4 Powerwalls is large-scale storage, not small-scale. Tesla is not capped out on that program. Large-scale is currently on Step 2 for PG&E. See this page for details: https://www.selfgenca.com/home/program_metrics/
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(4) Powerwalls with 8kw Solar Array cost concerns
- Thread starter tomguy
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4 Powerwalls is large-scale storage, not small-scale. Tesla is not capped out on that program. Large-scale is currently on Step 2 for PG&E. See this page for details: https://www.selfgenca.com/home/program_metrics/
Good information there, thanks for the link. Since I am in the design department, I don't always get the best details that the sales team works with.
Tesla's reasoning behind upgrading the panel is sound. As @SoundDaTrumpet points out, it's a backfeed issue. You have the capacity to discharge all four PWs while your PV is generating. I have a 9kW system with two PWs on a 200A panel but I'm completely maxed for backfeed. I have 400A service which is split, so I plan to install another two PWs and another 9kW ground mount solar on the other leg if possible. However, installation pricing has gone up significantly since they had fixed price installs (when I originally had mine installed). So I'll have to eye the financial side of things and weigh them against my needs. That other 200A leg doesn't have a lot of draw on it, as it's a small guest structure.
Depending on your load and system, I'm guessing there's an opportunity to derate your main panel breaker to stay inside of the 120% bus rating. But I bet you have to derate quite a bit, thanks to those four PWs, and it's not ideal.
Depending on your load and system, I'm guessing there's an opportunity to derate your main panel breaker to stay inside of the 120% bus rating. But I bet you have to derate quite a bit, thanks to those four PWs, and it's not ideal.
zanary
Active Member
I think SGIP is maxed out for Tesla as the installer, however I heard that California was doing to enhance SGIP and Tesla may get more opportunities to use this program. Source = California Passes Bill to Extend $800M in Incentives for Behind-the-Meter Batteries
Source = Powerwall and California SGIP | Tesla Support
I was lucky to get into Step 2 back in 2017 of Sept but it was a really bumpy ride, and it took 12 months to get paid after the install. I documented my SGIP story here = Powerwall 2 "waiting list"
Does your MLO main panel have 6 or fewer breakers (or handle-tied pairs of breakers)?
Cheers, Wayne
SoundDaTrumpet
Member
Yes, I have exactly 6 breakers. In 2016, breakers were relocated to a subpanel to accommodate for solar. Lug/strap kit (MCB12) for main breaker were obsolete with no direct replacement available (learned after contacting a couple of suppliers). Should I do a much more exhaustive search?
Siemens MC1224MC1200F:
Attachments
OK, you have a tandem in there, so my phrasing was not precise enough. Can you shut off all power to the building with just six operations, i.e. pushing six breaker handles or connected sets of handles? If your tandem has two independent handles, that would count as two operations.
If six operations or less, your MLO service panel complies with NEC 230.71. If seven or more, it is out of compliance, and circuits should be moved to a subpanel, or handle ties should be added, to comply with 230.71.
BTW, with an MLO service panel, you should be able to connect up to 100% of your service rating of power generation sources to the MLO service panel. MLO service panels are not subject to the requirements of 705.12(D) but instead are covered by 705.12(A). I believe it is unclear whether the breakers in the MLO service panel for interconnection of power generation sources count towards the limits of six operations in 230.71. Different inspectors may have different interpretations of this issue.
Also, note that with an MLO service panel, the only thing protecting your service conductors and service panel is the NEC load calculation itself. So when adding loads to your service, it is important to check the load calculation, although in practice that calculation is usually very conservative.
Cheers, Wayne
If six operations or less, your MLO service panel complies with NEC 230.71. If seven or more, it is out of compliance, and circuits should be moved to a subpanel, or handle ties should be added, to comply with 230.71.
