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2 solar panel systems a 1 powerwall (N. California)

Jky6

Member
Jan 3, 2020
9
4
San ramon
I am new to this space so would really appreciate any advice. Not sure if I'm even thinking about this correctly. Than you in advance.

- Currently have existing 3.8kwh solar panel system (not Tesla) (generate about 4500 kwh annual)
- I placed order for Tesla 4kwh solar panel system + 1 powerwall (tesla estimates 4574 kwh annual).
Tesla came back with partial home setup. I live in Bay Area in N. Calif.

1) Does the powerwall connect to both solar panel systems? Does it charge from both systems as if it's operating as one?

2) Do I need to order a 2nd powerwall? (prefer to not spend additional cost and don't need AC or Ev charger). Trying to understanding ramifications of 1 vs 2 powerwall beyond the cost. Would 2nd powerwall allow whole home backup vs partial?
 

woferry

Member
Mar 4, 2019
406
478
San Jose, CA
Do you know what your typical daily / overnight power consumption is? What's the biggest amperage breaker in your electrical panel(s) (actual loads, not counting any that feed subpanels)?

I suspect the combined 7.8 kW inverters might keep them from putting both on a single PW with 5kW max charge. My Tesla-installed 13kW system with 1x PW2 and 2x 5.2kW inverters has one inverter on the backup side and one on the grid side. I have whole-home backup except for that second inverter (the breaker for the Gateway and the breaker for the second inverter are all that's left in my original service panel). My largest load breaker (oven) is 30A (a single PW can't back-up any breaker >30A as its breaker is only 30A), my daily average power consumption was around 13kWh pre-covid (spending more time home has increased the draw noticeably), I have no trouble running overnight from the single PW. I've never exceeded 5kW consumption with my system, though I surely could if I fired-up all kitchen appliances and my washer at the same time (currently my cooktop is gas as is my dryer, hot water heater and furnace).
 

Jky6

Member
Jan 3, 2020
9
4
San ramon
Daily usage - 25kwh to 30kwh per day.

So if I got 2 powerwalls, I shoulld be able to get whole home backup(no ev charging) and have both solar systems tied to the powerwalls?
 

destructure00

Active Member
Mar 2, 2019
1,476
1,629
Scottsdale, AZ
I have 2 separate Tesla systems on my house. I'd assume they would set yours up like mine, where both solar systems are combined into 1 effective system that connects to the PW and backup load center.



Inverter 1 and inverter 2 are routed to a PV combiner panel.

Powerwall 1 and powerwall 2 are routed to a PW combiner panel. (you may skip this if you end up with 1 PW)

PV combiner panel and PW combiner panel are routed to a 3rd panel that combines them.

This 3rd panel routes to the backup load center.
 
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miimura

Well-Known Member
Aug 21, 2013
6,477
6,225
Los Altos, CA
Daily usage - 25kwh to 30kwh per day.

So if I got 2 powerwalls, I shoulld be able to get whole home backup(no ev charging) and have both solar systems tied to the powerwalls?
Yes. I recommend 2 Powerwalls if you can afford it so that you can have more runtime off-grid and all your solar can be wired to the backup side of the system. This will also keep you from incurring Peak power usage by having enough kWh in the batteries to power A/C during Peak hours. San Ramon certainly has more A/C requirement than Los Altos.
 

Kbreezy92

Member
Jul 26, 2020
20
7
Bay area
Similar situation. Got sized for a 8.16 kW system even though my usage fell between the small and medium panel sizes. I debated getting a single powerwall vs two powerwalls and in the end it came down to cost and need. Initially decided for just one powerwall and partial home backup, but due to the recent power outages and environmental problems in CA, we decided to get two. Also with one powerwall, it would only last us a day-ish with no a/c (even though we have a mini split they wouldn't allow us to have it on the backup). Be aware though if you want to change you should do it now since it will likely delay the permit by a few weeks since Tesla will need to amend the permits they sent out for you.
 

BrettS

Active Member
Mar 28, 2017
2,128
2,537
Orlando, FL
My 2 systems combined would be 7.8 kwh. That would be sufficient for entire home backup?

