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How long should a Powerwall maintain power in a standard 1800 sqft SFH in the event of a power failure?
- Thread starter MikeAW2010
- Start date
Short answer: Yes!
Longer answer: wow, trick question! Not answerable without more data.
Longer answer: wow, trick question! Not answerable without more data.
- To get usable an answer, what is your expected consumption? (kWh/day)
- How much solar (if any) do you have, and what are its production numbers for the time period of concern? (kWh/day, 0, if it is a blizzard...)
- How much could be throttled back if you had to? (kWh/day, leaving you at how many kWh/day)
- What time of year are we talking about (AC? Heat pump in a January snowstorm?)?
- What reserve level do you plan on running your powerwalls at?
As BGbreeder says, it all depends. If you really want a very specific answer. You'll have to do the legwork.
There are myriad home energy monitors that allow you to see your actual energy usage at an appliance or circuit level. Once you know what you will back up, you can determine how much energy those backed up items take per day, then calculate how many days of backup one ~13 kWh battery can provide you.
I posted about one option here, but there are others.
teslamotorsclub.com
For example, let's pretend the circuits that run the core household loads (refrigerator, bedrooms, living rooms, and extra refrigerators) consume an average 6 kWh per day. So with this logic, if you knew there was a power outage (and had zero solar production), one Powerwall could theoretically provide about 2 days of backup if you only focused on your core living needs.
And if you just sat in your house doing nothing but keeping your food from spoiling, you could maybe get a week of backup.
And on the other extreme, if you cook with electric, heat with electric, have air conditioning, and turned on a pool pump... you could wipe out this one battery in 2 hours.
That's why nobody can tell you how long a battery will last you. The battery just gives you some storage (which decays up to 30% over the useful life). It's up to you to figure out how long that storage can last.
For my specific house, I have 3 Powerwalls that give me about 39 kWh of stored energy potential. It turned out that in 2021 on the hottest day of the year when the air conditioners are running as hard as possible, my house pounded through 38 kWh of electricity from 3pm to midnight (9 hours).
So, my shortest backup is 9 hours. And on the other extreme... if I have solar production + aggressive load shedding, the 3 batteries could conceivably last an entire year.
There are myriad home energy monitors that allow you to see your actual energy usage at an appliance or circuit level. Once you know what you will back up, you can determine how much energy those backed up items take per day, then calculate how many days of backup one ~13 kWh battery can provide you.
I posted about one option here, but there are others.
Emporia Vue is an Interesting Companion to Solar and Powerwalls
I have been using Emporia vue for past few months now and love it. SCE also gave a $25 rebate for it. Once I found how much the dish heater from Costco consumes, I sold it the next day.
teslamotorsclub.com
For example, let's pretend the circuits that run the core household loads (refrigerator, bedrooms, living rooms, and extra refrigerators) consume an average 6 kWh per day. So with this logic, if you knew there was a power outage (and had zero solar production), one Powerwall could theoretically provide about 2 days of backup if you only focused on your core living needs.
And if you just sat in your house doing nothing but keeping your food from spoiling, you could maybe get a week of backup.
And on the other extreme, if you cook with electric, heat with electric, have air conditioning, and turned on a pool pump... you could wipe out this one battery in 2 hours.
That's why nobody can tell you how long a battery will last you. The battery just gives you some storage (which decays up to 30% over the useful life). It's up to you to figure out how long that storage can last.
For my specific house, I have 3 Powerwalls that give me about 39 kWh of stored energy potential. It turned out that in 2021 on the hottest day of the year when the air conditioners are running as hard as possible, my house pounded through 38 kWh of electricity from 3pm to midnight (9 hours).
So, my shortest backup is 9 hours. And on the other extreme... if I have solar production + aggressive load shedding, the 3 batteries could conceivably last an entire year.
Definitely going to be variable especially with the weather you have. We have a house in RR and the weather as you know it can be 80 bright and sunny one day and 30 and overcast the next, or 90, overcast and rain. We don't yet have solar on that home, so I don't currently have any specifics for Austin area weather's impact on Powerwalls.
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ucmndd
Well-Known Member
This is like asking "how long will a tank of gas last?"
I never understood how the Tesla math works there.
Given sufficient panels, If you have enough storage to last you till sun-up + 1 hour the next day, you're at infinite backup time.
Even in Winter, you're only looking at a few hours per day outage while the neighborhood is suffering during an extended outage.
Most everyone could make 2 Powerwalls last until the next morning, surely?
Given sufficient panels, If you have enough storage to last you till sun-up + 1 hour the next day, you're at infinite backup time.
Even in Winter, you're only looking at a few hours per day outage while the neighborhood is suffering during an extended outage.
Most everyone could make 2 Powerwalls last until the next morning, surely?
Depends on a number of factors. We have shading so our solar production drops from 80+ kWh/day in late June to 8-9 kWh/day in December. So even with 2 Powerwalls we cannot last the night unless we set the minimum very high such (80%). And it takes 3+ sunny winter days to charge the Powerwalls to that level.
In that part of Texas (and lots of the US east of the Rockies) it can be rainy and overcast with very hot temps and very humid at the same time. So lots of A/C usage in the rain and almost no solar production. We are definitely spoiled by our weather in California coastal areas.
Now that it's getting hot here in AZ, our production is starting to hit 50kW for the day. The Powerwalls charge to 100% by noon and even with the A/C going, we have 40% charge left come morning, (2 PWs).
EVRider-FL
Active Member
I had 2 Powerwalls initially, but based on their discharge rate after losing the sun, I didn’t think they would last until the next morning, so I added another one. I also added more panels to help charge the extra Powerwall. My home is about 2800sf in south FL.
