Dual Gateway Setup - Functionality

[Vines]

Theoretically as long as 200A doesn't cross the GW, your limit to deliver to loads in a single subpanel is 160A of PV, 240A of Powerwalls and 160A of grid.

I'm using continuous output numbers here but those would look like 200A, 300A and 200A breakers.

 

[holeydonut]

Theoretically as long as 200A doesn't cross the GW, your limit to deliver to loads in a single subpanel is 160A of PV, 240A of Powerwalls and 160A of grid.

I'm using continuous output numbers here but those would look like 200A, 300A and 200A breakers.

Huh wow... ok so that explains why you said it's not wise to use the TEG2 internal panelboard to plant the backup loads; and instead said it was best to have a 200A breaker over the top of a separate sub panel that had the backup loads. (Advice unique to my situation with whole home backup and 200A service).

 

[h2ofun]

Huh wow... ok so that explains why you said it's not wise to use the TEG2 internal panelboard to plant the backup loads; and instead said it was best to have a 200A breaker over the top of a separate sub panel that had the backup loads. (Advice unique to my situation with whole home backup and 200A service).

I am not going to use the TEG2 internal panelboard since it has limits. By using 225 generation panels, I have a lot more flexibility down the road if I want to add more solar or PW's.

 

[slazinger_7]

@Vines - I pulled the green button data for the 12 months prior to our solar install (May 2020 to May 2019) (I can't download anything recent) and our maximum kWh usage for any one block is 3.22 kWh. The blocks are in 15 minute increments, so I'm assuming that's 12.88 kWh instantaneous.

How do you calculate the amperage from the data in the excel sheet to see: (1) average loads; and (2) whether we are over 200 amp for long peaks?

One thought was to take one of the ranges and put it into the non-backup side, which could bring us down 32 amp or so to about 166 amp, which should be comfortably below 200 amp.

Yes, we would want to keep the other 200 amp sub-panel and add any new loads to that side. I don't think we'd be adding anything in the foreseeable future, but I guess you never know.

 

[slazinger_7]

Ok - I think I figured out how to do the green button calculation to arrive at avg. load in amps:

(Total monthly kWh) / hours in month * 1,000 (convert to watts) / 240 (local mains voltage).

So, for January, we would have:

1,138 kWh (total Jan. 2020 usage) / 744 (hours in Jan.) * 1,000 / 120 = 12.75 avg. amps

Since the green button provides a breakdown by 15 minute increments, I can run those increments by the following equation:

(Current kWh) / 0.25 (quarter hour) * 1,000 (convert to watts) / 120 (local mains voltage).

Assuming my math is right, our highest amp draw is:

3.22 kWh / 0.25 * 1,000 / 120 = 107.33 max instant amp

Unless I'm missing something here, while we theoretically could exceed 200 amp, it seems we should be able to easily place everything behind a single 200 amp gateway since our actual peak usage is only coming in around half.

 

[power.saver]

Divide by 240 volts, not 120 volts in your calculations.

 

[slazinger_7]

If we divide by 240 volts, then we are 1/2 of 107.33 amp, i.e., our max amp draw over the course of the last year would be 53.65 amps. That's nowhere near 200 amps.

I feel like I must be missing something because this should be a no-brainer to put everything behind a single gateway, despite the fact that we have 400 amp service and sub-panel.

 

[power.saver]

Just because you have a 400A service panel doesn't mean you are using all of it. My 3000+ sq. ft. house with A/C has never used more than 40A. So your numbers look reasonable. If you have an EV, be sure to factor in how much it draws. Even if that's an additional 48A, you are still below 200A for the GW (and you could put the EV outside the backup circuit if necessary).

 

[Vines]

If we divide by 240 volts, then we are 1/2 of 107.33 amp, i.e., our max amp draw over the course of the last year would be 53.65 amps. That's nowhere near 200 amps.

I feel like I must be missing something because this should be a no-brainer to put everything behind a single gateway, despite the fact that we have 400 amp service and sub-panel.

While this method of green button data is useless to measure peaks, its good to see that there is never an hour when you draw even close to 200A continuous. Likely a couple more electric cars and a hot tub would change this, so just understand those limitations.

However with all your loads you could use over 200A. In those rare cases and if if your Powerwalls are drained your main breaker will trip. As long as you charge at night with only 1 EV this problem isn't likely to surface. Just keep this in mind on days off really heavy draw from the grid.

 

[slazinger_7]

We'd just like to have one electric car backed-up in case of an emergency, namely a fire evacuation. I doubt we'd have much if anything else running at that time (other than maybe internet and a TV so we can track the fires).

Backing up additional cars and/or other toys such as a pool pump (wish we had a pool!) can go on the side that's not backed up. Would it make a huge difference if a pool pump went down for a couple days during a PSPS anyway? We only charge at midnight each night, and generally alternate our EVs every other night when we have two on site anyway. In an outage, we could probably charge during the day after Noon when we have excess solar anyway.

I've sent all our information and suggestions to our contact at Tesla, and no real response as usual. We'll continue playing the waiting game, and I'll provide an update when we hear something (and/or get a solution), for those who may be interested.

 

[slazinger_7]

Tesla sent out "the guy" today and he managed to solve the problem. Apparently it was not a CT issue, but a wiring issue. GW1 was apparently communicating with PW bank 2 and GW2 was communicating with PW bank 1. Very odd.