Tesla Solar Order Cancelled / Fire Setbacks

[MB2020]

Do you have AC?

Yes we do. AC and heat are all electric and it is a small unit from the 60s. The home is only 800 sq ft.

 

[MB2020]

I forgot OP said that "all appliances are electric", when I asked if OP has AC. If OP desired to be able to use any electric appliances in a power outage situation, they would likely need to have 2 powerwalls (depending on the electric needs of most of those appliances).

Its likely the electric oven and dryer require more power than 1 powerwall can provide to run them, let alone any electric heater etc.

Also, good reminder on using the powerwalls to fill an electric vehicle. Until a person starts researching it, it seems like a really reasonable thing to want / request / expect. But, as you noted, most electric vehicles have batteries several times the size of a powerwall. Even small leafs etc have batteries bigger than a powerwall.

The analogy I like to use is, trying to use a powerwall to fill an EV is like trying to use an AAA battery to fill 1 or more D batteries. Even though you could rig up something to do that, it wouldnt make a lot of sense. The main use for powerwalls is being able to use your own solar power when the sun is not shining, as well as providing backup power somewhat like people use a generator, but with automatic, fast switching.

Avoiding electricity usage during Peak time on a time of use plan if a utility makes its customers sign up for those is another benefit.

OPs current electric usage seems really reasonable, actually reasonable enough for only 1 powerwall if wanted as a backup, but OP would need to research to see if one powerwall would even be able to start / run those electric only appliances.

Otherwise, just regular wall plugs would be backed up, which would save the food in the fridge for example, but at least to me, seems a pretty expensive way to backup some regular outlets.

I should also mention the entire home is on one electric sub panel. That then goes to the main panel at the detached garage. So trying to put only certain circuits or plugs from the home on backup is really impossible without a re-wire I am guessing. The main panel has one breaker for the entire house, one for sockets in the garage, another for the water heater, and then the electric dryer.

 

[BrettS]

An overly simplified way of looking at it is that one powerwall can back up anything with a 30A circuit breaker or less. If your oven, for example has a 40A circuit breaker then tesla will not allow you to put the oven on the backed up loads panel with just a single powerwall. Two powerwalls can back up anything with a 60A circuit breaker or less. And three powerwalls can back up anything with a 90A circuit breaker or less.

Again, that’s a bit overly simplified in that even with two powerwalls only a limited amount of power can be supplied at once. So, for example, with two powerwalls you could put your drier and your oven on your backed up loads panel, even if they both had 40A circuit breakers, but you probably couldn’t use them both at the same time in the event of a power outage.

Additionally, the powerwalls can only supply so much power over time. Even if you were able to get your electric heat on the backed up loads panel with two powerwalls it’s likely that your electric heat could drain the two powerwalls within a few hours on a cold night.

So when you are trying to determine how many powerwall to get you need to look at how much power you might draw at any given instant with several things running, as well as how much power you will use over the time from when the sun goes down until the sun comes back up.

 

[JeremyWhaling]

What size breaker is in the main panel that feeds the sub?

Sounds like you have a somewhat unique case where whole house backup is basically your only option for powerwall (can't economically run some circuits back to the garage to the main panel).

 

[jboy210]

I should also mention the entire home is on one electric sub panel. That then goes to the main panel at the detached garage. So trying to put only certain circuits or plugs from the home on backup is really impossible without a re-wire I am guessing. The main panel has one breaker for the entire house, one for sockets in the garage, another for the water heater, and then the electric dryer.

A rewire is exactly what happens, sort of. They move some of the circuits to a new critical loads panel that is backed up. As Jay mentioned this would likely just be 120V outlets if you only have 1 PowerWall. If you had two powerwalls this critical loads panel would like not be needed.

 

[eisenb11]

View attachment 579254 Thank you all for the suggestions and guidance.

After many phone calls with my local Fire Authority, the city building and code enforcement office, and my Tesla sales advisor I was finally able to convince Tesla to break their cookie cutter design and update the project layout to install all 12 panels on the garage. No need for a 4’ setback on all sides!

My plan has been to get a PowerWall installed at the same time. All appliances are electric in our home and there is no natural gas service. We use about 580 kWh per month. Average daily usage is about 19 kWh. The want for a PowerWall is partially to use stored solar after sunset, partially for the nerdy cool factor. An electric car is likely in the cards within the next 3-4 years.

Power service is pretty reliable in the area. So far in 2020 we have seen a handful of blips in the power that last long enough to make the lights flicker but never anything longer than a few minutes.

For a system as small as 4.08 kWh and with our usage pattern, does it make sense to upgrade and have two PowerWalls?

Again, thanks for the guidance and being a place to talk through these topics.

I know this is an old post - but how did you convince Tesla to change their mind?

Currently going through this. They claim I need a 4' setback all around my flat roof. Best I can find in the fire code is 3' setbacks on the edges. That difference of 1' may potentially cost me 3 panels that I really need to have some buffer. Any pointers?

I'm in SoCal.