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what is a partial home backup?

so the battery powers non-critical loads and does not power critical loads when the grid is running - why the difference? doesn't the opposite seem more logical? why should it ever give battery power to non-critical loads?

Still seems like a wiring error to me.
The battery provides power to the house wiring, not to specific loads, critical or not. When the grid is up, the non-critical loads are connected to your house wiring through the gateway. The batteries simply put as much energy as the gateway requests into the wires which is then used by the loads. If the loads don't consume it all, the rest flows to the grid. If there isn't enough for all the loads, energy flows from the grid. In your case, the AC is included in the loads that the gateway measures to compute the power requirement, so it will ask the batteries to provide enough power to cover the AC. Does this make it clearer?


Moderator, Model 3, Tesla Energy Forums
Nov 28, 2018
Riverside Co. CA
hi jj
one contradiction just entered my mind - you said:

> What you have is a partial home backup, but your AC is running through a power line that the tesla gateway can see, and provide power for when the grid is on.

so the battery provides power for the non critical loads via the measuring device when the grid is operating.

however you also said:

> What you are describing is the type of battery backup system where all power is served through the battery backup system and that system is then re filled from other sources. Thats not how powerwalls (or other home batteries) work.

so that says the critical loads are NOT powered by the battery...

so the battery powers non-critical loads and does not power critical loads when the grid is running - why the difference? doesn't the opposite seem more logical? why should it ever give battery power to non-critical loads?

Still seems like a wiring error to me.

No, the battery powers both critical and non critical loads when the grid is up. There is no "wiring error" in your system using battery power to power all loads when the grid is up.

You were talking about "100% clean energy" and that isnt what happens. The system is not designed to run "ALL POWER' through the batteries. There is a difference in running all power through the batteries, and the batteries being able to provide power to all loads. A data center or hospital (something that can not tolerate even a little bit of switch over time to battery backup) will be setup in such a way as all power, at all times comes from the batteries, and the batteries are re filled from "sources".

Our home systems are not setup that way, and that doesnt have anything to do with the fact that the battery is setup to power loads.

An analogy would be if I was standing with you and your family, and said "I can give you some muffins for your family", I could hand you, your significant other, and any children you have each a muffin, and I would have given you all muffins.

Or, If you said "no, you will give ME all the muffins and I will hand them to my family", in this case I hand you the muffins and then you hand them to your family. In both cases they end up with the muffins, but in one case I gave them out myself (to all the loads), in the other case I handed them all to you, and you handed them out (to all the loads). In both cases all the loads got muffins.

You keep saying its mis wired, and I am telling you its not mis wired, its designed to operate that way. "Mis wired" means "wrong" and its not wrong, you just dont want it that way for <reasons> and thats up to you but its not "wrong".

In any case, I am obviously failing at explaining this, so I will again just wish you good luck with it, and encourage you to continue to find out from your installer if your specific install can be setup to remove the AC since it appears that is what you want.


Well-Known Member
Mar 10, 2016
You seem to have a fundamental misunderstanding of how Powerwalls work.

Piecing together the description of your setup from your posts, it sounds like you're using time based control to maximize cost savings during your peak period. Makes sense and a great use of Powerwalls. When your home is connected to the grid, the Powerwall will power as much of your home loads as possible during peak period from the battery, while also exporting your solar production for energy credits. It does this with ALL the loads in your home that the gateway can see, backed up or not. This is how basically everyone prefers it to operate, as the goal of time based control is cost savings.

The distinction you're trying to draw between AC load and other home load is meaningless. Actively wanting to sell power at 26 cents so you can immediately buy it back at 35 cents is not a normal use case nor a particularly sensical thing to do.

Backed up vs. not backed up circuits ONLY come into play when the grid is down. As others have said already, power does not "flow through" the battery in any sort of power conditioning way. The battery is either providing current (discharging), accepting current (charging), or doing nothing (standby) based on settings and demand - that's it.

As you've seen, your single Powerwall has insufficient storage to power your actual home loads for any meaningful amount of time with the AC running, so it no doubt is draining quickly during the daily peak period doing what you've programmed it to do. If your primary concern is health and longevity of the system, you might want to re-think using time based control at all and just using it as a backup.

Running the math - you're charging your 13kwh Powerwall in the morning with power worth 3.75 cents/kwh. Ignoring round trip losses and other such complicating nonsense, if you dump the ENTIRE Powerwall (reserve set to 0%) back out to the grid during peak time at 26 cents/kwh, you'll "earn" a little less than $3 per day by cycling the Powerwall. Now consider 10% round trip losses, the fact that your reserve is probably set to at least 20%, and really we're talking less than $2. Is that worth it? $700/year is nothing to sneeze at, but we're talking about a $7,000+ battery.

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