New Tesla Solar & Powerwall Installation!! How many powerwalls??

[tfan2018]

For 6.12kw system, would 3 or 4 powerwalls be overkill?

 

[h2ofun]

For 6.12kw system, would 3 or 4 powerwalls be overkill?

IF you have money to blow, get 10

I believe rule of thumb is like 5kw per PW. If you cannot fill them, why get them?

 

[Caladain]

For 6.12kw system, would 3 or 4 powerwalls be overkill?

Depends on what you are using them for, and what your utility allows.
1.)if you are looking for protection from power outages, then the powerwalls will sit charged most of the time. Living in PA, having powerwalls with our grid has been super awesome (we find out we lost power when the app alerts us lol)
2.) Your utility offers a Time of Use plan that provides significant savings and also allows you to charge the powerwalls from the grid during the Super off peak times. Basically when peak starts your system switches to powerwall and charges back up at night.
3.) you want to be off the grid as much as possible.

A 6kw system, I don’t think, will charge 3 or 4 powerwalls except under the most optimal super sunny days.

 

[jjrandorin]

For 6.12kw system, would 3 or 4 powerwalls be overkill?

I would think 4 would be overkill for that relatively little PV, but I think @bmah has 3 powerwalls and a similar sized PV (if I am remembering this correctly).

 

[BGbreeder]

For 6.12kw system, would 3 or 4 powerwalls be overkill?

It isn't about overkill; it is about how large a load do you want to support for how long, and what time of year. I.e. do you have an older 5T AC that draws 120A at startup, or do you want to be able to run your AC from six to midnight off of the powerwalls?

At some point, yes, you have to factor in whether you are 100% off grid due to an outage, or whether you are trying not to use a peak rate kWh.

I have a little over 6kW of solar and three Powerwalls, which works great. The off grid 5kW "rule" that @h2ofun mentioned is the other way around. Ideally, you want to have no more than 5kW of solar per Powerwall (due to the maximum charge rate), ideally nor more than 3kW (closer to the optimal charge rate) to make best use of the solar power that you have and the maximum and optimal charging rates of Powerwalls. On grid, it doesn't matter as the excess solar gets shunted to the grid.

All the best,

BG

 

[Matt-FL]

As a reference, I have 20.4kw solar and 4 powerwalls. I am able to fully charge on ~80% of summer days (by far the highest electricity usage). I have mine set to 80/20 consumption mode (20% reserve), and during the summer I probably hit the 20% mark one day per week - usually just before the sun comes up. During the fall/winter/spring, I do much better - I rarely go below 50% by the time the sun comes up and am able to charge 95% of days.

Could I go two days in the summer without sun and grid? No, at least not without adjusting loads. In the rest of the year? Yeah, probably could.

 

[X-pilot]

I know this has been discussed 100 times, but since every situation is a bit different I wanted to get some more opinions. Installer is recommending 2 Powerwalls. 15KW Solar System. Should offset us about 92-95%. I am looking a whole house backup situation. We have 2 Air Units. I am OK not backing up our upstairs unit if need be. I have 400a service. 3000 sq ft house. Around 20,500 KW annual energy use. I live in North Carolina. Hot Summers and mostly mild winters. I just know it will never be cheaper to add a third one than now. 3 is about the max of our budget. View attachment 965963View attachment 965964View attachment 965965View attachment 965966View attachment 965967View attachment 965968

I initially wanted 4 & the "engineers" suggested 2. Well, 2 wouldn't get me through the night, so I added 2 more. Now adding a 5th. My suggestion would be to get what you can afford at the start & save the hassle of multiple permits & installation costs.

 

[GregBallantyne]

I initially wanted 4 & the "engineers" suggested 2. Well, 2 wouldn't get me through the night, so I added 2 more. Now adding a 5th. My suggestion would be to get what you can afford at the start & save the hassle of multiple permits & installation costs.

