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solar, batteries, inverters?

h2ofun

Active Member
Aug 11, 2020
3,637
870
auburn, ca
So, I have my 5 batteries installed between 2 gateways. These are driven by 2 11.4K SE inverters, 36 panels on one, 13 panels on another.
These 14.5K panels were all installed and working on the 11.4K SE for a year.

So, I have been looking at adding more PV. I put in a second 11.4K with the assumption I add more panels, and end up with like 15K, about 50 panels,
on each inverter.

So talking to the installer company a few minutes ago, he was told by his technical folks that no this would not work, I would have to add a 3rd inverter
if I added another 14K of PV. He had no technical reason why, and this was new to me. But he said it had am impact because of the batteries. I said but
what you installed is working now, so logically I do not understand.

I wrote these questions to him and he will pass along to get us some answers.

So, for you technical battery, PV folks, what am I missing to just add more PV panels without the expense of needed a third inverter?
 

arnolddeleon

Member
Supporting Member
Jul 21, 2012
996
1,066
SF Bay Area
Since we are talking about Solar Edge with optimizers presumably here you should be super flexible. MPPT channel limits shouldn't be an issue. They can even be on different roof planes.

I'm trying parse out what you mean.

I'm going to ignore the panel count and focus on the size of the system. It sounds like asking for 15kW DC of panels on your second inverter after the expansion. That's an acceptable DC to AC ratio (1.31). Maybe they are not familiar with doing greater than 1 DC to AC ratios?

It looks like you can have a maximum 30 optimizers in a string for Solar Edge. Do you know how many inputs your inverter has?

I believe you own your equipment. There might be warranty issues if you modify the configuration but if you own it that's your call.
 
So talking to the installer company a few minutes ago, he was told by his technical folks that no this would not work, I would have to add a 3rd inverter
Did the installer that put in the second inverter get a permit and comply with the 120% rule? Your system is complicated enough that I would not know if that was the issue but it is worth getting the other installers opinion. The rule is based on breaker size so adding panels would not affect that. Maybe these guys just don't want the job of installing panels to someone elses system. It could be as simple as a warranty overlap issue.
 

h2ofun

Active Member
Aug 11, 2020
3,637
870
auburn, ca
Since we are talking about Solar Edge with optimizers presumably here you should be super flexible. MPPT channel limits shouldn't be an issue. They can even be on different roof planes.

I'm trying parse out what you mean.

I'm going to ignore the panel count and focus on the size of the system. It sounds like asking for 15kW DC of panels on your second inverter after the expansion. That's an acceptable DC to AC ratio (1.31). Maybe they are not familiar with doing greater than 1 DC to AC ratios?

It looks like you can have a maximum 30 optimizers in a string for Solar Edge. Do you know how many inputs your inverter has?

I believe you own your equipment. There might be warranty issues if you modify the configuration but if you own it that's your call.
This was a total out of the blue comment from them. And he had no idea why. I have 3 strings, 2 16 panel strings and 1 18 panel string.

So for the life of me, I am not seeing any limits. But the comment about the batteries impact things is where I have no idea what is being talked about,
since they connected stuff up now, and I assume it is okay.

weird.
 

h2ofun

Active Member
Aug 11, 2020
3,637
870
auburn, ca
Did the installer that put in the second inverter get a permit and comply with the 120% rule? Your system is complicated enough that I would not know if that was the issue but it is worth getting the other installers opinion. The rule is based on breaker size so adding panels would not affect that. Maybe these guys just don't want the job of installing panels to someone elses system. It could be as simple as a warranty overlap issue.
Yep, the battery folks got all the permits for battery, second inverter, etc. All on the plans.

What is the 120% rule? All subpanels are either 200 or 225 amps. Nope of them are close to be loaded. The whole design is all the inverters, etc where sized, coded, and wired so adding more panels like the first inverter would be a no brainer, I thought. Something is just missing. Will see what they come back with.
If things are too nuts and expensive, I just do nothing.
 
It does not sound like the 120% rule is an issue if the second inverter was installed with a permit. If I understand that the second inverter was installed by a different company than you are asking for a quote, I would guess it is an issue of warranty ambiguity. Ask the company that installed the second inverter for a quote.
 

h2ofun

Active Member
Aug 11, 2020
3,637
870
auburn, ca
It does not sound like the 120% rule is an issue if the second inverter was installed with a permit. If I understand that the second inverter was installed by a different company than you are asking for a quote, I would guess it is an issue of warranty ambiguity. Ask the company that installed the second inverter for a quote.
Nope the company I am asking for the solar bid is the same company who just installed the batteries, GW's, inverter, generation panels, etc. And yep, ALL
of this is in the engineering plans approved, and inspected by the county. Everything is above board!!
 
