Evaluating a Tesla Power wall

I am thinking of pulling the trigger on a Tesla 2 Battery Wall for my solar panel’s home .

Anyone with positive or negative info - please chime in:

Due diligence :
Cost : $23k - after rebates $11.4k (2 Battery system)
Current Monthly electric bill - $3 per month, $800 annual adjustment.
Future change: add a Tesla 3 car to my fleet of cars. Currently no electric car in the driveway .
Goal: eliminate reliance on the grid at night as consumption expected to increase

  • have a battery back up as CA has been experiencing extra black outs on windy days as utility companies can no longer risk fires during high windy days (big issue). plus, my neighborhood in general has a black outs often (month on average) - due to so many trees and issues with power lines interferes.
    Profit - not expecting a cash on cash return. Maybe after the electric car comes to the picture, the savings of not being on the grid at night will have a 7 year payback.

Questions : do these power-walls hum? Buzz in sound ? Do they add a fire risk ?

Anyone with feedback - please

I saw a documentary a while ago where people plug their EVs into the grid at night and allow the grid to take say 50% of their storage overnight. I think it may have been somewhere like Madeira. Not sure if it feasible for home use.

Where I live, there is almost no solar generation during our storm season when we have most of our power outages so I had to go to a generator as I couldn’t get a wall to work for my house in my climate.

Buddy just did a couple non-tesla for around $80k with a 10yr break even IIRC and nightly surplus as backup in lieu of a generator. Permitting was a nightmare and took longer than anticipated FWIW.

I have 4 (in 2 pairs of 2) in my house in Tahoe. Use it primary for backup during power outages. Have had them for 2 years now. They are solid. Pricing sounds about right though my pricing data is 2 years old.

No hum from them. They just sit in the garage and glow quietly. Biggest issue i’ve had is that it’s embarrassing when the 'hood losses power and my house is still lit up like a Christmas tree and there’s no generator noise. Neighbors are like “WTF”?

Cutover from street to battery is completely transparent.

I’ve thought about the fire risk but not looked into it in detail. There are banks of these now in places like Australia and Puerto Rico so i guess if they had a habit of going on fire it would be public by now.


There were two styles of PowerWall when I looked at them a few years ago.

One was designed for backup; held charge better, was smaller, better energy density… However it had limited cycles.

The other was designed for solar and would support many more cycles.

I never got further than preliminary research.


What do you need to run?

I live in the foothills and have a 60 panel solar system… my primary goal was for backup power.

I figured I needed a 4 wall system to meet basic usage including AC u nits etc. Obviously could have load shed and used less. We had a 16kw backup generator as it was insufficient… powered about half the house. We have a complicated split electric system.

This summer with many hot powerless nights I got more serious.

Keep in mind your solar is offline during grid shutdown so there is no regeneration until power restored

We figured less than 2 days with miserly use of 4 power walls so that just seemed nuts cost benefit wise. We lost power several times for several days in the winds.

I ended up upgrading my generator to a 24 KW Kohler which is quiet (4 cyl cheverolet engine) and this will run for about a week on our propane supply powering everything in the house

Cost was about $24k but we have a complex dual switch install.

Much quieter and more reliable than the Generac we took out.

The walls are cool, but I just don’t think the juice is worth the squeeze yet.

We generate enough electricity to have nearly a zero annual bill so banking for night use is just to feel good for us.

Good advice / direction so far .
No doubt - each home, family, and area has a different mission profile aka needs.

When On the grid “night time”, the car(s) will be plugged in (factoring a Tesla car is coming soon). I believe the battery wall will pay for the night charging over 7 years (IRR) . The extra benefit would be black out protection. - which in CA is a new “real” issue as wild fires from wind storms has created a new protocol for utility companies to keep pulling the plug randomly and often on municipal power.

Any others in CA seeing power walls as something of interest ?

My solar generation is great (offsets $300 a month). But most importantly, it’s a great lifestyle change when electric bills are trivial

Similar question. Why can’t I just run my house off of my model x when the power goes out. I already purchased a battery from Tesla, it’s just in the car.

somebody must be working on that.

Tesla has a nice calculator on its website.

Each power wall has a 14KW capacity. For small things like LED lights and TV it goes along way.

However it won’t run a fridge for 24h or 6h of AC or a couple of loads in the dryer.

One wall will only charge a Model S 40 miles… they seem sexy but once you start adding up the “necessities” they have tiny capacity.

You can buy a 5000w gas generator at Lowe’s for $600 and a sub panel to run some key circuits installed for less than $2k total… not sexy but running for 24h has roughly 10x the capacity of a Power Wall. Kinda grim unless you have very meager needs.

A cheap Generac whole house generator ($5 grand) 12-16kw produces more power in 1h than the capacity of a single power wall total capacity.

With several day outages they are not very useful.

Also PGE offers an EV rate and charging after midnight (car has a timer) is really cheap

When I got my Model S in 2013, I was spending $400/mo on gas for my Range Rover. With the Model S and PGE discount my house power bill (no solar) dropper by $300/mo including charging the S! That’s cool

If you have batteries why does your solar go offline without the grid? Sounds like it’s not set up right. I have two 5kW solar systems, one with a 5kWh battery - if the grid goes off the battery and one of the solar systems stay on line (the second system is on a separate inverter with no battery, so it does go offline.)

That’s enough to keep the essentials running as long as there is some sun. The battery is not quite enough to last all night - I have thought about doubling it but have not persuaded myself it’s necessary yet.

I can’t imagine what you’re running that a 16kVA generator won’t power - I don’t even have that much available from the grid - I’m on a 16kVA transformer, but it serves another property as well.

via COPAme
Samsung SM-T820

If you are looking to protect against PG&E induced “voluntary” outages of multiple days I’d look very closely at the duration any battery system can sustain… I’d be very surprised if it fit the bill. Cheapish whole house generator running on propane was our solution for backwoods end of grid NH.

We basically have 2 kinds of solar system choices here in CA.

On grid (feeds power back to PGE to reduce bill) requires grid power to be enabled. With power out the solar shuts off. This is by design to keep the grid cold when turned off… dont want a bunch of solar panels back charging the grid and string up fires or hurting workers etc.

Off grid are completely independent and solar charges batteries etc with out grid connection. These are usually remote lodges etc.

I was really annoyed when I found out I couldn’t legally or practically use solar to charge batteries when power was out.

I suspect there are some bootlegged systems but not what I wanted.


Very surprised to hear that CA does not allow auto disconnect with batteries connected to both grid and panels.

This was the setup my neighbors had when I was kid; and a co-worker did just a few years ago (both in MD).


That is strange. No matter where you are the system always has to disconnect from the grid when the grid goes down (which is partly for safety reasons but also because your inverter could not possibiy feed the load that would probably still exist from neighbouring consumers.) And if you have no battery the inverter has to shut down because it can’t supply stable power with fluctuations in sun energy, but with a battery there is no technical reason for it not to revert to stand-alone operation. I would not have bothered with a battery if that were not possible.

I wonder why you’re allowed to keep the inverter running off battery power but not off solar power? The inverter doesn’t care where it gets its DC from.

Unless of course you have a separate inverter for the solar panels - I believe the Powerall 2 has an inbuilt inverter. My setup has a hybrid inverter that combines DC input from the battery and the solar panels. It’'s not Tesla.