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Manually conserving Powerwall energy during a grid outage via complete shutdown?

ClarDold

Member
Dec 30, 2018
24
7
Santa Rosa
In several grid outages prior to installing my Powerwalls, I was providing backup power to the house from an inverter connected to my Nissan LEAF.
I was running essential loads in the house all day, and then shutting off the inverter at night.
My refrigerator was still at 38°F in the morning, and I didn't care about anything else.
My house was drawing an average of 600 watts back then, judging from the drain of the battery in the LEAF over time.
Now that I have two Powerwalls and the Tesla app, it looks like my house has a minimal load of 800 watts. That is an accumulation of an aquarium that was added after I last paid attention to the draw, and some other parasitic loads that weren't powered from the LEAF setup.

If I allow that 800 watts to continue for 10 hours overnight, I will have lost 1/3 of my battery storage. Or is my math wrong? .8 kw times 10 hours = 8 kWh.
I would like to shut off "everything" overnight, and turn it back on when the sun starts shining, so my PV panels can recharge the Powerwalls.

What I would really like is to shut the Powerwalls off, and then immediately let them do their own attempted PV restart, as if they had run too low on battery.

I've read about other people turning off as many breakers as they can, to get rid of parasitic loads (like my DirecTV dish, sound system, networking equipment, etc.)
That seems inconvenient and as much manual intervention as I had with my standalone LEAF inverter.

If I shut them off with the little switches on the Powerwalls, I can't restart them without grid power for five minutes, or the 12 volt battery jumper inside the Gateway.
That doesn't seem like a good idea.

Does anyone else worry about the battery drain overnight during grid outage?
 

bmah

Moderator
Supporting Member
Mar 17, 2015
4,175
7,746
Lafayette, CA, USA
In several grid outages prior to installing my Powerwalls, I was providing backup power to the house from an inverter connected to my Nissan LEAF.
I was running essential loads in the house all day, and then shutting off the inverter at night.
My refrigerator was still at 38°F in the morning, and I didn't care about anything else.
My house was drawing an average of 600 watts back then, judging from the drain of the battery in the LEAF over time.
Now that I have two Powerwalls and the Tesla app, it looks like my house has a minimal load of 800 watts. That is an accumulation of an aquarium that was added after I last paid attention to the draw, and some other parasitic loads that weren't powered from the LEAF setup.

If I allow that 800 watts to continue for 10 hours overnight, I will have lost 1/3 of my battery storage. Or is my math wrong? .8 kw times 10 hours = 8 kWh.
I would like to shut off "everything" overnight, and turn it back on when the sun starts shining, so my PV panels can recharge the Powerwalls.

What I would really like is to shut the Powerwalls off, and then immediately let them do their own attempted PV restart, as if they had run too low on battery.

I've read about other people turning off as many breakers as they can, to get rid of parasitic loads (like my DirecTV dish, sound system, networking equipment, etc.)
That seems inconvenient and as much manual intervention as I had with my standalone LEAF inverter.

If I shut them off with the little switches on the Powerwalls, I can't restart them without grid power for five minutes, or the 12 volt battery jumper inside the Gateway.
That doesn't seem like a good idea.

Does anyone else worry about the battery drain overnight during grid outage?
I don't. In my thinking (and I think many other peoples' as well) part of the point of Powerwalls is to run the house during outages, at night, when there's no solar production. I'm not sure what you're saving the Powerwall's energy for, if not that. Using up 1/3 of your battery storage overnight should be fine as long as you can make that back up (and run your house) with the solar production during the day.

(Your math seems correct BTW. My house has a baseline load of around 600W, a lot of that is probably networking and servers.)

We've been through multiple PG&E PSPS scenarios, some lasting several days. We took care not to use heavy appliances during the outages, adjusted HVAC settings, and stopped charging our EVs. That was about it...we didn't go through the exercise of turning off breakers / unplugging random things because we figured those would have an insignificant effect overall.

Note that everybody's home energy situation is different. The Powerwall's current meters give you nearly instant feedback about your energy usage so you can experiment a bit to see the effect of shutting off certain loads.

Bruce.
 

arnolddeleon

Supporting Member
Supporting Member
Jul 21, 2012
892
948
SF Bay Area
What problem are you trying to solve?

