what happens when a powerwall2 fails?

[astrorob]

as i understand it, the way a powerwall2 keeps your solar online during a grid failure is that as far as the inverter is concerned, your powerwall is the grid.

so what happens if a powerwall2 fails even when the grid is up? do you lose power, or does the PW2 have some way of bypassing itself if it finds itself in a bad state? is there a way to manually bypass the PW2 if you find yourself in this situation?

thanks

 

[Ampster]

so what happens if a powerwall2 fails even when the grid is up? do you lose power, or does the PW2 have some way of bypassing itself if it finds itself in a bad state? is there a way to manually bypass the PW2 if you find yourself in this situation?

The gateway is the device that controls the switching between Grid and Off Grid mode. I would hope that the switch in the gateway would fail in the Grid mode but I honestly don't know. It may have a manual overide.

 

[miimura]

The Powerwall 2 has two fundamental operating modes, grid interactive, and grid master (for lack of a better term).

When the grid is up, the Powerwall inverter is grid interactive. That means that the Gateway is giving it power flow commands to charge or discharge to accomplish whatever strategy is desired at that moment. For example, it can charge to absorb All Solar, or charge to absorb Surplus Solar or discharge to match the household loads. If there is a failure when the grid is up, it should just shut down and do nothing and your loads will be supported by the grid. If a Powerwall really goes haywire, it will probably trip the circuit breaker.

When the grid is down, the Powerwall inverter is acting as the grid master and is trying to maintain the voltage and frequency for the islanded micro-grid. It will charge or discharge as needed to maintain those parameters. It can also change those parameters off nominal to signal solar inverters that they should curtail their output or shut down. If the Powerwall cannot maintain the voltage and frequency due to low battery or excessive load, it will shut down.

 

[astrorob]

@Ampster, @miimura thanks for the replies. it sounds like at least in theory the PW2 should do the right thing in this scenario. do you guys know if there is any technical documentation floating around out there, which might show how everything is wired together?

 

[ElectricOrgan]

as i understand it, the way a powerwall2 keeps your solar online during a grid failure is that as far as the inverter is concerned, your powerwall is the grid.

so what happens if a powerwall2 fails even when the grid is up? do you lose power, or does the PW2 have some way of bypassing itself if it finds itself in a bad state? is there a way to manually bypass the PW2 if you find yourself in this situation?

thanks

I don't know for sure, but I'm relatively certain that all power to the home does not go through the powerwall in the same way a UPS powers your computer. This would require a very large generation circuit in the powerwall.

Instead I believe the powerwall detects the phase of the power line into the home and matches that. Then it provides as much power as the home needs up to the limit of the powerwall. If the powerwall is receiving more power from the solar panels than it needs that power can flow back to the gridd. Once the power required by the home reaches the max available from the powerwall/solar, current can flow in from the grid.

In the event that external power from the grid is not available, there should be a relay that disconnects the power for the home from the grid and the powerwall can supply what is needed up to the limit of the powerwall and solar.

Some systems do not support a stand alone mode. I'm not sure why since it is not a complex circuit that is needed to detect the presence/absence of incoming power and disconnect the entire home. It's a few dollars worth of electronics and a relay. The delta cost should be two hundred dollars... retail.

 

[astrorob]

I don't know for sure, but I'm relatively certain that all power to the home does not go through the powerwall in the same way a UPS powers your computer. This would require a very large generation circuit in the powerwall.

yes certainly that makes sense, given that a single powerwall is only good for 5KW.

 

[miimura]

@Ampster, @miimura thanks for the replies. it sounds like at least in theory the PW2 should do the right thing in this scenario. do you guys know if there is any technical documentation floating around out there, which might show how everything is wired together?

I found the installation manual online with a quick search. I don't know of any other useful documentation.
TESLA POWERWALL 2 AC INSTALLATION MANUAL Pdf Download.

 

[Tam]

...show how everything is wired together?

The wiring setup:

Tesla shows that solar panels can bypass Powerwall (in your question if powerwall is broken):

And if powerwall is not broken, it can direct solar panels to both home and powerwall

 

[cwied]

Here's my understanding of how the system works. Note that I've skipped the solar in the diagram, since it's mostly a passive component of the system. I think it helps to understand the Powerwall system as a collection of components working together. In particular the gateway has three important components: the transfer switch/relay, the Neurio monitor to measure power flow and the controller itself that sends the commands to the Powerwalls to control their operation.

