Discussion: "Powerwall +"

[slcasner]

I think it is dc coupled. The powerwall nameplate shows it is accepts dc voltage.

Is that a nameplate for the Powerwall+ as a complete unit? If so, perhaps that nameplate simply reflects the fact that the inverter has to accept DC voltage from the panels. Really the key question is whether the Powerwall part of the Powerwall+ (that is, the bottom box) no longer contains an inverter/charger of its own.

 

[SilverSp33d3r]

Is that a nameplate for the Powerwall+ as a complete unit? If so, perhaps that nameplate simply reflects the fact that the inverter has to accept DC voltage from the panels. Really the key question is whether the Powerwall part of the Powerwall+ (that is, the bottom box) no longer contains an inverter/charger of its own.

Tech is coming to commission my system tomorrow. I’ll ask all possible questions. I will take measurements to/from powerwall from inverter under charging and discharging conditions

the nameplate has a small sticker that was after the fact to call it powerwall +

 

[jsurpless]

Is that a nameplate for the Powerwall+ as a complete unit? If so, perhaps that nameplate simply reflects the fact that the inverter has to accept DC voltage from the panels. Really the key question is whether the Powerwall part of the Powerwall+ (that is, the bottom box) no longer contains an inverter/charger of its own.

If that is the case, does that mean that the solar inverter is also used to convert to AC when discharging and to DC when charging from sources other than solar?

 

[wwhitney]

Are there any pictures of the Powerwall+ top compartment with the covers off? Looking at what wiring goes does to the Powerwall 2 portion of it might be informative.

Personally, I'm doubtful they've changed the Powerwall 2 portion of it, so it would have to be AC coupled, but maybe they have.

Cheers, Wayne

 

[jsurpless]

Dailo posted this of his system the other day. I think that black box is the component you were asking if there was a pic?

 

[wwhitney]

Yes, that's the component. Looks crowded enough that it wouldn't be possible to tell what the conductor routing is from a picture. But it definitely looks like a box bolted on top of the Powerwall 2, so any connections between them should be via wires. A qualified person could trace the internal wiring to see if there is any sign of a DC path from the solar panels to the Powerwall 2 below.

Cheers, Wayne

 

[mongo]

Are there any pictures of the Powerwall+ top compartment with the covers off? Looking at what wiring goes does to the Powerwall 2 portion of it might be informative.

Personally, I'm doubtful they've changed the Powerwall 2 portion of it, so it would have to be AC coupled, but maybe they have.

Cheers, Wayne

Post 269, looks ACish.

Here is the outside picture. The only thing in the gateway is 2 breakers, one for the Powerwalls and the inverter. But attached is also an inside look at the inverter that sits above the Powerwalls.

 

[wwhitney]

Post 269, looks ACish.

I agree that if the wire bundle in the lower left of the picture are the only wires connecting the upper compartment to the lower compartment (Powerwall 2), it very likely is AC coupled.

If we assume that there are inverters in the lower Powerwall, then there has to be L1, L2, N, and G AC conductors in the connection. Which would be black, red, white, and green as shown. The other wires are too small to be power conductors, they are just communications conductors. So no DC connection.

One could hypothesize that the inverters have been removed from the Powerwall below, and the inverter above handles both PV and battery (I'm unclear if it is physically large enough for that to be plausible). Then there would need to be DC +, DC -, and ground connections. So why the white wire?

Sticking with AC coupling would have been a much quicker way to bring this product to market. They just had to marry their existing inverter innards with the existing Powerwall 2 and maybe add some controller logic to manage the combined AC connection to the rest of the house wiring.

So very likely AC coupled. [Hopefully I'm not repeating earlier analysis in this thread, just responding to some recent comments about DC coupling.]

Cheers, Wayne

 

[slcasner]

So very likely AC coupled. [Hopefully I'm not repeating earlier analysis in this thread, just responding to some recent comments about DC coupling.]

I think you are correct. That's why I said I doubted the DC connection despite the fact that I wish it were true.

 

[dailo]

On my install wires on the top conduit are from the Solar panels and bottom conduit are to the other Powerwall and breaker panel. Would be nice if the PW+ could be charged with DC from the solar.

 

[SilverSp33d3r]

I agree that if the wire bundle in the lower left of the picture are the only wires connecting the upper compartment to the lower compartment (Powerwall 2), it very likely is AC coupled.

If we assume that there are inverters in the lower Powerwall, then there has to be L1, L2, N, and G AC conductors in the connection. Which would be black, red, white, and green as shown. The other wires are too small to be power conductors, they are just communications conductors. So no DC connection.

One could hypothesize that the inverters have been removed from the Powerwall below, and the inverter above handles both PV and battery (I'm unclear if it is physically large enough for that to be plausible). Then there would need to be DC +, DC -, and ground connections. So why the white wire?

