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

Your system design would have to thread the rules for both Tesla (5kW-7kW max recommendation), and panel bus bar capacity (city/inspector)

The no-risk design is going to be to put the extra panels before the gateway, and the only mitigation there is to re-arrange the strings so that you have up to 7kW on the backed up side and the remainder feeding before the gateway since that is what you'll lose during an outage.

I was able to get my installer to do 11kW on a single PW, since it didn't cause a bus bar mismatch, but I did have the 200amp main breaker reduced to 150amp.

I don't think you'll get to a design that leaves space for future PW expansion.

Ignoring cost concerns, you'll get a better system all round by going to 3 PWs or possibly 2 with a waiver.
 
If the Solar was all feeding into the gateway, it will know it can't sink it all to the battery + house, so will immediately frequency shift to curtail the inverters, but if that doesn't work it will shut down the whole system.
Then every 10 minutes or so it will wake up and try again.
So worse case, you are out of power completely.
Best case, the system stays on battery at elevated frequency, with no solar power coming in at all (fully curtailed).
Later in the day when the solar output falls, the retry will succeed and the solar will come online for the remainder of the solar day.

What we don't know is how often it will retry, or if once you lose solar to failed curtailment, it won't work again until grid is restored.
 
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This thread has me wondering.
In a grid outage, if my system is putting out let's say 10kw, and my house is drawing only 2kw, and the PW is charging at 5kw, will I have a problem because of the excess not being "absorbed" by the grid?
Precisely. The microgrid has to balance at all times, so when the PW (the grid forming inverter here) senses the imbalance, it will raise its AC frequency to try to knock the PV off-line. Worst case if the PV inverter misbehaved and didn't shut off, the PW would have to shut down.

Cheers, Wayne
 
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Precisely. The microgrid has to balance at all times, so when the PW (the grid forming inverter here) senses the imbalance, it will raise its AC frequency to try to knock the PV off-line. Worst case if the PV inverter misbehaved and didn't shut off, the PW would have to shut down.

Cheers, Wayne
I guess I'm further confused now. I have basic electronics knowledge, but don't know much about how solar really works.
If you have a regular NiHM AA battery that has 1500ma max output, it has a set voltage and a maximum amperage that it puts out, if you only draw, let's say 10ma, all is well.
With a solar system, if you don't put a load on the system to "absorb" the excess, you've got problems.
 
One way to look at it is that a grid-forming inverter acts like a voltage source, and is able to discharge/charge within certain current limits. While a grid-interactive (grid-following) inverter acts more like a current source. So on a microgrid you have a problem when the net current, positive or negative, exceeds the limits of the grid-forming inverter.

Cheers, Wayne
 
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This thread has me wondering.
In a grid outage, if my system is putting out let's say 10kw, and my house is drawing only 2kw, and the PW is charging at 5kw, will I have a problem because of the excess not being "absorbed" by the grid?
In essence that is the issue, and it is complicated by some things:
1. Battery temperature - They cant always charge at 5 kW
2. Battery SOC, they cant always take a 5 kW charge
3. Inverter compliance with partial curtailment - Do your inverters support this? Does your house work fine with the final frequency shift?
4. House load of 2 kW will naturally surge up and down
5. PV generation will vary with irradiance and weather, so can jump up and down quite a bit on a cloudy and sunny day. My PV array typically maxes at 6.8 kW but today we saw brief spikes up to 7.8 kW as the sun reflected off the clouds, with cool PV panels due to the rainy weather. This effect is smaller if your DC/AC ratio is significantly larger than 1.0, since the inverter will be clipping already.

In this backup scenario, the PW and TEG will start pushing the microgrid frequency towards 62-65 hz, depending on the settings and your current PV inverters. This either takes the PV totally offline, or reduces their output, based on partial curtailment.
 
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.
Does It drive the frequency up to 65mhz immediately, or does it gradually increase it, which would cause newer inverters to “curtail”, followed at the higher rate, by the older ones, that just turn completely off.