Right. I started with a contract with two, went to three before it was finished, and now am wondering about going to four after a few months of operation. And I have one 2 ton central air system, one 200A load center, and a small house. Two would have gotten me over the whole house backup threshold, three put me squarely in that space, and four would give me the luxury of getting thru a hot night with AC running, followed by a cloudy day with lower solar production and the next night, during a grid outage. Just had one of those three day outages where exactly that happened, about three weeks ago....
If I had a 4 ton HVAC unit I would be knowing I wanted four PWs. No question.

And for the OP - go with more than 15 kw production, if you can get it on the roof. You'll be glad you did - I stuffed a couple more KW onto mine, and have been glad of it ever since. I never really max out the two 7.6 kw inverters, but get consistently closer to doing that. Better production. Cost me an other $5k, but its all paid already and almost forgotten.

 

[cliftonrouse]

Right. I started with a contract with two, went to three before it was finished, and now am wondering about going to four after a few months of operation. And I have one 2 ton central air system, one 200A load center, and a small house. Two would have gotten me over the whole house backup threshold, three put me squarely in that space, and four would give me the luxury of getting thru a hot night with AC running, followed by a cloudy day with lower solar production and the next night, during a grid outage. Just had one of those three day outages where exactly that happened, about three weeks ago....
If I had a 4 ton HVAC unit I would be knowing I wanted four PWs. No question.

And for the OP - go with more than 15 kw production, if you can get it on the roof. You'll be glad you did - I stuffed a couple more KW onto mine, and have been glad of it ever since. I never really max out the two 7.6 kw inverters, but get consistently closer to doing that. Better production. Cost me an other $5k, but its all paid already and almost forgotten.

I am with you. I wanted to stay within budget. I started with a 13k system and 1 Powerwall. Now I am at a 15K system with 3 powerwalls. Probably the better thing to do, would be up the system and get 2 powerwalls. I have net metering. 1-1 ratio for 5 years.

 

[Matt-FL]

I was in the same boat! My original design was 16kw and 3 powerwalls. After Tesla and my utility fought for nine months over trying to get the PW+ inverters approved, Tesla called me and said they needed to redesign using the prior gen inverters. I said, 'well, if you're going to redesign, let's add stuff'. Adjusted to 20.4kw and 4 powerwalls. I had spent those nine months perusing forums and reading as much as I could. I was locked in with Tesla at 0.99% financing, so it didn't make much difference. And I can say without a doubt, I am very happy I requested the increase change. I'm at 123% solar offset, so I've got some room to grow. Makes a great point for a possible future EV purchase for local driving.

 

[cliftonrouse]

I was in the same boat! My original design was 16kw and 3 powerwalls. After Tesla and my utility fought for nine months over trying to get the PW+ inverters approved, Tesla called me and said they needed to redesign using the prior gen inverters. I said, 'well, if you're going to redesign, let's add stuff'. Adjusted to 20.4kw and 4 powerwalls. I had spent those nine months perusing forums and reading as much as I could. I was locked in with Tesla at 0.99% financing, so it didn't make much difference. And I can say without a doubt, I am very happy I requested the increase change. I'm at 123% solar offset, so I've got some room to grow. Makes a great point for a possible future EV purchase for local driving.

I am at 6.99% financing. We are at 92-95% offset. I think with the 3 powerwalls we can get close to 100%. I guess adding 2-3 panels wouldn't cost that much more.

 

[GregBallantyne]

I am at 6.99% financing. We are at 92-95% offset. I think with the 3 powerwalls we can get close to 100%. I guess adding 2-3 panels wouldn't cost that much more.

We've been self powering since going into operation. It hasn't been that long, and we haven't seen a winter season yet....The estimated offset percentage was lower than yours. Tesla's estimated production appears to have been low, but we haven't seen a full year so I make that statement based on projection of current generation rather than a full year's actual numbers.
I'll guess that your actual ability to self power is driven both by storage and generation capacity, but generation is the main driver. If you're looking to self power, I'd say the 3 PW's are a minimum. If you can add the panels, go for it....