load share all the power drain equally while in backup. This would suggest that all loads combined while on backup must not exceed 15KW but it doesn't really matter where the load exists on any of the sub-panels. Is this true?

What happens if by chance the PW2's are overloaded during backup - load exceeds 15KW. Do they shut down nicely? If the load is removed, will they come back on? Can they be restarted manually? How is this done?

If in backup, the 40.5KWh is reached, do they shut down cleanly? Then when the sun comes up and solar begins charging the PW2's, how do they restart? How is all this managed? Automatically? Manually? Could someone explain how all the various cases work and how much is automatic and how much is manual?

Will backup work if the internet is out? Can things like restart be done without the internet? besides the nice data collection and app features, do things basically work for backup when the internet is down? I suspect most peoples internet is dependent on local power and therefore is lost during a major outage or emergency like an earthquake or fire.

thanks

I feel like it might be simpler to set it up as one bank of PowerWalls in one easy location that serves one panel, under which all backed up loads exist.

Maybe it makes sense to select "Whole House Backup" mode in that operation. I believe that allows higher amperage, and for that reason alone, makes it an easier installation. In that mode, according to you, you have 3 loads you don't want backed up, but I dispute that. In case you are sticking to your guns, you would want to set up a few relay switches (pretty inexpensive: A/C line-level input from the grid to the relay, and when it goes off, it would set the relay into off state on the output leg of the device you never want running while the PowerWalls are in backup, or something like that). I argue that you only want to do that with the pool pump (i.e., when the grid power goes down, so does the pool pump); in that case, both well pumps should get soft starts installed.

If you don't like the Whole House Backup option, maybe it makes sense to select Backed Up Loads panel in that operation. If so, they could throw in a third panel, which acts as a subpanel to the main unbacked up panel, but has both your other panels underneath it. In this mode, the main panel would not be backed up, but every other panel would be. The PowerWalls would just work in concert. I think that might be something like what Tesla is suggesting. I don't exactly understand what you are saying, though, so maybe posting some diagrams of what is being proposed would be in order.

I'm sure you've seen discussions of motor loads, especially compressor motor loads, starting. There are various ways around this. For instance, for A/C, inverter A/C systems seem to have a low power startup aspect to their designs that makes them superior in a few ways. But we're not talking about designing a new house with a new A/C, so we can forget about that interesting discussion. Let's look instead at your pump. Now, I'm totally ignorant about water pumps: I would presume they are less starting power than traditional A/C compressors, but more than, say, a A/C with an inverter on it. Next thought is does your water pump have a softstart option for it? Look up the various soft start upgrade companies and see if they can wire in a softstart for your water pumps. That would be great if they have that option, and you can call it done and solved. To me it seems like it would be nice for you to do this and put the well pumps on backed up panels. That's why the whole home backup option looks easier and easier, but it would also make installation for putting those on the backed up panels easier as well. Anyway, soft start is better for the grid and is said to make motors last longer, if I'm not mistaken, so it might be a good idea to just hire an electrician right now to put soft start on them or at least design that into the system.

The PowerWalls rest on the floor and are attached to a vertical thing, which should be strong enough to prevent them from tipping over (and crushing someone). If you're not looking, they'd flatten your head if they started falling. Think baby and them just flopping over on the baby: dead. Tesla rightly wants a strong vertical thing to attach the PowerWalls to. Your job is making sure that exists. Now that you know that, you can probably see through some of their specs as just filling in the paper, and know the difference between requirements and just extra expense. In a garage or on the side of a house, a standard house wall is more than enough for this task (provided the installation crew actually screws into the studs properly; shoddy workmanship could easily skip doing so). That's why I hate today's insurance and anti-DIY culture: shoddy workers do better work than average people, but people that care can do better work with DIY than usual workers. Our planet would be better if we did our own work and insurance companies and governments let us. Not everyone has that knowledge, but when I was born, all the real men and real fathers already knew all that stuff.