Sticking with AC coupling would have been a much quicker way to bring this product to market. They just had to marry their existing inverter innards with the existing Powerwall 2 and maybe add some controller logic to manage the combined AC connection to the rest of the house wiring.

So very likely AC coupled. [Hopefully I'm not repeating earlier analysis in this thread, just responding to some recent comments about DC coupling.]

Cheers, Wayne

You are correct once again sir!
My system was commissioned today and sure enough powerwall 2 still has its own separate inverter/ a/c coupled.

 

[slcasner]

You are correct once again sir!
My system was commissioned today and sure enough powerwall 2 still has its own separate inverter/ a/c coupled.

My hope is that the integration of functions in the PW+ means that the firmware has sufficient communication capabilities so the off-grid behavior could be controlled without raising the line frequency. I thought I saw a statement in early announcements of the PW+ that it achieved "more seamless" transition to battery backup when the grid fails.

 

[mongo]

My hope is that the integration of functions in the PW+ means that the firmware has sufficient communication capabilities so the off-grid behavior could be controlled without raising the line frequency. I thought I saw a statement in early announcements of the PW+ that it achieved "more seamless" transition to battery backup when the grid fails.

Yah, along with the AC looking wires, there are a bunch of low gauge communication looking ones in the bottom left corner. I'm guessing that is for battery/ solar coordination.

 

[s0schen]

My hope is that the integration of functions in the PW+ means that the firmware has sufficient communication capabilities so the off-grid behavior could be controlled without raising the line frequency. I thought I saw a statement in early announcements of the PW+ that it achieved "more seamless" transition to battery backup when the grid fails.

I have been on self consumption mode and have not noticed any change in line frequency when the inverters ramp down.

 

[MP3Mike]

My hope is that the integration of functions in the PW+ means that the firmware has sufficient communication capabilities so the off-grid behavior could be controlled without raising the line frequency. I thought I saw a statement in early announcements of the PW+ that it achieved "more seamless" transition to battery backup when the grid fails.

I think the problem is that they have to raise the frequency to meet the UL standards. What if you have additional solar from another company? It has to know to curtail generation as well.

 

[mongo]

I think the problem is that they have to raise the frequency to meet the UL standards. What if you have additional solar from another company? It has to know to curtail generation as well.

Is frequency feedback a requirement for battery systems, or just solar inverters?
Regardless, with communication, PW+ could control its solar output without frequency offset and then shift Hz if it is still getting over filled (say >98%).

 

[MP3Mike]

Is frequency feedback a requirement for battery systems, or just solar inverters?
Regardless, with communication, PW+ could control its solar output without frequency offset and then shift Hz if it is still getting over filled (say >98%).

Solar inverters have to respond to frequency shift. Battery systems have to shift the frequency when off grid and full to prevent damage.

 

[mongo]

Solar inverters have to respond to frequency shift. Battery systems have to shift the frequency when off grid and full to prevent damage.

Agree that the solar inverter UL requirements include shut off for out of range frequency (which can be augmented with tapering).
I disagree that battery systems will be damaged though. If a battery system prioritized line regulation over battery limits, that would be bad (from both design and result point of views). Baring that, they can cut off charging entirely (thus removing frequency regulation and causing solar to shutdown). Reducing charge rate below net production would also cause voltage or frequency shifting.
So I was curious if UL actually requires frequency based feedback functionality from battery systems.

 

[power.saver]

Agree that the solar inverter UL requirements include shut off for out of range frequency (which can be augmented with tapering).
I disagree that battery systems will be damaged though. If a battery system prioritized line regulation over battery limits, that would be bad (from both design and result point of views). Baring that, they can cut off charging entirely (thus removing frequency regulation and causing solar to shutdown). Reducing charge rate below net production would also cause voltage or frequency shifting.
So I was curious if UL actually requires frequency based feedback functionality from battery systems.

UL 9450 governs ESS and incorporates the requirements of UL 1741 including that grid interactive inverters meet frequency standards. So grid interactive ESS have to react to frequency shifting wile on-grid. During island mode, they can use this feature to curtail solar, but it's not the only way to do it (e.g. a dedicated comm link between the ESS and solar inverter is another option).

 

[slcasner]

I think the problem is that they have to raise the frequency to meet the UL standards. What if you have additional solar from another company? It has to know to curtail generation as well.

Agreed that the batteries need to have the capability to shift frequency to signal solar inverters according to the UL standard, but it should be possible to configure the batteries to not do that if there is no solar inverter that needs such signaling -- either because there is no solar installed or because there is direct coordination with the solar inverter. If another solar inverter is added later that cannot coordinate directly, then the battery configuration could be changed. The frequency shift is clearly a backwards-compatibility hack taking advantage of the fact that solar inverters were already required to disconnect from the grid if the frequency (or voltage) was outside a specified range.