what is a partial home backup?

[Brad Waddell]

Hello
Does anyone here have a PowerWall partial home backup and can explain to me how it works when the grid is on?
I ordered a partial home backup system, and my understanding of this system from the sales team is that there are 2 breaker panels - one for the critical loads that goes thru the PowerWall 24/7 - and one outside the system served by the grid ONLY for my 2 30-amp AC units.
What i have now is a full home backup and the PowerWall battery is being drained by the AC running, which i think should not be happening since it is not in the critical loads panel inside the PowerWall system - it is wired to the outside panel and should be served only by the Grid.
Can anyone with a partial home backup please tell me if the non-critical loads are draining the PowerWall battery when the grid is on?
thanks much!
brad

 

[jjrandorin]

Yes, the partial backup statement is just that, "partial backup (when grid is OFF)".

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. This is the desired state for almost everyone, actually, being able to both monitor and provide power for non backed up loads when the grid is up, but not having those loads connected when the grid is down.

TL ; DR -- That is operating exactly as expected, in your case, and is usually the desired operation.

I realize that I did not answer the thread title question, really.

"What is partial backup?"

A. Partial backup is splitting the electrical loads in the home into a critical loads panel, which is backed up, and a non critical loads panel, which is not backed up and will not operate IN A GRID OUTAGE. Whether a load is monitored by the tesla gateway or not is not a function of "partial vs full backup". It is a function of whether the Current Transducers / Transformers (CTs, I can never remember what the T is in the CT), are connected in such a manner to monitor the non backed up loads.

 

[Brad Waddell]

hello jj
very helpful BUT why is it necessary or desirable for the battery to be continually pounded by the AC if it is in the non-critical loads breakers section?
Aren't they non-critical by definition and should not use the battery since the sizing is way too small?
I can't see any benefit to the battery trying to take on this hopeless task.
I was told by the sales guy when i was setting the system up that if i wanted a full home backup (which you are describing) that i would need 2 powerwalls, but i wanted to have one powerwall because i'm in las vegas, it is super hot, i want the system to remain clear of huge stress and not touch the AC loads at all.
The one powerwall is plenty of backup for my non-critical loads and works great in the winter.
I can see no reason why the system should not MEASURE the amount of grid usage by the AC - but why should the battery be pounded 24/7 by providing power for the AC rather than just measuring it?
I was told there is a diode that measures the AC power usage - and because that diode is connected, the loads are then served by the battery.
If this is the case i'd rather remove the diode and not measure the AC if it means the battery can handle the loads for which it has been designed.
advice?
brad

 

[jgleigh]

Depending on how your system is wired, you can remove your ACs from your system. In that setup, the gateway won't see them at all and they will only pull directly from the grid. They will also not report as Home usage in the app since they are invisible to the gateway at that point.

You can also set your backup reserve to 100% if you only want it to use the battery when the grid is down.

 

[jjrandorin]

hello jj
very helpful BUT why is it necessary or desirable for the battery to be continually pounded by the AC if it is in the non-critical loads breakers section?
Aren't they non-critical by definition and should not use the battery since the sizing is way too small?
I can't see any benefit to the battery trying to take on this hopeless task.
I was told by the sales guy when i was setting the system up that if i wanted a full home backup (which you are describing) that i would need 2 powerwalls, but i wanted to have one powerwall because i'm in las vegas, it is super hot, i want the system to remain clear of huge stress and not touch the AC loads at all.
The one powerwall is plenty of backup for my non-critical loads and works great in the winter.
I can see no reason why the system should not MEASURE the amount of grid usage by the AC - but why should the battery be pounded 24/7 by providing power for the AC rather than just measuring it?
I was told there is a diode that measures the AC power usage - and because that diode is connected, the loads are then served by the battery.
If this is the case i'd rather remove the diode and not measure the AC if it means the battery can handle the loads for which it has been designed.
advice?
brad

The "diode" you appear to be talking about is the CT that measures loads, and, in general, people want to be able to use their solar power to supplement their home loads when the grid is up, and they usually want to see those loads.

if the gateway cant see it, it wont try to power it, but you also wont see the draw in the app (or in any of the usage charts etc) leading to "why does the app say I used XXX energy this month by the utility says YYYY?"

If you have NO desire to see, or ever power those loads when the grid is up with your powerwall then you can ask tesla about removing the CT monitoring it but we have no idea how your home is wired electrically. You could end up losing the ability to see (or serve) anything in the backup loads panel, etc.

The reason its desirable is because right now you have options. If you dont want the powerwall to power much of those loads when the grid is up, raise your reserve, or explore using the peak / off peak etc pricing setup to get the behavior you want.

Not monitored = no options.

 

[Brad Waddell]

Depending on how your system is wired, you can remove your ACs from your system. In that setup, the gateway won't see them at all and they will only pull directly from the grid. They will also not report as Home usage in the app since they are invisible to the gateway at that point.

