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Best way to connect 17kW of solar PV to one Powerwall?

Doug83

New Member
Mar 24, 2022
2
0
Kansas
I currently have a 5kW solar array with Enphase micro inverters on the East slope of my roof.
I would like to add 9.5 kW to my West roof slope & 2.5 kW to my South garage roof slope.
I also want to add a Powerwall to the system for backup power. My home consumes about 30 kWh’s of electricity per day even with the current 5 kW system & I plan to add a second EV in 1-2 years.
I realize the Powerwall can only handle 5000 continuous watts so I’m trying to figure out the best way to connect all of this solar.

I am curious what will happen if I connect the existing 5 kW’s of solar to the PW & backfeed the remaining 12 kW’s into my main breaker panel? What happens to the 12 kW’s of solar in this situation if the grid goes down? Does it shut down or will it try to power loads & charge the Powerwall?

Can I wire all 3 of the arrays into the Gateway & just manually disconnect certain arrays during a power outage to keep the Powerwall from receiving more than 5000 watts?

Any other ideas?
I guess the easiest & most expensive option would be to just get more Powerwalls.
 

gpez

Member
Apr 25, 2019
794
661
USA
I have 1 Powerwall with 8.6kw of PV. Max I get during the summer peaks is about 6.3kW, which is still below the PW2's 7kw surge limit.

If you don't want to buy more Powerwalls consider restringing your existing + some new to the single Powerwall and the rest to the non-backed up side. I don't believe you'll be able to backfeed the full 17kW.
 

Doug83

New Member
Mar 24, 2022
2
0
Kansas
I have 1 Powerwall with 8.6kw of PV. Max I get during the summer peaks is about 6.3kW, which is still below the PW2's 7kw surge limit.

If you don't want to buy more Powerwalls consider restringing your existing + some new to the single Powerwall and the rest to the non-backed up side. I don't believe you'll be able to backfeed the full 17kW.
Isn’t the surge limit just for a short duration though(10 seconds)?
 
I am afraid it is not possible unless you go with unconventional design.Tesla gateway will have 5KW of solar connected to solar input and your new extension would feed with line side taps into supply line of GW. In case of blackout PV extension would be disabled. You would need 2 separate exterior cutoff switches for each PV segment, if your state requires it.

I should probably add that I have 17KW AC side solar and had to get 3 PWs from Tesla to continue with my order. They did not want to split my existing system to accommodate 2PWs. My original intention was to order 2. Now I am glad that I ended up with 3 batteries since my electric company has a program where they use stored electricity during peak hours. If this program continues as is it will pay for all PWs in 4-5 years, essentially making them free.
 
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The biggest issue @Doug83 might face is the capacity of his main panel when adding that much solar to the main panel. His workaround would work to avoid the solar max of the Powerwall. Presumably he understands that extra solar would not function when the grid is down.
I do not think backfeeding extra 12KW is doable (120% rule for panel). In case of blackout GW disconnects from the grid and uses PV to charge battery. Combined PV power exceeds ability of PW to absorb it and it does not matter if it is connected to GW solar input or main breaker panel. This assumes full house backup wiring for Tesla GW.

the only way to make it doable is to have automatic disabling of new PV extension, in case of blackout, and it requires having PV extension upstream from GW.

Since Tesla is rather picky in selection of projects they take I doubt that they would even go for this unusual option.
 
I currently have a 5kW solar array with Enphase micro inverters on the East slope of my roof.
I would like to add 9.5 kW to my West roof slope & 2.5 kW to my South garage roof slope.
I also want to add a Powerwall to the system for backup power. My home consumes about 30 kWh’s of electricity per day even with the current 5 kW system & I plan to add a second EV in 1-2 years.
I realize the Powerwall can only handle 5000 continuous watts so I’m trying to figure out the best way to connect all of this solar.

I am curious what will happen if I connect the existing 5 kW’s of solar to the PW & backfeed the remaining 12 kW’s into my main breaker panel? What happens to the 12 kW’s of solar in this situation if the grid goes down? Does it shut down or will it try to power loads & charge the Powerwall?

Can I wire all 3 of the arrays into the Gateway & just manually disconnect certain arrays during a power outage to keep the Powerwall from receiving more than 5000 watts?

Any other ideas?
I guess the easiest & most expensive option would be to just get more Powerwalls.
In your situation, I would connect the excess PV greater than about 5 kW to the main panel as you suggest, and try to have the PV that is part of the backup system be the best exposure panels you have, probably south. This excess PV greater than 5 kW would also not have any gateway CT's on it so the Tesla system would be blind to it.

In a backup situation, the extra PV would automatically drop off because it is not part of the backup system and cannot make a microgrid on its own without the GW and PW. Also, this PV would only backfeed the grid, and would not be available except incidentally to charge the PW.