It’s not the size of the solar system that determines whether you can do whole home backup, but the number of powerwalls. Typically you need a minimum of 2 powerwalls to do whole home backup and often 3 or 4, depending on how much power your house draws. Usually one powerwall would back up critical loads only, but you might be able to do whole home backup with a single powerwall if you have all gas appliances and no air conditioning. If you have anything with a breaker that’s bigger than 30A then you won’t be able to back that up with a single powerwall.
 
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heytae

Member
Mar 9, 2015
149
64
Cupertino, CA
I have 2 separate Tesla systems on my house. I'd assume they would set yours up like mine, where both solar systems are combined into 1 effective system that connects to the PW and backup load center.



Inverter 1 and inverter 2 are routed to a PV combiner panel.

Powerwall 1 and powerwall 2 are routed to a PW combiner panel. (you may skip this if you end up with 1 PW)

PV combiner panel and PW combiner panel are routed to a 3rd panel that combines them.

This 3rd panel routes to the backup load center.

It's been hard finding info about adding a 2nd system and the app behavior afterwards. I'm considering adding a 2nd PV system onto our home using Tesla panels. 1st system is non-Tesla. Does your Powerwall app simply show the output of BOTH combined PV systems, as if the 1st one just "grew larger?" Meaning, now the PV output just shows a much higher output during the hour/day. Or does the app somehow show the two systems as separate/itemized PV sources? If the latter, would you please be able to show a screenshot of the app's screen? I haven't been able to get a straight answer from Tesla.
 

miimura

Well-Known Member
Aug 21, 2013
6,477
6,225
Los Altos, CA
It's been hard finding info about adding a 2nd system and the app behavior afterwards. I'm considering adding a 2nd PV system onto our home using Tesla panels. 1st system is non-Tesla. Does your Powerwall app simply show the output of BOTH combined PV systems, as if the 1st one just "grew larger?" Meaning, now the PV output just shows a much higher output during the hour/day. Or does the app somehow show the two systems as separate/itemized PV sources? If the latter, would you please be able to show a screenshot of the app's screen? I haven't been able to get a straight answer from Tesla.
If you add Tesla Solar to a Powerwall system that already has solar paired to it, you may get an additional solar system showing in the app. That will be populated with solar production data from the new solar inverter(s). However, the solar in the Powerwall system should be aggregated if the CTs are properly configured to measure all the solar together. However, if the solar breakers are not in the same panel, that could be difficult to arrange. People with solar production metering have this problem because the new solar would have to have its own production meter between the Powerwall Gateway and the solar breaker. In PG&E territory this should not be an issue.
 

jboy210

Supporting Member
Supporting Member
Dec 2, 2016
5,382
3,332
Northern California
It's been hard finding info about adding a 2nd system and the app behavior afterwards. I'm considering adding a 2nd PV system onto our home using Tesla panels. 1st system is non-Tesla. Does your Powerwall app simply show the output of BOTH combined PV systems, as if the 1st one just "grew larger?" Meaning, now the PV output just shows a much higher output during the hour/day. Or does the app somehow show the two systems as separate/itemized PV sources? If the latter, would you please be able to show a screenshot of the app's screen? I haven't been able to get a straight answer from Tesla.
I don't know if it is the same thing, but we have 2 inverters. In the App the 2 inverter outputs are added together to come up with the solar number.
 
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heytae

Member
Mar 9, 2015
149
64
Cupertino, CA
If you add Tesla Solar to a Powerwall system that already has solar paired to it, you may get an additional solar system showing in the app. That will be populated with solar production data from the new solar inverter(s). However, the solar in the Powerwall system should be aggregated if the CTs are properly configured to measure all the solar together. However, if the solar breakers are not in the same panel, that could be difficult to arrange. People with solar production metering have this problem because the new solar would have to have its own production meter between the Powerwall Gateway and the solar breaker. In PG&E territory this should not be an issue.

My solar breakers are in the same panel as the CTs so it sounds like the two PV system's generation would be combined. I wonder though if it'd be better to have them separate, if Tesla supports that, so that I can see which PV is producing more or less throughout the day as the sun moves. Some of the new panels will be west facing somewhat, unlike the rest of them. I'm imagining the possibility of getting 2 generation peak "humps" in the hourly graphs, like a double humped camel. =) Probably just a flatter plateau though.