Or like " How long will a 20 ounce tri-tip roast last for dinner? (which is why the OP is getting varying answers).
roblab
Active Member
Right. I have THREE power walls, but that's because I already knew that my house uses around 13 kwh a day (small house), and a power wall supplies around 7 kwh. Right there, I'd need two at least. For any extra consumption scenarios, I'd quickly need more, so three would be minimum. I live in only 400 sq. ft., so not much extra. A few lights, a refrigerator, a freezer in the garage, and a furnace fan. That's about it.
Most people have NO idea how much power they use per day. My house is somewhat large, but it's heated by natural gas. I live in a 20x20 area, or about the size of a garage, so this is MUCH smaller than most homes, and the only thing running would be the heater fan and a TV and my computer. But one power wall only gives you about 7.5 kwh, which is hardly enough to run anything. I'd recommend you start with three and figure you'll need more, or else figure that with a power outage you'll be able to run a few lights and that's about all.
Where I live, the power goes out often, and can stay off for days. This is why I also have SOLAR, which can help keep the batteries charged. But NO WAY will only one power wall do more than look good. Go figure what your usage is (check your electric bill) and be prepared to be shocked. You use far more than a power wall will supply, unless you figure you won't care if the freezer doesn't need to run or the heater fan can sit idle. Buy as many power walls as you can afford. My 3 cost $20K several years ago. Or, you can just do without power.
This is why Tesla won't allow people to use their cars in an outage. You'd drain your car in a day and then not be able to get out in an emergency. People don't realize how little a car battery actually holds.
Most people have NO idea how much power they use per day. My house is somewhat large, but it's heated by natural gas. I live in a 20x20 area, or about the size of a garage, so this is MUCH smaller than most homes, and the only thing running would be the heater fan and a TV and my computer. But one power wall only gives you about 7.5 kwh, which is hardly enough to run anything. I'd recommend you start with three and figure you'll need more, or else figure that with a power outage you'll be able to run a few lights and that's about all.
Where I live, the power goes out often, and can stay off for days. This is why I also have SOLAR, which can help keep the batteries charged. But NO WAY will only one power wall do more than look good. Go figure what your usage is (check your electric bill) and be prepared to be shocked. You use far more than a power wall will supply, unless you figure you won't care if the freezer doesn't need to run or the heater fan can sit idle. Buy as many power walls as you can afford. My 3 cost $20K several years ago. Or, you can just do without power.
This is why Tesla won't allow people to use their cars in an outage. You'd drain your car in a day and then not be able to get out in an emergency. People don't realize how little a car battery actually holds.
ucmndd
Well-Known Member
I think he has the original Powerwall 1 which was 6.4 kWh?
I usually make the mistake of just referring to my Powerwalls as "Powerwall". But this kind of marginalizes the actual Powerwall 1 folks lol.
I guess to be ultra-precise I should refer to my ESS as "Powerwall 2 but before Elon tweeted some random stuff about increasing battery capacity and Tesla added a +"
Not even sure where to start with this.
Yeah they could be powerwall 1s as someone above me said. We tend to refer to powerwall 2s as "powerwalls" in this subforum, but there are likely people out there with powerwall 1s. I believe the install base for this is small, at least relative to powerwall 2, but they are out there.
The rest of the post is a quite a bit of opinion and hyperbole, in my opinion anyway. There is a lot of opinion in the post you referenced that I dont agree with, but I figured I would just "agree to disagree" internally with a lot of it and move on from it.
Maybe you have an PW1 with only 6.4kWh, but the Powerwall 2/2+ have 13.5 kWh of storage. The average EV battery size is currently 60.3 kWh according to EV Database and the smallest on the list is still 16.9 kWh which is still more than a single Powerwall 2/2+. Tesla doesn't support V2H (vehicle to home) because it is complicated and they don't want to, not because of the battery size.
The only comment that is useful here is that most people don't know how much electricity they use and they should understand this first before sizing solar and ESS.
ucmndd
Well-Known Member
To the original poster..... it will be a learning experience for you, it certainly was for me.
If you are not beholden to AC, electric heat, electric dryer, electric range, and/or electric hot water in a grid outage, you should be able to keep your household consumption down around 10-12kwh daily.
I can do 10-12kwh per day comfortably in a 3200sq foot house with 2 fridges and a well pump (relying on wood and fuel oil for heat in the winter). The only real sacrifice is foregoing central AC during summer outages. Household essentials for me equates to one fridge (I unplug one of them in outages), LED lights, modem/router, TV, well pump, ceiling fans.....about a 450-500kw average draw.
During extended outages I keep an eye on the weather forecast like a hawk so I can anticipate what kind of solar production to expect the next day.
If you are not beholden to AC, electric heat, electric dryer, electric range, and/or electric hot water in a grid outage, you should be able to keep your household consumption down around 10-12kwh daily.
I can do 10-12kwh per day comfortably in a 3200sq foot house with 2 fridges and a well pump (relying on wood and fuel oil for heat in the winter). The only real sacrifice is foregoing central AC during summer outages. Household essentials for me equates to one fridge (I unplug one of them in outages), LED lights, modem/router, TV, well pump, ceiling fans.....about a 450-500kw average draw.
During extended outages I keep an eye on the weather forecast like a hawk so I can anticipate what kind of solar production to expect the next day.
I can do 10-12kwh per day comfortably in a 3200sq foot house with 2 fridges and a well pump (relying on wood and fuel oil for heat in the winter). The only real sacrifice is foregoing central AC during summer outages. Household essentials for me equates to one fridge (I unplug one of them in outages), LED lights, modem/router, TV, well pump, ceiling fans.....about a 450-500kw average draw.
I think you might have an extra "k" in there... Or that's one really big ceiling fan
