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Tesla Removing System Performance & Seasonality Language from website

iorchii

Member
May 18, 2014
36
21
United States
While researching if my solar production is producing as expected for the DC system size I purchased - I realized that Tesla removed the following seasonality factor info on 03/24/2021 to approximate estimated solar generation by month.

How can I ensure my system is working well?
System performance is measured in how many kilowatt-hours (kWh) it produces over a given period of time. A simple way to tell if the system is performing as expected is to utilize the “Daily kWh Rule-Of-Thumb” method below:
DC SYSTEM SIZE: Gather your DC (direct current) system size from your system designs or under "System Description" on your contract.
  1. SEASONALITY FACTOR: Systems perform differently based on the time of year and so the production estimate will vary throughout the year. Seasonality Factors are based on the knowledge that the longest day of the year is June 21st and the shortest December 21st. Use the Seasonality Factor listed below:
    • Summer
      • May- June-July: 5 to 7
    • Fall/Spring
      • August-September-October/February-March-April: 3 to 5
    • Winter
      • November-December- January: 1 to 3
  2. CALCULATE ENERGY PRODUCTION ESTIMATE: Estimated daily kWh system production= DC System Size X Seasonality Factor
  3. ACTUAL ENERGY PRODUCTION: In your Tesla app, review the actual daily solar energy production for a recent full day. It's best to use a day where the cloud cover percentage is near zero.
  4. ANALYZE: Compare the estimate you calculated to the production. If the production is equal to or greater than the estimate, then the system is performing as expected. If the production is less than the estimated, look to see whether shading or weather are a factor and if the low performance is consistent from day to day. In winter, performance for some systems may be near zero due to a combination of shading and weather.


Based on the seasonality factor noted above - does it equate what the estimated solar generation you have for either Solar Roof or Solar Panels?
 

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jjrandorin

Moderator, Model 3, Tesla Energy Forums
Nov 28, 2018
10,874
12,597
Riverside Co. CA
Those seasonality factors are fairly accurate for me as a ballpark, for where I live in southern california. No idea if or how they might work for someone else in another state. Its a pretty wide range, though.

My system size is 8.6kW. That means during the May to June timeframe, based on that calculation, the numbers are 43 - 60 kWh. My system generates, on a cloudless day, between 45-54kWh.
 

iorchii

Member
May 18, 2014
36
21
United States
Thank you for your feedback. I may have to wait for PTO & have the Tesla Solar Roof team come out to check my inverter & tiles.
Currently at a 10kW system & my highest is 47 kWh with cloudy days at 36 kWh & located in SCA also - none of the tiles are shaded with ideal West & East solar generation. Quite odd for such low kWh.
 

jjrandorin

Moderator, Model 3, Tesla Energy Forums
Nov 28, 2018
10,874
12,597
Riverside Co. CA
Thank you for your feedback. I may have to wait for PTO & have the Tesla Solar Roof team come out to check my inverter & tiles.
Currently at a 10kW system & my highest is 47 kWh with cloudy days at 36 kWh & located in SCA also - none of the tiles are shaded with ideal West & East solar generation. Quite odd for such low kWh.

Ideal generation is south, from what I understand.
 

hurjio

Member
Feb 3, 2018
130
42
Southern California
Just to clarify, you have solar roof tiles and not solar panels, right? You'll have to find people with solar roof for comparison, as performance between solar roof and solar panels are probably not equivalent. Also, I would guess that the seasonality wording from your original post likely is directed at solar panel performance and not necessarily solar roof, but I could be wrong.

Also as stated by @jjrandorin, south facing tiles/panels is the most optimized direction.
 

jboy210

Supporting Member
Supporting Member
Dec 2, 2016
5,518
3,508
Northern California
Thank you for your feedback. I may have to wait for PTO & have the Tesla Solar Roof team come out to check my inverter & tiles.
Currently at a 10kW system & my highest is 47 kWh with cloudy days at 36 kWh & located in SCA also - none of the tiles are shaded with ideal West & East solar generation. Quite odd for such low kWh.
Solar roofs produce less than panels of the same size. We have a 12.75 system with 7.5 kW facing due south (181 degrees) and the remainder on the North side. Average daily production is around 50 kWh. However we have shading to the West that starts cutting into production 3-4 PM. Peak production is around 8.4 kW.
 

iorchii

Member
May 18, 2014
36
21
United States
Just to clarify, you have solar roof tiles and not solar panels, right? You'll have to find people with solar roof for comparison, as performance between solar roof and solar panels are probably not equivalent. Also, I would guess that the seasonality wording from your original post likely is directed at solar panel performance and not necessarily solar roof, but I could be wrong.

Also as stated by @jjrandorin, south facing tiles/panels is the most optimized direction.
You are correct - solar roof tiles & seasonality wording were for solar panels.
 

iorchii

Member
May 18, 2014
36
21
United States
Solar roofs produce less than panels of the same size. We have a 12.75 system with 7.5 kW facing due south (181 degrees) and the remainder on the North side. Average daily production is around 50 kWh. However we have shading to the West that starts cutting into production 3-4 PM. Peak production is around 8.4 kW.
Thank you for your response. Per your numbers than should be on par.
My peak production is 5.7 kW.
Can your Powerwall charge more than 5kW from your Solar roof?
 

wwu123

Member
Apr 11, 2017
429
355
Silicon Valley, CA
Thank you for your response. Per your numbers than should be on par.
My peak production is 5.7 kW.
Can your Powerwall charge more than 5kW from your Solar roof?

Your 47kwh max daily production could indicate a bit of concern, but note that with your solar tiles split between east and west, your daily peak (5.7 kw) is going to be lower vs a comparable system all facing in one direction. Your output graph over the day is going to be spread over a wider and flatter period, because your east tiles will peak in the morning and decline in the afternoon, while your west tiles will do the opposite. 5.7 kw sounds reasonable for that size if split between east and west, but there should be long flat period mid-day where it is generating close to that.
 

iorchii

Member
May 18, 2014
36
21
United States
Your 47kwh max daily production could indicate a bit of concern, but note that with your solar tiles split between east and west, your daily peak (5.7 kw) is going to be lower vs a comparable system all facing in one direction. Your output graph over the day is going to be spread over a wider and flatter period, because your east tiles will peak in the morning and decline in the afternoon, while your west tiles will do the opposite. 5.7 kw sounds reasonable for that size if split between east and west, but there should be long flat period mid-day where it is generating close to that.
CEADA1B4-13D1-4F3F-840F-9AC6867D75D5.png

Would this be considered long flat period mid-day. The 2nd is just one of those very ugly days.
 

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