Considering powerwall

[Jdouglas22]

Hey everyone!

I’m the typical lurker just reading people’s posts every now and then. But I have a question as I am new to all of this. I am looking into eventually getting a few powerwalls, 2 maybe 3. I’m leaning towards 3 so if a day is cloudy and production isn’t that great I can still maintain a sense of “off-grid” and make it until the next sunny day instead of having to pull from the grid at all. I am also going to do solar panels, which I would install myself. I am planning on getting the cyber truck dual motor as well. My question is that I know people size their systems and use online tools and calculators. But is there anything stopping someone from installing a (Hypothetical) 20kwh solar panel system? (Besides price) It seems that I’ve seen roughly the same size solar setups in kWh from other people. Is there a limit to how much power the powerwalls can take in from solar so the excess would just get put back into the grid? I’d like to produce enough that in a semi-sunny condition I could charge my powerwalls and cyber truck without issue or without worrying if I have enough power. Any suggestions greatly appreciated!

 

[jjrandorin]

Hey everyone!

I’m the typical lurker just reading people’s posts every now and then. But I have a question as I am new to all of this. I am looking into eventually getting a few powerwalls, 2 maybe 3. I’m leaning towards 3 so if a day is cloudy and production isn’t that great I can still maintain a sense of “off-grid” and make it until the next sunny day instead of having to pull from the grid at all. I am also going to do solar panels, which I would install myself. I am planning on getting the cyber truck dual motor as well. My question is that I know people size their systems and use online tools and calculators. But is there anything stopping someone from installing a (Hypothetical) 20kwh solar panel system? (Besides price) It seems that I’ve seen roughly the same size solar setups in kWh from other people. Is there a limit to how much power the powerwalls can take in from solar so the excess would just get put back into the grid? I’d like to produce enough that in a semi-sunny condition I could charge my powerwalls and cyber truck without issue or without worrying if I have enough power. Any suggestions greatly appreciated!

interconnect agreements (the agreement that the utility makes you sign in order to export power to the grid) usually have some sort of language in there stating that your system size needs to be what you expect to draw for the year. If you expect a large change in the next 12 months, they sometimes will have you fill out additional forms stating so.

If your yearly draw is 11,000 kW for example, you are going to have a hard time convincing them to let you install a 20k system on your garage.

 

[Jdouglas22]

interconnect agreements (tIf your yearly draw is 11,000 kW for example, you are going to have a hard time convincing them to let you install a 20k system on your garage.

Makes sense, thanks for the quick reply.

 

[Gwgan]

The typical sizes are based on multiples of inverter size. 7.6kW/inverter is common but now SolarEdge has more size options. Not all states have current use restrictions.

 

[bob_p]

When we configured our 15.4KW/4 PowerWall system, the recommendation was to have 1 PowerWall for each 4KW of solar panels.

During the spring, this was enough to operate off-grid (excluding EV charging) for 4 to 5 days, as long as we had a reasonable amount of sun. If there is a lot of cloud cover for multiple days or the temperatures are high (causing the air conditioners to run a lot), then our system won't have enough power to get through an entire day.

Our goal was to reduce our annual energy consumption by at least 50% with our system, and have enough solar/PowerWall power to operate essential systems in the house for multiple days during an extended power outage (after a hurricane).

Since we aren't generating 100% of our power, we recently shifted to a Free Nights plan, which focuses our solar and PowerWall usage during the prime daytime hours (9AM to 9PM), and uses as much grid power as possible during the free night hours (when we charge our EVs). And under that plan, we can get close to using 0 grid power during many days.

We've been on a Free Nights plan for only one month so far. Last year, the electric bill for June was $540 - this year it was $70!

 

[andy.connor.e]

I'll share my personal situation and thoughts. We have all probably heard about Vehicle to Grid coming, and i am also getting the cybertruck. My thoughts are as follows; if vehicle to grid becomes a thing, then i do not have a use for powerwalls as my outages are infrequent, and i have no immediate necessity to keep the power on when im not home. If the power goes out, i will open my garage manually, plug my cybertruck in, and have power. No big deal. That being said, im also going to get a solar roof this year, so if vehicle to grid becomes a thing then i have basically a mobile powerwall in which i also have net metering with my utility company so they also act as a powerwall in some sense that i can use excess energy production later on as if i had a powerwalls in my house. So my specific situation doesnt require them IMO. Additionally, my solar roof price came to $32,000 for 9.36kW awaiting installation date, and Tesla wanted to charge me $11,500 for 1 powerwall, or $17,500 for two powerwalls. I needed 3 powerwalls to avoid installing a sub-panel to backup specific circuits while not backing up things like stove, AC unit and such. Each powerwall can provide 5000W of power, for some reference a typical central AC unit uses about 3000W, some much more. I did not feel that nearly doubling the price of the solar roof made sense for battery backup that i really did not need. The other scenario i thought of, was that it would cost almost $20k for two powerwalls, and those are not something i can really bring with me to my next house, in which the cybertruck comes with me regardless. A roof is a sunk cost so thats how i was able to justify it.