If you are still forced to colocate a PowerWall with something on the ground (which I'm saying doesn't sound true unless they're doing something special and nice that I didn't catch), then I think they're just looking at having it rest on a concrete pad. It's nothing more than dirt and a flat unburnable solid surface plus a backing so it doesn't tip. Essentially, compacted soil with some flat stones and a vertical pole pounded into the ground ought to do it. The PowerWalls could be clamped to that, or if they want a screw surface, you could just stick a 2x4 horizontal across two poles which have a cheap strap to the two vertical poles (at the correct height). Maybe a couple of them depending on attachment points. The poles could be as simple as 2" steel pipe pounded vertically into the ground about 3 feet. They'd rot after a few decades (and crush babies so don't do that; see above), but I'm just giving you an idea of the basics, the fundamentals, of their minimums. Of course, Tesla would probably scoff at such a sort of cruddy installation, so you could dress it up by throwing a sack of premixed concrete there and making it flat on top around the poles and just say you dug down all 3' with the concrete around the poles so they wouldn't corrode. What they don't know won't hurt them. If it were me, I'd actually dig down, though, which means some more sacks. But my point is that they want a solid surface to sit on, and a vertical thing on back to attach to. Tesla gave you the minimum width, height, dimensions of the backing because it gets attached on the left and right on the back of the PowerWalls, and also specified an additional three feet in front of the PowerWalls and to the sides of them for human worker access, per code, and enough space for the PowerWalls to vent a little. From my point of view, the human accessible area could just be a bunch of gardening walkway squares set out nice enough they don't trip someone working there; no need to get out a rebar crew and concrete crew for what seems like enough space to park a car. I think the code requires the working space, and the jurisdiction is worried weeds would cover up that area, so they would scoff if it wasn't covered with something plants would not be able to grow through. I tend to agree with them on one point: not letting nature take over the PowerWalls. That's why I prefer the idea of the PowerWalls, all of them, on the same whole house backup panel inside the garage rather than having to deal with outside questions (and it also prevents outside vandals interrupting your backup system). In my case, our exterior installation was easy, since we had an old shed concrete pad up against the home with the shed removed that we store garbage cans on (yes, I would have preferred interior installation, but we didn't have space, and I didn't have the choice to move stuff around in my situation; had I those choices, I would have designated a location for them inside, likely a little utility shed built to spec, which would have been WAAAY more expensive than your concrete pad, but since I'm a carpenter, I would have considered it fun). We mounted the PowerWalls on that pad against the outside wall of the home. There's still space to put the garbage cans there after our PowerWall installation. Our 3' access is solved by just taking the garbage cans out of the way! Can't get any easier than that! Also, when they installed the PowerWalls, there was clearance on their left and right. Any inspector would have said, no problem. If you are looking at dirt, the architects fearing reprisal from inspectors would probably want to build something up, and then the intermediaries might beef something up by accident, and you're off to the races -- bad idea -- you're right to question that. Maybe now that you have an idea of argument points, you can get their specs down to size. I was wondering why the frame of the solar panels was insufficient as the vertical member; you'd just put some throw stones down for the batteries. Anyway, use their spec sheets to look for the things you really need vs. the things they just drew in to make a complete picture; you (and the architect) might be seeing dollar signs looking at the fill in pieces that aren't really explaining what's going on; that's seriously just some cheap cheap handyman stuff, so as long as you get the mount points sufficient, you'd good. If Tesla won't let you do it with a few poles vertically in the ground, then you could just put an L-shaped cinderblock wall on top of a few sacks of concrete. The L-shape would give the wall its sturdiness to not fall over. The L-shape could wrap around some feature so that it doesn't end up taking any more space than the cinderblocks themselves. Find out minimum height and width for the PowerWall facing location. That would require rebar stuck into the cinderblocks and properly settled concrete inside the cinderblocks. Easy work for a handyman, but if you want to hire licensed guild workers, you are suddenly hiring engineers, taking out permits, getting a variance with lawyers in front of a full sitting of the County Board of Supervisors, taking out an ad in your paper ... life was so much easier before monarchy took over our country.

Here's mine mounted to the house on the old shed pad. Tomorrow is garbage day, so conveniently, the garbage cans aren't in the way (except for one overflow). Mine was one of the earliest installations, so they probably have plenty of policies being made to prevent some subsequent errors. The stack of panels to the left of the PowerWalls is away from their vents and will not burn (they are left over glass from an old store display I replaced). Ideally, that garbage can with the wood sticking out should be a foot further away or even further; I didn't put it there, and now you can see why policies are built to stop dumb people from doing dumb things -- when the smart people design stuff based upon good workmanship and good stewardship, everything gets messed up when we let just anyone live with us. Also check out my pics at Index of /tesla/energy/powerwall/pictures/ (note the fricking mess they made of the wiring and the down-ratings they had to do because it was NOT a whole-home backup; I think it's way cheaper and way more capable to do a whole house backup, and they didn't really fully explain that to me when they asked, but they did tell me about it, and I didn't fully think it through).