Understanding Solar Production and Usage

Please help me understand the calculation used by Sense found under the Solar heading menu:
I understand the math used to calculate Production vs Usage vs To Grid vs From Grid: it should work like this: Usage = Production + from Grid - to Grid.

So for yesterday my figures look like this: 26.5 (U) = 31.9 (P) + 11.6 (toG) - 17.1 (fromG) and the math comes out to within 1 decimal point.

BUT, at the bottom of that page (under Solar) says my Powered by Solar was 56%. Where did Sense get that figure?

AND, when I look at the new Dashboard menu, View Detailed Usage, it shows my Solar % of Total as 120.5%. That looks more like the truth than the 56% shown on the other page. The Solar Production is shown as the same 31.9kWh and Usage the same 26.5kWh% as on that other page.

So, can anyone explain where the previous figure of 56% comes from?
[Edited to change 31.9% and 26.5% to correct measures of kWh.]

PoweredBySolar = 100*(Usage - FromGrid)/Usage

That calculation works for my numbers, would need to see your yesterday Solar screen to see what’s up with yours.

The sense solar % is a 0-100% production that is time based. You don’t get 150% or 275% when you are sending it back to the grid, so if your using 1000w and producing 2,750w… during that time you get 100%. Then if your using 1000w and producing 500w… it’s “50%”.

So the only way you could get “100%” is if you were making at least what you are using all day.

The other screen works as % of net production.

Thanks for the two input kevin1 and ccook. I can see that your screen shot does calculate, and show correctly the math. But I don’t see completely the logic to your example ccook.

So here’s the screenshot for yesterday:

Does that make any sense (yukyuk) to anyone?

As well, that 56% figure changes when I view each day separately, or weekly, so I’m sure it is not carried from period to period in the calculation.

And here is the screen from the Dashboard for the same period.

I know the graph does not show from 8-12PM, but usage was minimal. So on this page, where does the 120% come from, following your example ccook?
Thanks for your help.

So the formula I gave you was accurate for your screenshot. I was initially a little confused because you transposed “from grid” and “to grid” in your original post.

  (26.5-11.6) / 26.5 = 0.562 = 56%

That’s computed on a daily/weekly/yearly/bill basis, depending on date range settings, and shows how much of your Total Usage was supplied by Solar without considering “to grid” offsets. That’s important because some people get far less monetary credit for “to grid” solar electricity than they do for solar electricity that directly offsets “from grid” (i.e the different between buy and sell back rate).

The 120.5% expresses the total Solar Production divided by the Total Usage for the daily/weekly/yearly/bill time period.

31.9 / 26.5= 1.204 = 120.4%

ps: Off by 0.1% because there are hidden additional decimal places in data.

Both are useful metrics for the date range selected, depending how your solar tariff works. But the most useful thing to me is the actual TOU pricing.

Thank you again kevin1 and ccook! I do see the logic of it all now. But, as with so many things pertaining to Sense, it seems so convoluted that it takes a while to figure out.

ps - what does TOU stand for?

Regards. fredg

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TOU is time if use… some electric companies charge different rate during different times of the day/ weekend. Like 15¢ per kWH from 8am-6pm then 33¢ after 6

Thank you ccook. As we have constant rates here in Alberta, it hadn’t occurred to me what TOU might mean.

On another tack, I have been trying to write a comprehensive instruction manual for the Sense web based app. I find that there is no real explanation anywhere that I have looked, that explains what you just cleared up for me – and a lot more. I was doing fine until Sense changed the Usage window to Dashboard! This seems to be a rather useless step, as there’s nothing much there, until you click on the View Detailed Usage heading – which then only seems to bring up repeats of data and graphs which are already on other pages.

Would you be interested in vetting my writing, and then posting it on the forum if, and when, it make everything clear?
Fred Griffiths
Calgary, AB

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I think sense created their “% powered by solar” for those people who have the much more complex -hybrid grid tied/ AC coupling & DC coupling systems. Some of these systems, they will run off battery during the high TOU rates or the electric company doesn’t have a 1:1 rate for the electric going back to the grid.

