Dual Gateways (US)

[boltzzz]

Does anyone in the US with 2 (or more) gateways know if they have the ability to share capacity with the powerwalls behind them? I've seen some good discussion on the desire for 400A gateways but, since that is not yet an option, I'm curious what happens when 2 200A gateways are run in parallel each feeding their own 200A subpanel. I'm worried in my case that unless the 2 panels are drawing at the same rate (unlikely), I'll forfeit some capacity on one or the other. Worse, I may not be able to drive any larger circuits since each gateway in my case would be backed by 1 powerwall.

I'd love whole house backup, but UNLESS they are cross tied in some way this seems worse than the pain of choosing individual backup circuits and a single gateway.

 

[miimura]

If Tesla were to do dual Gateway systems you would have to separate the loads to each one and not cross-connect them. However, it would look like one big system. The problem is that if you did have an outage, one system might run out of energy before the other. You would have to make sure that each system had enough Powerwalls and solar to keep running through an extended outage.

 

[boltzzz]

If Tesla were to do dual Gateway systems you would have to separate the loads to each one and not cross-connect them. However, it would look like one big system. The problem is that if you did have an outage, one system might run out of energy before the other. You would have to make sure that each system had enough Powerwalls and solar to keep running through an extended outage.

Yeah, that seems like a worse way to go- it probably also means that I'd be limited on recharging during a grid outage via my SolarEdge 10000. I think it's time to plan out an essential bus, or at least designate one of the 2 200A panels to be behind a single gateway.

 

[bob_p]

We have a large house with 2 150A breaker panels for all of the circuits in our house. One of the configurations considered for our new system, was to split our 44 solar panels and 4 PowerWalls into two systems (22 solar panels and 2 PowerWalls each), with a Gateway for each of the breaker panels.

We reviewed the 2 year history of energy usage from our smart meter - and also reviewed the circuits being used on both of the 150A panels and concluded that our peak usage was well below the theoretical 300A of load supported by the two panels.

So instead of implementing a split Gateway system, we were able to go with a single Gateway with a 200A breaker to the grid, with the PowerWalls able to provide sustained 20KW of power in off-gird mode (without any solar power). A major problem with the split Gateway configuration was that the loads weren't balanced between the 2 150A breaker panels, which would have required rewiring (further complicated because the HVAC upstairs units and outside compressors were split between the 2 panels).

After the system was installed, I ran some tests and confirmed that under a peak load (all of our pool pumps running, all 3 air conditioners running, and both electric ovens on), we were under 200A of load.

However, that configuration was using 22 KW of power, so in a worst case scenario, we could have problems if everything was on when we encountered an grid power loss - and we didn't have any power coming from the solar panels.

We also talked about the possibility of a dual Gateway configuration with both Gateways sharing all of the solar panels and PowerWalls with one Gateway connected to each of the 150A breaker panels. But even if that configuration was supported by Tesla, it would have been overkill - since we are still limited by the power being provided by the 15.4 KW (more likely a peak of around 10 KW) of solar panels and the 20 KW from 4 PowerWalls.

When we started the planning process, having whole home backup - and using all of the solar panels and PowerWalls for the entire house - was our desired goal, but based on our basic research that didn't appear likely - and that we'd have to settle for some type of split system and then dealing with the imbalance between the two house breaker panels.

But after the electricians reviewed our actual loads - we were pleasantly surprised we'd be able to get a whole home configuration with one Tesla Gateway providing power for the entire house (with the exception of our two Tesla Wall Connectors for charging our S & X).

Boltzzz - if you have smart meter data, recommend you pull that data down into a spreadsheet and look at your peak power usage for as far back as the data is available. Also, with a smart meter, you could also do some measurements on your own by turning on all of your heavy power devices and then looking at the actual power draw on the meter. It's very possible that even if you have 2 200A breaker panels, the actual load could be much less - and that you may be able to operate on a single Tesla Gateway with a single 200A breaker to the grid, and then plan for enough PowerWalls to support your actual load.

 

[aesculus]

We reviewed the 2 year history of energy usage from our smart meter - and also reviewed the circuits being used on both of the 150A panels and concluded that our peak usage was well below the theoretical 300A of load supported by the two panels.

I agree with this approach, at least to look at. Our theoretical connected load is also above 300 amps but it never approaches that because some of the load can be scheduled (ie car charging) and some is spotty (ie the oven thing).

I had the load reviewed by a PG&E engineer once to look over the need to have two separate panels and his recommendation was to do what you did in the review and carefully monitor the usage over time looking for voltage drops etc. After three years we have never gotten close. I drive my usage based on the EVA rate schedule for more than the car if I can (ie spa, well pumps, clothes washing/drying, baking). It's a bit of a PITA but not that bad. In addition it helps lower the costs if you are willing to make a few lifestyle sacrifices about when you do something on average. Since we only have 2 powerwalls we say goodbye to summer AC cooling during a PSPS, but we feel that's a small price to pay vs the alternative.

 

[boltzzz]

I think it will work fine on one gateway. I've started digging into my panels a bit more and there are many circuits that are not needed in an outage. It looks to be possible to consolidate everything essential on to one panel.

I don't have smart meter data, but I do use rtlsdr to sniff my usage every few minutes. From this I can tell that my power usage is rarely more than 7kW (and energy is ~30kwH per day) and so 2 Powerwalls will be about adequate even if I could get the whole house wired up.

 

[bob_p]

While I'm confident we can manage our electricity use to stay within the limits of our PowerWalls, when we (eventually) sell our house, we'll need to include recommendations on how the new owners should use the system.