Power wall plus 170% capacity?

[Pearl1!]

Yesterday, the Tesla rep said that post PTO, via software, the PW+ (inverter) will be able to output 170% rated AC capacity. That would be 7.6 to 12.92 kW AC peak power (specs 9.6 max kWh off-grid). The rep stated this is why they “overbuild” system (or why they underbuild on the inverter size). Has anyone experienced the 170%, or anything greater than published specs?

Also, the rep said that this was possible because the PW+ can skip the inverter and put surplus DC from the panels directly into the PW battery. PW documentation is quite limited. Is there anywhere we can go to get more details?

thanks

 

[Vines]

Yesterday, the Tesla rep said that post PTO, via software, the PW+ (inverter) will be able to output 170% rated AC capacity. That would be 7.6 to 12.92 kW AC peak power (specs 9.6 max kWh off-grid). The rep stated this is why they “overbuild” system (or why they underbuild on the inverter size). Has anyone experienced the 170%, or anything greater than published specs?

Also, the rep said that this was possible because the PW+ can skip the inverter and put surplus DC from the panels directly into the PW battery. PW documentation is quite limited. Is there anywhere we can go to get more details?

thanks

What you said doesn't make sense. What does the increase in AC output have to do with DC utilization of solar energy by the the Powerwall +?

However reading between the lines this might make sense why Tesla is overdriving the 7.6 kW PW+ inverters. If the ESS is able to utilize some of the DC energy in its own inverter, then the PV system wont be clipping as much as it looks to be on the surface, at least while the ESS portion still has room to accept charge.

EDIT: I agree with @Bitslizer that there doesn't seem to be any DC connections from the PW ess portion and the Inverter portion of the PW+. I cannot be sure there is some AC power flowing from the PV inverter to the ESS inverter however.

 

[Bitslizer]

1) Never take "new feature via software" as a promise, treat it as a bonus if it comes through, most likely won't
2) No, never seen it goes above 7.8kw max and those 7.8kw are a short blip 7.7kw sustain i have seen.
3) There's no physical DC wire to go from anywhere to the battery of the PW+, the connection between the inverter and the battery are literally 2 AC hot wire, 1 neutral, 1 ground, and a bunch of tiny comm cable that can't carry a load. No way any DC can get fed into the battery.

Know where the 9.6kw max comes from? They use a 50a breaker for the PW+ inverter/battery combo. three's a 80% usage rule. 50a* 80% = 40a. 40a*240v = 9.6kw. The battery+inverter maybe capable of outputting 12.6kw combine, but that will trip the breaker. they software limit it to 9.6kw

The inverter is UL certified to a certain spec, they can't just update it via software and get higher spec and still retain UL certification, not to mention all the wire and breaker are for the lower spec

 

[Vines]

1) Never take "new feature via software" as a promise, treat it as a bonus if it comes through, most likely won't
2) No, never seen it goes above 7.8kw max and those 7.8kw are a short blip 7.7kw sustain i have seen.
3) There's no physical DC wire to go from anywhere to the battery of the PW+, the connection between the inverter and the battery are literally 2 AC hot wire, 1 neutral, 1 ground, and a bunch of tiny comm cable that can't carry a load. No way any DC can get fed into the battery.

Know where the 9.6kw max comes from? They use a 50a breaker for the PW+ inverter/battery combo. three's a 80% usage rule. 50a* 80% = 40a. 40a*240v = 9.6kw. The battery+inverter maybe capable of outputting 12.6kw combine, but that will trip the breaker. they software limit it to 9.6kw

The inverter is UL certified to a certain spec, they can't just update it via software and get higher spec and still retain UL certification, not to mention all the wire and breaker are for the lower spec

I edited my post above, since I haven't dug into the PW+ really deeply. I believe you are correct.

However, this keeps being something customers so there must be something behind it, or it's just marketing speak? It is possible that the 7.6 kW PV inverter is allowed to send the excess of the 7.6 kW to the battery ESS through the AC connection. I hesitate to say Tesla is outright wrong without more explanation.

 

[Bitslizer]

I edited my post above, since I haven't dug into the PW+ really deeply. I believe you are correct.

However, this keeps being something customers so there must be something behind it, or it's just marketing speak? It is possible that the 7.6 kW PV inverter is allowed to send the excess of the 7.6 kW to the battery ESS through the AC connection. I hesitate to say Tesla is outright wrong without more explanation.

