12.24 Kw system and one powerwall

[James88]

Current model 3 owner and looking to expand my Tesla gear!

In the starting phases of solar through Tesla yet I really only find a good ROI for the solar panels since the walls are much more and Tesla only guarantees a 10yr lifespan, I wish it was 25 to match the system.

I ordered my system 12.24kw systems with 2 walls. We probably only lose power maybe once or twice a year therefore I see the value but not around the extra cost since it will be mainly used as backup.

The idea is to at least have some functionality off grid with one wall VS no functionality from the panels.

So the question is can I get away with ONE powerwall? Can I add more later? Would it be cheaper to get an additional wall later on because there is some hardware In place?

 

[patrick40363]

Go with 2 if your budget allows.

 

[mstgkillr]

I believe you could run into issues with only one Powerwall... if the power goes out and you are producing more power than the Powerwall can handle, everything shuts down. I would definitely go with two and consider three, especially if you need to run an A/C.

And it will be more expensive for Tesla to add another Powerwall down the road.

1 Powerwall = $6,290
2 Powerwalls = $10,730, only $4,440 to add a second one
3 Powerwalls = $15,170, and $4,440 more to add a third one.

 

[Twiglett]

@James88 be careful with estimating how many powerwalls you need.
You can't just use the battery size, you also need to allow for how much power each unit can deliver.
The current Powerwall is 5kW continuous, 7kW peak
So you need to also factor in what your home needs to run.
The Tesla calculator will add powerwalls depending on how much of your home you will run - especially if you want your AC to run off the batteries.

 

[jjrandorin]

Current model 3 owner and looking to expand my Tesla gear!

In the starting phases of solar through Tesla yet I really only find a good ROI for the solar panels since the walls are much more and Tesla only guarantees a 10yr lifespan, I wish it was 25 to match the system.

I ordered my system 12.24kw systems with 2 walls. We probably only lose power maybe once or twice a year therefore I see the value but not around the extra cost since it will be mainly used as backup.

The idea is to at least have some functionality off grid with one wall VS no functionality from the panels.

So the question is can I get away with ONE powerwall? Can I add more later? Would it be cheaper to get an additional wall later on because there is some hardware In place?

Not unless your installer / system designer designs your system such that part of the SOLAR will also NOT FUNCTION during any power outage.

We have had a couple of threads on this recently, if you want to read up on exactly "why" but the TL ; DR is:


==============================
Each powerwall can only accept 5k worth of power at a time. If your power is out and your solar generates more than 5k output, the power has no where to go, so the powerwall will shut the entire system down. Would only be a "thing" when you have a power outage, and sun is shining... but that would be EXACTLY when you would expect the system to be running normally with no issues.

Can be designed around if desired by having your designer disable part of the solar in an outage.... but if you actually need "12.X" solar to run your home, you then wont have enough power to run the things you planned on running
=============================

For 12.X solar you should be getting at least 2 powerwalls, and depending on house load, 3, or alternatively, ensuring that part of your system does not run during an outage by design... which would be extremely frustrating, at least to me, to have spent "10s of thousands" of dollars, and then actually need the equipment, and only be able to have a few things on.

Discussion on this topic is in these two threads.

Considering powerwall

Just Ordered 16.32kW w/2 Powerwalls

In particular, the first link has an explanation from one of our members who works in the solar industry, and is a solar system designer for the company he works for (so not just some "shlub" like me (lol).

 

[jjrandorin]

One more thing, OP. The "10 year warranty" is a warranty that guarantees "70% usable capacity within 10 years". The system should still operate after 10 years, it just wont be under the "maintain at least 70% capacity" warranty.

Slightly different, at least to me, since the expectation would be that the system would still continue to function for many more years than 10, just with more degradation.

 

[Southpasfan]

jrandorin's cites are worth a read. In sum, the risk of not having enough poweralls is the rather strange risk that during an outage, with th sun shining, you might not either have any power, or limited power.

The risk of no power is exactly what any solar system without battery back up already has. This alone was surprising to me, but there is no question about it.

The risk of "limited power" means differnt things to different systems. You mention that you have a Model 3. One powerwall can only charge, at maximum about 1/6 of a Model 3's battery, or 50 miles.

But the real technical question is what that one Powerwall is going to do fo you during an extended outage. A central A/C system is probably out of the question. That one powerwall could run the rest of the house for some hours as long as the usage is not much.

But the real problem is that the Powerall has to curtail the PV system if its overmatched. A 12Kwh system could probably produce roughtly 60 kwh on a nice summer day, lets say. But with only one Powerwall, the mandatory shut off might mean the system only produces a fraction of that, becuase it would be shut down during the high production hours of the day, those hours when it is producing more than 5 kwh.

All of this requires math. But there is good news. These days, the price of PV and Powerwalls is less than just the PV was some years ago. This is highly subjective as to "how you look at it." But if you want to save the maximum amount of money, don't get battery back up if you want to accept the risk of outages. If you want the maximum performance, get the number of powerwalls that can handle the PV system.

 

[Vines]

Going with too little battery can certainly be an issue for some systems. You can get away with it, but the addition of another PW would be easiest now as the system is being created.

You *CAN make it work, with a newer Rule 21 complaint inverter, but you may have issues with devices that are sensitive to frequency shifting. You would frequency shift likely all day during an outage, until you started charging your car or something.

My advice is the same: Buy the second one now. If 12 kW is sized to your house load, then 1 PW will be frustratingly small both in capacity and power available to start loads. Also, the 20.8A continuous that one Powerwall can output is evenly split across both phases. It only takes overloading 1 phase before the PW trips off.

