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Is my Powerwall an energy vampire?

I use my Powerwall as back up only. I know it needs some energy for cooling and to top off the charge even ifI don’t have a power outage. But, the Tesla app doesn’t make it easy to see how much this energy cost is.

Does anyone have an idea? Will my standby battery energy consumption be greater because my batteries are outside in 95 degree temperatures?
 

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GenSao

Member
Aug 3, 2017
584
1,015
Pleasant Hill, CA
Unfortunately Tesla recently removed the ability to record "to Powerwall" input (charge).

Last I checked my average was about 1 KWH a day per Powerwall over a 1.5 year period. I used the difference of "From Powerwall" and "To Powewall". This excludes (deletes) the round trip cost of charging/discharge for TOU/backup usage. My two Powerwalls are located outside of the garage subject to California weather.
 
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JayClark

Member
Aug 6, 2019
258
236
Arizona
Thanks for responding GenSao. That’s equal to about half a month electric bill per year for me. Not trivial. Or conducive generating new Powerwall orders, possible why reporting it is now suppressed.

Just making sure I understand, so your house uses 2kWhrs per month (if 1kWh is half a months use), so your house uses 66 watt hrs per day (2000watts/month divided by 30 days). Since vampire losses are a concern you possibly would have been better off going with one or two $300-$500 500 watt-hour Jackery batteries to power/backup what ever is using those 66 watt-hours per day - versus a relatively huge Powerwall.

I think most people installing Powerwalls are using 500-2500 kWh's per month, thus the need for a larger battery like the Powerwall, and a turn-around loss of 1 kWh per day is more like in the 1% range for a house that uses 100Kwhrs per day (say summer in Arizona), or 2% for house that use 50kWhrs per day - if I have all my calculations correct. The numbers are not bad given those assumptions.
 
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GenSao

Member
Aug 3, 2017
584
1,015
Pleasant Hill, CA
Just making sure I understand, so your house uses 2kWhrs per month (if 1kWh is half a months use), so your house uses 66 watt hrs per day (2000watts/month divided by 30 days). You would have been better off going with one or two $300-$500 300-500 watt-hour Jackery batteries to power what ever is using those 66 watt-hours per day - versus a relatively huge Powerwall.

To clarify, the batteries roughly use 2 KWh/day for two Powerwalls. This vampire drain is used to maintain the battery (including monitoring, thermal management, battery conditioning).

My actual use is MUCH greater. Up to 1,278 KWh in one month. See below details.

Capture.JPG


As the Powerwalls server multiple purposes, I am ok with the energy loss. The combined features of max storage of 27 KWh with 10 KW (14 KW peak) power to use when the grid goes down, the use/charge of solar when the grid goes down, and TOU rate arbitrage is worth it.

The jackery batteries are too small to run our central AC unit. =)
 
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brkaus

Well-Known Member
Jul 8, 2014
8,257
6,823
Austin, TX
@GenSao Thanks for the data! Very useful. I'm considering all this stuff eventually.

Wouldn't that be different from a backup only case? You're moving energy through it so there will be losses in the conversion. Backup would just be loss from maintaining temp and any parasitics in the unit.
 
Unfortunately Tesla recently removed the ability to record "to Powerwall" input (charge).

Last I checked my average was about 1 KWH a day per Powerwall over a 1.5 year period. I used the difference of "From Powerwall" and "To Powewall". This excludes (deletes) the round trip cost of charging/discharge for TOU/backup usage. My two Powerwalls are located outside of the garage subject to California weather.
FYI, I already logged a ticket with Tesla on that and they called me last week saying they are adding it back (it's there when you select a single day). It's a bug.
 
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GenSao

Member
Aug 3, 2017
584
1,015
Pleasant Hill, CA
@GenSao Thanks for the data! Very useful. I'm considering all this stuff eventually.

Wouldn't that be different from a backup only case? You're moving energy through it so there will be losses in the conversion. Backup would just be loss from maintaining temp and any parasitics in the unit.

Yes. I subtracted 214.4 KWh (11% of 1,930 KWh) from the 511.9 kWh difference to account for the round trip energy loss.
 
