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!