Forums

Powerwall Microgrid with 400A Meter Base and 200A Main Breaker Panels

Powerwall Microgrid with 400A Meter Base and 200A Main Breaker Panels

Last week we learned something interesting regarding how things work with our new Powerwall microgrid configuration using a 400A meter base feeding two 200A main breaker panels, and a single TEG feeding one of the 200A main breaker panels. Posting the info here in case it may help others.

Given the 200A capacity limitation of a single Tesla energy gateway, we connected the first 200A main breaker panel (BP1) to the TEG on the microgrid. The other 200A breaker panel (BP2) was connected directly to the meter base like any non-solar home. Thus we assumed any home loads connected to circuit breakers in BP2 could not be self-powered by the microgrid.

This led us to divide our various home loads/breakers across BP1 and BP2, putting as many breakers as possible in BP1 until we hit its 200A capacity. Everything else in the home (less critical loads) was connected to breakers in BP2.

The microgrid CTs feeding the TEG and the SolarEdge inverter were all connected in the normal fashion to enable power monitoring of the utility grid, solar, PWs, and home consumption. At first I was surprised to see the installers setup consumption CTs on the 200A feeds to both BP1 and BP2, as only BP1 was wired into the microgrid. We then quickly saw the benefits as this arrangement allows the microgrid to have visibility into all the energy used by the entire home, not just the loads directly connected to BP1.

The nice surprise came after a few days of running the system, testing and verifying proper operation, and watching all the various monitoring numbers shown in the TEG portal and the Tesla mobile app. While able to monitor the energy consumption of the entire home given the CT setup described above, we assumed the Powerwalls would only provide energy to run loads directly connected to BP1.

By switching large HVAC loads on and off in various combinations, with one HVAC unit connected to breakers in BP1 and a second HVAC unit connected to BP2, with each unit pulling about 3 kW running in heat mode, we noticed the Powerwalls were actually cranking out enough juice to run the ENTIRE HOME - not just the loads connected to BP1 on the microgrid.

At first we thought maybe a few CTs were miswired, but after some head scratching and discussion we realized that even though the TEG has a 200A maximum capacity, and even though all the home circuit breakers won’t fit into a single 200A main breaker panel due to electric code limitations, in reality our microgrid was powering ALL the loads in both BP1 and BP2.

The reason why? BP2 and the microgrid actually ARE connected together - back at the 400A meter base. Since our microgrid could see the total power being consumed by both BP1 and BP2, the Tesla software simply told the PWs to release an equal amount of output power, which then flowed to both main breaker panels - one hardwired to the TEG and the other hardwired to the meter base. So simple and so elegant - and a very nice bonus.

Posting this info to let others know that it’s possible to use a single 200A TEG to power more than one 200A breaker panel while maintains compliance with building electrical codes. With hindsight maybe this is already obvious to some, but I didn’t see any discussion of this point in previous threads and wanted to share our positive experience.

Just another reason why Tesla-powered microgrids ROCK!

Passion2Fly | 12/01/2020

Yes, I can see how this whole setup works for you. However, I would argue that this is not the recommended setup...
The installer connected the CTs to the main 400A feeder. That’s fine, however there are a few issues:
First, I don’t know if the CTs are designed for up to 400A. However, it’s very unlikely that you will ever draw that much power... so, as long as the inside diameter of the CTs work with the 400A wire size, that’s fine...
Second, the TEG is bidirectional. So, power goes both ways, which means that the PW will feed both BP1 and BP2...
Third, in case of a power outage, don’t expect the PW to feed the BP2. It won’t.
Fourth, the SW was designed for 200A. I’m not sure what will happen if the CTs read more than 200A...

Passion2Fly | 12/01/2020

Also, I hope that you don’t void the warranty with such a setup...

Patrick | 12/01/2020

Passion - the CTs are not on the 400A meter base.

Passion2Fly | 12/01/2020

Ok, I obviously didn’t catch the trick... how are the CTs connected to sens both BP1 and BP2?
« CTs on the 200A feeds to both BP1 and BP2 « 

Passion2Fly | 12/01/2020

Are BP1 and BP2 wired as sub-panels of each other? Or is there a 400A main and two separate 200A sub-panels?

ir | 13/01/2020

Thank you Patrick! I have been trying to get this answered by Tesla throughout 2019!

It means I can put my EV chargers on BP2 and still take advantage of stored solar power from BP1. But in a blackout, the EVs would be disconnected, so they don’t load down the Powerwalls.

Patrick | 13/01/2020

You’re welcome IR - glad the info was helpful. This arrangement serves our needs perfectly as well. Loads in BP2 will lose power during utility grid failures, but it’s really nice to use the batteries to power loads in both breaker panels during normal operating conditions.

Another important piece of the puzzle in our case was designing the best grid-tied solution for use with the local rural power company as they do not support net-metering. This required us to deploy a “zero export” microgrid solution as we are not allowed to send any energy back to the grid. Optimizing the utilization of PWs is especially important in this environment.

Passion - we have two separate 200A feeds extending from the 400A meter base to our microgrid room inside the home. This design decision made it easy to setup the system as described.