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GenSao

Member
Aug 3, 2017
584
1,015
Pleasant Hill, CA
From my daily discrepancies between a RainForest Eagle-200, my utility, and the Tesla app numbers, my 2 PWs only drain ~647 Wh (together) a day. This is drain that isn't accounted for in the app's To/From grid.

That's ~19 kWh a 30-day month.

Quite a difference from my units that are outside and your that are inside (assumed from profile pic).

FYI, I already logged a ticket with Tesla on that and they called me last week saying they are adding it back (it's there when you select a single day). It's a bug.

Awesome. I'll update my table once data is back.
 
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JayClark

Member
Aug 6, 2019
258
236
Arizona
T
View attachment 456727

As the Powerwalls server multiple purposes, I am ok with the energy loss. The combined features of max storage of 27 KWh with 10 KW (14 KW peak) power to use when the grid goes down, the use/charge of solar when the grid goes down, and TOU rate arbitrage is worth it.

The jackery batteries are too small to run our central AC unit. =)

Yes, that makes sense to me, and I totally agree.

My comment about the Jackery battery was more in reference to the original poster (Alto Nimbus) who indicated their "total monthly" usage was 2kWhrs (and yet it appears they have a 13.4 kWh capacity PW for backup to cover their 66 watt hours of daily usage - actually the profile pic shows 4 PWs). I think my phone uses more than than 66 watts each day.

Anyway, Alto Nimbus wrote that might be why Tesla is "covering up" and not reporting on this data since it might slow down PW orders. It sounds like Tesla will be adding back that data point, and also maybe Alto Nimbus didn't have a good financial use case for a powerwall given such minimal household loads - yet was questioning the value based on their very "edge case" load scenario for their PW installation, and postulating that their edge case scenario would imply a reason for slowing down PW orders (i.e. demand for PWs). Something is not making sense to me with the original posters scenario or numbers, and then resulting derived implications.

Yet the vampire drain numbers from some of you is very informative, something I'm waiting to see for my system, where I have 4 PWs installed, just not turned on yet by the utility. Unlike the original poster in this thread, my household peak usage in summer in Arizona can get close to 3600 kWh's and AC is not optional and we have an electric car. I had assumed about 3-5% vampire drain, which was acceptable because of the huge cost savings given my utility companies crazy rate plans, and demand charges during peak - which I'll be avoiding entirely with the PWs.

At least in my area, the Tesla guys that wrapped our installation last week said they can no longer keep up with the PW install requests now that Tesla has apparently caught up on battery production for cars, that they can now spare batteries for Powerwalls and seem to be cranking them out for installations.

It sounds like to me Alto Nimbus is in pretty good shape, and with 4 Powerwalls (54kWhrs of backup, for 2kWhrs of monthly usage) can run their entire house for the entire duration any time they have one of those 24 month power outages. But still, it sure is a bummer about that vampire drain :) - I'm just not sure that's quite the right part of the equation to be worried about here, in Alto Nimbus's case.
 
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GenSao

Member
Aug 3, 2017
584
1,015
Pleasant Hill, CA
Yes, that makes sense to me, and I totally agree.

My comment about the Jackery battery was more in reference to the original poster (Alto Nimbus) who indicated their "total monthly" usage was 2kWhrs (and yet apparently they have a 13.4 kWh capacity PW for backup to cover their 66 watt hours of daily usage). I think my phone uses more than than 66 watts each day.

Anyway, Alto Nimbus wrote that might be why Tesla is "covering up" and not reporting on this data since it might slow down PW orders. It sounds like Tesla will be adding back that data point, and also maybe Alto Nimbus didn't have a good financial use case for a powerwall given such minimal household loads - yet was questioning the value based on their very "edge case" installation and household loads scenario, and implying that their edge case scenario would imply a reason for slowing down orders (i.e. demand for PWs).

At least in my area, the Tesla guys that wrapped our installation last week said they can no longer keep up with the PW install requests now that Tesla has apparently has caught up on battery production for cars, that they can now spare batteries for Powerwalls and seem to be cranking them out for installations.