BTW, with an MLO service panel, you should be able to connect up to 100% of your service rating of power generation sources to the MLO service panel. MLO service panels are not subject to the requirements of 705.12(D) but instead are covered by 705.12(A). I believe it is unclear whether the breakers in the MLO service panel for interconnection of power generation sources count towards the limits of six operations in 230.71. Different inspectors may have different interpretations of this issue.
Also, note that with an MLO service panel, the only thing protecting your service conductors and service panel is the NEC load calculation itself. So when adding loads to your service, it is important to check the load calculation, although in practice that calculation is usually very conservative.
Cheers, Wayne
Wayne is right on with the 705.12 and its various interpretations regarding sources vs loads.
If I wasn't going to do the service upgrade I'd leave the top breakers for the AC and pergola off the backup system and see if I could put the PV, and one or both of those subpanels in the backup circuit with a 125A max feed from that main panel. Depending on the load calculations between those 2 subpanels, a 125A breaker might be enough, and even if the load calcs are marginal, having 2 Powerwalls set to self consume will offset brief periods of what might have otherwise popped the 125A breaker in the main.
So you'd install a new Gateway and 200A subpanel next to the main off that 125A breaker, relocate all those subpanel feeds to that panel (or just choose to backup either garage or main house subs) and put the PV+PW in the same subpanel, though a separate generation panel is an option as well out of the 2nd lugs on the gateway.
Also, you can still self consume the AC loads even though they are not backed up and same with the garage or main subpanel. Just depends where and how many CT are installed, which determines where the TEG sees loads vs loads it cant see. Will still need a bit of stucco work but not the level of a new service panel.
If I wasn't going to do the service upgrade I'd leave the top breakers for the AC and pergola off the backup system and see if I could put the PV, and one or both of those subpanels in the backup circuit with a 125A max feed from that main panel. Depending on the load calculations between those 2 subpanels, a 125A breaker might be enough, and even if the load calcs are marginal, having 2 Powerwalls set to self consume will offset brief periods of what might have otherwise popped the 125A breaker in the main.
So you'd install a new Gateway and 200A subpanel next to the main off that 125A breaker, relocate all those subpanel feeds to that panel (or just choose to backup either garage or main house subs) and put the PV+PW in the same subpanel, though a separate generation panel is an option as well out of the 2nd lugs on the gateway.
Also, you can still self consume the AC loads even though they are not backed up and same with the garage or main subpanel. Just depends where and how many CT are installed, which determines where the TEG sees loads vs loads it cant see. Will still need a bit of stucco work but not the level of a new service panel.
SoundDaTrumpet
Member
Yes, six operations needed to shut off power. Prior to adding solar, I was at six operations. At time of adding solar, the garage subpanel was added to relocate breakers and land the 20A PV breaker.
@wwhitney Thanks for writing the requirements for 705.12 clearly. Are MLO service panels for generation a special topic? It seems like I can avoid the extra cost of a MPU (Main Panel Upgrade by Tesla). Is this clearly an advantage of a MLO service panel for the Powerwall user?
Tesla submitted a new contract price to my existing signed contract to include an MPU for $3800. Because it was entirely unplanned expense which doubles post-ITC/SGIP cost, I am trying to avoid MPU cost. I had a design that I signed contract for, expected whole house backup, Tesla noted that a 175A branch breaker that does not exist was implemented, loads exceed next highest available 125A breaker, and ultimately trigger MPU. Tesla is also conveying backfeed issues. This is where the distinction of MLO service panel for generation comes into play.
I am thinking it may be best to as @Vines recommends. Put all the Tesla equipment behind a 125A branch breaker, and go partial backup. The house panel has a calculated NEC load of 95A which includes a dryer circuit which I plan to never use. I have monitored the max meter load to be 18.6kW (79A) with EV, AC, oven, and lighting loads on a hot day. Is there any reason a Tesla electrical engineer or city inspector would halt this?
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OK, good, sounds like the last two people to touch that panel knew what there were doing in regards to 230.71.
