Should I get 1, or 2 powerwalls for my existing PV system?

[Jeff Hudson]

Any advice is welcome. I want to take advantage of the recent IRA and its 30% tax offset and I have an existing 6.76kW, 7yo PV system. I'm trying to decide between one or two Powerwalls. My consumption is greater than the PV system 10 months of the year. My HVAC would require two Powerwalls but I'm leaning towards one Powerwall and using my Tesla for comfortable climate control if needed. I have more considerations but I think the size of my PV system vs my consumption is the primary driver in this decision. After much thought I've come to the realization that this purchase in my particular case will be purely a consumer decision with the goal of avoiding future power outages. I've come to understand this only after a lot of thought. Oh and by the way cost is a significant part of the decision. Thanks in advance for any commentary about this decision.

 

[jboy210]

Any advice is welcome. I want to take advantage of the recent IRA and its 30% tax offset and I have an existing 6.76kW, 7yo PV system. I'm trying to decide between one or two Powerwalls. My consumption is greater than the PV system 10 months of the year. My HVAC would require two Powerwalls but I'm leaning towards one Powerwall and using my Tesla for comfortable climate control if needed. I have more considerations but I think the size of my PV system vs my consumption is the primary driver in this decision. After much thought I've come to the realization that this purchase in my particular case will be purely a consumer decision with the goal of avoiding future power outages. I've come to understand this only after a lot of thought. Oh and by the way cost is a significant part of the decision. Thanks in advance for any commentary about this decision.

In many installations, a single Powerwall will require a second "critical loads" electrical panel install to ensure you do not put too much load on the one Powerwall (5.8kW max continuous load). The critical loads panel circuits is backed up by the Powerwall and the remaining circuits are not. With 2 Powerwalls (11.6 max continuous load) you often do not need to split the loads. Be sure to factor the cost of any rewiring into your decision to go with one or two Powerwalls.

 

[cali8484]

What's your cost of electricity per kWh?

 

[ewoodrick]

Any advice is welcome. I want to take advantage of the recent IRA and its 30% tax offset and I have an existing 6.76kW, 7yo PV system. I'm trying to decide between one or two Powerwalls. My consumption is greater than the PV system 10 months of the year. My HVAC would require two Powerwalls but I'm leaning towards one Powerwall and using my Tesla for comfortable climate control if needed. I have more considerations but I think the size of my PV system vs my consumption is the primary driver in this decision. After much thought I've come to the realization that this purchase in my particular case will be purely a consumer decision with the goal of avoiding future power outages. I've come to understand this only after a lot of thought. Oh and by the way cost is a significant part of the decision. Thanks in advance for any commentary about this decision.

For power outages of any length, it is very probably that not even two Powerwalls will suffice. Air Conditioners require a LOT of power to run. I see that you are upper Alabama and I suspect that you are a prisoner to your A/C in the summer.
If you don't need your A/C, then you may be able to live with one, but not for long.

 

[holeydonut]

In many installations, a single Powerwall will require a second "critical loads" electrical panel install to ensure you do not put too much load on the one Powerwall (5.8kW max continuous load). The critical loads panel circuits is backed up by the Powerwall and the remaining circuits are not. With 2 Powerwalls (11.6 max continuous load) you often do not need to split the loads. Be sure to factor the cost of any rewiring into your decision to go with one or two Powerwalls.

In my experience, installers wouldn't include air conditioning in the backup loads unless there were 3 Powerwalls. But that was 2020 ... so maybe in 2023 Tesla's installers all recognize the burse/surge from a reasonable LRA external condensing unit can be started with 2 Powerwalls?

 

[RKCRLR]

In my experience, installers wouldn't include air conditioning in the backup loads unless there were 3 Powerwalls. But that was 2020 ... so maybe in 2023 Tesla's installers all recognize the burse/surge from a reasonable LRA external condensing unit can be started with 2 Powerwalls?

My 2020 installation of 2 Powerwalls by Tesla was supposed to back up my AC but didn't because my compressor wasn't compatible with the soft start device Tesla uses and I would up getting a 3rd Powerwall. However if the initial 2 Powerwalls had been the ones currently available there would have been no problem starting my compressor.

 

[ArizonaJon]

Check to see if you AC can do a soft start. If not, then your AC should be separated from the backup. I have 2 PWs and soft start so my AC is on backup. However, I have removed my EV EVSE (Charger) from the backup system.

 

[jboy210]

In my experience, installers wouldn't include air conditioning in the backup loads unless there were 3 Powerwalls. But that was 2020 ... so maybe in 2023 Tesla's installers all recognize the burse/surge from a reasonable LRA external condensing unit can be started with 2 Powerwalls?

My Tesla installers did in early 2020. But they installed a "soft start" device on our AC unit which lowers the peak.

 

[ucmndd]

2 powerwalls should be able to start any reasonably modern AC unit with a soft start if necessary (it wasn’t for my 4 ton dual stage 16 SEER).

As for OP, you’re gonna want two. Trust me. They’re a huge pain to add later so do it right the first time even though the cost will sting a bit.

 

[jboy210]

2 powerwalls should be able to start any reasonably modern AC unit with a soft start if necessary (it wasn’t for my 4 ton dual stage 16 SEER).

As for OP, you’re gonna want two. Trust me. They’re a huge pain to add later so do it right the first time even though the cost will sting a bit.

Yep. The first time the power cuts and the none of the lights flicker, the microwave continues running, etc. And the only way you know the power died is because of a message on your phone's Tesla app you will be glad you got 2 PWs.