Since you have a Powerwall you should have an idea what your house consumes. You also know what your PV produces in a typical day. How do those numbers compare?

I'm guessing that you have 2 Powerwalls if you consider 8 kWh 1/3 of your capacity. Is this correct? How large is your PV system? Is 0.8 kW the average for 24 hours?

Depending on how your system is wired to accomplish what you want could be a simple as flipping one breaker.
 

ClarDold

Member
Dec 30, 2018
24
7
Santa Rosa
I'm guessing that you have 2 Powerwalls if you consider 8 kWh 1/3 of your capacity. Is this correct? How large is your PV system? Is 0.8 kW the average for 24 hours?

I have two Powerwalls. I have about ~25 kWh of PV output per day at this time of year.
Some of my concern has to do with my prior experience, which was a ~15 kWh battery with no PV recharge.

I probably have enough PV energy, certainly at this time of year, maybe not on some other days. I have had enough fire smoke to flatten my PV output in the past few years.

Letting 8 kWh be used to keep the house idling while I am sleeping seems inefficient.
I would like to be able to put the Powerwall in Standby with a button in the app.
Letting it return to normal manually would be fine. It already has the ability to return to operation with the arrival of PV, which would be handy.

Date timeHome Usage (kWh)Solar Energy (kWh)From Powerwall (kWh)From Grid (kWh)To Grid (kWh)
2021-07-12T01:00:00.000-07:0030.127.311.512.921.2
 
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Electrph

Member
Aug 29, 2019
456
308
Central California
The way you've stated it here, you have a home efficiency problem, not a Powerwall problem.
agree with this ..
OP do you know what is causing 800w avg?consumption while you sleep?
I also have large aquarium (150g) .. my night consump fluctuates low as 200w to high 600w .. i know a lot of variables but you should be looking at only fridge / aquarium at night all other loads should be very little (led lights / cable box / routers / modems for me)
 

gpez

Member
Apr 25, 2019
722
589
USA
I have 1 Powerwall and my overnight loads are about the same: 800w-1200w depending when the fridge and garage freezer kick on. About 500w of that is my desktop PC, home server, security camera NAS, and various networking equipment. I'd guess another 150w is parasitic loads between TVs on standby, the Xboxes, and whatever other appliances in the house draw more power than they should while "off". There's also various fans and the outside landscaping lights that pull a few watts.

For a short term power outage over night I'll turn off the non-essential computer equipment to shed a couple hundred watt load and be careful not to leave lights on. In fact I have my home automation wired up to my Powerwall so that when there is an outage lights and some outlets automatically shut off, which is nice if I'm away or asleep. We haven't yet had anything more than a few hour outage since having the PV+PW installed but in the case of a multi-day outage I can easily see myself shutting off the main breaker to the backup loads panel overnight just so that something doesn't accidentally drain the PW without me knowing. The fridge and freezer will survive a few hours and there's really nothing else that is critical to have on, other than maybe the furnace during winter months. Shutting off that backup panel breaker won't prevent the Powerwall from recharging in the morning since the Powerwall and PV panel are on the other side of the backup panel.

In an extreme case similar to @ClarDold I have a 1250w inverter and harness for my gen2 Volt which is more than enough to run the fridge, freezer, and a couple of small things. Also good for driving to neighbors to top off their cell phones and run their fridge for a bit. I do charge extra for that service, though :)
 

Tim-in-CA

Member
Apr 23, 2018
312
140
SoCal
Can't the same be achieved by setting the Powerwall reserve setting percentage higher if the OP wants to be sure that they have enough PW reserve in the event of a power outage? For me, I keep my system in Self-Powered (as Advanced TOU doesn't seem to work properly for some reason) and set the PW reserve down to 5% as my goal is to get the MAX out of my system. My quiescent power draw is about 700-800 watt at night (1 Fridge, 1 Freezer, 2 electric point of use water heaters (4 gallons), 4x Eero Pros with MoCA adapters and MANY IOT devices). I don't tend to run the AC when I'm sleeping and so far have only had to draw from the grid a few times overnight for 2-3 hrs if batteries were depleted. Typically, I wake up with anywhere from 30-50% battery availability depending on how much AC I used during the day.
 