The issue as you mention is that your MLO service panel can only accept branch breakers up to 125A in rating (this is a common limit on branch breakers for a 200A panel). So if you are happy backing up only 125A of loads, and can segregate the other loads (e.g. EVSE, perhaps), then there is an NEC-compliant solution without replacing your current MLO service panel. [Note that NEC 705.12(D) would still apply to all the panels between the MLO service panel and the solar/Powerwalls.] Of course, Tesla may say that while NEC-compliant, it is not a configuration they support.
Seems to me if Tesla screwed up the design and you have a signed contract, they should eat the MPU cost.
Cheers, Wayne
TheTalkingMule
Distributed Energy Enthusiast
The original issue seems to be answered sufficiently, so I'd like to ask a related PW noob OT question...
If this 8kW array if for a normal house with normal electricity use, and the electricity demand profile isn't changing considerably, why do multiple Powerwalls require incremental panel upgrades? I assumed that the output(or input) of one Powerwall would be the same as 4(or 20) Powerwalls chained together. Can each Powerwall not be
If this home's consumption isn't changing, why can't 4 Powerwalls limit the amount of juice flowing through the panel?
If this 8kW array if for a normal house with normal electricity use, and the electricity demand profile isn't changing considerably, why do multiple Powerwalls require incremental panel upgrades? I assumed that the output(or input) of one Powerwall would be the same as 4(or 20) Powerwalls chained together. Can each Powerwall not be
If this home's consumption isn't changing, why can't 4 Powerwalls limit the amount of juice flowing through the panel?
SoundDaTrumpet
Member
Your question is not entirely off topic. You question is very fundamental minus the pricing politics the OP and myself encountered.
Most solar installers apply the 120% rule on the service panel bus bars. Typical 8kW installation would be on a 40A branch breaker, and that would be the most solar generation allowed for homes with a 200A service panel in the most straightforward manner possible. More solar can be added with downsizing the main breaker (if you have one, most do, I don't) to add more solar generation. Downsizing of the main breaker makes more backfeed available, but you limit loads to the house. At some point you choke the ability to backup whole house loads. For every Powerwall installed, 30A of generation is added to the service panel. This is why adding powerwalls require panel upgrades.
The multiple Powerwalls operate in parallel, so total backfeed is tallied up for every Powerwall added.
My service panel does not have a main breaker, so I have a different set of rules that Tesla can choose to apply or not to avoid an MPU. That's my dilemma.
Most solar installers apply the 120% rule on the service panel bus bars. Typical 8kW installation would be on a 40A branch breaker, and that would be the most solar generation allowed for homes with a 200A service panel in the most straightforward manner possible. More solar can be added with downsizing the main breaker (if you have one, most do, I don't) to add more solar generation. Downsizing of the main breaker makes more backfeed available, but you limit loads to the house. At some point you choke the ability to backup whole house loads. For every Powerwall installed, 30A of generation is added to the service panel. This is why adding powerwalls require panel upgrades.
The multiple Powerwalls operate in parallel, so total backfeed is tallied up for every Powerwall added.
My service panel does not have a main breaker, so I have a different set of rules that Tesla can choose to apply or not to avoid an MPU. That's my dilemma.
TheTalkingMule
Distributed Energy Enthusiast
Interesting. I'm just surprised a residential product doesn't purposely keep stringed Powerwalls out of parallel for just this reason. One Powerwall can absorb anything 8kW of panels produces and can handle anything the home demands, so what's the point of having them all in parallel if it causes so much difficulty and added cost?
One Powerwall can output about 21A continuously at 240VAC, this is not enough for many larger homes but maybe enough for smaller homes especially with Gas appliances.
For homes with electric appliances, a single oven, dryer, or hot water heater plus the normal house loads can overload a single Powerwall 2 AC. If its overloaded, it must be manually reset.
