400Amp Gateway workaround

[CrazyRabbit]

since Tesla doesn't seem interested in designing a 400 amp gateway. could Tesla implement a software solution where the PW would supplement the gateway to not overload the 200 amp capacity?
so if the house is drawing 260 amps then the powerwalls would supply 60 to 80 amps of the draw keeping the load passing thru the gateway below 200 amps.

 

[BrettS]

The way that the gateway works is that it will support up to a 200A critical loads panel behind it. The powerwalls would be connected directly to the critical loads panel (or indirectly to the critical loads panel through a generation panel).

If you’re asking if you can put a 400A (or just more than a 200A) critical loads panel behind the gateway and then use the powerwalls to make sure that no more than 200A is flowing through the gateway then the answer is no. Not only does the gateway software not support this, but what happens if the powerwall’s are drained and the critical loads panel is trying to draw more than 200A?

It seems that the solution (workaround) Tesla has for 400A panels is essentially to have two separate gateways and powerwall systems, each with 200A behind them. But they are separate systems, so it could be difficult to balance them such that they have equal loads and similar runtimes.

 

[Vines]

The GW2 has this functionality built in @CrazyRabbit. More than 200A loads can be served on the load side of the gateway, within limitations. The Average load cannot be more than 200A but spikes are ok within the PV and powerwall capcaity.

 

[BrettS]

The GW2 has this functionality built in @CrazyRabbit. More than 200A loads can be served on the load side of the gateway, within limitations. The Average load cannot be more than 200A but spikes are ok within the PV and powerwall capcaity.

But in reading his post it sounds like he wants to put an average load of 260A behind the gateway and use the powerwalls to supply 60A so that there is only 200A going through the gateway from the grid.

 

[Vines]

The difference between the average or calculated load, vs the largest load is the key here.

Powerwalls can supply more than 200A of peak load, as long as there are PV and PW resources to supply that load.

GW2 has additional functionality to ensure the 200A breaker doesn't pop.

 

[miimura]

The difference between the average or calculated load, vs the largest load is the key here.

Powerwalls can supply more than 200A of peak load, as long as there are PV and PW resources to supply that load.

GW2 has additional functionality to ensure the 200A breaker doesn't pop.

You can configure Outback Power inverters to fill in for a small grid connection. Are you saying that the GW2 has logic to do this too? Can you configure it for smaller grid breaker like 100A?? Does the new load shedding feature come into the picture in this case?

 

[Vines]

You can configure Outback Power inverters to fill in for a small grid connection. Are you saying that the GW2 has logic to do this too? Can you configure it for smaller grid breaker like 100A?? Does the new load shedding feature come into the picture in this case?

I don't have public details to release regarding this, review the "Site and Conductor Limits" function in the new GW2 manual. Its not my place to say more right now.

Charge and discharge have a separate setting that the GW2 will enforce as much as it can by ramping PW discharge up or down. It will discharge Powerwall power if setup to do so and offset more than 200A of loads.

 

[fresnoboy]

I don't have public details to release regarding this, review the "Site and Conductor Limits" function in the new GW2 manual. Its not my place to say more right now.

Charge and discharge have a separate setting that the GW2 will enforce as much as it can by ramping PW discharge up or down. It will discharge Powerwall power if setup to do so and offset more than 200A of loads.

Vines, thanks for this info. Perhaps you could give me some insight in terms of whether or not the Gateway 2 could actually enables me to add some powerwalls?

My situation is that we have a large new house, accessory unit, and pool (with the usual equipment) and an EV. Everything is super efficient (all LED lighting, Mitsubishi VRF HVAC, gas hot water heater, excellent insulation, etc...). We have about 20KW of solar installed as well with a solaredge system.

Due to the way the NEC works, PGE and the electricians made us to go 400A service (we were close to needing 600A by their calcs!) yet the biggest load hour I can find in the billing is about 11 KWh. I am getting ready to install some power monitoring equipment that will give me 5 sec load numbers off the Main AC breakers so can verify typical and peak load.

My solar installer said Tesla would not work for whole home backup in this case, because 200A can't switch 400A. And to deal with an extended outage, I wanted a generator anyway, so we have a 30KW generator that backs everything up except the pool equipment. I would love to add some powerwalls to shift load so that my entire peak and partial peak times can be covered by solar, as my peak solar output is closer to noon and with EV-2A tarriff from PGE, the power is more than double the price in peak as compared with offpeak.

Does the new Gateway 2 handle this sort of configuration more flexibly that gateway 1?