Also, Alto Nimbus has a picture of 4 Powerwalls installed, with usage needs of 2kWrs per month. Guess they can run their house during a 24 month power outage. :)

No worries... =)

From Alto Nimbus' profile picture, I would assume he/she has 4x Powerwalls. Going back to their original question, "Will my standby battery energy consumption be greater because my batteries are outside in 95 degree temperatures?"

NuShrike states "~647 Wh (together) a day" for 2X powewalls. Presuming they are inside from their profile pic, and in simple comparison to mine, it is roughly 3X energy cost (vampire drain) to have Powerwalls outside vs. inside.
 

JayClark

Member
Aug 6, 2019
258
236
Arizona
No worries... =)

From Alto Nimbus' profile picture, I would assume he/she has 4x Powerwalls. Going back to their original question, "Will my standby battery energy consumption be greater because my batteries are outside in 95 degree temperatures?"

NuShrike states "~647 Wh (together) a day" for 2X powewalls. Presuming they are inside from their profile pic, and in simple comparison to mine, it is roughly 3X energy cost (vampire drain) to have Powerwalls outside vs. inside.

Great information. Mine are inside the garage, but in the summer it can stay hotter in there for longer, but maybe the overall daily temperature is closer to an average than the high/lows of being outside.

@NuShrike - when you're seeing ~647 Wh of drain for 2 PWs, do you have an a general idea of how much you're putting in, and taking out on those days? i.e. are you completely filling them to 100%, and draining them to 0% each day, for instance? When less is pulled from the PWs, do they have the same losses, more, or less? Just curious, a lot of questions I know.

Just wondering if the level of cycling also comes in to play, and has to be calculated. I.e. if NuShrike puts 3x amount of energy in, and takes 3x out on average, as compared to you (GenSao) that might also be a factor that has to be accounted for in addition to temperature.
 
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miimura

Well-Known Member
Aug 21, 2013
6,833
6,728
Los Altos, CA
Just for another data point, it is easy for me to see the losses in my Powerwalls when they are bouncing off the Reserve every day in the Winter. Last Winter, I observed several different days when the Powerwall charged and drained back about 5kWh across both Powerwalls and it took about 1kWh more power input that it output. So, this encompasses maintenance energy and charge/discharge losses in 40-60F weather.
 
If it is any comfort, I have an OUTBACK Skybox and it has about the same overhead. That seems to be the cost of having back up. My alternative is to turn it off but then I lose the advantage of backup if the power goes off while I am gone.
Do you have solar?
Yes, a little under the level that I’d be required to buy an insurance policy for my electric utility. 12 kw.
 
Just making sure I understand, so your house uses 2kWhrs per month (if 1kWh is half a months use), so your house uses 66 watt hrs per day (2000watts/month divided by 30 days). Since vampire losses are a concern you possibly would have been better off going with one or two $300-$500 500 watt-hour Jackery batteries to power/backup what ever is using those 66 watt-hours per day - versus a relatively huge Powerwall.

I think most people installing Powerwalls are using 500-2500 kWh's per month, thus the need for a larger battery like the Powerwall, and a turn-around loss of 1 kWh per day is more like in the 1% range for a house that uses 100Kwhrs per day (say summer in Arizona), or 2% for house that use 50kWhrs per day - if I have all my calculations correct. The numbers are not bad given those assumptions.

Sorry if I misled you. I was doubling GenSao’s usage because I had twice as many Powerwalls. That amount x 30 days x 12 months, was roughly half a months consumption, just to condition the batteries for a year. My Powerwall installation messed up the Envoy consumption monitoring I had relied on, but I’m using about 1700 kWhs per month this time of year.

Overdoing things has been my way of life. Heavy Duty, More HP then needed, etc... My wife said do something about the power outages that follow most hurricanes. Because she was unlikely to proactively manage the electric load I wanted enough power for every electric motor and high draw device to start up simultaneously.
 
Yes, that makes sense to me, and I totally agree.