A DC coupled system, while it has its own limitations, does get around the backfeed issue, since the battery and pv share the same inverter, so do not increase the back feed load beyond what the PV already requires. DC coupled systems also theoretically have less of a round trip loss, since the DC PV source doesn't need to be Inverted to AC, only to be inverted back to DC, and stored in the batteries. To be used it must be again inverted to AC, which is 3 trips across the inverters. DC coupled systems take the DC PV output and charge DC batteries or invert to AC depending on need, so are overall more efficient. Tesla and Solar Edge used to have a DC coupled solution, but I dont think that partnership has continued. Now I see Solar Edge paired with LG Batteries.
For homes with electric appliances, a single oven, dryer, or hot water heater plus the normal house loads can overload a single Powerwall 2 AC. If its overloaded, it must be manually reset.
A DC coupled system, while it has its own limitations, does get around the backfeed issue, since the battery and pv share the same inverter, so do not increase the back feed load beyond what the PV already requires. DC coupled systems also theoretically have less of a round trip loss, since the DC PV source doesn't need to be Inverted to AC, only to be inverted back to DC, and stored in the batteries. To be used it must be again inverted to AC, which is 3 trips across the inverters. DC coupled systems take the DC PV output and charge DC batteries or invert to AC depending on need, so are overall more efficient. Tesla and Solar Edge used to have a DC coupled solution, but I dont think that partnership has continued. Now I see Solar Edge paired with LG Batteries.
I completely agree with the question to ask. The reason I'm upset over this is that the house originally had a 100A panel. Upon installing the 200A panel I'd asked Tesla to look at the house and tell me if I needed to do anything special. They told me the spec on the 200A panel to install, so I'd paid already almost 4000 dollars to have that installed. Then Tesla put in a 2400 fee to upgrade the MPU and upon further evaluation, the fee is now almost 8000 for a MPU. In total I would be spending 12,000 for this panel plus the cost of the powerwalls.
While Powerwalls can limit the power they discharge, the NEC does not recognize that as an effective means to protect the busbar.
As to your question @tomguy It simply sounds like the Tesla team are in over their heads, or there was some confusion as to what panel was supposed to be installed. Pictures would help, and include the picture of the sticker, if you are comfortable with doing so, turn off power and remove the dead front and we can really see whats going on. I'm surprised after multiple site visits they didn't recognize that you had installed a main panel with distribution, rather than the Main breaker only panel, or a separate meter socket, that would have made this easiest. Now that things are sealed up under the stucco its tough to go and change things. Depending on the guts of the panel, there may be other options.
For those considering multiple backup systems in parallel @ohmman , Tesla may not allow that at all. They have told us that they do not want us to do this again, as it causes issues with the App, and the customer experience.
If parallel Powerwall systems (more than 1 Backup Gateway) cause a problem, they should allow you to provision them as separate systems tied to different e-mail addresses. That should remove any conflict or strangeness in the app. The fact that they're behind the same meter seems irrelevant to me.
Depends how they are setup, if 2 gateway and backup systems are setup in parallel with the CT in identical locations around the main wires then the 2 systems will attempt to offset the same loads. You would have to make sure you setup the CT appropriately so they don't overlap, you want them to read different loads.
If setup incorrectly, I'm not sure 2 system in parallel like that wouldn't happily backfeed the grid from the batteries, though its designed not to in this market. I can see why they might not want installers doing it.
If setup incorrectly, I'm not sure 2 system in parallel like that wouldn't happily backfeed the grid from the batteries, though its designed not to in this market. I can see why they might not want installers doing it.
Putting both sets of "Grid" CTs from two different Backup Gateway Neurio devices on the same main feed is obviously the wrong way to do it. You could have one set of CTs on the main feed and one on its own Gateway input like they place them at the factory. I see no reason that wouldn't work. It may not lead to equal loading and cycling on both sets of Powerwalls, but the customer should know that going in when they sign off on a parallel installation serving over 200A.
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