Is The Tesla Powerwall Worth It?

geek comments edit

Tesla Powerwall I was listening to the Energy Storage Geek Out episode on and they were talking about the new Tesla Powerwall. I really love this concept - charge the battery at night when electricity is cheap and then use the power from the battery during peak hours when electricity is expensive. Brilliant!

But it got me wondering: does it make financial sense? So I pulled out my calculator and crunched some numbers.

Here are my assumptions (which could all be wrong, so make sure you do your own homework):

  • The daily-use Powerwall can provide 7kWh per day and costs about $3000 (plus installation).
  • According to the podcast, the unit is designed to be used for 5000 days (a little over 13 years) before it starts to degrade.

In Phoenix

I live in the Phoenix area and most people here use a time-of-use plan. So that means, in June, we pay about 7 cents a kWh during the evenings and about 19 cents during the middle of the day. That means if I use the Tesla Powerwall, I can use 7 kWh of electricity during the heat of the day. Since I charge the battery in the evening, I only paid 49 cents instead of almost $1.40, saving me 84 cents per day (7kWh x 12 cents = 84 cents)

Now we have different rates during each season, so I applied this logic for an entire year:

Season Hi/Low Diff Days Savings/Day Savings/Year
Nov-Apr 0.0309 180 0.2163 38.934
May-Jun 0.1219 61 0.8533 52.0513
Jul-Aug 0.1485 62 1.0395 64.449
Sep-Oct 0.1219 61 0.8533 52.0513
Total       207.4856

So, by my calculation, with a savings of $207/year, it will take 14.5 years to recoup the initial investment of $3000. Bummer.

Los Angeles

I wanted to get at least one more data point, so I looked up time-of-use rates from Los Angeles Department of Water and Power. As near as I determine from their site, it looks like it will take even longer to recoup the cost

Season Hi/Low Diff Days Savings/Day Savings/Year
Jun-Sep 0.08 122 0.56 68.32
Oct-May 0.01 243 0.07 17.01
Total       85.33

Over 35 years to get your money back.


Perhaps if I had solar panels on my roof, this might make more sense. I’m not sure what the trade-off is for storing power in a battery compared to selling it back to the grid. Maybe in other area, where the difference between peak and off-peak rates is greater, it would also make more sense.

But until the prices come down for this technology, it doesn’t make financial sense for me.


Los Angeles Department of Water and Power

Phoenix Salt River Project Time-of-use Rates