Is Telsa proposing the right thing for my Powerwall installation?

[Jeff P]

Long time listener, first time caller in the energy category. Last year I had Tesla install a 10 kW solar system, and it was a pretty terrible experience. One inverter was wired incorrectly, the other was configured incorrectly, so I was actually capturing less than half of what the system could produce. Then they wouldn't come out to check it because they had not heard from the utility, even though a tech had seen the door tag, so they wouldn't turn on monitoring. To top it off, they underprovisioned one of the inverters, so I'm clipping an hour or two a day in typical Florida sun, probably missing out on a kWh or 2 every day.

So while my trust with Tesla is already pretty low given how inept they were with the install, after two years of waiting for a Powerwall 2 earned by referral, they're ready put one in for me. My solar setup consists of two parts: 4 kW of panels on a 4.2 kW inverter, and 6 kW of panels on a 5 kW inverter. I don't fully understand what happens between the inverters and the meter, but from the mains there are two 150 amp panels and a 40 amp circuit directly to one of my AC pumps outside (the second one is wired to one of the panels, which doesn't make a lot of sense to me).

For my "free" Powerwall, which I'll have to pay them to install, they're saying that in a power outage situation, only the 5 kW inverter can feed my house, so I'll lose half of my generation while disconnected from the grid. I realize the Powerwall can only take something like 7 kW as an input, but that they can't make this work leaves me skeptical.

I do realize that the Powerwall probably requires some circuit shuffling so it can power just the essentials in an extended outage (think hurricane), but the suggestion that I have to leave half the solar system idle, unless I buy a second unit of course, leaves me feeling like their system is terrible or they just don't know what they're doing.

Any thoughts or suggestions?

 

[cwied]

I'm sure some of the more technical folks on this board will chime in, but in a nutshell what they're saying makes sense. The issue is that at this point, the Powerwall can't roll back the solar production partially. It's either on or off. This means that in order to prevent the solar from overloading the Powerwall's capacity, it'd have trouble letting the full 10 kW system run. I also suspect that they're worried the solar inverter will not react quickly enough to the Powerwall's frequency shift and could cause issues if the solar production is higher than the Powerwall's input capacity.

I believe it is normal that they will not install with more generation capacity on the backup panel than the Powerwall(s) can handle.

There's something to be said for having two Powerwalls so you can do whole-house backup, though. That's the configuration I have. You may regret only having the one (although I do understand the disinclination to spend more money since you're getting the first one for free). I'm very happy that I didn't have to pick essential loads and can essentially weather short power outages with no impact whatsoever. In fact if the timing is right, I could probably handle a 6 month outage with only a little conservation on my part.

 

[miimura]

With only one Powerwall, you really don't want to put the second inverter on the backed up side. They are correct. The right way is to put the 5kW inverter with the Powerwall. If the grid is up, you can still charge from both inverters, up to 5kW. If you really want to be able to use ALL the solar, then you need to spend extra for the second Powerwall. It will allow you to run more of your house during an outage too.

Don't be too upset about the clipping either. The broader curve is collecting more energy with a cheaper inverter. This is very common in solar system engineering.

 

[Jeff P]

Yeah, the quote with installation for a second unit is about $10k, which is not worth it in any universe where I can calculate ROI. Obviously the only scenario I'm trying to cover is a post-hurricane extended outage, and even then it's hard to say if that will be a thing. Six years living in Florida and I've had maybe an hour total of outages (far less than I ever had in Ohio). I mean, I'm mostly thinking about being smug that my beer is cold after a hurricane.

If I'm really getting down to it, I don't even care that much about having backup power overnight. What I'm really trying to optimize for is automatic disconnect from the grid so I can use solar during the day of an outage.

The entire situation feels like an extraordinary failure of product design.

 

[RoBoRaT]

I'm sure some of the more technical folks on this board will chime in, but in a nutshell what they're saying makes sense. The issue is that at this point, the Powerwall can't roll back the solar production partially. It's either on or off. This means that in order to prevent the solar from overloading the Powerwall's capacity, it'd have trouble letting the full 10 kW system run. I also suspect that they're worried the solar inverter will not react quickly enough to the Powerwall's frequency shift and could cause issues if the solar production is higher than the Powerwall's input capacity.

I believe it is normal that they will not install with more generation capacity on the backup panel than the Powerwall(s) can handle.

There's something to be said for having two Powerwalls so you can do whole-house backup, though. That's the configuration I have. You may regret only having the one (although I do understand the disinclination to spend more money since you're getting the first one for free). I'm very happy that I didn't have to pick essential loads and can essentially weather short power outages with no impact whatsoever. In fact if the timing is right, I could probably handle a 6 month outage with only a little conservation on my part.

