Powerwall efficiency 86%....

[Ampster]

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.

 

[Briar_Reed]

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

 

[sorka]

My overall April efficiency went from 86% in March to 89% which is a pretty large jump.

 

[aesculus]

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.

 

[eml2]

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.

 

[Southpasfan]

Huh.

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?

 

[sorka]

My efficiency has gone up dramatically in June with the high heat. I thought it would go down with the amount of energy required to actively cool the batteries but it hasn't been the case.

94% in June so far. I we assume 4% of that is the overhead just to keep the powerwalls up and running, then I'm only losing 2% on the conversion which doesn't seem possible.

 

[power.saver]

My efficiency has gone up dramatically in June with the high heat. I thought it would go down with the amount of energy required to actively cool the batteries but it hasn't been the case.

View attachment 675705

94% in June so far. I we assume 4% of that is the overhead just to keep the powerwalls up and running, then I'm only losing 2% on the conversion which doesn't seem possible.

Are you taking all your readings with the PWs at the same SOC? If not, then you should adjust for that. For example, if the last reading was not at 100%, and there is 24kWh to make it 100%, then kWh Into PWs should be closer to -450kWh and your percentage for June 21 would be 89% which is similar to the other months.

 

[sorka]

Roughly the same soc.

It was also up significantly in May.

 

[Briar_Reed]

A bit late in adding my June input, but for some strange reason my efficiency dropped to 83.2%, after being up the previous 2 months and is about what it was during past winter (cold) months.

 

[sorka]

Mine is holding about 90% for July so far.

 

[Briar_Reed]

Mine is holding about 90% for July so far.

View attachment 684291

Would you mind sharing the method do you use to obtain your kWh into & Out of the PW's? For some reason, I have not figured out how to do this with the Tesla app.

 

[aesculus]

If I use the api/meters/aggregates and the energy_exported/energy_imported I get 84% efficiency. This is for 18 month old PW 2's that run in Cost Savings mode.

Is this energy_exported and energy_imported for the life of my system? I ask because the instant power is the current power (well maybe 15 seconds behind)

• battery:
  
  {
  • last_communication_time: "2021-07-14T10:43:01.089846416-07:00",
  • instant_power: -3670,
  • instant_reactive_power: -30,
  • instant_apparent_power: 3670.1226137555677,
  • frequency: 59.987,
  • energy_exported: 3413300,
  • energy_imported: 4054340,
  • instant_average_voltage: 244.65000000000003,
  • instant_total_current: 75.4,
  • i_a_current: 0,
  • i_b_current: 0,
  • i_c_current: 0,
  • last_phase_voltage_communication_time: "0001-01-01T00:00:00Z",
  • last_phase_power_communication_time: "0001-01-01T00:00:00Z",
  • timeout: 1500000000,
  • num_meters_aggregated: 2,
  },

 

[ArizonaJon]

Would you mind sharing the method do you use to obtain your kWh into & Out of the PW's? For some reason, I have not figured out how to do this with the Tesla app.

Go to the Energy Usage Screen and activate all options - home, solar, battery and grid. See Left snippet below. Then scroll down to show the data - right snippet, the numbers next to the green battery shows the from and to powerwall. (If you can't find the Energy Usage screen, from the POWER FLOW screen click on the 3 vertical bars at the right of the words POWER FLOW.) Note to get useful information you need to take many days of data to mitigate the changes in the battery state of charge. I just checked my data for my first year of usage. From powerwall was 4,966 KWh and to powerwall was 5,605 kWh for a 88.6% efficiency.

 

[Briar_Reed]

Go to the Energy Usage Screen and activate all options - home, solar, battery and grid. See Left snippet below. Then scroll down to show the data - right snippet, the numbers next to the green battery shows the from and to powerwall. (If you can't find the Energy Usage screen, from the POWER FLOW screen click on the 3 vertical bars at the right of the words POWER FLOW.) Note to get useful information you need to take many days of data to mitigate the changes in the battery state of charge. I just checked my data for my first year of usage. From powerwall was 4,966 KWh and to powerwall was 5,605 kWh for a 88.6% efficiency.

View attachment 684530View attachment 684531

Thx, I can see and download the From/To Powerwall data in the Day view, but not for the week/month/year setting, or am I missing something?

 

[Southpasfan]

I only get "to" and "from" in the day view as well, I think to get it for longer stretches you have to download the data or simply add it up day by day.

 

[ArizonaJon]

I have a spreadsheet that I use to record each days resuts. You can go back on the day view for some period of time - not sure how long. It's a real pain. Tesla should provide weekly, monthly and annual summaries, but ?????

 

[MorrisonHiker]

I have a spreadsheet that I use to record each days resuts. You can go back on the day view for some period of time - not sure how long. It's a real pain. Tesla should provide weekly, monthly and annual summaries, but ?????

They used to provide the To Powerwall value for all report periods but removed it a while back, probably because people were wondering where the energy went.

I really wish they would add a date picker we could quickly jump to a specific date. Web pages have had date pickers/calendars for decades but in the Tesla app, you have to go one day at a time.

 

[sorka]

Would you mind sharing the method do you use to obtain your kWh into & Out of the PW's? For some reason, I have not figured out how to do this with the Tesla app.

I'm using their API in a google sheets script to fetch and fill in each days worth of data. It can fetch as many days as are missing but the API itself will only fetch one day at at time.

https://owner-api.teslamotors.com/api/1/energy_sites/<site id>/calendar_history?kind=power&end_date=<date>

date is of the format:
2020-12-17T07%3A59%3A59.999Z

You need to add the auth header with a valid token which can be a pain to generate with the new process. I just grab mine from teslafi every few months:

"Authorization": "Bearer qts-7c54f5fe32f3678c8319d0848fefb678179aafedfce849817c613caa14df0bfe"

My example does not include a valid token

 

[aesculus]

If I use the api/meters/aggregates and the energy_exported/energy_imported I get 84% efficiency. This is for 18 month old PW 2's that run in Cost Savings mode.

Is this energy_exported and energy_imported for the life of my system? I ask because the instant power is the current power (well maybe 15 seconds behind)

I realized that this is the total efficiency which includes near term AC-DC-AC losses as well as long term degradation. If we assume that the AC-DC-AC losses are on the order of 10% then I am seeing more like 5% degradation.