When the grid goes down, the transfer switch is opened and the Powerwall switches to islanding mode. In this mode, it just tries to maintain power at a certain frequency and voltage. I'm not clear on whether the controller is involved at all in this mode. It may just be the Powerwall itself that decides to raise frequency to curtail solar production, for example. I'm assuming the controller can program certain parameters of the operation, like the maximum frequency.

When the grid is up, the controller controls the operation to implement things like the time-based control modes. I'm assuming it can request that the Powerwall charge or discharge at any speed.

If the Powerwall itself fails, it shouldn't impact power to the house. Likewise, if the gateway controller fails, power should still flow from the grid. Obviously if the transfer switch gets stuck open, the house will have no power, but it seems to me that that would be unlikely to happen.

I'm not an expert, but I think this model describes the behavior that I've observed and have heard described on this board. Note that I believe that the connection between load panel and Powerwall is probably physically in the gateway box, but from a functional point of view, that doesn't change the way everything is connected.

 

[astrorob]

thanks - that's what i was looking for.

 

[astrorob]

and looking some more at that schematic... unfortunately, it seems i'm going to need a completely new panel, as in my house the meter and load panel are two halves of the same chassis, and the whole thing has been embedded into the wall so that it's mostly flush with the wall. i suppose there is probably a switch/breaker on the service side where the gateway could connect but that would probably be custom work (and maybe verboten since that side belongs to PGE?)

 

[miimura]

and looking some more at that schematic... unfortunately, it seems i'm going to need a completely new panel, as in my house the meter and load panel are two halves of the same chassis, and the whole thing has been embedded into the wall so that it's mostly flush with the wall. i suppose there is probably a switch/breaker on the service side where the gateway could connect but that would probably be custom work (and maybe verboten since that side belongs to PGE?)

There are many ways to skin this cat depending on the actual panels installed at your house already, how many Powerwalls you are installing, and how many and what kind of loads you have. If you have any loads that will not be backed up, they will just leave those in the main panel. A standard installation includes at least one new panel, usually used as a "Generation Panel". Another new load panel may be needed as well. These are not really that expensive in the scope of a Powerwall installation.

I should really make a diagram of my home electrical system before and after Powerwall installation to illustrate how it works in practice.

 

[astrorob]

There are many ways to skin this cat depending on the actual panels installed at your house already, how many Powerwalls you are installing, and how many and what kind of loads you have. If you have any loads that will not be backed up, they will just leave those in the main panel. A standard installation includes at least one new panel, usually used as a "Generation Panel". Another new load panel may be needed as well. These are not really that expensive in the scope of a Powerwall installation.

I should really make a diagram of my home electrical system before and after Powerwall installation to illustrate how it works in practice.

that would be really helpful.

it's not the expense for the new sub-panel(s) that concerns me... at this point it's the actual installation that has me worried.

i think my house could be somewhat unusual in the fact that the panels are set into the wall and then stuccoed around. seems like breaking out some number of the circuits into a generation panel might be really difficult. i suppose there is a risk tesla looks at this job and 10,000 other easier jobs and just elects to drop this one. or, maybe they just charge me a lot more than the $2500 they have quoted for installation. we'll have to see. it might be the kind of job they need to send someone out to to evaluate rather than just going off the photos i have provided them.

 

[GenSao]

and looking some more at that schematic... unfortunately, it seems i'm going to need a completely new panel, as in my house the meter and load panel are two halves of the same chassis, and the whole thing has been embedded into the wall so that it's mostly flush with the wall. i suppose there is probably a switch/breaker on the service side where the gateway could connect but that would probably be custom work (and maybe verboten since that side belongs to PGE?)

You are correct, you'll likely need a new load panel with all existing loads (and solar) moved to the new backup load center. See below plan on how my home is wired with a similar configuration.

Y = 200 A Backup load center
Z = Tesla Backup Gateway

that would be really helpful.

it's not the expense for the new sub-panel(s) that concerns me... at this point it's the actual installation that has me worried.

i think my house could be somewhat unusual in the fact that the panels are set into the wall and then stuccoed around. seems like breaking out some number of the circuits into a generation panel might be really difficult. i suppose there is a risk tesla looks at this job and 10,000 other easier jobs and just elects to drop this one. or, maybe they just charge me a lot more than the $2500 they have quoted for installation. we'll have to see. it might be the kind of job they need to send someone out to to evaluate rather than just going off the photos i have provided them.