I'm about to have 10.72 kW of 16 LG 335 panels with 2 Powerwalls. Which I will ask to split 16 panels each on 2 SolarEdge SE5000H. Almost the same config as the OPs.

One of the listed parts to be installed is a Essential Load panel.

Can I ditch the Essential Loads Panel and do whole house back up?

My usual consumption is 25-30 kWh per month, plus 800 kWh if I count charging my M3 for daily drive (160 miles/day).

Why would I need to use Essential Loads panel when 2 PW is sufficient to do Whole House Backup?

I don't want to pay extra for this Essential Loads panel unless its needed. Thanks for any feedback.

 

[Vines]

I'm about to have 10.72 kW of 16 LG 335 panels with 2 Powerwalls. Which I will ask to split 16 panels each on 2 SolarEdge SE5000H. Almost the same config as the OPs.

One of the listed parts to be installed is a Essential Load panel.

Can I ditch the Essential Loads Panel and do whole house back up?

My usual consumption is 25-30 kWh per month, plus 800 kWh if I count charging my M3 for daily drive (160 miles/day).

Why would I need to use Essential Loads panel when 2 PW is sufficient to do Whole House Backup?

I don't want to pay extra for this Essential Loads panel unless its needed. Thanks for any feedback.

Whole home backup depends on the configuration of your main service. If your main service has distribution, then to get that much backfeed power (just over 100A) you would have to downsize your main breaker way too far.

Its pretty difficult to give advice without pictures of at least the main panel. However its possible to move all your loads to the essential panel in some cases, so you still have whole home backup. To get any certainty, I'd have to see pictures of the main service preferably with no dead front installed.

 

[Vines]

As to the OP question, its been answered correctly above. Solar that is significantly larger than the powerwall will actually have a negative effect on the user experience. The only way to get around this is to use tons of power during the day. There is simply no way to cram 10 kW of PV into a battery with a 5kW charger.

 

[dortor4ev]

there is _NO_ ROI for a Powerwall - I tried I really really tried - but I changed my perspective and decided it was a home appliance and determined it was worth while for me to be semi-self-sufficient and have a bridge during power outages - once I got over the lack of an ROI it made sense to install the Powerwall as an enhancement to my home - and it's bonus that it keeps the solar panels running during an outage...I'd humbly suggest you go for two Powerwalls and be happy next time the power is out that your entire solar system is running the house and your batteries and you'll have power as long as you have sunshine...my $0.02

 

[zanary]

there is _NO_ ROI for a Powerwall - I tried I really really tried - but I changed my perspective and decided it was a home appliance and determined it was worth while for me to be semi-self-sufficient and have a bridge during power outages - once I got over the lack of an ROI it made sense to install the Powerwall as an enhancement to my home - and it's bonus that it keeps the solar panels running during an outage...I'd humbly suggest you go for two Powerwalls and be happy next time the power is out that your entire solar system is running the house and your batteries and you'll have power as long as you have sunshine...my $0.02

Your statement is partially true. I was able to get in as a early adopter with Quantity 2 Powerwalls while SGIP was available. My entire out the door cost was around $13500, and then I got a check back from PG&E for $9200 because I got into SGIP Step 2. The process was incredibly painful, and took about a year (source = Powerwall 2 "waiting list")

that being said, my out of pocket cost after the cash back rebate (which was an actual check), was $4600 for two Powerwalls fully installed. Now, I calculated that it allowed me to run my house at $0.127/kw which is the PG&E Non-Peak price for EV-A Plan, while everyone was paying up to $0.467/kw during peak-hours (partial peak was around $0.34/kw I think). Regardless my daily consumption is around 17kw, so I had sufficient capacity with two Powerwalls.

My calculations shows that I would get a ROI within 3 to 4 years, but that also really depends on how much my energy usage goes up or down as my kids grow up.

Now if it wasn't for SGIP, then I think the ROI can be calculated in decades if any as you pointed out.

Note: When I did Powerwalls, I did not have solar, so I was looking for Time of Use savings, however a year later I installed 10 panels (largest number I could put on my roof). I've setup my system to do Advanced/Cost Savings with a 33% reserve.

 

[K-MTG]

Doesn't referral Powerwall include installation? Maybe the early programs didn't offer it? The last program said $2k in installation

 

[patrick40363]

Doesn't referral Powerwall include installation? Maybe the early programs didn't offer it? The last program said $2k in installation

$1000 toward the installation cost. It also might be as high as $2000 depending on the region.

