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Want to add separate DIY system to existing Tesla solar and Powerwalls. Where to connect?

I have just received PTO on an 8.16 kWh Tesla solar system with 2 powerwalls (see photos). I have whole home back up. However, PV isn't quite enough for my needs, one reason being that Tesla wouldn't entertain installing panels on a porch roof (which can definitely hold them). So, my brilliant idea is to put up 4 panels on there myself with micro inverters. The panels I've picked out are 440W so it would take total PV array size to just a hair under 10 kW. I may have room elsewhere for 3 more, which would take it to 11.2 kW.

I like DIY and am confident with regular electrics. However, I'm not clear where to connect the output from the micro inverters to. It seems like the logical place to do so is the "PV combiner panel", but that's actually the output from the Powerwalls, not directly the PV. I've also read here that the powerwall needs to be aware of all solar if it's to charge from them. I've no idea where the CTs are, I've looked and the only obvious ones are built into the backup gateway.

So I'm looking for your help and advice! I'd hire an electrician but sceptical I can find someone who understands Tesla ESS. This isn't really any different from someone who had an existing PV only system them installed a separate Tesla solar system with Powerwalls. So I know this is possible I just don't know how to do it. Wishing now that I'd got the number of the Tesla electrician who installed it in the first place.
 

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arnolddeleon

Active Member
Supporting Member
Jul 21, 2012
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SF Bay Area
There are several possible approaches like installing in the load center and just add "negative load' but you would still need to make sure you don't exceed the capacity of the panel. I'm skipping a bunch of details here. The only time your "negative load" aka additional solar would possibly be an issue is when its generation exceeds your load.

Ignoring a bunch of possible issues like the solar generation meter, I will speculate on how you might 'hack it" without Tesla's assistance. I would install my new PV breaker in the "PV Combiner" panel since that looks like a "generation panel" to me. A wiring diagram would be helpful in being more certain. You can probably also pass your new PV AC lines through the same CTs (if there are CTs in this panel) taking care to have keep the same phase alignment. Assuming the Tesla Inverter and Powerwall Gateway aren't communicating via a side channel the system will just see more PV production. On the other hand if the Teslas are communicating then they don't need additional CTs to determine PV generation. If there are pictures of the inside some of the panels it would also be easier to come up with suggestions.

My system uses a GW1 and I have 3 different PV systems. The 3rd one uses a Tesla inverter but all the PV AC outputs meet at "generation panel" and there is a set of CTs for each PV system.

This is all speculation from some random guy on Internet. Use it at your own peril.
 
I have just received PTO on an 8.16 kWh Tesla solar system with 2 powerwalls (see photos). I have whole home back up. However, PV isn't quite enough for my needs, one reason being that Tesla wouldn't entertain installing panels on a porch roof (which can definitely hold them). So, my brilliant idea is to put up 4 panels on there myself with micro inverters. The panels I've picked out are 440W so it would take total PV array size to just a hair under 10 kW. I may have room elsewhere for 3 more, which would take it to 11.2 kW.

I like DIY and am confident with regular electrics. However, I'm not clear where to connect the output from the micro inverters to. It seems like the logical place to do so is the "PV combiner panel", but that's actually the output from the Powerwalls, not directly the PV. I've also read here that the powerwall needs to be aware of all solar if it's to charge from them. I've no idea where the CTs are, I've looked and the only obvious ones are built into the backup gateway.

So I'm looking for your help and advice! I'd hire an electrician but sceptical I can find someone who understands Tesla ESS. This isn't really any different from someone who had an existing PV only system them installed a separate Tesla solar system with Powerwalls. So I know this is possible I just don't know how to do it. Wishing now that I'd got the number of the Tesla electrician who installed it in the first place.

With the Powerwall+ this is different. All your PV otherwise is monitored by the internal PW+ inverter meter. Adding new PV to the system where you propose will cause problems off grid and the batteries will not know about the PV when on grid, so the PW and PW+ batteries cannot charge from them either (except incidentally).

I recommend hiring a professional. At a minimum, I believe you will need to add additional CT hardware to the GW2 and re-commission the system.
 
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There are several possible approaches like installing in the load center and just add "negative load' but you would still need to make sure you don't exceed the capacity of the panel. I'm skipping a bunch of details here. The only time your "negative load" aka additional solar would possibly be an issue is when its generation exceeds your load.

Ignoring a bunch of possible issues like the solar generation meter, I will speculate on how you might 'hack it" without Tesla's assistance. I would install my new PV breaker in the "PV Combiner" panel since that looks like a "generation panel" to me. A wiring diagram would be helpful in being more certain. You can probably also pass your new PV AC lines through the same CTs (if there are CTs in this panel) taking care to have keep the same phase alignment. Assuming the Tesla Inverter and Powerwall Gateway aren't communicating via a side channel the system will just see more PV production. On the other hand if the Teslas are communicating then they don't need additional CTs to determine PV generation. If there are pictures of the inside some of the panels it would also be easier to come up with suggestions.

My system uses a GW1 and I have 3 different PV systems. The 3rd one uses a Tesla inverter but all the PV AC outputs meet at "generation panel" and there is a set of CTs for each PV system.

This is all speculation from some random guy on Internet. Use it at your own peril.

Thanks!

Video of me doing a walk-through of the wiring (before Tesla added the official labels) is here.

