Calculation behind Power By Solar Percentage

I’m curious if someone can confirm how the solar percentage is being calculated, or point me to documentation that explains it. My guess is that it’s technically coincident solar percentage, as opposed to net solar. Both of which are useful, and in fact it would be really cool to see them both calculated next to each other to help try to move loads around to coincide with generation better. For example, last week I produced 86.2 kWh, and used 56.1, so my net solar would be 153.6%, however Sense is telling me it’s 36%, which feels about right for coincident generation considering most of my big loads happen late at night when it’s beneficial based on my TOU rate schedule.

I think most of the answer is right here in the v30 Introduction. The one piece of missing info is what interval is used for the calculation. (that would mean Solar Production / Total Usage for a short period of time)

In both sections, you can see your percent “powered by solar." This is an important metric that indicates how much of your usage has actually been covered by your solar production, rather than just being sent to the grid.

I did a quick experiment to figure out the update interval - It looks like that value updates in the same 1/2 second interval that the rest of the solar display does.

Initial Solar

5 seconds later, after starting my Tesla Charger

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Thanks, I think that confirms my assumption, but I wasn’t quite specific enough. Right there on your screen shot it makes perfect sense and is intuitive, because that screen is areal time snapshot. I was more referring to the summary in the trends or solar tabs, which provide a percentage for the day/week/month/etc time period that is selected. Extrapolating what you said, it looks like the same interval is probably used for those calculations, but given that the graphs are summing the usage and solar, it’s not quite intuitive to me that the number shown is the percentage of direct solar usage - i.e. the graph and other four statistics do not relate to the percentage number (sums vs a timeseries calculation). At least I think that’s what’s happening.

Good question. Two things.

First I was a little wrong in my definition above. The function for calculation should be:

Powered by Sunshine =  min(Solar Production, Total Usage) / Total Usage x 100%

That min is the key to the % difference you see between the orange and green bars and the “Powered by sunshine” number, both long term and short term.

I’m betting that the daily, weekly, monthly, and yearly powered by solar is the same calculation, but based on the summations/integrals of those two values. So the “to grid” solar is stripped off the solar production by that min function, which explains why the % number is lower than you would expect.

Thanks for confirming that. I guess it would be a little clearer to me if the number that I’ve circled in that screen shot had a slightly more descriptive label - I’m not sure without making it too long, but something like “Directly powered by solar”. Or alternatively, if another calculation appeared next to it showing “Net powered by solar” or something, just being a simple production/usage calculation, that would help to imply what the other one is. Maybe I’m the only one who thinks that way, but if not, could I request that it be considered as a feature update?

Must be confusing @benjamin.t.brannon…you have the same question as another post 2 days ago:
powered-by-solar-is-it-really-though
I believe there have been 1 or 2 prior posts since this “powered by solar” feature was rolled out that expressed similar confusion.

I agree - the % “Powered by sunshine” or “Powered by Solar” is confusing, especially for folks who have solar via net metering, because the “Powered by Solar” really doesn’t have a direct bearing on costs unless one is on TOU plan where the sell-back less than the buy price. Then it behooves one to squeeze as much into the “Powered by Solar” as possible (match usage to solar production). I also looked out into some of the utility/solar websites, but haven’t been able to find terminology for this measure… Two thoughts for Sense:

  1. It might be better if Sense had a switch fo the solar UI, either TOU or Net Metering that would show the more relevant values. Or just show all for both.

  2. Might also be good to have a glossary of terms as new ones are invented.

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My personal preference would be for both @kevin1 . I have TOU and net metering oddly, but also a personal desire to adjust my usage to times when the power is cleanest (either because it’s directly solar powered, or at times with the electric grid is cleaner).

Ah, thanks for that other post @james_reilley, I tried to search before posting my own, but I guess used the wrong keywords.