I could run the just the main house and HVAC through the PW, which would be just fine with 200A (though again the way the NEC calculates load would be greater than 200A). The Mitsubishi HVAC units start up at 5A and spool up to a max of 35A each (there are 2), so there is no LRA issue with them. But I do;'t want to give up on the generator for whole home backup. It would be nice if the generator had an issue to have at least some backup from the powerwalls or have them act as a whole home UPS to handle the transition until the generator powers up and the 400A Kohler ATS switches over to emergency power.

I have the had installer propose using other systems that can lever a 3rd party transfer switch (so 400A is not a problem), but the cost of the battery units made it non cost effective. Tesla's system has great batteries, but because they only can use their own gateways, its more limiting for my type of setup.

Can Tesla handle my configuration now with the new gateway? Nothing in the specs seems to indicate it can according to my installer.

thx
mike

 

[Vines]

We are just now turning a customers service into a 200A service and installing about 80 A of PV and 5 Powerwalls. Calculated load is 180A in this case, when using the alternate method.

It all depends on the load calcs, which are pretty easy to do yourself as an estimate.

It certainly can be done, whether it should be done will take some measurement and investigation. You will be limited to 200A of grid power, which isn't an issue as long as the Powerwalls have and the GW2 is setup properly.

You absolutely want the GW2 in a system like this.

 

[fresnoboy]

We are just now turning a customers service into a 200A service and installing about 80 A of PV and 5 Powerwalls. Calculated load is 180A in this case, when using the alternate method.

It all depends on the load calcs, which are pretty easy to do yourself as an estimate.

It certainly can be done, whether it should be done will take some measurement and investigation. You will be limited to 200A of grid power, which isn't an issue as long as the Powerwalls have and the GW2 is setup properly.

You absolutely want the GW2 in a system like this.

Thanks for the note. Does the GW2 have more flexibility in terms of using a generator? I don't think the city will let me downsize the main feed to 200A, as it was quite a chore to convince them to let us "settle" for 400A than 600A.

My perfect world would be a system where the powerwalls would carry the home's power consumption in an outage until the PW's were drained, and then start the generator up when they were exhausted. When the solar kicked and and the powerwalls could handle the load the generator could switch off. And of course push all the stored energy back to PGE in the peak hour in the normal case.

I have given up on that goal and would settle for just the TOU offset if the financials made sense, but then the GW2 would be behind the main generator ATS. I confess I don't understand why they don't have a 400A variant of the GW2.

This brings up another question. Is there a excel spreadsheet where I could put in my consumption and add the solar generation numbers and tariff structure and calculate my savings if I could do the TOU shifting? I can do some of this myself, but something that could talk PGE data in a CSV as an input would save a lot of typing.

Thx
Mike

 

[Vines]

GW2 has some thought of generator support but nothing official. Currently its not allowed to charge the PW from a generator, but a generator can be downstream of the gateway, so backup when the batteries are empty.

As far as the financials, cant help you there sorry, its not my department really.

 

[wwhitney]

The Gateway 2 installation manual is publicly available here at the "Download Manual" link:

Installing Powerwall | Tesla Support

Appendix F briefly describes what I think Vines was referring to, but the level of detail is less than optimal.

One thing that is immutable is that the Backup Gateway 2 is only rated for 200A, and so the loads behind it that could be backed up by it in a power failure have to have an NEC calculated load of 200A or less.

Also your choices on whether those loads run on the Powerwall or generator when the generator comes on line are somewhat limited: you could have Powerwall just until generator is up, or Powerwall until empty and then no power for those loads, or Powerwall until empty, then switch to generator (which would require a second transfer switch fed by the generator). Lastly, getting solar to play well with the generator is hard and would be simplest in the last case; otherwise it would mostly need to be configured to just turn off when the grid is off (as it must currently be).

As far as load shifting when the grid is up, the Backup Gateway details don't matter, that can be done in any case.

Cheers, Wayne

 

[fresnoboy]

Thanks for the comments. There is a detached garage where the inverters and all the panels and main transfer switch connect to. The layout is designed to support having a few powerwalls. If the GW2 can deal with a generator ATS being upstream from the unit, then it's an easy install and all the wiring is there to support that. That's how the inverters tie in, and I could get the gateway installed there pretty easily.

To do any form of backup is complicated because of the 400A feed. I get what the vines is saying about being able to use PW's to moderate demand on the panel, but that isn't my situation - I have a 400A feed already.

In an outage, the generator will kick in, so if it's running, having the GW enabling the main house load to be fulfilled by the PW's might be useful, but because the generator's efficiency when running at very low power levels (just the garage and the accessory unit) is terrible (and you get soot buildup) that doesn't seem that good a situation, but maybe I am missing something.

