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Actual available energy in Powerwall

m3-pw2

Member
May 3, 2019
98
51
USA
I’ve signed up for virtual power plant, and today was the first event. The battery was charged to 100%, and kept at that level without depleting until it started to discharge. The event took around 3 hours, and the two Powerwalls discharged to 20% while providing 17.5kwh based on app. The Powerwall portal through WiFi had a battery level of 25% instead of 20%.

Does someone know how much energy is expected to be provided? My numbers are not adding up to 17.5kwh. Each battery has useable storage of 13.5kwh, so total of 27kwh. 80% is 21.6kwh which is far from 17.5kwh.

I am aware that the Powerwall round trip efficiency is 92.5%. So single trip is 96.25%?

Also when I called Tesla energy support, I was told that the Powerwall keeps 1kwh, and it is not included in the reported battery level. The purpose is to avoid draining the battery entirely which would need tech intervention to bring it back to life.

Has anyone done any tests and could share some data points?
 

jakestgermain

Member
Jun 26, 2019
120
27
North Smithfield, RI
I have had three events with the VPP this year. All three times my powerwalls discharged between 18.4-19.1. I think if you hold 29% in reserve 20%+5% on the actual gateway+4% for one way losses. You will get around 19kwh
 

m3-pw2

Member
May 3, 2019
98
51
USA
I have had three events with the VPP this year. All three times my powerwalls discharged between 18.4-19.1. I think if you hold 29% in reserve 20%+5% on the actual gateway+4% for one way losses. You will get around 19kwh

Thanks for this feedback. So you have 2 Powerwalls, and during VPP events, they discharge 18.4-19.1KWh?

19KWh or so is what I would have expected as well for this event of 80% discharge, and accounting for the 5% the powerwall reserves, and the one-way losses of about 5% (Tesla spec says it is 90% efficiency round-trip, not 92.5% as I mentioned in my original post). And there is maybe 2-5% error in measuring the energy in gateway.

So I am not sure why I only got 17.5KWh. I will try to reach out Tesla support. My batteries are about 1 year and 4 months old.
 

jboy210

Supporting Member
Supporting Member
Dec 2, 2016
5,386
3,340
Northern California
I read somewhere on this forum about inconsistencies between PW data obtained by the using the API. Also, I seems to remember they being different that provided by the app. Hopefully someone will more experience will chime in
 

wjgjr

Active Member
May 11, 2020
1,300
1,034
Silver Spring, MD
There is a difference - if you use the API or directly access the gateway via your web browser, you will see it scale from 0%-100%, and it appears that - on that scale, your home power will shut off at 10% remaining power. If you look at the powerwall reserve on the app, it appears that same scale would be roughly -5% (as in below 0%) to 100%, and shutoff occurs at 5% remaining.

So, in general, the API/browser view will show a higher number than the app, with the biggest difference being where the PW is depleted.
 

m3-pw2

Member
May 3, 2019
98
51
USA
What I remember is that Tesla keeps a small amount of energy in the Powerwall so that it doesn't drain entirely. When it drains entirely, the Powerwall will not be able to come back to life on its own, and a technician must come to the house to resuscitate it.

Imagine there is a power outage, and that solar doesn't provide any production for a day and two. After Powerwall drains fully, it still needs some power to keep checking when solar system can start producing energy again.

So the app shows battery charge % excluding this hidden reserve, while the API/gateway portal has the battery charge % including this hidden reserve.
 

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