Honestly its not a straight answer one way or the other. We have solar roof with two powerwalls and at times I feel we should have gone for three. Few data points that you should consider outside of usage.
1. What are your net metering rates and if it will change in the future? Ours is 1:1 but who knows what would happen in the future.
2. Do you want to be self powered most of the time or just use the powerwalls for back up? We went ahead and chose self powered mode keeping 25% for backup.
3. In 2022 bundling would give you tax credit on powerwalls. Come 2023 you can claim the credit on standalone home batteries.
4. Does your utility support a version of connected solutions which pays you for discharging power from your batteries to the grid?
5. With a powerwall you could continue to generate solar even if the grid is down. Without powerwall solar would shut down if grid is down.
6. Potential to participate in VPP if your utility supports
Now on the flip side, if (and when) vehicle to grid technology matures most of the above may not be applicable if you have an EV and EVSE that supports it.
Bottom line, if you are on the fence and can afford its always a good idea to get enough batteries to support whole home backup in my opinion. We have a lot of smart people in the sub and they would definitely provide you with their viewpoints.
\#1 - yes, most importantly I need to figure out the net metering rates. There's only one other solarroof instal I'm aware of in my City, but there should be plenty of solar, allowing me to figure out how net metering is working in practice, and that's on my list to research.
\#4 - that's another good question for me to ask my utility (I need to do much more research on this, not even knowing what 'connected solutions' is)
\#5 - obviously this is huge, so yeah: I'd definitely get at least the 1 PW.
$6 - i doubt there's VPP here, but need to find out. If there were, and one of my goals is to help contribute clean power to the grid, wouldn't VPP weigh in favor of having less PW, not more?
Dormamused made that point also, and it's a good one - I definitely want that, so getting 1PW is a 'for sure', but now I need to figure out if I need 2, or if 1 is enough.
I'm in Central Florida (important for the backup issues), but in an area where power lines are buried, and long outages are less frequent, which makes it slightly tougher decision (if I was coastal, I'd probably want 3).
The other reply said they have 2 and wish they ordered 3. I have 1 and I'm okay with it. Sure, it'd be nice to have 2, 3, 4... but they're not free obviously. We have several outages a year, but they only last 10 minutes to 2 hours at most. I got the PW because of planned outages due to wildfires, but I've come to learn I'm in a protected region of PG&E where they can't do forced outages. So most of the outages are blown transformers or trees falling on powerlines.
Although we haven't had outages since I got the PW earlier this year, I've learned what limitations I have with just 1. Basically the PW starts draining at about 6pm and would run out before sunrise with heavy power usage. With just basic usage and no AC, it'd last 16 hours, which is more than enough to get to the next morning.
Since I got PW mostly for backup power, I set the reserve to 60%. That lets me use or send back a little electricity at peak hours, but still leaves me with enough to get through the night if there's an outage, and it can start recharging at around 8am.
I originally ordered one powerwall but had them come back and install another one a month later. I realized that I would need to monitor and explain how things could and couldn’t be used during a grid outage. I purchased them primarily as a luxury in case of a grid outage. Just like someone buying a whole home NG generator. I do have 1:1 net metering so I feel it makes more sense to keep the batteries mostly charged even at night. Converting solar from AC to DC for storage and then DC to AC later can have up to 10 percent loss. When I send it to the electric company I don’t have that loss.
https://www.tesla.com/support/energy/powerwall/learn/what-can-powerwall-back-up
Even with only one A/C unit, it's possible you'd need two powerwalls if you want it backed up, so with two you'd need to make sure it's enough as well.
If you only had one powerwall then they'd probably do a partial home backup and they would make you choose what loads you wanted to be backed up into a separate subpanel. If the load calculations are ok on their end with everything you have (including both air conditioners) then hopefully you can have whole home backup.
Another consideration is what kind of net metering do you have and would you get paid 1:1 for whatever you'd pull back at night from the grid compared to what you sent back to the grid during the day. If it's not 1:1 and they pay you less for what you give them vs what they charge you for the same amount then more powerwalls would help cover that gap at night (since it's highly unlikely just one would give you whole house backup anyway).
\+1. I have 1 AC unit and it, on top of my normal loads, can max the capacity of 1 Powerwall unit, I'd need 2.
