Tesla Says I Can Only Get *ONE* Powerwall bc of my Utility's Rules

[Jeremy3292]

Coming once again to this forum for help as Tesla is giving me the runaround and what I think are some BS lines.

I ordered 3 Powerwalls with a 9.315 kW solar array. Tesla is saying I can only have *ONE* Powerwall 3 bc my utility has a limit of 20 kW AC (see snippet below); PW3 has 11.5 kW of power output.

First, I thought 11.5 kW was the *max* power and it could be "set" or "turned down" by wiring/breaker specific to your install.

Second, ironically enough I was told "PW3 doesn't exist" when I ordered and now they aren't even bringing up an option for PW+/2 for me which has a lower power rating. 1 PW+ and 2 PW2's would be under this alleged 20 kW limit I believe.

Third, direct from the utility (Duke Energy) website the application you have to fill out for interconnection is worded as a "certified inverter-based generating facility no larger than 20 kW." Well my solar array is 9.315 kW so it will likely have a 7.6 kW inverter, far less than 20 kW as noted below. I am not disputing there is a 20 kW solar array limit, but I don't see how battery backup has anything to do with that. The battery power output is to run your house loads; what does that have to do with my utility?

Fourth, I called the "Duke Renewables" line which is just a customer service line for solar basically and they said what I said above. The 20 kW limit is related to your "solar generating facility" and the batteries don't matter.

What I am missing here everyone? Am I crazy?

Link directly to Duke:

Interconnection for Smaller Capacity - Duke Energy

Interconnection process for business projects less than or equal to 20 kW. To submit a request, learn more at Duke Energy.

www.duke-energy.com

From Tesla:

From Duke:

 

[offandonagain]

The battery power output is to run your house loads; what does that have to do with my utility?

This changes with the Export Everything option, where you could be exporting to the grid from solar and batteries simultaneously. They have options to set "site export limits" in software, and I agree you seem to be under the limits with PW2s, so I'm not sure why they're giving you the runaround. Just commenting on why batteries matter for grid export.

 

[cali8484]

The 20kW appears to apply to the max power from PV and batteries. Each PW3 can technically provide 11.5kW to the grid from batteries on top of PV. You might check with the POCO to see if they would allow a larger system if you put in export limit control to ensure no more than 20kW export.

 

[Jeremy3292]

Update: I am now being told by my advisor I can have 1 PW3 and 2 PW2's - LOL. Bc that somehow makes sense???

He is going to see if I can get 3 PW3's bc I told him this "utility restriction" is bogus.

When everyone said Tesla customer service sucks, they really weren't joking. Man this is a PITA being your own project advisor.

 

[MP3Mike]

Update: I am now being told by my advisor I can have 1 PW3 and 2 PW2's - LOL. Bc that somehow makes sense???

Interesting as Tesla says PW3s and PW2s aren't compatible with each other.

 

[Jeremy3292]

Interesting as Tesla says PW3s and PW2s aren't compatible with each other.

My thoughts exactly which I brought up before to my advisor. Can't trust anything they say, but he said the FAQ page is about existing installs and not new installs...take that with a grain of salt.

Another red flag in the process.

 

[BGbreeder]

On the bright side, think how much you are learning about your system to be.

Sorry that it is a pain, but I find that doing things the hard way sometimes comes up roses because of what I learned. I would be reminding myself how much I saved...

All the best,

BG

 

[cali8484]

When everyone said Tesla customer service sucks, they really weren't joking. Man this is a PITA being your own project advisor.

Has Tesla done an install in your area? Hope this is last hurdle for you.

 

[Jeremy3292]

Has Tesla done an install in your area? Hope this is last hurdle for you.

Yeah - I've pulled local old Tesla Energy permits, called Duke Energy (my utility), talked to local installers, etc. I told my advisor everything I could think of under the sun earlier today. I was like this doesn't even make logical sense. I could have 1,000 Powerwalls and they are just dead weight bricks without a power source - either the grid or solar. Hence the 20 kW AC solar limit per Duke Energy. It's all total BS by Tesla. Some idiot in engineering/design won't take 5 minutes to think critically and look at other installs in the area.