The more the better perhaps, i.e. “both”. I can see modal options getting somewhat confusing in the UI for other reasons. And yes, a glossary/legend would be good. Better would be some more clarity in the display so it’s immediately obvious what’s what.

e.g In @benjamin.t.brannon’s screenshot, I kinda want the following (at least conceptually) to simplify things:

  • Solar = YELLOW
  • Home/Sense = ORANGE (well, of course)
  • From Grid = GREEN … ok, maybe it should be red but …
  • To Grid = RED … because it’s less than ideal to be sending power to the grid.

The bar graph could include the from & to grid amounts for that period and use the appropriate colors or perhaps “styles”. If you take a step back from the graph you see you need to confirm through number-matching that “orange = production” and “green=usage” in a way that then establishes a mismatch of color in regard to both fromGrid/toGrid and TOU/Net Metering. I sympathize with the graphic designers here.

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There should be an option that says “I have net metering”. When checked it will show your production in excess of your use. At times I am producing 880% of my usage and it says 100%.
That electricity is stored at full value so I want to know about it.
I find it annoying that while I produced 87% of my electric used Sense says 39%.

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I am highly confused by this calculation and its purpose. I’m assuming everyone with using this sense with solar is grid tied and sense is assuming everyone is running hybrid grid tied systems (grid tied with batteries) which I’m not super familiar with. I think sense think our goal is to run off the panels and charge the batteries during the day night then live off the batteries at night. That being said… still if your batteries get to 100% and you are feeding the grid, why wouldn’t you want to see 120% powered by solar? I think everyone here would like to see solar production % vs usage.

And not what % of the time was the sun out today.

@ccook,
The calculation isn’t confusing, just different than what is important to folks like me and you, who have solar with some form of net metering and billing. With net metering, we only care about what the net usage is, and maybe when (I have TOU). But more and more solar service plans are moving to time-of-use metering (TOU) where there are different from-grid (retail) and to-grid prices (lower) prices. In that situation, a user wants to use as much of the energy being produced by solar as possible since that’s the only way they get full retail value for it. Otherwise they sell it back at a lower price. So the powered by solar calculation is really designed to help that growing body of users…

I think the time of use rates are just the power companies are buying solar kWH from customers at a lower rate. I must say … I went a month thinking I was only producing ~20% of my total usage. Then I had a few days were I had more production than usage and notice it was still at 20% then I had a crappy rainy/ cloudy day where I produced ~1 1/2 sun hours but this “calculation” shows 38%.

I defiantly wish sense would expand on their electricity cost section. For instance I have a line fee $12 then I have 1 rate until we reach 500 kWH, 2nd rate 500-1350 and then a 3rd rate for over 1350. I will probaby never be in the 3rd rate again but I’ve hit the 2nd step a few times.

@ccook You only need to look briefly at @kevin1’s truly exhaustive dives into TOU and tariffs to know that for Sense to “expand on their electricity cost section” is pretty much the definition of non-trivial:

In my mind the dynamics of TOU/tariffs, meaning the frequency of change and feedback loop to solar producers/consumers on the grid, is going to get faster than any statically-entered numbers could accommodate. So, beyond being able to encode in some way the many varied TOU rates, you also have the issue of “by the time you’ve entered it it changed”. It’s a tough ask and I can understand why Sense might want to focus elsewhere for now.

One can imagine a viable solution though: A neat little button in Sense along the lines of

“Subscribe to TOUP”;
Enter server name ___________.

TOUP = Time Of Use Protocol.

Like all protocols, a many-varied industry would need to get behind it and standardize things. Non-trivial and mostly beyond Sense’s control. But some things do get going from the bottom-up!

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It might simplify things to remove utility cost rates from this discussion, or at least separate them out, since currently they don’t yet exist in sense unless you have a very simple pricing structure and the graph/page we’re talking about is really just showing energy. With that in mind, I agree with @ixu above (though I’m not too concerned with colors as long as there’s a legend), and along with that, the two different solar percentage calculations. I’m pretty sure all the numbers for all this already exists, it’s just a GUI change.

@kevin1 an option for TOU or Net Metering style sounds reasonable, but I’d hope that they’d each have a checkbox or something to allow both to be selected if desired, or neither just in case. Like I said for me personally, my sustainability motives don’t align with my utility pricing scheme, so ideally I’d like to check both quickly.

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