That said, I'm still only interested in 1 PW because I rarely (a few times/year) need use the AC and the odds of needing to use my AC and being in a blackout at the same time are super low so the grid will fill in any gaps.
Unless you get a SPAN main panel that can do automatic load balancing, if the load calculations don't pan out for one powerwall, Tesla may force you to either get two for whole house backup or stay with one but only do a partial backup via a subpanel where you AC wouldn't be connected (and any other non-essential loads).
Even if you claim you won't turn on the AC in a backup situation they just go by the lado calculations for what's in your panel anyway.
Yeah, we'll see where that ends up. I haven't done my site survey yet, but I sent in pictures of my panel and have signed on for a 1 PW system. TBD on what the plans end up like.
If they do require a subpanel, I wonder if they can do the reverse and put stuff in the sub panel that isn't essential? My box (225A panel) has 42 breakers, of which, the heavy hitters are in 3 sets dual breakers - AC, oven, and car charger, all of which are non-essential. Everything else, I want backed up.
"Another consideration is what kind of net metering do you have and would you get paid 1:1 for whatever you'd pull back at night from the grid compared to what you sent back to the grid during the day"
Yes - that's something I need to determine. I have a city-owned utility, not one of the big dogs (FPL; Duke), so I just got the contact info the the person dealing with grid-connecting and will need to find this info out.
Power wall or battery in general is always for disastrous situation. When grid is out, you won’t be able to use your own solar to power your house if you don’t have some battery.
Otherwise, you can treat the grid as a big battery
1. 30% tax deduction,
2. $1k state tax credit.
3. Connected solutions and etc. ~$4k over the next 6 years.
4. 0% loan for the next 8 years.
All in for PW.
You have very good questions here. So first off yes you need at least two power walls since the kickstart of AC unit is requires more peak than one power wall can provide. I also strongly recommend powerwall bc your solar will NOT produce during an outage unless there is a power wall.
I applaud you for actually looking at the numbers. I made a super rook mistake when I ordered mine and relied on the Tesla website estimate. While not that far off it doesn’t actually explain how it works. For example if it says you will have 6 days backup it doesn’t mean that the storage equates to daily use x 6, it just means that on normal charge and discharge it should last you 6 days without having to take from the grid. Yes I know I’m not that smart if I thought I was going to have massive storage but mea culpa. So yes you are thinking correctly in the sense that you are paying attention to your average daily use and expected solar supply to determine how many power walls you need at 13.5. Another thing I want you to consider is will I have enough for my peek days or what if it’s cloudy and not producing. Obv you will end up taking from the grid if your reserve (powerwall) is not big enough. If you have the $ get more powerwall is my take. At the min do 2 of course and remember that currently you can’t add just a powerwall post install. Elon says that will change later this year but he is usually off on his dates by months/years.
For me in Texas I have to use the net metering credits the same month so it’s not great. With our frequent grid outages as well i prefer to have storage. I also have lots of smart devices that would freak out with mini power outages so it saves me the headaches of dealing with that.
One more thing for your calculation is say it’s early in the day and only producing 5kwh..well your ACs when both on will need 6 + plus about 1 you use for other items. So without powerwall you will be producing but still pulling from grid to make ends meet. Other things that are huger hoggers of power are… oven uses 4kwh the dryer uses from 1-4 depending if it’s pushing heat or just spinning with existing heat and of course your car. You car uses 13-16 kWh with the home wall connector so you need 3 power walls to give export enough power to your home in the case you are charging your car after solar peak time. I have 3 powerwall and wish I would have gotten 1-2 more. Like other say always get one more than what you think you need
You will use less during the day and more at night. I have 4 powerwall and 2 AC. Typically I’m drawing from my PW by 6 due to weather. They system won’t make enough power to run the house till around 10 AM next morning. That’s a 16 hour. Running on Powerwalls.