You can also set your backup reserve to 100% if you only want it to use the battery when the grid is down.

hi so you have your system setup this way then? AC is ignored by powerwall? can you tell me how to set that up because apparently Tesla Solar has no idea. Setting the battery to 100% would not then serve the critical loads during brownouts and spikes such so i don't want to use that option, i want the 100% clean battery filtered AC for my critical loads and security system. thanks!

 

[Brad Waddell]

The "diode" you appear to be talking about is the CT that measures loads, and, in general, people want to be able to use their solar power to supplement their home loads when the grid is up, and they usually want to see those loads.

if the gateway cant see it, it wont try to power it, but you also wont see the draw in the app (or in any of the usage charts etc) leading to "why does the app say I used XXX energy this month by the utility says YYYY?"

If you have NO desire to see, or ever power those loads when the grid is up with your powerwall then you can ask tesla about removing the CT monitoring it but we have no idea how your home is wired electrically. You could end up losing the ability to see (or serve) anything in the backup loads panel, etc.

The reason its desirable is because right now you have options. If you dont want the powerwall to power much of those loads when the grid is up, raise your reserve, or explore using the peak / off peak etc pricing setup to get the behavior you want.

Not monitored = no options.

jj - extremely helpful - thanks for getting me those very helpful details.
in my case i do not want the AC loads to affect the battery levels so that:
1. if i am overseas and there is a power outage the battery will be able to backup the critical loads. right now the battery drains to nothing at dusk. You can't sell power back to the grid if your reserve is 100%.
2. no changes in settings required if there is an extended power outage
3. no interest in seeing how much power the AC draws - i have 120% offset which means i will create more power than the entire house uses so net payments to the power company will be negative.
4. less wear and tear and heat on the PowerWall in the extreme desert heat of my garage.
i think i will get MORE control over the system when this CT is removed (or switchable) because then the PowerWall will give normal numbers like it does in the wintertime, and i will be able to use my generated solar at night without having to use the grid power because the battery will be full from solar input during the day.
i don't think the smart peak system will change based on what the AC is doing since it is not a factor in the timing of when power is sold back to the grid, that is a set schedule.
i'm just wondering why - if this CT is a measuring device - why the PowerWall attempts to power that non-critical load? It sends power over a line designed for testing results? That seems unsafe and the battery is totally undersized to make that work and it was not in the design that i chose at purchase time. Making the CT switchable seems to be the best of both worlds because i can try it both ways and so can the next owner who buys this house.
thanks!

 

[jjrandorin]

i'm just wondering why - if this CT is a measuring device - why the PowerWall attempts to power that non-critical load? It sends power over a line designed for testing results

I tried to explain that. its by design, the CT measures the load so "the system" can cover it. I have no idea if you can remove the CT that is capturing the load of your AC without removing "the rest" of your loads from monitoring. This is something you will have to ask to see if its possible. There is nothing unsafe, and it IS within the design of the system to cover those loads when the grid is up.

There is no such thing as the CT being "switchable". its either there, or its not there, monitoring the loads.

In any case, You can contact tesla to see what removing that CT will do to your system. I am betting it wont remove just the AC, but have no idea.

In any case, good luck with it.

 

[yblaser]

hi so you have your system setup this way then? AC is ignored by powerwall? can you tell me how to set that up because apparently Tesla Solar has no idea. Setting the battery to 100% would not then serve the critical loads during brownouts and spikes such so i don't want to use that option, i want the 100% clean battery filtered AC for my critical loads and security system. thanks!

When connected to the grid the powerwalls are grid-following and do not provide any sort of filtering of your power quality. If there is a power outage or significant excursion in the voltage, the gateway will disconnect you from the grid and the powerwalls will take over supplying power to your backed up loads. Depending on the exact circumstances this switch over may or may not be seemless and sensitive electronics can be affected (e.g. reboot). Once off grid the powerwalls will power your backed up loads until they are empty regardless of your reserve setting.

 

[wwu123]

All of the behavior you don't like is solely during grid-tied operation, i.e. when utility power is up, so won't affect when power is down - by definition and design, your A/C and other non-backed up loads (thus tied to the grid) CANNOT be powered during an outage, because they are outside the Gateway, which cuts itself off from the grid for safety reasons (line workers and neighbors, not you per se).

So in normal grid-tie operation, the Powerwalls can export nothing, a small amount, a lot, or max, it's all about the algorithms and modes in the software. You're operating in one of the modes where in the evening, it is exporting enough for your backed-up loads, plus exporting an additional amount goes outside the Gateway as measured by those CT's, that equals what the total of your non-backed-up loads are consuming. That includes your A/C and anything else on the non-backed-up panel.