On the bright side, think how much you are learning about your system to be.

Sorry that it is a pain, but I find that doing things the hard way sometimes comes up roses because of what I learned. I would be reminding myself how much I saved...

All the best,

BG

Yeah it's $20k less than my local reputable installer lol. It'll be worth it in the end...if I can ever get to the end.

Bright side is they're saying PW3 is what they are installing everywhere these days...another "take it with a grain of salt"

 

[Jeremy3292]

I got an update from another project advisor who is not mine personally:

This actually makes somewhat good sense for once. What is interesting is that it sounds like ALL PW3's have a PV inverter inside vs. the PW+ has a PV inverter and the PW2 does not. I can't imagine I am the only one who has a utility with a PV array/inverter limit, so Tesla is going to be running into this issue everywhere across the country bc of their design choice with the PW3.

I still don't believe this actually matters but it at least makes somewhat of logical sense. What doesn't make sense is how my inverter would be 20 kW when my solar array is 9.315 kW with more than one PW3. That is a DC/AC ratio well under one? Weird.

 

[MP3Mike]

This actually makes somewhat good sense for once. What is interesting is that it sounds like ALL PW3's have a PV inverter inside vs. the PW+ has a PV inverter and the PW2 does not.

I wondered about that, since as you said every PW3 has a built in PV inverter.

I still don't believe this actually matters but it at least makes somewhat of logical sense.

Would they allow you to install three 7.5kW inverters with each inverter only having 3kW of panels hooked to them? (I doubt it. Probably because they are afraid that you would just add panels in the future to the already installed, and approved, PV inverters.)

 

[Jeremy3292]

I wondered about that, since as you said every PW3 has a built in PV inverter.

Would they allow you to install three 7.5kW inverters with each inverter only having 3kW of panels hooked to them? (I doubt it. Probably because they are afraid that you would just add panels in the future to the already installed, and approved, PV inverters.)

You are probably right bc the limit is the PV AC inverter. This is going to be an issue for Tesla across the country. Many utilities have solar array limits that are logically tied to PV AC inverter sizing.

I talked with a local reputable installer and he said the most they can install for Duke Energy territory here is about a 31 kW DC solar array with a 20 kW AC inverter limit (1.55 DC/AC ratio).

A curious design decision by Tesla with the PW3. Yes, 1 or 2 PW3 can power almost every house due to the increased power output, but the storage capacity is still the same - tiny. I'm getting 3 PW's to hopefully "future proof" myself due to the ever-changing and ever-increasing TOU plans. Even then with one or two cloudy days in the winter with my all electric house and my 3 PW's are likely depleted.

 

[jhn_]

You are probably right bc the limit is the PV AC inverter. This is going to be an issue for Tesla across the country. Many utilities have solar array limits that are logically tied to PV AC inverter sizing.

I talked with a local reputable installer and he said the most they can install for Duke Energy territory here is about a 31 kW DC solar array with a 20 kW AC inverter limit (1.55 DC/AC ratio).

A curious design decision by Tesla with the PW3. Yes, 1 or 2 PW3 can power almost every house due to the increased power output, but the storage capacity is still the same - tiny. I'm getting 3 PW's to hopefully "future proof" myself due to the ever-changing and ever-increasing TOU plans. Even then with one or two cloudy days in the winter with my all electric house and my 3 PW's are likely depleted.

12kW limit in my neck of the woods. Had to apply for an exception from the utility for my 12.24kW.

 

[Jeremy3292]

Anyone have any opinions on inverter size? The advisor just emailed me back and said he thinks they will use 2 PW+ and 1 PW2 with a “smaller inverter” on the second PW+ but will let me know for sure.

I thought Tesla usually just gives you one 7.6 kW inverter for a higher DC/AC ratio, especially for my 9.315 kW array size. One 7.6 kW inverter + one 3.8 kW inverter would leave me with a DC/AC ratio of 0.82.