I can't seem to find anyone that can describe what exactly Tesla's generator support is, so it's difficult to engineer it into systems with them. Right now, if you have a generator, installers basically say you can't use the powerwall at all. I wish Tesla would implement real support for them, as I think people who live in areas where the power can be out for days are forced to decide between PW's and generators, and I think most people go the genset route.

thx
mike

 

[Vines]

Currently you have 3 official options for generator support.

1. Off grid- Generator becomes the source, controlled by the PW and will charge batteries
2. Generator ATS downstream of Gateway
3. Manual transfer switches

There's rumors of on-grid generator support that could charge Powerwalls in a backup event. Its possible to DIY it safely as well.

 

[fresnoboy]

Well, I'm not off grid, so that choice doesn't seem to work. I can't put the ATS behind the GW because the GW can't do 400A. And I don't want my wife to have to do manual start of a generator if the power goes out in a storm and I'm away. I guess that's why I keep getting told I can't use powerwalls, even for TOU load shifting.

 

[Vines]

There are ganged ATS which could be used in a 2x200 configuration, but its not ideal, especially if you don't have a backup system on both sides.

If you do a 2 GW design it could work. Alternatively, convince the AHJ that the Powerwalls will provide the additional service required to satisfy them.

 

[fresnoboy]

Maybe this doesn't really make sense anyway:

Let's do the math here about what can be saved through time shifting. Summer EV-2A rates here in PGE land are approx $0.48 a KWh for peak, and $0.17 a KWh for offpeak. So if I had 4 PWs all dedicated to doing load shifting on a daily basis, that seems to be a maximum of 14KWh (storage) *4 (# of PWs) * (.48-17) (the difference between offpeak and peak) = ~$17/day in savings. Let's just use summer rates all year as an approximation (winter peak to offpeak difference is only $0.18) , and assume there is enough solar to fill the 4 PW's every day), and that we have 14*4 KWh of peak demand. That means we save a bit over $6K/year, so payback is 6 years from the load shifting in this highly overoptimized analysis...

Do I have that analysis right?

thx
mike

 

[gpez]

Maybe this doesn't really make sense anyway:

Let's do the math here about what can be saved through time shifting. Summer EV-2A rates here in PGE land are approx $0.48 a KWh for peak, and $0.17 a KWh for offpeak. So if I had 4 PWs all dedicated to doing load shifting on a daily basis, that seems to be a maximum of 14KWh (storage) *4 (# of PWs) * (.48-17) (the difference between offpeak and peak) = ~$17/day in savings. Let's just use summer rates all year as an approximation (winter peak to offpeak difference is only $0.18) , and assume there is enough solar to fill the 4 PW's every day), and that we have 14*4 KWh of peak demand. That means we save a bit over $6K/year, so payback is 6 years from the load shifting in this highly overoptimized analysis...

Do I have that analysis right?

thx
mike

I think your analysis is correct however some of the numbers need to be a bit more realistic. Each Powerwall has only 13.5kWh usable and in reality won't allow itself to drain below 13kWh during normal circumstances. There is also a 90% roundtrip efficiency to consider so you're really only getting 95% of the 13kWh out. Powerwalls degrade over time so over those 6 years your capacity will be down about 15% (the Powerwall is warrantied to 70% of original capacity after 10 years but of course that curve isn't perfectly straight). You already identified summer vs winter production, usage, and costs. Also consider potential rate changes in the future.

Lots of little things like that will nip at your payback calculation.

 

[fresnoboy]

I think your analysis is correct however some of the numbers need to be a bit more realistic. Each Powerwall has only 13.5kWh usable and in reality won't allow itself to drain below 13kWh during normal circumstances. There is also a 90% roundtrip efficiency to consider so you're really only getting 95% of the 13kWh out. Powerwalls degrade over time so over those 6 years your capacity will be down about 15% (the Powerwall is warrantied to 70% of original capacity after 10 years but of course that curve isn't perfectly straight). You already identified summer vs winter production, usage, and costs. Also consider potential rate changes in the future.

Lots of little things like that will nip at your payback calculation.

Well, I was trying to look at the best case, which isn't that good. This is a bit puzzling to me, as PGE has some of the highest prices in the US, so I can't understand why powerwalls for load shifting make sense in other cases if they don't work here...

 

[Vines]

I mean if the worst thing possible is you buy something that pays itself back approximately over its lifetime, you made a decent choice. Most luxuries do not do this.

So for the cost of prepaying for the power over 10 years-ish you get the ability to run somewhat independently of the grid, or in total battery backup mode and consume something like 40 kWh every day? That's pretty awesome living if I say so myself