The $2,500 for installation should include the backup-load panel. For my installation, Tesla did not need to send someone out to evaluate. I believe you should be the same.

 

[astrorob]

thanks, yes i just happened to read your other post with that diagram.

it's not the addition of the panel (which seems pretty standard), it's the fact that the existing panel is embedded in the house and all the wiring is coming in from behind the panel. is that how yours was? or was there conduit containing all the circuit wiring coming into the existing box from the side or top? just seems to me that it could be a more difficult install. for instance my solar guys had to punch thru the stucco into the wall and thread the AC up behind the box. i don't know, maybe this kind of embedded box is totally normal.

anyway i guess i'm saying that this job may represent more labor than the typical job.

 

[GenSao]

thanks, yes i just happened to read your other post with that diagram.

it's not the addition of the panel (which seems pretty standard), it's the fact that the existing panel is embedded in the house and all the wiring is coming in from behind the panel. is that how yours was? or was there conduit containing all the circuit wiring coming into the existing box from the side or top? just seems to me that it could be a more difficult install. for instance my solar guys had to punch thru the stucco into the wall and thread the AC up behind the box. i don't know, maybe this kind of embedded box is totally normal.

anyway i guess i'm saying that this job may represent more labor than the typical job.

My panel was not embedded in the house. Al the wires were coming from the top though the wall to the back of the existing panel. Although not pretty, Tesla did relocate all the loads using external conduits with a gutter box.

In your case, assuming your main load panel is by the garage. Depending on your preference, Tesla may install the backup load panel and gateway inside on the opposite side of the meter. Ultimately, even if your project is above average for labor, Tesla should honor the original install price.

 

[astrorob]

hopefully they would honor the price... and yes the main load panel is on the exterior wall of the garage. however, just behind the panel on the inside wall of the garage is integrated closet storage, so there's no access to the wall without removing all that garbage, which is something i don't want to do for a lot of reasons. i already had to remove the door and remove all the shelves from one of the closets for my EVSE...

 

[miimura]

that would be really helpful.

it's not the expense for the new sub-panel(s) that concerns me... at this point it's the actual installation that has me worried.

i think my house could be somewhat unusual in the fact that the panels are set into the wall and then stuccoed around. seems like breaking out some number of the circuits into a generation panel might be really difficult. i suppose there is a risk tesla looks at this job and 10,000 other easier jobs and just elects to drop this one. or, maybe they just charge me a lot more than the $2500 they have quoted for installation. we'll have to see. it might be the kind of job they need to send someone out to to evaluate rather than just going off the photos i have provided them.

Mine is the same. They just added a gutter box below it and pulled wires from the main panel into that. No stucco work necessary.

My Powerwalls are on the wall out of the frame to the right beyond the side gate, fed by the conduit coming out of the bottom of the Generation Panel. The box with the two black things on top is the Backup Gateway.

 

[astrorob]

thanks for that image... that looks suspiciously like my existing panel. so did they gut most of the user breaker box to extend the wiring?

and they cut a hole in the wall right underneath the existing panel?

looks like everything goes into the gateway and then just the various home circuit wires go into the generation panel?

 

[miimura]

thanks for that image... that looks suspiciously like my existing panel. so did they gut most of the user breaker box to extend the wiring?

and they cut a hole in the wall right underneath the existing panel?

looks like everything goes into the gateway and then just the various home circuit wires go into the generation panel?

Actually, most of my household 120V loads were already in a 125A subpanel. So, that 125A breaker was used to feed the gateway and one set of lugs on the bottom of the Gateway Switch, the output side, goes back into the main panel to be tied into the original feed with Polaris connectors for that subpanel. There are 2 or 3 incidental 120V circuits that were in the main panel that needed to be backed up, so they were extended into the Generation Panel. Of course, the solar was also extended into the Generation Panel. All my big 240V circuits are still in my main panel and not backed up. Several of them were never populated with loads. For example, I have a 50A circuit for the kitchen range, but it's not used because we have a gas range. Same for the clothes dryer. I also have two HVAC zones that are pre-plumbed and wired for A/C but the compressors were never installed. Those two 240V 40A circuits are also unused.