And I've also attached some photos below. From left to right: Load Center, PV Combiner panel, Backup gateway.

BTW, the CTs in the load center are my Emporia energy monitor. There are no other CTs in here.
 

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With the Powerwall+ this is different. All your PV otherwise is monitored by the internal PW+ inverter meter. Adding new PV to the system where you propose will cause problems off grid and the batteries will not know about the PV when on grid, so the PW and PW+ batteries cannot charge from them either (except incidentally).

I recommend hiring a professional. At a minimum, I believe you will need to add additional CT hardware to the GW2 and re-commission the system.
Darn. More complicated than I was hoping. Appreciate the intel!
 
With the Powerwall+ this is different. All your PV otherwise is monitored by the internal PW+ inverter meter.
So do you know how the solar generation meter can be installed with a PW+? That implies that the AC output of the PV inverter can be intercepted inside the top box of the PW+ Which I guess seems plausible, as I don't expect the PW+ to have integrated the PW and the PV inverter that closely. I wonder if the PW+ was designed for this possibility, or some factory installed conductor has to be cut and spliced.

Cheers, Wayne
 
With microinverters, for the solar generation meter it's going to be necessary to add a combiner panel between the PW+'s PV inverter and the solar meter. That will be where you can land the new microinverter circuit, so that the new PV production is metered along with the existing. Then as Vines commented, you'd need to be able to add CTs on the new microinverter circuit, and connect them to the Backup Gateway 2. I'm not familiar enough with the details of that product to know exactly where they go or how it will support another set of CTs.

It would be a lot easier to add a DC string to the existing PV inverter. Figuring out if that is possible would require knowing the details on the existing strings and how they are wired, along with the number inputs on the PV inverter and how the strings are connected, along with the acceptable string parameters (length/voltage). Best case is an unused input and (4) 440W panels being a suitable string to connect to it. Worst case would lead you back to a microinverter solution.

Cheers, Wayne
 
So do you know how the solar generation meter can be installed with a PW+? That implies that the AC output of the PV inverter can be intercepted inside the top box of the PW+ Which I guess seems plausible, as I don't expect the PW+ to have integrated the PW and the PV inverter that closely. I wonder if the PW+ was designed for this possibility, or some factory installed conductor has to be cut and spliced.

Cheers, Wayne
I am not clear what the case is for PW+ with the Backup Switch, but in this case the OP has a GW2 and PW+ so the CT's for extra PV will plug in there.

I suspect the PW+ has its own place for additional CT's when used with the backup switch but I am not sure this is true.
 
I am not clear what the case is for PW+ with the Backup Switch, but in this case the OP has a GW2 and PW+ so the CT's for extra PV will plug in there.

I suspect the PW+ has its own place for additional CT's when used with the backup switch but I am not sure this is true.
The backup switch has all the metering built in, so no additional CT's required with the backup switch. Inside the PW+ there is a Neurio that is used to monitor the Solar, but I think they are moving away from it since it doesn't seem to impact anything when it is working or not. For my additional solar system, they added a separate Neurio to monitor that load.
 
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The backup switch has all the metering built in, so no additional CT's required with the backup switch. Inside the PW+ there is a Neurio that is used to monitor the Solar, but I think they are moving away from it since it doesn't seem to impact anything when it is working or not. For my additional solar system, they added a separate Neurio to monitor that load.
The backup switch has all the metering built in for the Tesla ecosystem, but what if the backup switch and PW+ was used on a home with an existing PV system? I suspect that an additional PV meter would be needed for this application, but am not sure.
 
The backup switch has all the metering built in for the Tesla ecosystem, but what if the backup switch and PW+ was used on a home with an existing PV system? I suspect that an additional PV meter would be needed for this application, but am not sure.
Yup, they have to install another Neurio meter. I added a PW+ and solar alongside my existing Fronius inverter setup. The additional Neurio has CTs that go to the solar breaker and is wirelessly paired to the PW+. The Neurio has its own Tesla firmware, so not sure if it can be purchased elsewhere.
 
Yup, they have to install another Neurio meter. I added a PW+ and solar alongside my existing Fronius inverter setup. The additional Neurio has CTs that go to the solar breaker and is wirelessly paired to the PW+. The Neurio has its own Tesla firmware, so not sure if it can be purchased elsewhere.
Good to know thaty even with the backup switch, the additional PV can be metered with an additional Neurio.
 

miimura

Well-Known Member
Aug 21, 2013
7,316
7,297
Los Altos, CA
Why would you use an additional Neurio when there are at least 3 empty CT channels in the Gateway 2 pictured in this thread? The only reason I can think of is that the distance exceeds normal CT wiring, which probably doesn't apply to this case. The reason the CTs are empty in this case is that the solar production is reported digitally by the Tesla inverter. Adding 3rd party solar would require CT metering to be logically added in the Gateway to the solar quantity reported by the Tesla inverter.
 
Why would you use an additional Neurio when there are at least 3 empty CT channels in the Gateway 2 pictured in this thread? The only reason I can think of is that the distance exceeds normal CT wiring, which probably doesn't apply to this case. The reason the CTs are empty in this case is that the solar production is reported digitally by the Tesla inverter. Adding 3rd party solar would require CT metering to be logically added in the Gateway to the solar quantity reported by the Tesla inverter.
If you had a backup switch instead of GW2.
 

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