Yes, I agree, we can and should use all electricity that is being produced. What I should have said is that with the current setup and facilities, there is no desire to store or use the excess electricity. I think the potential is there to be able to use all the electricity being generated by renewables. But my personal opinion, I just don't see this happening anytime soon. Planning and regulation management won't be done especially here in the U.S., it would cost to much money (taxes) to redo the grid and make the changes necessary to harness all the solar energy being produced. I can imagine a huge political battle and I am sure there are some stockholders somewhere who will be resistant to changing over to a system that all though far more beneficial and efficient, offers much smaller profits. Anyway...just my two cents.
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Powerwall 2: Installation
- Thread starter JeffreyY
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- Powerwall Tesla Energy
Distribution companies are the ones with the primary problem. Managing voltage and frequency during peak solar/wind events is critical. This can include shuttling power to heavy loads or tweaking solar output to change their output profiles. Also, setting up EVs to only charge "when the grid says to take excess power", for example. But the grid is kind of a one-way street being used both ways. Distribution points are called "feeders" and you cannot overpower feeders with too much local high-voltage solar. So, distribution of renewables is essential in not messing up the feeder model until they have more of a hashed "matrix" model in place.
https://www.gegridsolutions.com/multilin/resource/Feeder/UniFlip_Publication/document.pdf
GE Grid Solutions works with one of my local power distribution companies and is working on some DoE sponsored test cases to create high-amounts of Solar in a test-case within set of feeders and applying regulation and management tasks to be modeled in larger scale later on in the next decade. All of it is happening slowly as is the growth of Solar PV in the state. Compared to Wind, Solar is about 1/6th wind peak regulated production. Unregulated Solar is pretty big and this is what lowers mid-day demand on the overall region.
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We're waiting on Tesla to install two Powerwalls for us, and a design concern has come up. Tesla is going to move all of our circuits into a "load center" subpanel for "whole home" backup purposes. I understand that the load center will be supplied via the Tesla Energy Gateway, and Tesla intends to connect the Energy Gateway to our 200A main service panel using a 100A breaker.
I'm not sure why Tesla wants to use a 100A breaker and am waiting to hear back from our contact person on this. I don't see why they'd use anything smaller than 150A or 200A, since the Energy Gateway can handle 200A as far as I'm aware. My concern is that 100A is on the low side and also leaves little room for us to add new circuits to the load center in the future. I've explained to Tesla that we want to be prepared to switch some of our appliances from natural gas to electricity.
For those of you who've already had two or more Powerwalls installed, what size breaker did Tesla use in connecting your Energy Gateway to your main service panel? Has this been a concern for anyone else?
I'm not sure why Tesla wants to use a 100A breaker and am waiting to hear back from our contact person on this. I don't see why they'd use anything smaller than 150A or 200A, since the Energy Gateway can handle 200A as far as I'm aware. My concern is that 100A is on the low side and also leaves little room for us to add new circuits to the load center in the future. I've explained to Tesla that we want to be prepared to switch some of our appliances from natural gas to electricity.
For those of you who've already had two or more Powerwalls installed, what size breaker did Tesla use in connecting your Energy Gateway to your main service panel? Has this been a concern for anyone else?
GenSao
Member
Tesla recently installed a 150A breaker to our load center for whole house backup. I believe by code, the breaker to the sub-panel (the energy gateway) from your main 200A main service panel must be less than 200A. The code assumes that you may (how ever unlikely) add more breakers to your existing panel.
At the very least you should require a 150A breaker and make sure there are spare slots for future breakers for growth.
Thanks, this is exactly what I told Tesla - that I need at a least a 150A breaker and room for expansion. I appreciate the confirmation!
eml2
Member
I’ve been told that Tesla is updating the 200A backup gateway so that two can be used in the same installation. The word is that this is intended to bridge the gap until they can get the 400A version to market. For my installation with 200A x 2 legs, it’ll be ideal.
I’ll update as I hear more.
I’ll update as I hear more.
Two Powerwalls in parallel provide a rated maximum output of 10 kW continuous real power ( = 41.7A @ 240V) and 14.4 kVA peak apparent power (= 60A @ 240V). As long as there are no loads in the house that would exceed either of those limits, backing up the entire house panel works. If there are larger loads, they would need to be segregated into a "Noncritical Loads" panel that is on the power company side of the Backup Gateway.
A couple questions about your installation: prior to the Powerwalls, was the 200A main panel the service entrance? I.e. was the 200A main breaker the first breaker after the meter? If so, then I assume you Backup Gateway has a 200A breaker inside of it, as it is now the service entrance.
Also, where was the output of the two PowerWalls connected? Each PowerWall uses a 30A double pole output breaker, so where are those two breakers located?
When a panel is fed by multiple sources (the power company and the PowerWalls), the NEC has rules limiting the total power fed to a panel. The usual case is the 120% rule, which says that as long as certain conditions are met, the sum of the breaker for the power company supply (200A) and (approximately) the breaker(s) from the other sources (2 * 30A = 60A for 2 Powerwalls) can be up to 120% of the rating of the busbar in the panel.
So if the two Powerwall 30A breakers are in your main panel, then either (a) if the busbar in the panel is rated only 200A, the main breaker should have been downsized to 175A, as 120% * 200A < 200A + 60A, but 120% * 200A > 175A + 60A or (b) sometimes the busbar in a 200A panel is rated 225A, in which case no problem as 120% * 225A > 200A + 60A.