 

[ssq]

$1000 toward the installation cost. It also might be as high as $2000 depending on the region.

I was quoted with $1k installation credit, got rectified to $2k. The inside sales adviser mentioned they will be rolling out these corrections to all ongoing and upcoming installs. I have 3 founder series PW2s, did ask if the credit is higher when one has 3 PW2 vs 1.. answer was no, its a flat credit.

 

[RoBoRaT]

Whole home backup depends on the configuration of your main service. If your main service has distribution, then to get that much backfeed power (just over 100A) you would have to downsize your main breaker way too far.

Its pretty difficult to give advice without pictures of at least the main panel. However its possible to move all your loads to the essential panel in some cases, so you still have whole home backup. To get any certainty, I'd have to see pictures of the main service preferably with no dead front installed.

Here are pictures of the main panel.

My installer includes moving up to 8 circuit, up to 30A single pole breakers within 10ft of main panel.

Note that I have Wall Connector and 240 NEMA 14-50 behind the Main Panel in the garage where I charge my Model 3.

I am ok with backing up only one of the AC unit (30A A/C 1), and few essentials - since limited to 100A.

Any recommendation for/against whole house vs essential load (100A) panel?

 

[Vines]

I'd recommend an essential load panel in your situation. Your 80A HPWC cannot be served by 2 powerwalls, as its larger than they can support. Your main service has distribution, so you must adhere to the 120% or 100% rules.

Whole home backup doesn't make sense unless you go to a smaller feed for your HPWC, and also your main panel is capable of one of the ways to get 200A backed up, which may require an essential panel anyway.

 

[RoBoRaT]

I'd recommend an essential load panel in your situation. Your 80A HPWC cannot be served by 2 powerwalls, as its larger than they can support. Your main service has distribution, so you must adhere to the 120% or 100% rules.

Whole home backup doesn't make sense unless you go to a smaller feed for your HPWC, and also your main panel is capable of one of the ways to get 200A backed up, which may require an essential panel anyway.

Thank you for the feedback.
Essential Load panel it is

BTW, If I leave the Wall Connector the way it is (80A breaker in the Main Panel), will the 2 Powerwalls able to provide/charge my M3?

 

[Vines]

Maximum output of the Powerwall is just about 21A, and the HPWC will send up to 48A to the Model 3. If you were on pure backup, this load would trip your Powerwalls into overload even if nothing else in the house was on.

 

[miimura]

If the grid is up and the Powerwalls are set up to monitor the main panel, the Powerwalls can still send power to your car if you want them to. I purposely don't send Powerwall energy into my cars. It's cheaper for me to use Off-Peak energy between 11pm and 7am to charge the cars. Time Based Control on the Powerwalls can prevent the Powerwalls from discharging during that period.

 

[RoBoRaT]

If the grid is up and the Powerwalls are set up to monitor the main panel, the Powerwalls can still send power to your car if you want them to. I purposely don't send Powerwall energy into my cars. It's cheaper for me to use Off-Peak energy between 11pm and 7am to charge the cars. Time Based Control on the Powerwalls can prevent the Powerwalls from discharging during that period.

Got it, I'm tracking.
On Back-up mode PW will charge my car by HPWC but ensure no more than 10kW from 2 PW.

With the grid up, Solar/Grid/PW can support charging the car by HPWC up to max 48A 9f LR Model 3 onboard charger.

And, best to charge at super off peak (10PM-08AM on out TOU scheme) by Time Based Control to avoid discharging PW (but use it for House Load)

 

[RoBoRaT]

Thanks for the info (Vines & Miimura).

Slowly getting good gouge here - in time for Solar system and PW install before summer time.

Cheers!

 

[miimura]

Got it, I'm tracking.
On Back-up mode PW will charge my car by HPWC but ensure no more than 10kW from 2 PW.

With the grid up, Solar/Grid/PW can support charging the car by HPWC up to max 48A 9f LR Model 3 onboard charger.

And, best to charge at super off peak (10PM-08AM on out TOU scheme) by Time Based Control to avoid discharging PW (but use it for House Load)

The issue is that Tesla will not put any breaker on the backup side of the Gateway that is larger than 30A times the number of Powerwalls you have. So, even if you have two Powerwalls, you cannot have a HPWC with 80A breaker on the backup side of the Gateway. I don't see this as a problem. My two EV charging circuits remained in my main panel where they are not backed up.

HVAC (electric heating and cooling) requires a little more consideration because it is more critical. In addition, many AC compressors have very large startup current that cannot be provided by the Powerwalls. A soft-start system can be added to many compressor motors. Variable speed compressors are even better since they have a very low startup current.