the maximum charge rate is 5kw per powerwall, so maximum production would need to be lower on each gateway.
so the solar edge that is on the two powerwall installation would need to be below 10kw.

i know you don't want to hear this, but rip out the second gateway, but your 200 amp service on one gateway. i seem to remember that your meter is cl200.
 
the maximum charge rate is 5kw per powerwall, so maximum production would need to be lower on each gateway.
so the solar edge that is on the two powerwall installation would need to be below 10kw.

i know you don't want to hear this, but rip out the second gateway, but your 200 amp service on one gateway. i seem to remember that your meter is cl200.
Can you elaborate on why the solar generation capability would need to be less than the maximum charging rate? Some PWs are installed without any solar generation, and are charged by the grid. I expect that the PW can limit its charging rate regardless of available current.
 
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h2ofun

Active Member
Aug 11, 2020
3,637
870
auburn, ca
the maximum charge rate is 5kw per powerwall, so maximum production would need to be lower on each gateway.
so the solar edge that is on the two powerwall installation would need to be below 10kw.

i know you don't want to hear this, but rip out the second gateway, but your 200 amp service on one gateway. i seem to remember that your meter is cl200.
I cannot use one gateway on my home and have back. 2 separate 200 amp panels with must loads.

I have seen my PW's charge in storm watch, with full PGE charging. So, sure seems the PW's have the ability to determine level of charge they can handle, no matter what the input could be.
 

arnolddeleon

Member
Supporting Member
Jul 21, 2012
996
1,066
SF Bay Area
the maximum charge rate is 5kw per powerwall, so maximum production would need to be lower on each gateway.
so the solar edge that is on the two powerwall installation would need to be below 10kw.
This isn't absolutely required. It took some back and forth with Tesla but I was able to get a system where the PV generation could exceed what the Powerwalls could absorb. I made it clear that I understood the edge of case being unable to charge.

The SolarEdge inverters in this case may even support modulating their production via frequency shifting so less likely to be an issue.
 
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h2ofun

Active Member
Aug 11, 2020
3,637
870
auburn, ca
Can you elaborate on why the solar generation capability would need to be less than the maximum charging rate? Some PWs are installed without any solar generation, and are charged by the grid. I expect that the PW can limit its charging rate regardless of available current.
Logically I do not understand. Storm watch charges no issues with batteries with full PGE power.
This isn't absolutely required. It took some back and forth with Tesla but I was able to get a system where the PV generation could exceed what the Powerwalls could absorb. I made it clear that I understood the edge of case being unable to charge.

The SolarEdge inverters in this case may even support modulating their production via frequency shifting so less likely to be an issue.
 

miimura

Well-Known Member
Aug 21, 2013
7,206
7,156
Los Altos, CA
When the grid is down and the solar is producing more than the batteries can accept, the Powerwalls will force the solar offline. This can lead to a situation where you have ample solar capacity, but it can't charge the batteries because it overloads. If you have more than one solar inverter per Gateway, you can turn one off to limit the solar production during high production hours, then turn the second one on later in the afternoon. Alternatively, you can increase your household load by cranking the A/C or charging a car to absorb the extra solar so the Powerwalls can charge within their power limit.
 

arnolddeleon

Member
Supporting Member
Jul 21, 2012
996
1,066
SF Bay Area
When the grid is down and the solar is producing more than the batteries can accept, the Powerwalls will force the solar offline. This can lead to a situation where you have ample solar capacity, but it can't charge the batteries because it overloads. If you have more than one solar inverter per Gateway, you can turn one off to limit the solar production during high production hours, then turn the second one on later in the afternoon. Alternatively, you can increase your household load by cranking the A/C or charging a car to absorb the extra solar so the Powerwalls can charge within their power limit.
Yes, this is exactly I was referring to. If I'm remembering his configuration correctly he likely has one inverter per bank of Powerwalls. But given he has 5 Powerwalls it is likely that has a minimum of 2 Powerwalls gateway and that is 10 kW of charging capacity.

Another option just wait until the solar production drops to match, I believe the Powerwall will retry enabling solar at some interval

The corner case should be relatively rare, if the batteries are depleted in the morning then they should charge as the amount of solar increases until the amount of solar exceeds their capacity to absorb and then they should resume charging as the sun starts setting. If there is load during the middle of day then it is more likely that they will be able to charge. If there is no load then then it probably doesn't matter anyway when the battery gets charged.

Of course this likely moot anyway since I believe the Solar Edge will respond to the frequency shifts to nudge their production down.
 

h2ofun

Active Member
Aug 11, 2020
3,637
870
auburn, ca
Yes, this is exactly I was referring to. If I'm remembering his configuration correctly he likely has one inverter per bank of Powerwalls. But given he has 5 Powerwalls it is likely that has a minimum of 2 Powerwalls gateway and that is 10 kW of charging capacity.