My comment about the Jackery battery was more in reference to the original poster (Alto Nimbus) who indicated their "total monthly" usage was 2kWhrs (and yet it appears they have a 13.4 kWh capacity PW for backup to cover their 66 watt hours of daily usage - actually the profile pic shows 4 PWs). I think my phone uses more than than 66 watts each day.

Anyway, Alto Nimbus wrote that might be why Tesla is "covering up" and not reporting on this data since it might slow down PW orders. It sounds like Tesla will be adding back that data point, and also maybe Alto Nimbus didn't have a good financial use case for a powerwall given such minimal household loads - yet was questioning the value based on their very "edge case" load scenario for their PW installation, and postulating that their edge case scenario would imply a reason for slowing down PW orders (i.e. demand for PWs). Something is not making sense to me with the original posters scenario or numbers, and then resulting derived implications.

Yet the vampire drain numbers from some of you is very informative, something I'm waiting to see for my system, where I have 4 PWs installed, just not turned on yet by the utility. Unlike the original poster in this thread, my household peak usage in summer in Arizona can get close to 3600 kWh's and AC is not optional and we have an electric car. I had assumed about 3-5% vampire drain, which was acceptable because of the huge cost savings given my utility companies crazy rate plans, and demand charges during peak - which I'll be avoiding entirely with the PWs.

At least in my area, the Tesla guys that wrapped our installation last week said they can no longer keep up with the PW install requests now that Tesla has apparently caught up on battery production for cars, that they can now spare batteries for Powerwalls and seem to be cranking them out for installations.

It sounds like to me Alto Nimbus is in pretty good shape, and with 4 Powerwalls (54kWhrs of backup, for 2kWhrs of monthly usage) can run their entire house for the entire duration any time they have one of those 24 month power outages. But still, it sure is a bummer about that vampire drain :) - I'm just not sure that's quite the right part of the equation to be worried about here, in Alto Nimbus's case.

Sorry to mislead you. My electric use last month was 1700 kWhs. The 4 Powerwalls are for Peak Energy in the unlikely event evert thing starts simultaneously.

I worked pretty hard to get my use that low in the summer. Lots of insulation, high r rating hurricane glass. Solar operated fans ventilating the attic. High efficiency multi speed compressor AC unit. Each room is individually zoned with motion sensors and temperature sensors that know when the room is occupied and opens and closes the ac ducts in that room. The house knows when it’s not occupied and automatically resets AC temperature. It geo locates my phone to know I’m about re-enter the neighborhood and cools down again by the time I open the door. LED lights also on smart home automation system.etc, etc, etc...

That 2 kWhs figure arose from someone else’s assumptions and calculations.

So I read quit a bit about Powerwall before they were installed the end of last month. I’m learning even more from monitoring them, and the most yet from the collective insights and helpful remarks of the very intelligent members of this forum. Thank you!
 
FYI, I already logged a ticket with Tesla on that and they called me last week saying they are adding it back (it's there when you select a single day). It's a bug.

Thank you. I’m using an iPad, the “to powerwall”usage was below what the displayed showed on the screen.. I didn’t know more data was available if I scrolled down.

I have net metering so the Powerwalls are on 100% backup. By looking at the single day Powerwall consumption, I see, on some days the Powerwall will come on line once at 7 am and draw 1.8 kWh. That’s it, for the day. The next day no draw at all. This is with the Powerwall in standby only. The next day 1.5 kWh, again around 7am, just as the Enphase microinverters are waking up with the rising sun. My PV array points 180 degrees, so I’m not generating enough energy to meet what the Powerwalls are demanding, the Tesla app displays flow both from the PV array and the grid. The next day again a single spike of Powerwall draw, but this time around 3 pm, but most often it starts at at about 7:30 am and finishes about 8:45 am.

I don’t know what to make of this. Why a single spike of draw. Why not every day. 7 am is almost the coolest part of the day, but it’s still about 80 degrees outside. The Powerwalls are mounted on a North facing wall shaded from the sun. 1 Powerwall does have a little sunshine on the side of the unit in the summertime in the morning.
 

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