This design is not an ideal situation but could be made to work. I am not sure TE would entertain this configuration.
 
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Any insight into how your installed worked around the limitation of 5kW of solar connected to your Powerwall. Have you experienced an off grid situation yet?
The Powerwall basically draws up to 5kw from the panel production, leaving the rest for everything else in the house to consume.
So far, I have not had a power outage, since the system was only installed back early last month.
 
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The Powerwall basically draws up to 5kw from the panel production, leaving the rest for everything else in the house to consume.
So far, I have not had a power outage, since the system was only installed back early last month.
It would be interesting to know what happens when you have an outage.

My guess is that your microgrid will never reach the proper 60 hz during the daytime. The GW will send a partial curtailment signal (approx 61-63 hz) to the inverters during the day most of the day if they are less than 2-3 years old.

If the Enphase inverters are older than that they might go from fully on to fully off and the microgrid frequency will be more like 65 hz. In this scenario, the PW will not charge from the PV at all except possibly first thing in the morning and late in the afternoon when PV production is less than the inverters maximum charge ability.

Definitely make sure your grid profile in the Enphase setup is a powerwall friendly grid profile.
 
This excess PV greater than 5 kW would also not have any gateway CT's on it so the Tesla system would be blind to it.
I'm not aware of any reason it would be necessary to avoid putting gateway CTs on the solar outside the GW (on the non-backed up side). To my understanding the CTs are only used during grid operation, and are not used during an outage.

Cheers, Wayne
 
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I'm not aware of any reason it would be necessary to avoid putting gateway CTs on the solar outside the GW (on the non-backed up side). To my understanding the CTs are only used during grid operation, and are not used during an outage.

Cheers, Wayne
Good point, and in thinking about this what you say makes sense. Once a microgrid is formed, the need for CT's goes away.
 
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I have a whole house back up set up. I had 15,000 watts on Enphase inverters on three arrays.
I started with one powerwall then added another and finally added two more.

The each powerwall can only charge at 5,000 watts max. Grid connected up to 5,000 to powerwall the rest to the grid.

In a power out condition if the powerwall is near 100% the powerwall increases the ac frequency enough to shut down the solar. With 1 powerwall and 15,000 watts you will miss a lot of solar. The solar might not charge at all for hours until the powerwall drops enough to absorb the power. Mine works alot better now with 4 powerwalls.

quad powewalls.jpg
 
It would be interesting to know what happens when you have an outage.

My guess is that your microgrid will never reach the proper 60 hz during the daytime. The GW will send a partial curtailment signal (approx 61-63 hz) to the inverters during the day most of the day if they are less than 2-3 years old.

Would PW shift frequency in this config even if the battery SOC is low? Also, frequency-watt response takes time. Assuming the extreme situation (battery full, max PV array production, little load), I find it doubtful that one PW can handle the max output from a 16.5kW array for even a short time without risk of damage.
 
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It can not handle charging16.5kw only 5kw. There is no damage it just turns your solar off.
16.5kw of solar will be on more than 1 breaker. Shut off 2/3 of it and it will play nice in a grid down situation. Leave it all on in the grid interactive mode and save up for more powerwalls.
Where I live we lost power 22 times in the last 12 months.
Below is a power down full charge condition with solar shut down by the powerwall system. It was in storm mode at at 100% charge.
storm.jpg
 
Would PW shift frequency in this config even if the battery SOC is low? Also, frequency-watt response takes time. Assuming the extreme situation (battery full, max PV array production, little load), I find it doubtful that one PW can handle the max output from a 16.5kW array for even a short time without risk of damage.
Yes, it would frequency shift until the total PV is less than the PW ability to charge (5 kW) plus the home load at the time. If you had 15 kW of PV output, and only 1 powerwall, you could charge your EV to use the excess for instance.
 
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Yes, it would frequency shift until the total PV is less than the PW ability to charge (5 kW) plus the home load at the time. If you had 15 kW of PV output, and only 1 powerwall, you could charge your EV to use the excess for instance.
So, Tesla approves and supports such setup? Most other hybrid inverter vendors have strict criteria on supported max PV capacity that can be AC coupled. I am not aware of another vendor that supports AC coupling ratio of 3:1 (PV capacity:inverter power capacity).
 
So, Tesla approves and supports such setup? Most other hybrid inverter vendors have strict criteria on supported max PV capacity that can be AC coupled. I am not aware of another vendor that supports AC coupling ratio of 3:1 (PV capacity:inverter power capacity).
Tesla Guidance is 5-7 kW of PV per Powerwall.

I would suspect Tesla Energy would follow this guidance. 3rd party installers have more flexibility.
 

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