I have PG&E so I'm counting on that they won't require me to add a NGOM (net generation output meter), since they were finally convinced that that was no longer necessary, when they added our powerwalls last year. If that's what you're talking about when you say "...its own production meter." Thanks @miimura!

Thanks @jboy210
 

RobbL

Member
Jul 13, 2018
115
42
Oakland, CA
I had two rows of solar panels on my house installed by Solar City about eight years ago. Last Spring, I had another row of panels, different manufacturer, installed by Infinity Energy along with a Powerwall. In the Tesla app, under My Home, I only see the output of the original panels. However, if instead, using the Gear on the top left, using Switch Product, I choose Home Energy Gateway, I see the combined output of all three rows of panels listed together as a single source under Solar. And it is fully integrated as a single source with the other elements Grid, Home, and Powerwall. Because we have gas heat, stove, and water heater and no AC or swimming pool, we have had no problem powering the house through outages. As long as there is sufficient sun during the day, the Powerwall can recharge from solar and then take us through the night.
 
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heytae

Member
Mar 9, 2015
149
64
Cupertino, CA
I had two rows of solar panels on my house installed by Solar City about eight years ago. Last Spring, I had another row of panels, different manufacturer, installed by Infinity Energy along with a Powerwall. In the Tesla app, under My Home, I only see the output of the original panels. However, if instead, using the Gear on the top left, using Switch Product, I choose Home Energy Gateway, I see the combined output of all three rows of panels listed together as a single source under Solar. And it is fully integrated as a single source with the other elements Grid, Home, and Powerwall. Because we have gas heat, stove, and water heater and no AC or swimming pool, we have had no problem powering the house through outages. As long as there is sufficient sun during the day, the Powerwall can recharge from solar and then take us through the night.

Oh that's nice. It sounds like you have the best of both worlds. Well, I guess the most flexible solution would to able to choose system 1, system 2, or systems 1 & 2, but that's probably asking for too much. :D Most likely, the way it's wired up will determine how it'll be shown in the app. Thanks.
 

miimura

Well-Known Member
Aug 21, 2013
6,477
6,225
Los Altos, CA
My solar breakers are in the same panel as the CTs so it sounds like the two PV system's generation would be combined. I wonder though if it'd be better to have them separate, if Tesla supports that, so that I can see which PV is producing more or less throughout the day as the sun moves. Some of the new panels will be west facing somewhat, unlike the rest of them. I'm imagining the possibility of getting 2 generation peak "humps" in the hourly graphs, like a double humped camel. =) Probably just a flatter plateau though.

I have PG&E so I'm counting on that they won't require me to add a NGOM (net generation output meter), since they were finally convinced that that was no longer necessary, when they added our powerwalls last year. If that's what you're talking about when you say "...its own production meter." Thanks @miimura!

Thanks @jboy210
In order for the Powerwalls to charge from solar correctly, the solar CTs need to be configured to measure all the solar. In my case, I have two circuit breakers for solar and the two L1 wires go through one CT and the two L2 wires go through the other CT. This is the easiest way to measure the production from multiple solar inverters. It does not matter whether the multiple inverters are part of one system or multiple systems. In my case, I have Enphase micro-inverters, so I already have per-panel production monitoring. If you have SolarEdge inverters and get their monitoring app, you will also have per panel production information, so the per system information is redundant.
 

Monkfamilynz

New Member
Dec 20, 2020
2
2
New Zealand
It's been hard finding info about adding a 2nd system and the app behavior afterwards. I'm considering adding a 2nd PV system onto our home using Tesla panels. 1st system is non-Tesla. Does your Powerwall app simply show the output of BOTH combined PV systems, as if the 1st one just "grew larger?" Meaning, now the PV output just shows a much higher output during the hour/day. Or does the app somehow show the two systems as separate/itemized PV sources? If the latter, would you please be able to show a screenshot of the app's screen? I haven't been able to get a straight answer from Tesla.


Our system is a split inverter system with 3.8kWh on system 1 and 4.5kWh on system 2. Installer configured both systems to be monitored on one input and it works fine. Our single pw2 can only charge at a max rate of 5kWh peak so some energy is not sent to the battery. That said there is plenty left over to heat our hot water, charge cars and run the house. We have the pw2 configured to run the whole house. Very happy with how it works, installer had a few issues figuring out how it would work but got it right in the end.
 