Another option just wait until the solar production drops to match, I believe the Powerwall will retry enabling solar at some interval

The corner case should be relatively rare, if the batteries are depleted in the morning then they should charge as the amount of solar increases until the amount of solar exceeds their capacity to absorb and then they should resume charging as the sun starts setting. If there is load during the middle of day then it is more likely that they will be able to charge. If there is no load then then it probably doesn't matter anyway when the battery gets charged.

Of course this likely moot anyway since I believe the Solar Edge will respond to the frequency shifts to nudge their production down.
I basically have 2 complete home setups. They basically do not talk to each other.

When I was in storm watch mode, the max per battery I saw charging was 3.3kw. So my 2 pack was at 6.6kw, my 3 pack was at 9.9kw charging from grid.

I only have one inverter per gateway, currently both at 11.4 SE, even though solar at the moment is not close that that on either.
 

miimura

Well-Known Member
Aug 21, 2013
7,206
7,156
Los Altos, CA
I basically have 2 complete home setups. They basically do not talk to each other.

When I was in storm watch mode, the max per battery I saw charging was 3.3kw. So my 2 pack was at 6.6kw, my 3 pack was at 9.9kw charging from grid.

I only have one inverter per gateway, currently both at 11.4 SE, even though solar at the moment is not close that that on either.
The issue is probably unlikely to come up for you then. Assuming your larger array is paired with the 3 Powerwalls, I don't think you will have surplus solar in excess of the 10kW or 15kW charging capability of the Powerwalls. Again, this has nothing to do with Storm Watch, it has to do with solar generation and battery charging during a power outage. If you are going to add a significant number of panels to the 2 Powerwall system, this may become an issue. However, with a 11.4k inverter, it would be relatively easy to turn on some loads to soak up that 1.4kW excess AC power if the need did come up.
 

h2ofun

Active Member
Aug 11, 2020
3,637
870
auburn, ca
The issue is probably unlikely to come up for you then. Assuming your larger array is paired with the 3 Powerwalls, I don't think you will have surplus solar in excess of the 10kW or 15kW charging capability of the Powerwalls. Again, this has nothing to do with Storm Watch, it has to do with solar generation and battery charging during a power outage. If you are going to add a significant number of panels to the 2 Powerwall system, this may become an issue. However, with a 11.4k inverter, it would be relatively easy to turn on some loads to soak up that 1.4kW excess AC power if the need did come up.
I have yet to hear back why the comment from my installer. Worst case I just leave what I have alone. Would be MUCH cheaper!!!
 
Can you elaborate on why the solar generation capability would need to be less than the maximum charging rate? Some PWs are installed without any solar generation, and are charged by the grid. I expect that the PW can limit its charging rate regardless of available current.
Solar Inverter are designed to inject power on to the grid, if you have more solar then your powerwalls can consume the powerwall will trip and shutdown. they are limited to charge at 5kw each and the inverter wasn't designed to regulate current.
if you want more solar then powerwalls, they will install your excess solar out side of your gateway so it will not be available to charge your powerwalls in a grid out condition.
 
Last edited:
I cannot use one gateway on my home and have back. 2 separate 200 amp panels with must loads.

I have seen my PW's charge in storm watch, with full PGE charging. So, sure seems the PW's have the ability to determine level of charge they can handle, no matter what the input could be.
you can put both panels on a single gateway. do the "alternate load" calculation and you will see. you would literally have to have a mansion to need more. your installer has to design your generator or battery system to be able to run all expected loads. if you had greater then 10 powerwall i wouldn't bring this up, but you don't. i'm all electric with three central AC systems that have electric resistive heat and im good with a 3hp well pump (4.2kw)) to boot.

powerwalls are limited to a 5kw maximum charge, charge rate in storm watch is usually at 3kw.
 
Solar Inverter are designed to inject power on to the grid, if you have more solar then your powerwalls can consume the powerwall will trip and shutdown. they are limited to charge at 5kw each and the inverter wasn't designed to regulate current.
if you want more solar then powerwalls, they will install your excess solar out side of your gateway so it will not be available to charge your powerwalls in a grid out condition.
Here's my understanding: If the grid is available, there is no issue. If the grid is disconnected, and the solar power available is more than the total of the house load and the 5kW/PW limit, then some classes of inverter will be shutdown by the PW. Others are capable of curtailing the power inverted by running well away from the MPP. Either way, the PWs are capable of limiting their own charge rates, including slowing down the charge rate as they approach 100% SOC. In fact, quoting from the PW spec sheet: "In Backup mode, grid charge power is limited to 3.3 kW". PW installations don't include a power limiter between the grid and the PW, so the charging power limitation is set with the PW itself.
 

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