Solar Offset vs Energy Offset

[RonNJ]

Hi All,
After waiting for more than 3 months after installation, we finally got our solar turned on! Got in touch with Tesla to get the app runnind and found the following numbers: can you guys help me decipher what these numbers mean?
Impact page showed 22.3 kwh solar and 31.6 kwh home. energy offset

 

[BrettS]

Hi All,
After waiting for more than 3 months after installation, we finally got our solar turned on! Got in touch with Tesla to get the app runnind and found the following numbers: can you guys help me decipher what these numbers mean?
Impact page showed 22.3 kwh solar and 31.6 kwh home. energy offset

That is showing that your solar system produced 22.3kWh of power and your home used 31.6kWh of power. If you were looking at today’s numbers, then it will show the current numbers at the time you looked, so the numbers will change by the end of the day.

The energy offset percentage is the amount of power that you used that was offset by the solar you produced. So in your case, with the above numbers, that would be about 70%.

 

[wjgjr]

I am assuming you are looking at "Impact" screen on the app. I see 4 numbers (noting I have PWs - not sure how it differs otherwise.) The kWh numbers are the amount of solar generated for the time period (22.3 for you) and the amount of energy your home used (31.6 for you.) There is also an "Energy Offset" percent, which is 100 * solar / home.

The last number is the self-powered percent, and it is intended to capture the amount of your home load that comes directly from your solar power (so if you send some of your solar to the grid and then get grid power back later, your "self-powered" score will go down.)

That said, I have found the calculation to be a bit odd, though it might be because my PW use all happened before PTO. As best I can tell, the calculation for me seems to be 100 * (total solar generated - solar exported - PW used**) / home.

**This seems to include both the PW energy exported as reported in the app and the PW energy expended to operate, which is not reported in the app and includes the losses associated with charging the PW and operating it.

Why I found the calculation odd is that I would consider the PW energy used to be part of being self-powered since it is charged by solar. Others who use their PWs daily to manage peak times might be able to confirm the correct behavior. Maybe now that I have PTO it would behave differently (but I use backup only mode, so I cannot test this.)

 

[BrettS]

When I was running off grid what I noticed was the following:

The self powered percentage is only solar power that directly powered your home at the time it was produced. It doesn’t take powerwall power into account at all, even though it came from your solar system. So even though I might have been off grid for the entire day I would still get around a 40-50% self powered score since the powerwalls would power the house for 50-60% of the day when the sun was down.

The energy offset also doesn’t take powerwall power into account. It simply looks at the amount of power your home used that day (from any source) as compared to the amount of power that your solar system produced. It doesn’t matter where that solar power went, it’s just comparing the amount of power that was generated to the amount of power that your home used.

 

[wjgjr]

When I was running off grid what I noticed was the following:

The self powered percentage is only solar power that directly powered your home at the time it was produced. It doesn’t take powerwall power into account at all, even though it came from your solar system. So even though I might have been off grid for the entire day I would still get around a 40-50% self powered score since the powerwalls would power the house for 50-60% of the day when the sun was down.

The energy offset also doesn’t take powerwall power into account. It simply looks at the amount of power your home used that day (from any source) as compared to the amount of power that your solar system produced. It doesn’t matter where that solar power went, it’s just comparing the amount of power that was generated to the amount of power that your home used.

So, same thing I am seeing. For energy offset, that seems to make sense as a way to calculate it, and it balances out in the end (looking at month or year charts.)

But I feel like the self powered calculation doesn't seem to make sense or match how they describe the goal of the self-powered mode. It seems like as long as the PW is tied to charging from solar, it should count as being self-powered, because it really is - it is energy generated and consumed without need of the grid. That is why I was wondering if post-PTO, PW use might factor into the self-powered percentage and I just wasn't aware because I have not tried operating off PWs so far since I got PTO. Since my goal has not been to get a high self-powered score, I haven't concerned myself too much with it - just find the calculation odd.

 

[BrettS]

Actually I just remembered one more thing. You only get the impact screen if you’re in backup only mode (or, apparently, have a solar only system). If you go into self powered mode then you get a “Performance” screen instead that does take powerwall use into account. I’m not sure which screen you get for the Advanced option.

 

[RonNJ]

Thank you all for your replies. Your explanations gave me an idea and I was able to figure out how to calculate the self powered %.

Below is how I calculated self powered %:
My Energy usage page shows 22.3 kWh produced. Scrolling down I found that out of 22.3 kWh, 60% was sent to home (60% x 22.3 = 13.38 kWh) and 40% to grid. Since my home usage is 41.6 kWh, my self powered is 13.38/41.6 x 100% = 32% which matches the number from the Impact page.

thanks again for all your help!