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jjrandorin

Moderator, Model 3, Tesla Energy Forums
Nov 28, 2018
10,328
11,670
Riverside Co. CA
Can't the same be achieved by setting the Powerwall reserve setting percentage higher if the OP wants to be sure that they have enough PW reserve in the event of a power outage? For me, I keep my system in Self-Powered (as Advanced TOU doesn't seem to work properly for some reason) and set the PW reserve down to 5% as my goal is to get the MAX out of my system. My quiescent power draw is about 700-800 watt at night (1 Fridge, 1 Freezer, 2 electric point of use water heaters (4 gallons), 4x Eero Pros with MoCA adapters and MANY IOT devices). I don't tend to run the AC when I'm sleeping and so far have only had to draw from the grid a few times overnight for 2-3 hrs if batteries were depleted. Typically, I wake up with anywhere from 30-50% battery availability depending on how much AC I used during the day.

The OP could get a feel for how much power they use on a day up until they go to sleep (how much is in the battery) then set the reserve to a limit that wont drain lower than that, IF THERE IS GRID.

The problem with that is, thats not what the OP appears to be talking about. They seem to be saying they dont want the powerwalls to be used during the night, when OFF GRID, during an outage. The powerwalls will ignore any reserve setting if you are off grid.

I still dont understand why anyone would go through the considerable expense of installing powerwalls but then want to turn them off in the middle of the night because "I only care about my fridge".

If the only concern for backup was a fridge, there are much cheaper ways to do that other than 2 powerwalls + installation. It could probably be done with a cheap, portable generator connected directly to the fridge in question or something.


So, I dont quite get it, because the main reason to buy powerwalls is either rate arbitrage, or being able to "live like normal or close to normal" when off grid, provided there is sun. Everyone has their own motivations though.
 

h2ofun

Active Member
Aug 11, 2020
2,927
558
auburn, ca
The OP could get a feel for how much power they use on a day up until they go to sleep (how much is in the battery) then set the reserve to a limit that wont drain lower than that, IF THERE IS GRID.

The problem with that is, thats not what the OP appears to be talking about. They seem to be saying they dont want the powerwalls to be used during the night, when OFF GRID, during an outage. The powerwalls will ignore any reserve setting if you are off grid.

I still dont understand why anyone would go through the considerable expense of installing powerwalls but then want to turn them off in the middle of the night because "I only care about my fridge".

If the only concern for backup was a fridge, there are much cheaper ways to do that other than 2 powerwalls + installation. It could probably be done with a cheap, portable generator connected directly to the fridge in question or something.


So, I dont quite get it, because the main reason to buy powerwalls is either rate arbitrage, or being able to "live like normal or close to normal" when off grid, provided there is sun. Everyone has their own motivations though.
Yep, this is what I have been posting since I joined, but have been ......
 

Electrph

Member
Aug 29, 2019
456
308
Central California
The OP could get a feel for how much power they use on a day up until they go to sleep (how much is in the battery) then set the reserve to a limit that wont drain lower than that, IF THERE IS GRID.

The problem with that is, thats not what the OP appears to be talking about. They seem to be saying they dont want the powerwalls to be used during the night, when OFF GRID, during an outage. The powerwalls will ignore any reserve setting if you are off grid.

I still dont understand why anyone would go through the considerable expense of installing powerwalls but then want to turn them off in the middle of the night because "I only care about my fridge".

If the only concern for backup was a fridge, there are much cheaper ways to do that other than 2 powerwalls + installation. It could probably be done with a cheap, portable generator connected directly to the fridge in question or something.


So, I dont quite get it, because the main reason to buy powerwalls is either rate arbitrage, or being able to "live like normal or close to normal" when off grid, provided there is sun. Everyone has their own motivations though.
i dont understand not wanting to "use" the pw either ... its ur money of course so do what you choose .. but mine are going to put work in everyday .. esp during an outage .. thats their time to shine 🙌🏼
 

Tim-in-CA

Member
Apr 23, 2018
312
140
SoCal
The problem with that is, thats not what the OP appears to be talking about. They seem to be saying they dont want the powerwalls to be used during the night, when OFF GRID, during an outage. The powerwalls will ignore any reserve setting if you are off grid.