Until someone provide some proof of the PW+ inverter exceeding 7.8kw wheter to the grid or combine with charging the battery, just a bunch of BS as far as I'm personally concern.

Just Tesla advisor trying to explain away why Tesla is trying to stuff a 12kw DC system at 1.7 DC/AC ratio onto a single 7.6kw inverter because Tesla don't have a 10kw inverter (that's the inverter AC size limit in alot of area) and 7.6+3.8 is over the 10kw size limit accepted for interconnection.
Where the industry recommendation is about 1.2-1.3 ratio

1.7 Ratio may work well for layout with panels facing multiple direction.

1.7 Ratio will clip like crazy if all the PV generation are south facing (for USA). but unfortunately I have seen a few project design as such

I have a East West split system at 1.4 ratio 15.64kw on 7.6(pw+)+3.8 and I expected to be clipping on perfect sunny day from May through early Sept (Chicago Metro)

 

[Bitslizer]

Until someone provide some proof of the PW+ inverter exceeding 7.8kw wheter to the grid or combine with charging the battery, just a bunch of BS as far as I'm personally concern.

Just Tesla advisor trying to explain away why Tesla is trying to stuff a 12kw DC system at 1.7 DC/AC ratio onto a single 7.6kw inverter because Tesla don't have a 10kw inverter (that's the inverter AC size limit in alot of area) and 7.6+3.8 is over the 10kw size limit accepted for interconnection.
Where the industry recommendation is about 1.2-1.3 ratio

1.7 Ratio may work well for layout with panels facing multiple direction.

1.7 Ratio will clip like crazy if all the PV generation are south facing (for USA). but unfortunately I have seen a few project design as such

I have a East West split system at 1.4 ratio 15.64kw on 7.6(pw+)+3.8 and I expected to be clipping on perfect sunny day from May through early Sept (Chicago Metro)

estimate from PVwatts

1) 12.92kw system with a 7.6+3.8kw inverter, south facing chicago metro, DC/AC ratio 1.1 expect about 17400kwh per year
2) 12.92kw system with a 10kw inverter, south facing chicago metro, DC/AC ratio 1.3 expect about 17400kwh per year
3) 12.92kw system with a 7.6kw inverter, south facing chicago metro, DC/AC ratio 1.7 expect about 16400kwh per year
4) 9.88kw system with a 7.6kw inverter, south facing chicago metro, DC/AC ratio 1.3 expect about 13400kwh per year

Since Tesla charge by per Watt DC and not by module/component cost. Difference between 3 and 4 is that they get to charge you $6k+ more while giving you less actual output(1000kwh per year less) compare to 2. I don't know if this is by design or an accidental byproduct.

My advice is that if your local allow for greater than 10kw AC worth of inverter, get a 13.6kw+ system where that will exceed the 1.7 ratio and they should give you a 7.6+3.8 where you will be in the 1.2 ratio

 

[Ampster]

Just Tesla advisor trying to explain away why Tesla is trying to stuff a 12kw DC system at 1.7 DC/AC ratio onto a single 7.6kw inverter

The operative capacity for AC coupling is based on AC inverter size. Based on the 1.7 DC to AC ratio which is an AC capacity of 7kW. It seems like a perfect fit.

 

[Bitslizer]

The operative capacity for AC coupling is based on AC inverter size. Based on the 1.7 DC to AC ratio which is an AC capacity of 7kW. It seems like a perfect fit.

1.2 to 1.3 ratio is the industry Norm. If it's all south facing 1.7 will clip like crazy. See my example above you lose a 1000kwh from clipping going from 10kw 1.3 to 7.6kw 1.7 for the same DC size. That's a month worth of generation every year

 

[zƬesla]

For one inverter, I have a 1.29 ratio and have seen clipping of 4+ hours in a day. Sadly, the other inverter has a 0.94 ratio, meaning the installer could have better evened things out. All south facing.

 

[wwhitney]

The meaning of the 1.7 figure is surely getting garbled. It could either be a max allowable DC/AC ratio, or it could be a peak AC current rating (e.g. 10s rating vs continuous rating).

Cheers, Wayne

 

[Bitslizer]

For one inverter, I have a 1.29 ratio and have seen clipping of 4+ hours in a day. Sadly, the other inverter has a 0.94 ratio, meaning the installer could have better evened things out. All south facing.