 

[ewoodrick]

And then maybe 4, maybe 12, maybe 24 hours later, you'll be upset that you didn't get more, or go with a generator which can go for weeks.

 

[jboy210]

And then maybe 4, maybe 12, maybe 24 hours later, you'll be upset that you didn't get more, or go with a generator which can go for weeks.

Well, some members here have 5 or more ... So....

 

[zƬesla]

Well, some members here have 5 or more ... So....

That’s odd and prime.

Seriously, the OP should just get a Powerwall 3 like I have.

 

[patrick40363]

Any advice is welcome. I want to take advantage of the recent IRA and its 30% tax offset and I have an existing 6.76kW, 7yo PV system. I'm trying to decide between one or two Powerwalls. My consumption is greater than the PV system 10 months of the year. My HVAC would require two Powerwalls but I'm leaning towards one Powerwall and using my Tesla for comfortable climate control if needed. I have more considerations but I think the size of my PV system vs my consumption is the primary driver in this decision. After much thought I've come to the realization that this purchase in my particular case will be purely a consumer decision with the goal of avoiding future power outages. I've come to understand this only after a lot of thought. Oh and by the way cost is a significant part of the decision. Thanks in advance for any commentary about this decision.

Get 2. I have 2 and having a 3rd installed.

 

[Jeff Hudson]

Get 2. I have 2 and having a 3rd installed.

Did you give any consideration to the ratio of how much energy you generate vs how much energy you consume? For example I generated a monthly average of 608 kWh/month over the past 2 years which means ideally I average about 20 kWh/day, while during the same period I consumed an average of 1,022 kWh/month or an average of 34 kWh/day. My utility company doesn't have TOU billing. I need to find out if I need to cancel my PPA with them if I install a Powerwall(s). My point of PV interconnection is a 2nd "generation meter" and it is unclear to me how this connection could be re constructed to route generated energy to both the grid as well as through this 2nd meter which is read so that I am reimbursed for the electricity I give to the grid. This is probably too much information in this setting but I'm listening if anybody thinks they have something to add that might help me come to a decision.

 

[patrick40363]

Did you give any consideration to the ratio of how much energy you generate vs how much energy you consume? For example I generated a monthly average of 608 kWh/month over the past 2 years which means ideally I average about 20 kWh/day, while during the same period I consumed an average of 1,022 kWh/month or an average of 34 kWh/day. My utility company doesn't have TOU billing. I need to find out if I need to cancel my PPA with them if I install a Powerwall(s). My point of PV interconnection is a 2nd "generation meter" and it is unclear to me how this connection could be re constructed to route generated energy to both the grid as well as through this 2nd meter which is read so that I am reimbursed for the electricity I give to the grid. This is probably too much information in this setting but I'm listening if anybody thinks they have something to add that might help me come to a decision.

No. This year I was without grid power for 8 days. 2 powerwalls kept essential loads up but a 3rd Powerwall would have come in handy. I have a 12kw solar roof but no AC. I have net metering so don't have the same problem as you.

 

[daniel]

In my experience, installers wouldn't include air conditioning in the backup loads unless there were 3 Powerwalls. But that was 2020 ... so maybe in 2023 Tesla's installers all recognize the burse/surge from a reasonable LRA external condensing unit can be started with 2 Powerwalls?

Two Powerwalls plus whatever comes from the panels would not start my old A/C. That unit died and could not be repaired, so I replaced it with a soft-start unit, which starts just fine with my two Powerwalls. As an added advantage, it's variable, or stepped, or something, so that the hysteresis is much less. So the unit keeps the house at a more even temperature.

 

[Matt-FL]

I have four powerwalls, and I find it limiting on occasion. Granted, in an extended outage, I'd alter loads in my panel but in a house with kids, our laundry, hot water heater and AC run almost constantly. It's not uncommon to have a 15-17kw surge. I'm good on the surge front, but at times my powerwalls will go from 100% charge down to 20% in a single night because of kWh usage. If the next day is cloudy, I'm pulling from the grid at some point the next night.
My initial purchase of the powerwalls was for backup, however I've been spoiled with zero or less than zero power bills so I'm using them in deep consumption mode.

Tesla had suggested 2 powerwalls in my initial 'online' design, but that would have been subpanel and selected loads, or a SPAN panel, which almost costs as much as another PowerWall. I figured if I was doing this, I should go ahead and do it right - you know, like when you buy a boat that can support a 200hp motor but you opt for a 115hp, and then spend the rest of your ownership wishing you had just gone with the 200 . I opted for more panels than my current needs required and additional powerwalls to get that peace of mind. I'm very happy with the outcome and my decision.

 

[Jeff Hudson]

I have a question about Powerwall that I've been wondering about for a while. Are Powerwall's connected the same for every installation when solar panels are involved?

 

[Matt-FL]

I have a question about Powerwall that I've been wondering about for a while. Are Powerwall's connected the same for every installation when solar panels are involved?

They are all connected to a gateway of some sort, as a power source and power destination (depending on charging or supplying). They really only have a limited number of modes - backup reserve (which is really a sub-function of the latter two modes), self-powered or time-based control - those are controlled through the app.

As far as physically connected differences - yes, but they end up with the same functionality - charging and discharging.

For instance, my powerwalls were connected directly to the gateway using two split-220 breakers (to allow for 4 independent 220 circuits on 2 breaker slots). If you had more than 4, you would have a subpanel with a breaker for each powerwall that would supply the gateway breaker. Other vendor gateways would have their own system for attaching, but with the same result.

Actually, that makes an interesting question - anyone know of different connection methods to achieve unique results?