I still dont understand why anyone would go through the considerable expense of installing powerwalls but then want to turn them off in the middle of the night because "I only care about my fridge".
You are correct .. I missread the OP's original requirement. And I agree that this seems like a lot of work to manage PWs just in case a grid outage happens to occur. If they have constant grid outages overnight then they have a bigger problem and as you suggested probably need other power generation methods.
 

Big Earl

bnkwupt
Supporting Member
Jul 12, 2017
5,806
10,776
Springfield, VA
You are correct .. I missread the OP's original requirement. And I agree that this seems like a lot of work to manage PWs just in case a grid outage happens to occur. If they have constant grid outages overnight then they have a bigger problem and as you suggested probably need other power generation methods.

OP is talking about shedding night load (shutting off the Powerwalls) during an outage, not in preparation for an outage.

It seems like the OP's reasoning is to minimize the waste of battery energy in the overnight hours of an outage so that more energy is available in the event of an extended, multi-day outage that overlaps with low solar production (example: multi-day outage during a fire/smoke event that reduces solar production), providing more days of autonomy in adverse conditions.

Personally, I'd just manually turn off the biggest overnight consumers, leaving the PWs on and active. If the apocalypse comes, I might rethink that strategy in favor of something yielding less parasitic loss (complete shutdown).
 

arnolddeleon

Supporting Member
Supporting Member
Jul 21, 2012
892
948
SF Bay Area
I have two Powerwalls. I have about ~25 kWh of PV output per day at this time of year.
Some of my concern has to do with my prior experience, which was a ~15 kWh battery with no PV recharge.

I probably have enough PV energy, certainly at this time of year, maybe not on some other days. I have had enough fire smoke to flatten my PV output in the past few years.

Letting 8 kWh be used to keep the house idling while I am sleeping seems inefficient.
I would like to be able to put the Powerwall in Standby with a button in the app.
Letting it return to normal manually would be fine. It already has the ability to return to operation with the arrival of PV, which would be handy.

Date timeHome Usage (kWh)Solar Energy (kWh)From Powerwall (kWh)From Grid (kWh)To Grid (kWh)
2021-07-12T01:00:00.000-07:0030.127.311.512.921.2
ok, this is quite helpful. It looks like you are close to balancing out your usage with your production.

In an outage situation if you have excess solar production it is "spilled" unlike when the grid is on where it sent there. So trying to over conserve really doesn't buy you anything once your production exceeds your usage. Remember that some of your "wasted" energy will need to be recovered anyway (e.g. refrigeration will run longer to make up the difference). During the outage you will selectively manage loads anyway (at least I would)

The one row you are showing says you used about 3 kWh more than you produced. If this is a typical day you are consuming about 1.3 kW/hour. You indicated that your "idle" use was around 800 watts. This means during other hours your usage is higher than 1.3 kW. How much of that easy to shed load if you were aware that there is an outage? If you know there is an outage would you consume 30 kWh in a day? If you are naturally going to be inside your typical production (27 kWh) then easiest thing to do overnight during an outage is nothing.

If you are in an extended outage then you can see the next day if you are replacing your usage with your generation and make adjustments accordingly.

If your Powerwalls and solar are wired to dedicated generation panel and your have separate load center it would with breaker that controls it you could shutdown your loads with one switch throw while maintaining the ability have your Powerwalls be charged automatically.

TL;DR; if I was in your shoes I wouldn't complicate things by trying to shutdown the Powerwalls during an outage.
 
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ClarDold

Member
Dec 30, 2018
24
7
Santa Rosa
being able to "live like normal or close to normal" when off grid, provided there is sun.

That is the motivation, and the reason for not letting it run overnight, in one line.

I want to be able to use Powerwalls+PV when the sun is shining, but we have had days where the fire-induced cloud cover was thick enough to cut my PV production to less than half.
I do want to live normally without the grid during the day, but I don't care about what gets power when I am asleep.

8kWh was half of my off-grid supply from my LEAF. It is 1/3 of my off-grid supply with my two Powerwalls. A single Powerwall wouldn't last from sundown to sunrise.

From other people's comments, I guess I am in the wrong mindset. The sun will come up tomorrow. Sit back, relax, offer my powerless neighbors a cold beverage.

If the sun doesn't recharge the Powerwall, I still have my LEAF.
 

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