 

[BGbreeder]

Anyone have any opinions on inverter size? The advisor just emailed me back and said he thinks they will use 2 PW+ and 1 PW2 with a “smaller inverter” on the second PW+ but will let me know for sure.

I thought Tesla usually just gives you one 7.6 kW inverter for a higher DC/AC ratio, especially for my 9.315 kW array size. One 7.6 kW inverter + one 3.8 kW inverter would leave me with a DC/AC ratio of 0.82.

I wouldn't lose sleep on it either way. You will probably never saturate a 7.6kW inverter, unless your array will point due south, with a pretty steep roof (33 degrees or 8/12 +/-), but even if you do, the total energy losses year round are going to be minimal. Model it yourself on PVwatts. More inverter capacity is a slightly higher inverter base load, but again year round not going to make much of a difference to you, though it will to Tesla ($$).

All the best,

BG

 

[Jeremy3292]

I wouldn't lose sleep on it either way. You will probably never saturate a 7.6kW inverter, unless your array will point due south, with a pretty steep roof (33 degrees or 8/12 +/-), but even if you do, the total energy losses year round are going to be minimal. Model it yourself on PVwatts. More inverter capacity is a slightly higher inverter base load, but again year round not going to make much of a difference to you, though it will to Tesla ($$).

All the best,

BG

My array points almost south at 160ish degrees. I did just check PVWatts and you’re right the difference is negligible. I’ve read on here keeping an inverter closest to 100% is best, but not sure what that means exactly. Longevity of the inverter?

I was more so thinking people on here have had to kick and scream to get Tesla to give them another inverter with even larger solar arrays than mine, so it’s weird I would get another inverter when I don’t need it. Seems like that would cost Tesla more not less also.

 

[BGbreeder]

My array points almost south at 160ish degrees. I did just check PVWatts and you’re right the difference is negligible. I’ve read on here keeping an inverter closest to 100% is best, but not sure what that means exactly. Longevity of the inverter?

I was more so thinking people on here have had to kick and scream to get Tesla to give them another inverter with even larger solar arrays than mine, so it’s weird I would get another inverter when I don’t need it. Seems like that would cost Tesla more not less also.

You are not alone; the "100% is best" idea keeps coming up. However, I think that the advice is antiquated, from when solar inverters were (much) less efficient, with higher base (aka idle, fixed) loads. With a higher fixed based load, the inverter was most efficient when it was fully (100%) loaded. Modern inverters are very very efficient, and the difference between 60% load and 99% load efficiency is negligible for most inverters.

I would comment that for almost all terrestrial solar energy deployments, a few extra panels has better ROI than sweating the differences of particular inverter types and sizes, e.g. 11.4kW of inverter vs 7.4kW. Under most scenarios, investing in the extra panels, rather than the extra inverter capacity will return far more to you. YMMV...

If you care about inverter longevity, and / or reliability, microinverters are the way to go. Much, much higher MTBF, and if one fails, you lose a small percentage of your capacity.

All the best,

BG

 

[YRide]

On the bright side, think how much you are learning about your system to be.

Sorry that it is a pain, but I find that doing things the hard way sometimes comes up roses because of what I learned. I would be reminding myself how much I saved...

All the best,

BG

I feel like i literally got to re-learn my entire EE degree going through the install process. I'm generally interested in this stuff, so it was fun and valuable to know it inside and out as you say. But geez, as OP points out, there's way to much effort required to get things right...and too much risk if you dont watch Tesla and the proj advisors like a hawk.

 

[Ulmo]

Is it possible to install a one-way isolator that prevents any export to the grid but does allow grid to come into the system and allows an "oversized" system that is not technically grid-tied? More and more this is seeming like the best idea with all the restrictions grid providers impose. I tried to think perhaps a utility authorized one way isolator is what I have in mind. I know PowerWall 2's can be set to never export, but I don't know if my SolarEdge is programmable to output only to my batteries and home and not to the grid. I'm thinking the best option may be a low amperage AC-DC converter from the grid, diodes on the output to make sure the current only flows one way, and this supplied as a "solar" input to an inverter that would happily interact with the PowerWalls, or if the MPPT messes this setup up, then try some other method. I wonder what kind of circuit can mimick solar panels so MPPT will be fine?

