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Power Wall question about charging on solar

Alset2

Member
Supporting Member
Feb 20, 2020
120
39
Ocala. Fl
Hello all, I have searched but cant find the answer to this question ..
I am getting ready to pull trigger on solar system+ battery . My choice is between Tesla with 3 PWs or Local installer using 2 18kw Generac Power Cells.

Im all leaning towards Tesla and then the local installer points out that Power Walls can not "black Start"...is this an issue?

I mean it makes since but I was under the impression that during extended power outage, they all will charge battery during day as long as you have solar.

The local guy has been very upfront and honest , but this does not seem like something Tesla would over look .

I want a system , that during an extended power outage, can run off solar during the day, and battery at night. I thought they all did this , but this latest news from my local guy has me confused .

Any help or input is very welcome . There is a price difference (a big one) but It would be a waste to get a system that doesn't do what I want it to .
And the lack of responses to my question from Tesla is quickly eating away at my patience...but that is for a another thread lol

Thank you
Neil
 

jjrandorin

Moderator, Model 3, Tesla Energy Forums
Moderator
Nov 28, 2018
12,498
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Riverside Co. CA
I dont understand the question or term "black start".

Some of the confusion might be your saying "system runs off PV during the day, and batteries at night". That statement is not quite accurate for what happens.

In a power outage situation, a solar + storage system will:

1. Use the generated solar power to both power the home, and fill the storage (powerwalls or other batteries)
2. If solar is enough to power home and fill batteries, then when the batteries are full the solar will shut off (because the power has no place to go), and the home will drain some energy from the batteries.
3. Once batteries are drained a bit, the solar will kick back on and fill the battery again, then shut off.

Cycle repeats until sun goes down, then batteries power home overnight, draining, till PV comes back on with the sun.


Your statement makes it sound like you think the system, IN A POWER OUTAGE, would just have the solar "ON" all day, and the batteries in a backup situation till the sun goes down, then the batteries kick in. Thats not how any of them will work (tesla or otherwise).

PV will run house and fill batteries, and when batteries = full, PV = shut off.

If you were in a power outage, with PV + batteries, the most efficient thing to do would be to do energy draining things during the day, when the sun was up (like washing clothes, using dishwasher, maybe charging an EV a bit) if one wanted to "maximize" their PV and not have it shut off, again IN AN OUTAGE.

I keep repeating "in an outage" because operation in an outage is not the same as NOT in an outage.

The tesla system switches to powerwalls automatically, and depending on state of charge of batteries etc, may or may not be noticeable to you. "Black start", when I google it, says that its for starting up without grid. The tesla system will swap to a microgrid with no intervention from you. Not sure why they are mentioning black start to you.
 
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Congrats to your local installer for doing a good job confusing you and me, good way to sell. I am not saying one battery is better than another, they all perform the same function - provide you with power during grid outage and keep your solar system running if the sun is shining, all batteries including the PW. All batteries will get charged during grid outage including the PW, as a matter of fact some people had gone out of the way to turn off the main breaker to see how many days they could be off grid.
 
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h2ofun

Active Member
Aug 11, 2020
3,280
744
auburn, ca
Congrats to your local installer for doing a good job confusing you and me, good way to sell. I am not saying one battery is better than another, they all perform the same function - provide you with power during grid outage and keep your solar system running if the sun is shining, all batteries including the PW. All batteries will get charged during grid outage including the PW, as a matter of fact some people had gone out of the way to turn off the main breaker to see how many days they could be off grid.
I so so want to turn off my main breaker and see how long I can be off grid. It would be a long time :) But then I lose all the solar I send back to PGE, as long as we have NEM2
 
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zƬesla

Member
Apr 16, 2020
445
179
US-NH
Also unsure on the meaning of the term, but have a look at the Running Low on Energy section (and subsequent) of the following Tesla guide. Best guess, it would be related to one of these.

 
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Alset2

Member
Supporting Member
Feb 20, 2020
120
39
Ocala. Fl
Thank you for the explanation.
I Had never heard "black start " either. However ,you answered my main question and clarified how it works. I had the general idea of how it works but did not articulate it very well , but regardless, you explanation kind of confirmed that this "black Start" thing is more of a long shot to sway me from Tesla
The bottom line for me is , in an outage situation ,I want to keep power on in my house as long as the sun is shining. If Duke energy gets hacked for a week, I want to keep taking warm showers and live in an air conditioned house!! lol

Many thanks tot you for your response and I welcome any input on this choice between Tesla and local installer "A" with Generac.
I already paid my $100 deposit and have received initial layout, but I asked the to redesign it from the 16Kw system to an 18Kw system so I am now waiting on the new layout.
 