That's why I worked with the designer and the install crew to make sure I got the desired spilt between the 2 inverters and between the east and west roof planes to balance the inverter load minimize the clippings

 

[charlesj]

1.2 to 1.3 ratio is the industry Norm. If it's all south facing 1.7 will clip like crazy. See my example above you lose a 1000kwh from clipping going from 10kw 1.3 to 7.6kw 1.7 for the same DC size. That's a month worth of generation every year

Yes, you are correct if the inverter is downsized for no good reason. But, if you look at your number 3 and 4, same inverter but ratio is jumped to 1.7 from 1.3, you gain 3 megaWatthours for the year.

 

[Bitslizer]

Yes, you are correct if the inverter is downsized for no good reason. But, if you look at your number 3 and 4, same inverter but ratio is jumped to 1.7 from 1.3, you gain 3 megaWatthours for the year.

Goal is to generate the most output, 1.7 is leaving a lot on the table, while 1.3 to 1.1 is minimal gain.

 

[wwhitney]

Goal is to generate the most output, 1.7 is leaving a lot on the table, while 1.3 to 1.1 is minimal gain.

Generate the most output given what constraint? If the constraint is space, I agree with you, spend more $ on inverters to get more kWh/yr.

But if the constraint is $, then you have to look at whether the inverters are cost effective. I.e. in the example from PVWatts, from the (10 kWDC, 7.6 kWAC) basepoint, adding 3 kWDC with no additional inverters (going to (13 kWDC, 7.6 KWDC)) generates 75% as much additional energy as adding that 3 kWDC along with 2.4 kWAC of inverters (going to (13 kWDC, 10 kWAC)). Then how does the price of the inverter size increment compare to the price of the additional 3 kWDC of panels? If it's over 1/3 as much, adding the inverter size bump and the 3 kWDC is less efficient on a kWh/year/$ basis than adding the 3 kWDC alone. Maybe still worth it, or maybe the budget is maxed out and you just do the 3 kWDC of panels.

And if the constraint is AC inverter size (due to utility regulations), it's nice to know that you still get 75% of the benefit of the extra DC power when going from a DC/AC ratio of 1.3 to 1.7.

Cheers, Wayne

 

[Bitslizer]

Generate the most output given what constraint? If the constraint is space, I agree with you, spend more $ on inverters to get more kWh/yr.

But if the constraint is $, then you have to look at whether the inverters are cost effective. I.e. in the example from PVWatts, from the (10 kWDC, 7.6 kWAC) basepoint, adding 3 kWDC with no additional inverters (going to (13 kWDC, 7.6 KWDC)) generates 75% as much additional energy as adding that 3 kWDC along with 2.4 kWAC of inverters (going to (13 kWDC, 10 kWAC)). Then how does the price of the inverter size increment compare to the price of the additional 3 kWDC of panels? If it's over 1/3 as much, adding the inverter size bump and the 3 kWDC is less efficient on a kWh/year/$ basis than adding the 3 kWDC alone. Maybe still worth it, or maybe the budget is maxed out and you just do the 3 kWDC of panels.

And if the constraint is AC inverter size (due to utility regulations), it's nice to know that you still get 75% of the benefit of the extra DC power when going from a DC/AC ratio of 1.3 to 1.7.

Cheers, Wayne

Tesla charge by per watt DC, they charge thw same for a 7.6 alone or adding another 3.8. they used to charge the same when they used the solar edge 10kw inverter. We are getting only 7.6 now because Tesla in-house the inverter but dont offer a 10kw option. So in early 2021 they were installing 10kw solar edge inverter for 12...13kw DC, but now use a 7.6kw Tesla for the same DC. Ergo early 2021 install had higher output for the same price, and late 2021 for downgraded output due to lack of 10k inverter

They charge about $2.01 power watt DC, so about $25600 (before rebates and credits) for a 30x425w system (12.75) with a1.68 DC/AC ratio that clip alot with 1x 7.6 inverter
Vs
32x425 (13.6) about $27300 for a DC/AC is 1.19 with a 7.6+3.8 inverter that clip away less

About $1700 to have another 850w DC and a second inverter with the rebate and credit it is even less

I would gladly pay the minimal increase to get that extra inverter (assuming the area has no 10kw AC restriction)

My understanding is that around 16-20kw DC they tend to give you 2x 7.6 even at 20kw with 15.2 AC you are looking at about 1.31 ratio