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PV on power line side of gateway?

I currently have 26 solar panels generating 6kw. I’ve added a new Tesla vehicle, and am ordering a new 9 panel system generating 2.6kw, and a Powerwall.

The designer is suggesting that the new battery be installed on a sub panel with the house, existing PV system, and car charger. They are recommending putting the new PV system on the power line side of the gateway, in order to keep the maximum load from the PV below 7.6kw for the single Powerwall.

Under normal operations, this seems fine, but if we lose grid power, we’ll also lose power from the second system.

Is it possible/desirable to provide some way to utilize the power from the second system during a grid failure without overloading the Powerwall?

We typically feed power into the grid during the day, unless I’m charging the car, in which case I’m drawing power from it.

Does the gateway interact with the Tesla home connector to set the appropriate charging rate depending on available PV energy?

Are the tools in the Tesla app sufficient to monitor charging versus grid power if one of the PV systems is on the line side of the gateway?
 

arnolddeleon

Active Member
Supporting Member
Jul 21, 2012
1,041
1,123
SF Bay Area
I would put both PV systems behind the Powerwall. Worst case is you have to manually turn one of your PV systems.

If you have production and load data from your existing system you can probably predict how likely you are to produce more power than the Powerwall and your loads can absorb.

Your new PV system will likely respond to power curtailment signals from the Powerwall anyway. With some luck, your old system could also respond to the frequency shifts that the Powerwall uses to signal generators to lower production (and eventually shut it down).
 
I'm dealing with a similar situation. I'm adding extra PV to a system with PV and 1 PW. The installer (not Tesla) quoted the "max 7.6KW per PW" at me and initially refused to design it that way, but eventually I got them to agree - with a waiver that I know what I'm doing if it needs to shut itself down in the middle of a summer day if the grid goes down.
Installation is today!
 
I currently have 26 solar panels generating 6kw. I’ve added a new Tesla vehicle, and am ordering a new 9 panel system generating 2.6kw, and a Powerwall.

The designer is suggesting that the new battery be installed on a sub panel with the house, existing PV system, and car charger. They are recommending putting the new PV system on the power line side of the gateway, in order to keep the maximum load from the PV below 7.6kw for the single Powerwall.

Under normal operations, this seems fine, but if we lose grid power, we’ll also lose power from the second system.

Is it possible/desirable to provide some way to utilize the power from the second system during a grid failure without overloading the Powerwall?

We typically feed power into the grid during the day, unless I’m charging the car, in which case I’m drawing power from it.

Does the gateway interact with the Tesla home connector to set the appropriate charging rate depending on available PV energy?

Are the tools in the Tesla app sufficient to monitor charging versus grid power if one of the PV systems is on the line side of the gateway?
What inverters do you have on the existing system?

I generally agree that if you are comfortable with manually turning PV strings off, that you put all the PV on the backup side.
 
The new system is supposed to use IQ7PLUS-72-2-US inverters. That’s the only one I’d need to take offline in the event of a surplus of solar energy.
In the event of an outage and if you had a condition of too much PV and too little ability to use it through Powerwall and house loads, then control of any of the PV is as good as the other. Manual control works but it is inferior to the partial curtailment that the Powerwall makes possible.

Your older PV is the larger system and depending on the grid profile of the old system depends whether this PV can be partially curtailed. If 20% of your system responds to the frequency shift, that's really not ideal and Tesla might not adjust the frequency down from 65 hz to the more appropriate 62-63 hz.

Your newer IQ inverters will respond to this 62-63 hz signal, so it's a matter of getting the old inverter's on the same page, which is why I asked what model the old inverters were.

If you can get all the microinverters to respond to the frequency shift, you might not have to turn off any PV manually. Some of the older enphase microinverters have the option to change to a grid profile that recognizes PW will try to frequency shift to partially curtail solar generation, and loading this grid profile might work out so it's hands and worry-free.
 
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The older inverters are Enphase M215-60-2LL-S22. There are 26 of them.
I bet you have 2- 20A breakers. I have 17- 215s, one breaker. You will not generate 6000W peaks I bet.
My best was 225W per panel, one day in 10 years of operation, never again. You will have 3-20A and shutting down just 1 will get you under that 7.6 limit.

Of course, a worry-free system would be 2 PW. :D
 
The installer has now agreed to put everything on the home side of the GW. He has added a manual shutoff that shutdowns the battery and new solar system, in addition to the existing manual disconnect for the current solar system. Based on the responses, I doubt I will ever have to face overrunning the maximum charge rate for a single PW2.

Thank you to everyone who provided helpful information. Can’t wait to have the install scheduled.
 
The installer has now agreed to put everything on the home side of the GW. He has added a manual shutoff that shutdowns the battery and new solar system, in addition to the existing manual disconnect for the current solar system. Based on the responses, I doubt I will ever have to face overrunning the maximum charge rate for a single PW2.

Thank you to everyone who provided helpful information. Can’t wait to have the install scheduled.
Did you get installed? I'm curious how all of this was connected. Possible you could send photos? I ask because I'm trying to do something similar. I want to add in a small separate array with micro inverters to my Tesla solar + powerwall system.
 
Did you get installed? I'm curious how all of this was connected. Possible you could send photos? I ask because I'm trying to do something similar. I want to add in a small separate array with micro inverters to my Tesla solar + powerwall system.
Yes, I did. The only addition from the standard configuration was a manual cut off from both the new solar and for some reason the battery, in addition to the existing cutoff for the original solar system. In the event that I have a long term power failure, I’ll use one of the cutoffs to either disable the original 6KW system or the new 2.4KW one. If I don’t, I risk the system shutting down if either the battery has filled or the total insolation, less the total house load, exceeds 5KW, the maximum that the battery can handle.

In practice, this number is only reached for about 20 minutes in any sunny day, after the battery is fully charged.
 

miimura

Well-Known Member
Aug 21, 2013
7,383
7,382
Los Altos, CA
Yes, I did. The only addition from the standard configuration was a manual cut off from both the new solar and for some reason the battery, in addition to the existing cutoff for the original solar system. In the event that I have a long term power failure, I’ll use one of the cutoffs to either disable the original 6KW system or the new 2.4KW one. If I don’t, I risk the system shutting down if either the battery has filled or the total insolation, less the total house load, exceeds 5KW, the maximum that the battery can handle.

In practice, this number is only reached for about 20 minutes in any sunny day, after the battery is fully charged.
When the battery nears full charge, the Powerwalls will automatically force all the solar offline by increasing the micro-grid frequency. The situation you need to address is when the solar production is high and you do still need to charge the battery. Turning off a portion of your solar during peak generation will allow the battery to continue charging within the 5kW maximum.
 
When the battery nears full charge, the Powerwalls will automatically force all the solar offline by increasing the micro-grid frequency. The situation you need to address is when the solar production is high and you do still need to charge the battery. Turning off a portion of your solar during peak generation will allow the battery to continue charging within the 5kW maximum.

I haven’t yet tested this with my original Enphase inverters, which are the older M215 models. They do seem to offer the correct frequency limit triggers, so I think they will go offline properly.
 

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