I’ve got 6Kw of older inverters, and 2.5Kw of newer ones, so I’m hoping that 5Kw into the PW plus house load of ~1.5Kw will work nicely with the newer inverters reducing and then shutting down prior to reaching 65mhz at which point all solar will cycle off.

My sensitive but low power devices are on a UPS, which from what I’ve read will kick in once the frequency goes above 62mhz.
 
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Does It drive the frequency up to 65mhz immediately, or does it gradually increase it, which would cause newer inverters to “curtail”, followed at the higher rate, by the older ones, that just turn completely off.

I’ve got 6Kw of older inverters, and 2.5Kw of newer ones, so I’m hoping that 5Kw into the PW plus house load of ~1.5Kw will work nicely with the newer inverters reducing and then shutting down prior to reaching 65mhz at which point all solar will cycle off.

My sensitive but low power devices are on a UPS, which from what I’ve read will kick in once the frequency goes above 62mhz.
khz, not mhz. If your AC frequency went that high, you'd have some BIG problems. :)
 
Does It drive the frequency up to 65mhz immediately, or does it gradually increase it, which would cause newer inverters to “curtail”, followed at the higher rate, by the older ones, that just turn completely off.

I’ve got 6Kw of older inverters, and 2.5Kw of newer ones, so I’m hoping that 5Kw into the PW plus house load of ~1.5Kw will work nicely with the newer inverters reducing and then shutting down prior to reaching 65mhz at which point all solar will cycle off.

My sensitive but low power devices are on a UPS, which from what I’ve read will kick in once the frequency goes above 62mhz.
This depends on the inverter profile and the setting of the GW2. If the system is commissioned with a partial curtailment capable inverter specified in the commissioning wizard, then the frequency should rise slowly. When you start mixing new and older inverters it is not as clear what happens. The best way to understand this is to look at the frequency of your system in real time with an e-gauge or similar.

Tesla Level 2 tech support is able to change this setting for those inverters that support partial curtailment.
 
Does It drive the frequency up to 65mhz immediately, or does it gradually increase it, which would cause newer inverters to “curtail”, followed at the higher rate, by the older ones, that just turn completely off.

I’ve got 6Kw of older inverters, and 2.5Kw of newer ones, so I’m hoping that 5Kw into the PW plus house load of ~1.5Kw will work nicely with the newer inverters reducing and then shutting down prior to reaching 65mhz at which point all solar will cycle off.

My sensitive but low power devices are on a UPS, which from what I’ve read will kick in once the frequency goes above 62mhz.
I do not think we have supporting evidence that PW activates power curtailment when charging current exceeds known limits. It is known that when SOC reaches high 90s frequency does go up, based on stored configuration.
 
Does It drive the frequency up to 65mhz immediately, or does it gradually increase it, which would cause newer inverters to “curtail”, followed at the higher rate, by the older ones, that just turn completely off.

I’ve got 6Kw of older inverters, and 2.5Kw of newer ones, so I’m hoping that 5Kw into the PW plus house load of ~1.5Kw will work nicely with the newer inverters reducing and then shutting down prior to reaching 65mhz at which point all solar will cycle off.

My sensitive but low power devices are on a UPS, which from what I’ve read will kick in once the frequency goes above 62mhz.

khz, not mhz. If your AC frequency went that high, you'd have some BIG problems. :)
Actually, neither.

The AC frequency moves from 60.0Hz to 62.5-65Hz, that's just plain old Hertz, cycles per second. It moves up slowly until the incoming current to the Powerwall is down to a level that it can handle. Ideally, your inverter(s) taper output gradually down to maximize the energy delivered to the Powerwall, but not all do so. If your inverter is only on or off, it will only charge the Powerwall when the solar output is below what the Powerwall can handle, which is much less than optimal.

Having enough Powerwalls makes use of all of the available energy.

All the best,

BG
 
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