Non-Backup side behaviour

[mikemillar]

My Powerwall 2 with Backup Gateway 2 was installed in July and is working well. I had my Model S charger wired into the NON-backup side so that the Model S didn't empty the powerwall during a night grid outage. I'm on a dual rate tariff, and in Advanced cost saving mode, so the powerwall charges from the grid during the night rate period and the car is timed to charge at night too, which it does from the grid. That all works fine. During the peak period, usually, the powerwall supplies all the house load.

I carried out an experiment today. I set the Model S to start charging during the Peak rate period. As it's wired into the NON-bbackup side, in other words directly from the electricity meter via the Gateway NON-backup side, I expected it to take tall the power from the grid, not the powerwall. The Model S cranked up to 8kW load. In fact what happened was that it drew the maximum 5kW from the powerwall and the rest, plus the house load - 3.3kW, from the grid.

Is this normal behaviour? I suppose it makes sense in that it's charging the car from the cheap rate electricity stored in the Powerwall and would only draw Peak rate electricity once the powerwall was empty, although then there would be no backup reserve left, except the reserve level set in the app.

 

[chrisbailey13]

Hope this answers your question. During normal operations, if your powerwalls are in "self powered" mode they will provide power to all circuits in in the house as long as the grid is up. The only time they will exclusively power the circuits that have been segregated for backup is if the grid is down.

The exception is if you set your powerwalls to "Backup" mode. Then, they will only provide power if the grid is down to the circuits identified to be backed up.

 

[mikemillar]

Thanks Chris. However, the Advanced modes behave rather differently from Self Powered. This is the Tesla information on priorities:
Modes of Operation With Solar
In the UK, the Powerwall 2 has now been approved for backup operation. I have read a number of posts on this forum that indicate that at least some energy utilities int heUSA don't currently permit this.

My setup has the whole house on the Backup side, except the car charger. So in the event of a power outage there is no loss of power to the house - the powerwall either continues to supply during peak rate time, or switches in during night rate time. It does this seamlessly, even my NAS keeps running. However, if there is an outage during the night period, and the Model S is charging, it stops charging because the grid power has been removed. What I didn't expect was that during the Peak rate time, the Model S, on the NON-backup side, would draw power from the Powerwall.

 

[power.saver]

If the house CTs can see the Model S load, then yes, the PW will discharge to offset that load. They don't know (or care) where the load is, they just try to offset it. If you want to avoid this, the Model S will have to be upstream of the house CTs so that it can't be "seen".

 

[mikemillar]

Thanks power.saver. On the Gateway 2 the only visible CT is on the solar feed. I assume the other CT's are built into the gateway, or probably it uses more sophisticated direct monitoring, there's certainly a lot of instant data in the api download, about 10 lines of it, like reactive power, total energy consumed etc. Since the Gateway 2 monitors grid power in/out it must be aware of NON-backup side loads I think. The white TC's on the left of the photo are for non-powerwall related things by the way.