Another option would have been for the (2) 30A breakers to be installed in their own small panel, and the output of that panel connected to one of the pair of double lugs on the load side of the Backup Gateway. Since the Backup Gateway is a "panel" with only 0 or 1 breakers in it, other rules apply and allow that configuration.
For more details, see NEC section 705.12(D)(2).
Cheers, Wayne
GenSao
Member
Wayne,
Thank you for the clarification. For my case the Load Center is limited to 200A. Thus, 120% * 200A = 240A max power. 150A (PG&E Service) + 30A (Powewall 2) + 30A (Powewall 2) + 25A (Solar) = 235A Installed circuit breakers.
235A Installed < 240A Max
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You got it, that's why they had to reduce the size of the breaker in your meter main to 150A.
Note that if the solar panels are producing, or the Powerwalls are discharging, the wiring arrangement your diagram shows would in fact allow more than 150A total current to your load panel. Note also that if they had used a 225A panel for the new interconnection panel, then they could have used a 175A breaker in your meter main.
Cheers, Wayne
I just spoke with my Tesla representative. They are going to have to update the design and resubmit the permit application. It appears that San Bernardino County (our permitting authority) may have also had an issue with the size of the breaker in the main panel being only 100A, though it's not totally clear to me. While it appears that the designer may have screwed up, our rep seems to be doing whatever he can to help. Patience is a virtue here. We'll be fine as long as they get everything right. I asked that they give me a copy of the new line diagram before re-submitting the permit.
GenSao
Member
Too bad I did not request a 225A panel for the new interconnection panel. We should be OK, but It would be useful for a future renovation project. I want to bring the house up to current code/standards.
As a practical matter, it is very very unlikely to matter. The NEC load calculation for a house is extremely conservative, the actual peak power demand for a typical house will be 1/4 to 1/2 of what the NEC calculates.
So the only time it would be a problem would be when applying for a permit for an addition, the NEC load calculation might come out above 150A. In which case the meter main breaker, the interconnection panel and possibly the feeder from the meter main could be upgraded.
Cheers, Wayne
Yes. Not having any electrical knowledge, I have been consulting with my electrician about the main panel upgrade, future loads and etc. He said the same thing about the power demand being 1/2 of the NEC calculation. I talked to Tesla about it and their engineers said that they had to do certain upgrades, although not necessary, just to meet code compliance.
This is good to know, and it'll work in our favor in this case. I want to be sure that we'll have enough capacity to later add an electric induction range (50A breaker), an HVAC heat pump (40A breaker), and an electric water heater (30A breaker?), and the NEC calcs will essentially compel Tesla Energy to install a suitable "BLC" subpanel and breaker. I've been telling Tesla all along that this is what we'll need, though.
GenSao
Member
For the renovation we would be filing a permit to update the house within the existing shell. Although no new livable area is anticipated; walls will be moved, kitchen to be relocated, and the proper number of circuits would be installed. I would like to fix the hodgepodge of circuitry in the home.
Currently the house has only ONE 20A circuit for EVERYTHING in the kitchen except for a 40A oven circuit and overhead lights. From my count, I think we should add a 50A range circuit and 8 to 10 circuits at 20A or 15A for proper isolation of appliances. the 40A oven could be reused, replaced, removed, or re-purposed as a sub panel box for some of the 40A Circuits.
We use gas for cooking, home heating, and water heating, but want to make an allowance for at least an electric range and other future electrical needs.
Today Tesla clarified that the reason for our design having a 100A breaker in the main panel, to feed the Energy Gateway and the load center subpanel, is that our main service panel won't support breakers larger than 100A. Sure enough, this is indicated in the fine print inside our main panel. To free up capacity in the load center, Tesla is going to keep our existing 32A EV charging station (40A breaker) in the main panel instead of moving it to the load center. I'd still like to have some ability to charge EVs in the event of an extended power outage, but I suppose a standard 120V outlet will suffice for that, and there'll be less chance of inadvertently draining the Powerwalls if the power goes out in the middle of the night while charging an EV.
Unfortunately, the permit application still needs to be resubmitted, for some other reason that's not quite clear to me. While I'd rather not experience such delays, there's no point in getting impatient. This seems to be par for the course with new Tesla products. The fact is that the Powerwall 2, with installation, is a much better value than any other home battery system and I expect the wait will be worth it.
Unfortunately, the permit application still needs to be resubmitted, for some other reason that's not quite clear to me. While I'd rather not experience such delays, there's no point in getting impatient. This seems to be par for the course with new Tesla products. The fact is that the Powerwall 2, with installation, is a much better value than any other home battery system and I expect the wait will be worth it.
My 2 Powerwalls were scheduled to be installed on October 17/18. About two weeks before I received a call from Tesla that they were rescheduling due to sending batteries to help Puerto Rico. However, Tesla still came out on October 16 to do my main panel upgrade from 100 amps to 200 amps. They also added a whole house surge suppressor that I supplied them at that time. My new install date is December 18/19. So far no calls to reschedule again. Tesla said when they come out for the install they would be adding a second 200 amp panel and move all the circuit breakers to that panel. My guess is that main power will come into the main panel with only the 200 amp breaker in it, it would pass through their switch to the second panel with all the circuits. This to prevent backfeeding the grid when the grid power is out. Lost power here several times on Thanksgiving Day due to "equipment failure" according to SCE. So looking forward to being free of grid power failures.