It seems doable pretty trivially: Using an MPPT controller to charge from an AC to DC power supply: I need a sanity check here guys (see the last post): some DC output power devices have amperage limiters that can be used to keep an MPPT input in check. This seems like a simple method to create a one way supply from grid to an internally isolated system without any official grid tie. The grid to interior one way bridge can be relatively low amperage (say, 1kW to 4kW), because it's just make up amperage for the whole system that can be fed in over time and the inside batteries can store it up for when it's needed. Car charging would be problematic, but one solution is to have an isolation switch that allows it to be connected to the utility grid panel or the inside panel, to either feed full from grid power, or full from interior generation (solar and stored battery power). In this setup, one option would be to put the 1 Tesla PW3 on the grid-connected panel as the utility allows with, say, evening pointed solar panels connected to it, but the other 2 Tesla PW3's on the isolated interior panel system, that talk to, say, a morning and mid-day solar panel system. You could set the AC-DC charger to suck down the solar and battery power in the grid connected PW3 after your car is fully charged until the grid connected PW3 is low using something like Home Assistant.

I thought we'd have these products in the market in droves by now. What a pathetic lineup of products considering the regulatory headwinds we commonly face.

 

[Vines]

Is it possible to install a one-way isolator that prevents any export to the grid but does allow grid to come into the system and allows an "oversized" system that is not technically grid-tied? More and more this is seeming like the best idea with all the restrictions grid providers impose. I tried to think perhaps a utility authorized one way isolator is what I have in mind. I know PowerWall 2's can be set to never export, but I don't know if my SolarEdge is programmable to output only to my batteries and home and not to the grid. I'm thinking the best option may be a low amperage AC-DC converter from the grid, diodes on the output to make sure the current only flows one way, and this supplied as a "solar" input to an inverter that would happily interact with the PowerWalls, or if the MPPT messes this setup up, then try some other method. I wonder what kind of circuit can mimick solar panels so MPPT will be fine?

It seems doable pretty trivially: Using an MPPT controller to charge from an AC to DC power supply: I need a sanity check here guys (see the last post): some DC output power devices have amperage limiters that can be used to keep an MPPT input in check. This seems like a simple method to create a one way supply from grid to an internally isolated system without any official grid tie. The grid to interior one way bridge can be relatively low amperage (say, 1kW to 4kW), because it's just make up amperage for the whole system that can be fed in over time and the inside batteries can store it up for when it's needed. Car charging would be problematic, but one solution is to have an isolation switch that allows it to be connected to the utility grid panel or the inside panel, to either feed full from grid power, or full from interior generation (solar and stored battery power). In this setup, one option would be to put the 1 Tesla PW3 on the grid-connected panel as the utility allows with, say, evening pointed solar panels connected to it, but the other 2 Tesla PW3's on the isolated interior panel system, that talk to, say, a morning and mid-day solar panel system. You could set the AC-DC charger to suck down the solar and battery power in the grid connected PW3 after your car is fully charged until the grid connected PW3 is low using something like Home Assistant.

I thought we'd have these products in the market in droves by now. What a pathetic lineup of products considering the regulatory headwinds we commonly face.

Since NEM 3.0 has a path to non-export system expansions staying on NEM 2.0 I imagine over the next year or 2 the largest inverter manufacturers will be chasing down a PCS control system that can accomplish non-export and be utility certified. I believe SolarEdge already has one that is commonly used in Hawaii. https://knowledge-center.solaredge.com/sites/kc/files/feed-in_limitation_application_note.pdf

As far as DIY for this, why would the utility want to allow this without proper testing, listing etc.? While technically and electrically possible utilities want people to follow established paths.