Those were my thoughts through the process for my specific situation. I do not need to have battery backup 24/7, and my utility having net metering is in some sense an infinite annual powerwall. Some things to consider, is that you can always add powerwalls later on if you have a solar system installed and still qualify for tax credits. Yes if you dont install them this year you will miss out on 4%, and then after next year the tax incentives are gone. Another thing to consider is battery investor day is this year in September, which i (hopfully) am confident we will be shared the details of what i have touched on regarding vehicle to grid. If that does not happen, then powerwalls make all the sense in the world. Please remember these are my thoughts and opinions.

 

[jjrandorin]

I'll share my personal situation and thoughts. We have all probably heard about Vehicle to Grid coming, and i am also getting the cybertruck. My thoughts are as follows; if vehicle to grid becomes a thing, then i do not have a use for powerwalls as my outages are infrequent, and i have no immediate necessity to keep the power on when im not home. If the power goes out, i will open my garage manually, plug my cybertruck in, and have power. No big deal. That being said, im also going to get a solar roof this year, so if vehicle to grid becomes a thing then i have basically a mobile powerwall in which i also have net metering with my utility company so they also act as a powerwall in some sense that i can use excess energy production later on as if i had a powerwalls in my house. So my specific situation doesnt require them IMO. Additionally, my solar roof price came to $32,000 for 9.36kW awaiting installation date, and Tesla wanted to charge me $11,500 for 1 powerwall, or $17,500 for two powerwalls. I needed 3 powerwalls to avoid installing a sub-panel to backup specific circuits while not backing up things like stove, AC unit and such. Each powerwall can provide 5000W of power, for some reference a typical central AC unit uses about 3000W, some much more. I did not feel that nearly doubling the price of the solar roof made sense for battery backup that i really did not need. The other scenario i thought of, was that it would cost almost $20k for two powerwalls, and those are not something i can really bring with me to my next house, in which the cybertruck comes with me regardless. A roof is a sunk cost so thats how i was able to justify it.

Those were my thoughts through the process for my specific situation. I do not need to have battery backup 24/7, and my utility having net metering is in some sense an infinite annual powerwall. Some things to consider, is that you can always add powerwalls later on if you have a solar system installed and still qualify for tax credits. Yes if you dont install them this year you will miss out on 4%, and then after next year the tax incentives are gone. Another thing to consider is battery investor day is this year in September, which i (hopfully) am confident we will be shared the details of what i have touched on regarding vehicle to grid. If that does not happen, then powerwalls make all the sense in the world. Please remember these are my thoughts and opinions.

There are a lot of doubts about whether "vehicle to grid" will function like you expect. I for one do not expect it to work for anyone without in place, existing, interconnect agreements for anyone that happens to be connected to the grid at all (which is most people).

Translation, I dont think people without powerwalls (or some other permitted battery storage solution) will be plugging in their car to power their home in any capacity.

 

[BrettS]

There are a lot of doubts about whether "vehicle to grid" will function like you expect. I for one do not expect it to work for anyone without in place, existing, interconnect agreements for anyone that happens to be connected to the grid at all (which is most people).

Translation, I dont think people without powerwalls (or some other permitted battery storage solution) will be plugging in their car to power their home in any capacity.

I don’t know that an interconnect agreement would necessarily be required. I think it would more like a backup generator, where you wouldn’t need an interconnect agreement, but you absolutely would need some sort of transfer switch to make sure that you weren’t backfeeding into the grid when the grid was down.

However, if you wanted to use the car to time shift your power usage and allow it to actively feed your house while the grid was up, then an interconnect agreement might be necessary.

In either case, it’s not just a matter of enabling it in software and/or getting a different charger and magically the car becomes a powerwall. There would need to be additional hardware in place for that, like the tesla gateway that operates as an automatic transfer switch as well as manages the power flow from the powerwalls, the grid, and your solar system.

 

[andy.connor.e]

There are a lot of doubts about whether "vehicle to grid" will function like you expect. I for one do not expect it to work for anyone without in place, existing, interconnect agreements for anyone that happens to be connected to the grid at all (which is most people).

Translation, I dont think people without powerwalls (or some other permitted battery storage solution) will be plugging in their car to power their home in any capacity.