In reality, once the electrons go out past the gateway, they are indiscriminate, whether they are powering the A/C, or say a pool pump, or going out to you neighbor, is perception; only thing that is true is if the loads need more electrons, there will be a net inflow from the meter than an outflow. So there was a mode to have your Powerwalls export less, it's just perception whether the Powerwalls are going to a pool pump or your A/C; same with electrons being pulled from the grid to make up for the net demand.

The reason I'm saying this, is that one pair of CT's may not have a way to measure all your other non-backed up loads but not measure the A/C breaker. But perhaps you can game the system modes to achieve something similar. Since you're in Vegas (my folks live there), you're probably on the flat $0.11/kwh rate; there's also not much difference in drawing less at 6 pm and drawing more at 11 pm. At the end of the day, the net effect is you want to have exported XX less kwh, and thus imported XX more from the grid; it matters little when XX is imported if on a flat rate. So XX from the A/C is of course variable per day and season. But if you have a rough cut of what is it, or conversely roughly what the other non-backed up loads draw, you could fake a high-TOU rate for a few hours in the evening, that would be enough to have the Powerwalls cover your other non-backed-up loads, but not the A/C usage. Of course if you looked at the app, it wouldn't give you the nice inflow/outflow balance you want, but you might get the net effect you want in terms of arbitrage and reserve power.

And once again, doing any of this won't impact the power outage situation at all, the Powerwall cannot power your A/C during an outage, period.

 

[jjrandorin]

Setting the battery to 100% would not then serve the critical loads during brownouts and spikes such so i don't want to use that option, i want the 100% clean battery filtered AC for my critical loads and security system.

There is no "100% clean battery filtered AC" from a system just because you have a powerwall. A brown out / Sag / spikes will impact you (also by design) unless the power frequency is dirty enough to trigger a disconnect.

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.

 

[jgleigh]

hi so you have your system setup this way then? AC is ignored by powerwall? can you tell me how to set that up because apparently Tesla Solar has no idea. Setting the battery to 100% would not then serve the critical loads during brownouts and spikes such so i don't want to use that option, i want the 100% clean battery filtered AC for my critical loads and security system. thanks!

We don't know exactly how your system is connected, so we can't recommend the best way to achieve what you want.

 

[Brad Waddell]

Since you're in Vegas (my folks live there), you're probably on the flat $0.11/kwh rate;

again my primary concern is not outages but battery wear/heat during hottest parts of the day. i want this system calm and cool.
i am on the TOU - time of use program - 5 cents per KWH except M-F 1-7pm where it is 35 cents per KWH and NV energy pays me 75% of the current rate for KWH sold during those times - so the focus is on selling during those 6 hours of weekdays - that's why i don't want the AC involved - it pounds the battery to nothing and i can't sell. Yes i understand i'm buying at the same time via the AC but this is a better solution to my needs. thanks.

 

[Brad Waddell]

We don't know exactly how your system is connected, so we can't recommend the best way to achieve what you want.

yes unfortunately neither do i! they won't show me a diagram or work-order.

 

[Brad Waddell]

There is no "100% clean battery filtered AC" from a system just because you have a powerwall. A brown out / Sag / spikes will impact you (also by design) unless the power frequency is dirty enough to trigger a disconnect.

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.

ok well that's good news then, even less drain on the battery which is my goal - a happy cool long life battery. thanks for clarification.

 

[Will792]

There is no "100% clean battery filtered AC" from a system just because you have a powerwall. A brown out / Sag / spikes will impact you (also by design) unless the power frequency is dirty enough to trigger a disconnect.

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.

Grid voltage going outside of norms (not just frequency) does trigger disconnect for at least 5 minutes.

 

[jgleigh]

yes unfortunately neither do i! they won't show me a diagram or work-order.

Get on chat and ask for the final design plans. I had mine in a few minutes.

 

[jgleigh]

again my primary concern is not outages but battery wear/heat during hottest parts of the day. i want this system calm and cool.
i am on the TOU - time of use program - 5 cents per KWH except M-F 1-7pm where it is 35 cents per KWH and NV energy pays me 75% of the current rate for KWH sold during those times - so the focus is on selling during those 6 hours of weekdays - that's why i don't want the AC involved - it pounds the battery to nothing and i can't sell. Yes i understand i'm buying at the same time via the AC but this is a better solution to my needs. thanks.

Why would you want to buy power for your AC at $0.35/kWh so you can sell power back at $0.26/kWh? I don't get it.

 

[Brad Waddell]

Why would you want to buy power for your AC at $0.35/kWh so you can sell power back at $0.26/kWh? I don't get it.

cost wise it is not perfect, but that is not the goal - the goal is long lasting battery, heat management, better handling of outages, better ability to test critical loads when isolated from other loads, and keeping the battery at the level i want. if the software could exclude those loads i would do it that way but it is not an option.

 

[Brad Waddell]

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. This is the desired state for almost everyone, actually, being able to both monitor and provide power for non backed up loads when the grid is up, but not having those loads connected when the grid is down.

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.
thanks!