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SMAlset

Well-Known Member
Mar 4, 2017
9,178
9,905
SF Bay Area
It’s getting harder code wise for people to add battery back up in the homes. You said you are new to this space so may not be aware of what’s been going on relative to this here even in California where you’d think more battery back ups would be encouraged. Some cities/fire jurisdictions have some pretty stringent rules, things like bollards being required in garages for certain installs, need for hard-wired heat detectors as part of a whole hone security/alert system, number of units allow. The PWs have certain install perimeters as it is — distance apart from each other, limit on floor stacking, wall mounted can’t be stacked and needs to be within a certain height requirement for example.

You mentioned the possibility of adding a second PW and I’d encourage you to seriously pursue that route now for a couple of reasons. 1) never know what code changes will affect you later, 2) new permits open you up to updating other things in your garage to meet any new codes enacted since your initial install (opening up our walls for a kitchen remodel required us to update all of our kitchens downlight cans despite nothing being wrong with them for example and was a hard cost upfront when we already had an expensive remodel planned), 3) you would incur a new installation charge in full just to add an addition one, 4) no guarantees when you want to install an extra one if they will be in inventory and not limited — with install dates set months down the road.

Hard to comment on pricing. As you may know Tesla is working to increase all of its battery production but demand has been outstripping availability. It’s not just Tesla installs but also additional demand coming from third party installers who place orders from Tesla as well. I know PWs have gone up in price since our install in 2020Q3. At deposit contract time 2020Q1 they offered a panel/PW bundle which saved us some money and there was a graduated discount at one point Q2 or Q3 for ordering multiple PWs, but both have disappeared. However if you order now and lock in your place in line, Tesla has matched lower pricing when things have changed prior to install.

Just something to think about if you can financially be comfortable adding an extra PW.
 
Last edited:
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SMAlset

Well-Known Member
Mar 4, 2017
9,178
9,905
SF Bay Area
Whether one or two PWs will be best for you also really depends on what your goal is for having them. For us it was more about living more comfortably with A/C during an outage (we have gas heating and water heater). Not that people haven’t lived without A/C for years prior to it but we also are in a hot valley area and 90-100F isn’t too fun especially when it becomes longer than a day or two and your house doesn’t cool down at night when it’s in the 80s. Saving us on electricity was important, but there’s the system cost factor to take into consideration in pricing everything, so for us it really was more about the comfort factor during an outage.
 
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heytae

Member
Mar 9, 2015
149
64
Cupertino, CA
In order for the Powerwalls to charge from solar correctly, the solar CTs need to be configured to measure all the solar. In my case, I have two circuit breakers for solar and the two L1 wires go through one CT and the two L2 wires go through the other CT. This is the easiest way to measure the production from multiple solar inverters. It does not matter whether the multiple inverters are part of one system or multiple systems. In my case, I have Enphase micro-inverters, so I already have per-panel production monitoring. If you have SolarEdge inverters and get their monitoring app, you will also have per panel production information, so the per system information is redundant.

Tesla said that they're adding a SolarEdge inverter with String Optimizers for the 2nd system. If I'm understanding you right, it sounds like I should request that they wire it in such a way that a) I can see the separate output from each system, and b) the SolarEdge app should let me see what it's sole output is for the 2nd system, and c) the same app should give me per-panel production monitoring. Do I have that right @miimura ?
 

heytae

Member
Mar 9, 2015
149
64
Cupertino, CA
Our system is a split inverter system with 3.8kWh on system 1 and 4.5kWh on system 2. Installer configured both systems to be monitored on one input and it works fine. Our single pw2 can only charge at a max rate of 5kWh peak so some energy is not sent to the battery. That said there is plenty left over to heat our hot water, charge cars and run the house. We have the pw2 configured to run the whole house. Very happy with how it works, installer had a few issues figuring out how it would work but got it right in the end.

Did you have each system installed at different times? Guessing at different times since it sounds like you have two physically separate inverters combined and showing as one system in your Tesla app, is that right?
 

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