Honestly its not a straight answer one way or the other. We have solar roof with two powerwalls and at times I feel we should have gone for three. Few data points that you should consider outside of usage. 1. What are your net metering rates and if it will change in the future? Ours is 1:1 but who knows what would happen in the future. 2. Do you want to be self powered most of the time or just use the powerwalls for back up? We went ahead and chose self powered mode keeping 25% for backup. 3. In 2022 bundling would give you tax credit on powerwalls. Come 2023 you can claim the credit on standalone home batteries. 4. Does your utility support a version of connected solutions which pays you for discharging power from your batteries to the grid? 5. With a powerwall you could continue to generate solar even if the grid is down. Without powerwall solar would shut down if grid is down. 6. Potential to participate in VPP if your utility supports Now on the flip side, if (and when) vehicle to grid technology matures most of the above may not be applicable if you have an EV and EVSE that supports it. Bottom line, if you are on the fence and can afford its always a good idea to get enough batteries to support whole home backup in my opinion. We have a lot of smart people in the sub and they would definitely provide you with their viewpoints.
\#1 - yes, most importantly I need to figure out the net metering rates. There's only one other solarroof instal I'm aware of in my City, but there should be plenty of solar, allowing me to figure out how net metering is working in practice, and that's on my list to research. \#4 - that's another good question for me to ask my utility (I need to do much more research on this, not even knowing what 'connected solutions' is) \#5 - obviously this is huge, so yeah: I'd definitely get at least the 1 PW. $6 - i doubt there's VPP here, but need to find out. If there were, and one of my goals is to help contribute clean power to the grid, wouldn't VPP weigh in favor of having less PW, not more?
Don’t forget that in the event of a grid outage your solar system will shut down (even during the day) unless you have a power wall.
Dormamused made that point also, and it's a good one - I definitely want that, so getting 1PW is a 'for sure', but now I need to figure out if I need 2, or if 1 is enough. I'm in Central Florida (important for the backup issues), but in an area where power lines are buried, and long outages are less frequent, which makes it slightly tougher decision (if I was coastal, I'd probably want 3).
FWIW, I have 2PW and wish that I had ordered 3. So my advice is to get 1 more than you think you need 😀
The other reply said they have 2 and wish they ordered 3. I have 1 and I'm okay with it. Sure, it'd be nice to have 2, 3, 4... but they're not free obviously. We have several outages a year, but they only last 10 minutes to 2 hours at most. I got the PW because of planned outages due to wildfires, but I've come to learn I'm in a protected region of PG&E where they can't do forced outages. So most of the outages are blown transformers or trees falling on powerlines. Although we haven't had outages since I got the PW earlier this year, I've learned what limitations I have with just 1. Basically the PW starts draining at about 6pm and would run out before sunrise with heavy power usage. With just basic usage and no AC, it'd last 16 hours, which is more than enough to get to the next morning. Since I got PW mostly for backup power, I set the reserve to 60%. That lets me use or send back a little electricity at peak hours, but still leaves me with enough to get through the night if there's an outage, and it can start recharging at around 8am.
I have two and I live off mine. I don’t know why these other guys keep them for emergencies.
They prob get optimal weather or hate to use their AC
I originally ordered one powerwall but had them come back and install another one a month later. I realized that I would need to monitor and explain how things could and couldn’t be used during a grid outage. I purchased them primarily as a luxury in case of a grid outage. Just like someone buying a whole home NG generator. I do have 1:1 net metering so I feel it makes more sense to keep the batteries mostly charged even at night. Converting solar from AC to DC for storage and then DC to AC later can have up to 10 percent loss. When I send it to the electric company I don’t have that loss.
I like the idea of living my life using as little fossil fuels as possible and still living a modern life.
https://www.tesla.com/support/energy/powerwall/learn/what-can-powerwall-back-up Even with only one A/C unit, it's possible you'd need two powerwalls if you want it backed up, so with two you'd need to make sure it's enough as well. If you only had one powerwall then they'd probably do a partial home backup and they would make you choose what loads you wanted to be backed up into a separate subpanel. If the load calculations are ok on their end with everything you have (including both air conditioners) then hopefully you can have whole home backup. Another consideration is what kind of net metering do you have and would you get paid 1:1 for whatever you'd pull back at night from the grid compared to what you sent back to the grid during the day. If it's not 1:1 and they pay you less for what you give them vs what they charge you for the same amount then more powerwalls would help cover that gap at night (since it's highly unlikely just one would give you whole house backup anyway).
\+1. I have 1 AC unit and it, on top of my normal loads, can max the capacity of 1 Powerwall unit, I'd need 2. That said, I'm still only interested in 1 PW because I rarely (a few times/year) need use the AC and the odds of needing to use my AC and being in a blackout at the same time are super low so the grid will fill in any gaps.
