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Powerwall efficiency 86%....


Active Member
Oct 5, 2012
Kenwood, California
I still think the PG&E EV2-A time of use differential is far worse than a 12% round trip loss in the Powerwalls differential.

Exactly. With $0.30 per kWh rate differentials I can live with some inefficiency in an inverter/battery for the larger benefit of load shifting. Also if we are talking about efficiency, how about the global losses from transmission and distribution on the grid all of which happen before our meter.
Last edited:


Aug 12, 2019
Monterey Bay Area
I have been tracking my single PW for 17 months, with an overall average efficiency of 84.4%.
I used the data from the Tesla app, with the following calculation;
Efficiency = 1 - Losses
Losses = (Solar Energy + From Grid - To Grid - Home Usage) / From Powerwall, if others are using a different formula please advise.

Chart summaries are below




Still Trying to Figure This All Out
May 31, 2015
Northern California
Efficiency = 1 - Losses
Losses = (Solar Energy + From Grid - To Grid - Home Usage) / From Powerwall, if others are using a different formula please advise.
Using this formula I am at 81% for 2020 and 80% so far for 2021. Running in Cost Savings mode.

Reserve is always sufficient not to draw from the grid during peak. Not sure how Storm Watch fits into all of this.


Sep 28, 2017
I have my 2 Powerwall2 for more than 3 years. They are in the basement. Temp is between 55-70F.

I have been collecting data from my PW via local REST API for 3 years. But last August was my first time using Tesla's Owner API. One of the info is the Total Pack Energy.

On 8/22/2020, the Total Pack Energy was 27.333 kwh. On the same date, the battery.energy_import and battery.energy_export (obtained via local REST API) was 8974 and 7952 respectively.

Today, 6/6/2021, the Total Pack Energy is 26.997, battery.energy_import is 12707 and battery.energy_export is 11215.

Since the time lapse is almost 10 months, I am going to ignore the SoC when battery.energy_import and export are recorded.

My efficiency is roughly 11215/12707 = ~88.5%

In addition, battery degradation is (27.333 - 26.997) / 27.333 = ~1.2%. That is after importing (12707 - 8974) = 3733 kwh, or 3733/27 = ~138 charge cycles.
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Reactions: holeydonut


Jun 2, 2019

I too only get "to powerwall" for a day. I don't think you can do this calculation it from the app without that.

That's because "on the day," if you will, the numbers balance exactly. Solar minus home usage, minus "to the grid (net)" leaves a few kwh.

That number is the exact difference between from powerwall and to powerwall in my case (yesterday that was a positive number).

If it balances each day, it would balance over a lifetime, yes?

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