At first I was confused about the % and wished I could turn it off or know what my net usage was since I’m on a flat rate (teer-rate) where it decreases after the first 500kwh and my tariff rate is 1:1. But some of these guys have ridiculous TOU where it might be 15¢ during the day then on the weekend it’s 52¢ per kWh then many power companies feed in tariffs are lower than what they sell it for.

And yes, you can send me anything you want… I do not excel at English/ grammar though.

I’ll help review as well. Here’s what a TOU looks like - I’m on an EV plan in California.

I raise you:
Highest Rates: Weekdays 2-8 p.m.
Weekday Summer Rates
Off-Peak: 43 cents from 8 a.m. to 2 p.m., and 8 p.m. to 10 p.m.
Super Off-Peak: 19 cents from 10 p.m. to 8 a.m.
On-Peak: 75 cents from 2 p.m. to 8 p.m.

Charging my EV at the most expensive time of the day, but fully charged by photons :wink:

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We would be sitting in the dark with no AC at 75 cents a kwh here!


I’m still having trouble believing the percentage of Powered by Solar as shown by Sense. Yes, the figures and formula explained in reply posts can show the 56%, but I cannot see that being the true powered by solar. The percentage has nothing to do with TOU or rates of cost or reimbursement.

As shown in my screen shot, I am sending more of my solar produced power to the grid than I buy from the grid, so the % of “powered by solar” in my house must be 100%.

Anyone care to try again to show where the Powered by Solar figure comes from?

That’s the percentage of your home’s Total Usage that is powered DIRECTLY by solar. Excess Solar Production that you send to the grid, is not counted because it doesn’t power your house. Your utility will likely give you credit for that extra energy, and in general that excess solar will be good for the environment (places like California sometimes have too much solar production forcing curtailment which can cause problems).

You can internalize that excess Solar Production to power your home and to increase that “Powered by Solar” percentage by:

  • Moving your usage patterns to use more Solar Production during the hours you are producing, instead of shunting it to grid.
  • Adding storage (batteries) to capture excess production for your time shifted usage.
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@fred2g , what type of inverter do you have? Hybrid or Grid tie setup?

There are 2 things as others have explained:
first is while the sun is out, how much of what the house uses was produced by your solar installation.
That is the “powered by solar” label
As an example from my home today:

From all the green (usage of the home) 81% (so far) today was provided by solar power.

When you go to dashboard → view detailed usage you will find something like this:

So today my solar produced almost 3 times as much as my home used.

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I think here in the app. “Powered by Solar” … the title below it would be for fitting. Which is “independent from the grid”

For yesterday… the “Powered by Solar” was 15% at my house which I’m guessing somewhere around 12% of yesterday I was 100% Powered by Solar” then the additional 3% was added into there when I was 1-99% Powered by Solar.

However my net production 84% and luckily I’m on a flat rate with a 1:1 tariff. So my grid is a free battery to me. Logically with that set up … yesterday, I covered 84% of my power bill. This month I’m sure that I will produce (+100%)more than I use but my Powered by Solar will be something like 15-28%

If I could toggle those % to see the 84% (net production) in the dashboard. I would since that is more what I’m interested in.

I have a SMA - SB5.0. Which is just a 5200 watt string - grid tied inverter that has 3 MMP trackers on it (3 arrays) … I have 19 325w panels. Fairly simple setup.


Hi Kolia - my set up is grid tie - so of course I need grid power to activate and synchronize the inverters. Mine are micro inverters made by LeadSolar. They went out of business last year so I can no longer monitor production via their web site. The solar installer recommended Sense, so I went with it.

I’m not sure what a Hybrid system is.

Looks like conventional microinverters, grid tie only.
Nothing hybrid (battery storage) involved

Yes Danny… that is correct. Does that make any difference to your understanding of the original question I raised? I am still baffled.