Thats a good point. I dont think there would be any reason to need an interconnect agreement if you are not back feeding the grid, but i dont know that for sure. But IMO, if you have solar and dont have an interconnect agreement to back feed excess production, that defeats alot of the benefits of generating power all day if you have nowhere to store and use it.

But you're absolutely right about the vehicle to grid part, i have no idea how it will work quite frankly. I have my hopes up, but i am not sure about anything. Its something i've considered as we should know in about 2 months. If its not revealed then, i would move forward with the assumption vehicle to grid is not a thing and powerwalls would make sense for someone to be energy independent.

 

[Jdouglas22]

I'll share my personal situation and thoughts. We have all probably heard about Vehicle to Grid coming, and i am also getting the cybertruck. My thoughts are as follows; if vehicle to grid becomes a thing, then i do not have a use for powerwalls as my outages are infrequent, and i have no immediate necessity to keep the power on when im not home. If the power goes out, i will open my garage manually, plug my cybertruck in, and have power. No big deal. That being said, im also going to get a solar roof this year, so if vehicle to grid becomes a thing then i have basically a mobile powerwall in which i also have net metering with my utility company so they also act as a powerwall in some sense that i can use excess energy production later on as if i had a powerwalls in my house. So my specific situation doesnt require them IMO. Additionally, my solar roof price came to $32,000 for 9.36kW awaiting installation date, and Tesla wanted to charge me $11,500 for 1 powerwall, or $17,500 for two powerwalls. I needed 3 powerwalls to avoid installing a sub-panel to backup specific circuits while not backing up things like stove, AC unit and such. Each powerwall can provide 5000W of power, for some reference a typical central AC unit uses about 3000W, some much more. I did not feel that nearly doubling the price of the solar roof made sense for battery backup that i really did not need. The other scenario i thought of, was that it would cost almost $20k for two powerwalls, and those are not something i can really bring with me to my next house, in which the cybertruck comes with me regardless. A roof is a sunk cost so thats how i was able to justify it.

Those were my thoughts through the process for my specific situation. I do not need to have battery backup 24/7, and my utility having net metering is in some sense an infinite annual powerwall. Some things to consider, is that you can always add powerwalls later on if you have a solar system installed and still qualify for tax credits. Yes if you dont install them this year you will miss out on 4%, and then after next year the tax incentives are gone. Another thing to consider is battery investor day is this year in September, which i (hopfully) am confident we will be shared the details of what i have touched on regarding vehicle to grid. If that does not happen, then powerwalls make all the sense in the world. Please remember these are my thoughts and opinions.

I was also hoping for a V2G, if that was the case I might have to upgrade from the dual CT to the TRI. Hypothetically it would be nice to fill up at work and drive home and plug-in and use the CT to power the house. But I had thought I had read somewhere, where Tesla could essentially become a virtual power company. Where they were really waiting till they had leverage, meaning plenty of Tesla cars to prove they have the storage capacity to fill the local power needs.

 

[bob_p]

V2G should be considered only for use as an emergency backup when the power is out.

It's unlikely Tesla Superchargers, business chargers or utility companies will allow you to charge a vehicle for free (they're paying for that electricity) and then regularly use that power for normal home usage.

Plus, regularly using a vehicle for V2G will likely have an impact on the battery warranty.

Right now, we're on a Free Nights plan with our solar/PowerWall system - and on most days, we're able to run during the day using little or no grid power, running off solar and PowerWalls. We've shifted our EV charging and as much of the other electric usage to the Free Nights period. And, I expect if many people start doing this, the utility companies will exclude homes with solar/battery storage from their Free Nights plans.

And I expect something similar would happen with V2G - businesses won't pay for electricity that ends up being used to power homes for free...

 

[Vines]

As to the OP question, both too much and too little PV is not great for a battery backup system.

Too little and you end up with not enough resources during dark winter outages.

Too much PV per battery and you may be required to frequency shift to turn a newer 20kW system into a more manageable charge rate of ,10 kW for 2 powerwalls for instance during an outage. Or even worse with an older PV system you may not be able to turn on your PV at all until you turn on loads to account for the extra power going somewhere.

4kW PV generation per Powerwall is a good broad stroke answer but it really depends on your usage profile and generation.

 

[jboy210]

I would not configure my system based on the probability that V2G will work. Right now it is a someday technology in the US. And there are a number of technology and regulatory hurdles to get over.

 

[Willy3]

Too much PV per battery and you may be required to frequency shift to turn a newer 20kW system into a more manageable charge rate of ,10 kW for 2 powerwalls for instance during an outage. Or even worse with an older PV system you may not be able to turn on your PV at all until you turn on loads to account for the extra power going somewhere.
.

There’s been a debate concerning this. Some saying there would be a frequency shift and others saying it will shut the PV and PW(s) down completely. Do you have any experience/insight?