Alset2

Member
Supporting Member
Feb 20, 2020
120
39
Ocala. Fl
9E88D51429CB4080B52377771E9B473C.png





This is what the sales rep sent me via email

Even if its true, when the hell would I completely deplete my battery?
 
Just set them on self-powered, you would never draw from the grid but continue to send them excess solar produced. I’ve been on self-powered for close to 50 days since PTO and only use the grid for a few hours because I panicked during several heavy foggy days in a row. In hind sight, I should have left it in self-powered and draw not a kWh from the grid, I know better now.
 
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jjrandorin

Moderator, Model 3, Tesla Energy Forums
Moderator
Nov 28, 2018
12,498
14,893
Riverside Co. CA
Thank you for the explanation.
I Had never heard "black start " either. However ,you answered my main question and clarified how it works. I had the general idea of how it works but did not articulate it very well , but regardless, you explanation kind of confirmed that this "black Start" thing is more of a long shot to sway me from Tesla
The bottom line for me is , in an outage situation ,I want to keep power on in my house as long as the sun is shining. If Duke energy gets hacked for a week, I want to keep taking warm showers and live in an air conditioned house!! lol

Many thanks tot you for your response and I welcome any input on this choice between Tesla and local installer "A" with Generac.
I already paid my $100 deposit and have received initial layout, but I asked the to redesign it from the 16Kw system to an 18Kw system so I am now waiting on the new layout.

One thing to keep in mind is that, you need the sun for these systems to work (obviously, right?). Your statement of "if duke energy gets hacked I want to take keep taking warm showers and live in an air conditioned house", may or may not be an effective use case for solar + storage.

That would depend on how much sun you expected during that week they were hacked (what season it was), how much energy your AC uses (most of them use a LOT) and how much solar + storage you buy. I certainly am not trying to dissuade you from considering battery + storage. I have solar, and 2 powerwalls myself.

I believe that your statement above was a bit "tongue in cheek" but you likely are not running your AC the same way in an outage the way you would normally, even with solar + powerwalls, as an example. Many times people dont have a clue how much power AC units actually take, unless you are one who had measuring devices on it previously, until you see it in your app.

I personally think the tesla powerwalls are the current "best" home storage solution, once someone decides they want storage to go with their solar. Third party installers may steer people away from them simply because many of them cant get them, yet they still want to sell stuff.

I personally am not super impressed with other options for home storage (except for people who "roll their own", THAT impresses the heck out of me), but they are out there.
 

h2ofun

Active Member
Aug 11, 2020
3,280
744
auburn, ca
Just set them on self-powered, you would never draw from the grid but continue to send them excess solar produced. I’ve been on self-powered for close to 50 days since PTO and only use the grid for a few hours because I panicked during several heavy foggy days in a row. In hind sight, I should have left it in self-powered and draw not a kWh from the grid, I know better now.
I leave mine in balanced for the last 6 weeks. Been off the grid 99% of the time. I have to touch nothing
 
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Alset2

Member
Supporting Member
Feb 20, 2020
120
39
Ocala. Fl
One thing to keep in mind is that, you need the sun for these systems to work (obviously, right?). Your statement of "if duke energy gets hacked I want to take keep taking warm showers and live in an air conditioned house", may or may not be an effective use case for solar + storage.

That would depend on how much sun you expected during that week they were hacked (what season it was), how much energy your AC uses (most of them use a LOT) and how much solar + storage you buy. I certainly am not trying to dissuade you from considering battery + storage. I have solar, and 2 powerwalls myself.

I believe that your statement above was a bit "tongue in cheek" but you likely are not running your AC the same way in an outage the way you would normally, even with solar + powerwalls, as an example. Many times people dont have a clue how much power AC units actually take, unless you are one who had measuring devices on it previously, until you see it in your app.

I personally think the tesla powerwalls are the current "best" home storage solution, once someone decides they want storage to go with their solar. Third party installers may steer people away from them simply because many of them cant get them, yet they still want to sell stuff.

I personally am not super impressed with other options for home storage (except for people who "roll their own", THAT impresses the heck out of me), but they are out there.
You got exactly where I am coming from...lol
I understand all the variables but I felt like I was being told that Tesla PW and solar don't do what they do...if you know what I mean...

My only concern,so far, is their lack of response to my questions .
 

bmah

Moderator, Supercharger Hunter
Global Moderator
Mar 17, 2015
4,493
9,033
Lafayette, CA, USA
This is what the sales rep sent me via email

Even if its true, when the hell would I completely deplete my battery?

You probably wouldn't deplete your battery deliberately. But let's say you have no grid power and your house consumes all of the energy in the battery during the outage (for whatever reason...not everybody sizes their solar + battery to run off-grid indefinitely).

