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Larger PV systems with different inverters
- Thread starter stagepuppy
- Start date
I am certainly not an expert on this, but I believe what normally happens is a person in such a scenario actually has multiple SYSTEMS on their home. They all get tied back to the meter, but the "tesla inverter + panel" system does not talk to the "solar edge + panel" system. They are different PV systems, usually installed at different times, sometimes by different vendors, and they dont talk to "each other".
They all are connected to the same house, though, they just dont talk to each other in any way, and there really isnt any need for them to do so I dont think.
They all are connected to the same house, though, they just dont talk to each other in any way, and there really isnt any need for them to do so I dont think.
@stagepuppy you didn't mention Powerwalls in your post, but if you're talking about "when the power goes out" you must be considering the Powerwall use case. Since the Powerwalls are AC coupled and are very broadly compatible with different solar inverters, you are unlikely to have any significant issues with a Powerwall system that includes solar inverters from different manufacturers. The only significant difference between different solar inverters or different configurations of solar inverters is when they are able to proportionally curtail generation as the Powerwalls increase the micro-grid frequency as the batteries get full when islanded from the grid. Proportional curtailment is not a necessary feature - it only makes the system work in a more elegant way.
Miimura, yes, the scenario would be with Powerwalls, thanks for noting that. So during an outage in sunny conditions, would the Powerwall inverters take over as the reference 60Hz until curtailment, and Tesla and other inverters would continue pumping energy as long as the frequency is within what their settings see as a "grid is up" situation.
When the power comes back on, is it the Backup Gateway that senses the inverters are back in phase before allowing reconnection to the grid, or do the solar inverters each determine that before allowing current flow from the panels? With different solar inverters, would it be likely they reenable at different times?
jjrandorin, I guess a concern of mine would be phase differences from different inverters, if that would be a concern at all, I haven't read too much about different inverters feeding into a Backup Gateway. I see that extra open breaker slot in my setup and the "what ifs" are running amok in my mind.
When the power comes back on, is it the Backup Gateway that senses the inverters are back in phase before allowing reconnection to the grid, or do the solar inverters each determine that before allowing current flow from the panels? With different solar inverters, would it be likely they reenable at different times?
jjrandorin, I guess a concern of mine would be phase differences from different inverters, if that would be a concern at all, I haven't read too much about different inverters feeding into a Backup Gateway. I see that extra open breaker slot in my setup and the "what ifs" are running amok in my mind.
Different brand inverters may or may not support curtailment in a specific way, thats true. That means if one has 2 systems on their home, the panels connected to inverter A may behave differently than the panels connected to inverter B. One may curtail, the other may only support on / off.
A member here on TMC that has experience with having multiple systems on their home is @arnolddeleon who has, I believe, 3 separate systems on his home. Tagging him to see if he can provide some feedback.
The Powerwall Gateway is responsible for the master frequency and the solar inverters all just follow along. When the Gateway detects that the grid is back, it does some checks to make sure the power is stable and then gradually slews the waveform so that the micro-grid is synchronized with the utility grid. Then it closes the switch and goes back into grid-tied mode. The back-to-grid transition is usually undetectable and solar generation continues uninterrupted because of this synchronization.
I have multiple systems, 2 sets of enphase microinverters going into an enphase combiner, and a solar edge, from different sets of panels.
They take different amounts of time to come up from cold if they've been turned off, but I don't know yet how they'll behave with the gateway/powerwall shifting frequency to curtail them. I haven't had the default 65Hz setting changed yet, so my APC UPSs do trigger, but we'll have to see how the whole system behaves in a big outage.
My big loads (AC, EV charger) aren't backed up, so I have limited means for temporarily increasing consumption to help if I'm off grid and overproducing.
They take different amounts of time to come up from cold if they've been turned off, but I don't know yet how they'll behave with the gateway/powerwall shifting frequency to curtail them. I haven't had the default 65Hz setting changed yet, so my APC UPSs do trigger, but we'll have to see how the whole system behaves in a big outage.
My big loads (AC, EV charger) aren't backed up, so I have limited means for temporarily increasing consumption to help if I'm off grid and overproducing.
In your case, 11kW of solar and only one Powerwall could definitely be an issue. The solar can overpower the charging ability of the Powerwall. You should think in advance about how to disable half of your solar. I'm not familiar with the details of the Enphase Combiner since I have an old Enphase system with each string of micros having their own 20A breaker in my easily accessible breaker panel. I also have the opposite problem to you - I have way more Powerwall than solar.
I had to convince the installer that this is what I wanted.
But it's no different to when the powerwall is already at 100% and can't sink any solar output, it would curtail by shifting frequency.
I'm expecting my worse case to be, the system shuts down, I have to turn off half the solar and wait for it to try again.
I have all those breakers nicely together in a dedicated box, powerwall, enphase and solar edge, combining to one feed and comms back to the gateway.
Should be easy to add a second PW to this system.
Here's the nuance with my system. I did a quick test flipping the main breaker when I had 80% SOC, and more solar generation than 1PW can sink.
It curtailed and went into battery only mode (zero solar).
That's what you'd expect to see with a 100% SOC on any system, but the issue with mine is that when it tries again, it'll see too much power available still and stay on battery until the solar output is low enough. That just means I'll be on battery for those hours even though it's daylight.
But, I do have the advantage that with the two different inverters, they'll curtail at different rates, so the system may find that middle ground where only one inverter is active, and that would be low enough output to restart charging.
It curtailed and went into battery only mode (zero solar).
That's what you'd expect to see with a 100% SOC on any system, but the issue with mine is that when it tries again, it'll see too much power available still and stay on battery until the solar output is low enough. That just means I'll be on battery for those hours even though it's daylight.
But, I do have the advantage that with the two different inverters, they'll curtail at different rates, so the system may find that middle ground where only one inverter is active, and that would be low enough output to restart charging.
The problem with your situation is that you could drain the batteries during peak generation times, then when the sun is setting it starts to charge, but can't charge enough to leave you enough energy to make it through the night. Being able to turn off half of your solar during high generation hours will solve that problem. I don't expect your system to act like it has multiple inverters, the whole collection of micros should be acting as one even though they are arranged in multiple strings. The only improvement you can try to make is to get the installer to load a grid profile that allows proportional curtailment. However, they may tell you that those profiles are not compatible with California Grid Tie rules for things like ride-through.
Flipping the breaker for either inverter is sufficient, but the Solaredge does have a control toggle on it that would be less invasive, leaving it connected but not producing.
The enphase doesn't have any similar physical control, and the app while great is monitoring only.
So I think yes, in the worse case scenario where I'm producing 9kW in mid June, using only 1kW and going into an outage, it'll switch to run on battery continually, but I can turn off 4kW easily and be under 5kW instantly, which the powerwall can use if it is at low SOC, but maybe just an hour later it'll be low enough for normal charging at 3.3kW.
I want to try this for real as a test, but currently my internet connection is partly powered from non-backed up circuits, so I can't monitor it seamlessly as I run the experiment. (Ah, could go Cell data only on the phone).
There are two parts to your internet, getting the local data to the Tesla cloud, and the cloud to you. Using a cellphone only helps if your Gateway can failover to cell as well...there are also things like extension cords...
All the best,
BG
roblab
Active Member
I have 11 kW of possible power generation, and it is hooked to a Fronius inverter. It plays nicely. I even have a Sunny Boy thing on some of my panels. But whatever, they all are made to do the job, no matter who did the previous job.
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