There been two threads about it. could you comment? What is your Powerwall 2 charging rate?

 

[jjrandorin]

There’s been a debate concerning this. Some saying there would be a frequency shift and others saying it will shut the PV and PW(s) down completely. Do you have any experience/insight?

There been two threads about it. could you comment? What is your Powerwall 2 charging rate?

He did, though...

As to the OP question, both too much and too little PV is not great for a battery backup system.

Too little and you end up with not enough resources during dark winter outages.

Too much PV per battery and you may be required to frequency shift to turn a newer 20kW system into a more manageable charge rate of ,10 kW for 2 powerwalls for instance during an outage. Or even worse with an older PV system you may not be able to turn on your PV at all until you turn on loads to account for the extra power going somewhere.

4kW PV generation per Powerwall is a good broad stroke answer but it really depends on your usage profile and generation.

That covers exactly what the issue is. on a new system, the designer would have to design it to shut off part of the system during a power outage so it doesnt outpace what the powerwall can take in.

On an older system it might not turn on at all until there are extra loads... which how would you generate extra loads if the power was out to begin with?

 

[Southpasfan]

As a poster who raised the question, it is interesting that apparently no one who is reading these boards has a system where the size can produce power which exceeds 5kw times the number of powerwalls, and such person has also experienced an outage, and such person is willing to say what happened. BrettS tried to reproduce that situation, but turning off a couple of his four powerwalls did not work.

 

[jjrandorin]

As a poster who raised the question, it is interesting that apparently no one who is reading these boards has a system where the size can produce power which exceeds 5kw times the number of powerwalls, and such person has also experienced an outage, and such person is willing to say what happened. BrettS tried to reproduce that situation, but turning off a couple of his four powerwalls did not work.

There was one person who ended up in that situation. I forget the posters name at this point but I think @DrSmile pointed to them in your other thread. Their specific issue was, they were getting solar and powerwalls, and having two different vendors install them (one for solar, and one for powerwalls) but both were new installs.

If I remember correctly they didnt have enough powerwall for their solar (might be mis remembering it but thats what I remember).

The reason you really wouldnt see it often, no designer should really let it happen. They should either design the system so that part of the solar shuts down / is inaccessible, or, recommend more powerwalls.

 

[Willy3]

He did, though...



That covers exactly what the issue is. on a new system, the designer would have to design it to shut off part of the system during a power outage so it doesnt outpace what the powerwall can take in.

On an older system it might not turn on at all until there are extra loads... which how would you generate extra loads if the power was out to begin with?

I’m looking for personal experience, professional insights, evidence... something more tangible. There seems to be a lot of hypothesizing, but no one seems to know for sure one way or the other what would happen. Tesla reps have assured me that there would not be a shut down, let alone one that would disable the whole system until the grid recovered. If it was minimal, I don’t think a momentary decrease in production due to frequency shifting on the rare occasion that my usage fell below a threshold during an outage would be a deal breaker. Am I missing something?
Where I live, there are not extended outages, but I don’t want my PV system to useless during the occasional outage either. I don’t think I need as many power walls for back up as others may need and I don’t have TOU either.

 

[jjrandorin]

I’m looking for personal experience, professional insights, evidence... something more tangible. There seems to be a lot of hypothesizing, but no one seems to know for sure one way or the other what would happen. Tesla reps have assured me that there would not be a shut down, let alone one that would disable the whole system until the grid recovered. If it was minimal, I don’t think a momentary decrease in production due to frequency shifting on the rare occasion that my usage fell below a threshold during an outage would be a deal breaker. Am I missing something?
Where I live, there are not extended outages, but I don’t want my PV system to useless during the occasional outage either. I don’t think I need as many power walls for back up as others may need and I don’t have TOU either.

@Vines IS professional insights... he is in the solar industry and designs systems..... Not sure how much more tangible you want than that.

If you want more PV than roughly 5k per powerwall, you will need to have your designer design around it, to shut part of your system down in a power outage.

Its not "exactly" because you have to account for home load, etc.. If you want to put 15kW of PV but only 1 powerwall, your system design needs to disable some of your PV in a power outage.

You asked him "could you comment" when he did already, was my point.

 

[Willy3]

@Vines IS professional insights... he is in the solar industry and designs systems..... Not sure how much more tangible you want than that.

If you want more PV than roughly 5k per powerwall, you will need to have your designer design around it, to shut part of your system down in a power outage.

Its not "exactly" because you have to account for home load, etc.. If you want to put 15kW of PV but only 1 powerwall, your system design needs to disable some of your PV in a power outage.

You asked him "could you comment" when he did already, was my point.

Thank you and sorry if beating a dead horse