 

[James88]

One more thing, OP. The "10 year warranty" is a warranty that guarantees "70% usable capacity within 10 years". The system should still operate after 10 years, it just wont be under the "maintain at least 70% capacity" warranty.

Slightly different, at least to me, since the expectation would be that the system would still continue to function for many more years than 10, just with more degradation.

Thanks so much! I was trying to wrap my head around but it sounds like it make no sense having one PW. It's have what the system needs or skip PW and just get the panels.

I'm also curious if battery day will have any affect on PW tech and pricing.

 

[jjrandorin]

Thanks so much! I was trying to wrap my head around but it sounds like it make no sense having one PW. It's have what the system needs or skip PW and just get the panels.

I'm also curious if battery day will have any affect on PW tech and pricing.

Thats possible, for sure. No one knows. Could there be a PW 3? no idea.

 

[charlesj]

....
==============================
Each powerwall can only accept 5k worth of power at a time. If your power is out and your solar generates more than 5k output, the power has no where to go, so the powerwall will shut the entire system down. ....

That would depend on how much the house needs at the same time? If the generation is more than the PW can take and house uses, then it would shut the system down until generation is below the sum of those two numbers, no? I would suspect the air-conditioning will suck a lot of power, or not, no idea as I don't have one.

 

[jjrandorin]

That would depend on how much the house needs at the same time? If the generation is more than the PW can take and house uses, then it would shut the system down until generation is below the sum of those two numbers, no? I would suspect the air-conditioning will suck a lot of power, or not, no idea as I don't have one.

Correct... but house loads vary. Its not in doubt that this would happen in those circumstances. What needs to be confirmed is, what exactly can one do to bring oneself back online if they are in *this situation.

*this situation defined as: PV system outputting more power than Powerwall(s) can take, and house is off grid at the time (power outage, caused either by utility, or by homeowner throwing main breaker).

Some have said that you can "reset the system" somehow when in this "off grid / pv outputting more power than powerwalls can take" and it will come back online while you are still off grid. Perhaps one could somehow reboot the powerwalls and allow them to come back online, while manually throwing the breakers on the PV system (to keep it off) then introduce more home loads such that the PV could then be absorbed?

Shrug.. acedemic anyway, as any designer should not let one get into this state, as mentioned.

 

[jjrandorin]

One more thing on this (its been a somewhat hot topic recently here). On my statement "any designer should not let one get into this state". I truly believe that, however HOW that happens would likely be different between tesla and a competent third party company.

A competent third party company would likely have someone reach out to you if you ordered 12kW of PV and 1 powerwall, and say " are you sure? There are some things you might want to consider.... We can certainly do this if thats what you want, but you should know......."

If one orders 12kW from tesla and only one powerwall, what they would likely get was "Ok", and the designer would just design the system to shut off part of the PV. Maybe the home owner knows about that, maybe they dont. Maybe they dont find out till they are in a power outage and wondering why only 1/2 of their PV is active.

In both cases, the end result could be the same, but in one case, a competent third party would likely explain to a customer why they might not want to do that (whether they would be believed or not is another story, because it would seem they were just wanting to "sell more powerwalls").

Tesla would likely just take the order, and execute to what the customer ordered.

Being someone who works in a field where I "help customers" myself, (not solar), the difference people are normally talking about with "customer service" is stuff like this. Normally its "someones" job to ensure that the customer gets what they both need, and want, and understand what is being recommended to them (and even push back somewhat if the subject matter expert believes strongly in some setup or other the customer isnt considering). Removing that person makes the customer have to also perform that role, of self education, and "whats best for me", without any guidance really from tesla's end.

The fact that there is confusion on this topic, and its @Vines who is explaining it to us instead of having people say "well, tesla told me XXXXX", is very indicative of this.

Nothing wrong with tesla (I went through them myself, and like the company), but one has to decide how much of this stuff they want to "self learn" etc. where if you have a competent company helping you, it "should be" easier for you... and it will cost more, too.

/e climbs down off soapbox (lol)

 

[garrett5688]

Tesla’s online configurator does not allow picking 12kw system with only 1 Powerwall... so they probably try to disallow this from the beginning due to all the issues mentioned.

 

[gpez]

Also, the 20.8A continuous that one Powerwall can output is evenly split across both phases. It only takes overloading 1 phase before the PW trips off.

Unless I'm misreading something this statement seems to be in contradiction with the Powerwall 2 tech sheet which specifically says the Powerwall 2 can handle 30a with 100% phase imbalance (ie 0 amps on one phase and 30 on the other).

 

[Vines]

Unless I'm misreading something this statement seems to be in contradiction with the Powerwall 2 tech sheet which specifically says the Powerwall 2 can handle 30a with 100% phase imbalance (ie 0 amps on one phase and 30 on the other).

EDIT
You are correct, I misspoke. The available 20.8A at 240V can be any split, but not all 5kw is available to any single phase.
I confirmed this with Tesla. Sure it will surge to 7kw for up to 10 seconds for a real power of 29A, but that's not the operating condition for hours.

Operating is 20.8 A in any balance on 2 legs. you can pull 0A on one leg and full 20.8A on the other. For instance two plug in wall heaters set to high could overload one leg and trip the Powerwall.

Also, just pointing out that ALMOST EVERY modern PV system sold today has the ability to partially curtail the PV production. So its not a huge problem, especially if you are using the PV power overproduction for AC and house loads. This isn't a simple thing to evaluate though, and the average user in this situation just wants 2 Powerwalls.

Frequency shifting is an on off switch on older PV but all inverters installed today have this working, certainly 100% of the ones Tesla uses in a Powerwall system