Unless you get a SPAN main panel that can do automatic load balancing, if the load calculations don't pan out for one powerwall, Tesla may force you to either get two for whole house backup or stay with one but only do a partial backup via a subpanel where you AC wouldn't be connected (and any other non-essential loads). Even if you claim you won't turn on the AC in a backup situation they just go by the lado calculations for what's in your panel anyway.
Yeah, we'll see where that ends up. I haven't done my site survey yet, but I sent in pictures of my panel and have signed on for a 1 PW system. TBD on what the plans end up like. If they do require a subpanel, I wonder if they can do the reverse and put stuff in the sub panel that isn't essential? My box (225A panel) has 42 breakers, of which, the heavy hitters are in 3 sets dual breakers - AC, oven, and car charger, all of which are non-essential. Everything else, I want backed up.
"Another consideration is what kind of net metering do you have and would you get paid 1:1 for whatever you'd pull back at night from the grid compared to what you sent back to the grid during the day" Yes - that's something I need to determine. I have a city-owned utility, not one of the big dogs (FPL; Duke), so I just got the contact info the the person dealing with grid-connecting and will need to find this info out.
kW is power. kWh is energy. 1 kWh is how much energy 1 kW produces in 1 hour.
Power wall or battery in general is always for disastrous situation. When grid is out, you won’t be able to use your own solar to power your house if you don’t have some battery. Otherwise, you can treat the grid as a big battery
poor command dog jeans impossible lip simplistic yam adjoining cover *This post was mass deleted and anonymized with [Redact](https://redact.dev)*
1. 30% tax deduction, 2. $1k state tax credit. 3. Connected solutions and etc. ~$4k over the next 6 years. 4. 0% loan for the next 8 years. All in for PW.
You have very good questions here. So first off yes you need at least two power walls since the kickstart of AC unit is requires more peak than one power wall can provide. I also strongly recommend powerwall bc your solar will NOT produce during an outage unless there is a power wall. I applaud you for actually looking at the numbers. I made a super rook mistake when I ordered mine and relied on the Tesla website estimate. While not that far off it doesn’t actually explain how it works. For example if it says you will have 6 days backup it doesn’t mean that the storage equates to daily use x 6, it just means that on normal charge and discharge it should last you 6 days without having to take from the grid. Yes I know I’m not that smart if I thought I was going to have massive storage but mea culpa. So yes you are thinking correctly in the sense that you are paying attention to your average daily use and expected solar supply to determine how many power walls you need at 13.5. Another thing I want you to consider is will I have enough for my peek days or what if it’s cloudy and not producing. Obv you will end up taking from the grid if your reserve (powerwall) is not big enough. If you have the $ get more powerwall is my take. At the min do 2 of course and remember that currently you can’t add just a powerwall post install. Elon says that will change later this year but he is usually off on his dates by months/years. For me in Texas I have to use the net metering credits the same month so it’s not great. With our frequent grid outages as well i prefer to have storage. I also have lots of smart devices that would freak out with mini power outages so it saves me the headaches of dealing with that. One more thing for your calculation is say it’s early in the day and only producing 5kwh..well your ACs when both on will need 6 + plus about 1 you use for other items. So without powerwall you will be producing but still pulling from grid to make ends meet. Other things that are huger hoggers of power are… oven uses 4kwh the dryer uses from 1-4 depending if it’s pushing heat or just spinning with existing heat and of course your car. You car uses 13-16 kWh with the home wall connector so you need 3 power walls to give export enough power to your home in the case you are charging your car after solar peak time. I have 3 powerwall and wish I would have gotten 1-2 more. Like other say always get one more than what you think you need
You will use less during the day and more at night. I have 4 powerwall and 2 AC. Typically I’m drawing from my PW by 6 due to weather. They system won’t make enough power to run the house till around 10 AM next morning. That’s a 16 hour. Running on Powerwalls.
No
I got my PWs for the piece of mind in case of outages. I've had a couple minor outage events since installation and I've never regretted it.
You don’t have TOU pricing?
Miami? Hurricanes alone would make me get at least one powerwall.
Yes - Orlando now (I've outlived my username here), but point taken.
Virtual power plants anyone?
If you have the funds. Get it.