The issue they are talking about is in that situation, when the sun comes up, you normally need to have a little bit of energy in the battery to allow your solar inverter to turn on. I have never heard the term "black start" before (and I don't really like it, but that's another issue), but that sounds like what it refers to. It is true that Powerwalls have a bit of an issue with this, but I haven't heard of people getting into this situation very often. There's a procedure to recover from an empty battery and no grid power...I don't remember exactly what it is but I think it involves connecting a small (12V?) battery to some terminals on the gateway to give it power to start up and in turn get the inverter going.

Bruce.
 

h2ofun

Active Member
Aug 11, 2020
3,280
744
auburn, ca
You probably wouldn't deplete your battery deliberately. But let's say you have no grid power and your house consumes all of the energy in the battery during the outage (for whatever reason...not everybody sizes their solar + battery to run off-grid indefinitely).

The issue they are talking about is in that situation, when the sun comes up, you normally need to have a little bit of energy in the battery to allow your solar inverter to turn on. I have never heard the term "black start" before (and I don't really like it, but that's another issue), but that sounds like what it refers to. It is true that Powerwalls have a bit of an issue with this, but I haven't heard of people getting into this situation very often. There's a procedure to recover from an empty battery and no grid power...I don't remember exactly what it is but I think it involves connecting a small (12V?) battery to some terminals on the gateway to give it power to start up and in turn get the inverter going.

Bruce.
Seems to be a great reason to maybe never have the reserve set under 10% or does that not work that way?
 
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jjrandorin

Moderator, Model 3, Tesla Energy Forums
Moderator
Nov 28, 2018
12,498
14,893
Riverside Co. CA
Seems to be a great reason to maybe never have the reserve set under 10% or does that not work that way?
Powerwalls reserve some power to start up specifically for this reason. If they get to Zero, they shut down, and they will check periodically for power (they maintain some power for this purpose).

OP, here is the relevant page on teslas website:


While its true that powerwalls cant start like is mentioned (@bmah, after googling it appears "blackstart" is the term, shrug), it would likely be a rare occurance and unless one spends a lot of time in power outages wouldnt be a reason to choose one product over another.

OP, I spent a while in a sales role in my younger days, and that screenshot / data would be coming straight from a "overcoming objections / benefits of our product" section in sales training.
 
You probably wouldn't deplete your battery deliberately. But let's say you have no grid power and your house consumes all of the energy in the battery during the outage (for whatever reason...not everybody sizes their solar + battery to run off-grid indefinitely).

The issue they are talking about is in that situation, when the sun comes up, you normally need to have a little bit of energy in the battery to allow your solar inverter to turn on. I have never heard the term "black start" before (and I don't really like it, but that's another issue), but that sounds like what it refers to. It is true that Powerwalls have a bit of an issue with this, but I haven't heard of people getting into this situation very often. There's a procedure to recover from an empty battery and no grid power...I don't remember exactly what it is but I think it involves connecting a small (12V?) battery to some terminals on the gateway to give it power to start up and in turn get the inverter going.

Bruce.
i am unsure of how long or how truely empty a battery needs to be in order to req the above .. i can give you my one time experience with this .. when i was simulating grid outage by shutting off breaker for days or weeks at a time (pre pto / pv system with 2 powerwall 2's and gateway 2 ) i misjudged when using an electrical heater anyway battery went to "zero" at about 4 am and w/o pv power was down in house.. i did not bother turning grid breaker back on and waited to see what system would do once sun came up .. (was likely getting usable pv about 8am for that time of year so will say 4 hrs battery "zero" no pv) . my system came back on / power restored / batteries began to charge without any intervention from me.. i was carefull not to run any big loads 1st few hrs of course lest I consume more than pv putting out knock batteries back offline cause brief outage again
 

jjrandorin

Moderator, Model 3, Tesla Energy Forums
Moderator
Nov 28, 2018
12,498
14,893
Riverside Co. CA
Thank you all very much for taking time to explain this to me. I have learned a lot.

One other thing I noticed, OP.

That advertisement you linked says that the competing system has "up to 18kWh of storage", which as you likely know is "a bit more" than 1 powerwall. In your opening post, you mention you are looking at 3 powerwalls, which is 40.5kWh of storage. So, more than double the other solution.
 
Thank you all very much for taking time to explain this to me. I have learned a lot.
this is a great place to learn about real world experience with these products / get specific questions answered ...much more so than any sales brochure or often - sadly- Tesla support ...and most are eager to offer their help / experience
 
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aesculus

Still Trying to Figure This All Out
May 31, 2015
4,626
2,653
Northern California
I do like the feature that it seems to have which is one inverter for both solar and batteries and "implies" that solar goes directly to the batteries as DC vs being DC-AC-DC converted. But I am not 100% sure that is true.

Now if Tesla would add a DC bus that the car could plug into too, that would be super. In fact I would like a DC circuit throughout my house to run LED lamps and various USB like devices too. :)
 

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