# “Usage” v. “From Grid”

Hello All….

I am not an engineer! Nor am I a math guy. I am a retired lawyer so I can only divide numbers by 33.33%!

But my wife is an engineer and we are going through some electric bills and trying to make “sense” (pardon the pun) of our new FPL electric bill (we live along the eastern, central coast of FL) that now has a new minimum charge for individuals that do not use some threshold amount of electricity. Additionally, our solar panels were taken down recently as we needed a new roof due to the insurance crisis happening here.

I am posting a screen shot, below, of our energy usage for a day when we were not producing solar when the new rood was being put on. One will notice that our “Usage” of 60.9 kWh’s is different than our “From grid”, being 63.6 kWh’s.

How can that be?

Why would we get more electricity from FPL than we use?

And please, dumb it down for me?

Bob

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Anyone?

If not, I will have to make a liquor store run to get more rum to sip while pondering this dilemma….

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that is a 4.25% difference.
I would say this is an interesting question to send to support@sense.com.
Please post their reply, i for sure would be interested in that.

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Hmmm. I’m guessing there is just some numerical garbage lurking in your raw data at the Sense mother ship due to you still having the solar option on with no solar input. From the data science side, sometimes data we think is zeroed out, is stored as NA (not available) - that could be what Sense is seeing for your solar feed. NAs have weird behaviors when you do math and computational decisions based on them.

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A question for all solar users out there. I always thought that net usage (House usage - solar production) would always be the same as From Grid - To Grid, but I’m seeing smallish monthly or billing period differences:

House usage - solar production
1759.2 - 694.1 = 1065.1

From Grid - To Grid
1277.8 - 198.7 = 1079.1

I always thought the difference rule applied with f(x) (really f(t)) being Home usage and g(x) being solar and f(x)-g(x) being net. The only difference is that From Grid and To Grid splits that into positive and negative values.

House usage - solar production = -2130.8 kWh
From Grid - to Grid = -2139.6
dividing the one by the other gives a 0.4 % difference which I think are within measurement error range.

Your numbers give 1.3% difference though.

Thanks for checking yours. I’m wondering if Sense made a change to how they calculate To Grid / From Grid that created or expanded the difference between the net usage calculated those two different ways. There’s definitely some difference - I captured this screenshot of the Solar tab for May 9th on May 10th, 2022.

A screenshot of the same day, May 9th today shows a From Grid that is 1.0kWh larger.

Hmmm.

I keep track of a lot of numbers in a spreadsheet.
I write down most numbers like PV generation and “to grid” after sunset.
Next morning I go back to previous day to enter usage & “from grid”.
every day the numbers for PV generation & to grid differ from differ from the next morning reading.
During the day they are always higher, no exception. Most of the times 0.1kWh, sometimes 0.2 and I think I remember 0.3kWh (but not 100% sure).
30 days x 0.1 = 3kWh difference in a month.

Do you see the same? I will take some screenshots and post tomorrow.

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I have not checked the numbers in that way but I know our SMA inverters use small amounts of electricity. On Sense, the electricity we are producing at night is a negative number. That makes sense to me because the inverters are “on,” and drawing some electricity.

I will contact Sense and send them the screen shot.

The mystery continues for me….

Exactly what we are seeing.

I sent an email to Sense Support. I will post what they advise.

Bob

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Yesterday evening 8pm after sunset

This mornings looking back at yesterday

Given the fact my inverters use 35 watt of power from the grid when there is no sun:
24:00-20:00= 4 hours x 0.035 = 0.14 kWh
So @bob4 is spot on.
The difference I see is the usage of my inverters after sunset till end of day.
Further proven by this mornings numbers from midnight till the sun came out:

Thanks @bob4 for clearing that up for me

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@bob4 , I’m interested in what support has to say as well. I wish I had more old screenshots of the Solar tab to compare, but it sure seems like there was a change made in how From Grid is aggregated / integrated from the underlying data. I’m also interested in hearing from anybody about thoughts on situations (that don’t involve batteries, or utility credit limiting) where Total Usage - Solar Production gives a different Net Usage than From Grid - To Grid.

From Sense Support:

Hello Bob,

Thank you for contacting Sense.

We understand that your “Usage” is different than your “From Grid” kWh.

Upon review, we found a problem with your Sense monitor. It looks like there is a signal problem between the sensor and the monitor. We’ve seen some cases where there is some corrosion in the pins where the sensor plugs into the monitor, this could explain the disparity between your “usage” and “from grid” power.

I have escalated this ticket to my colleague to review this issue. They will be reaching out to you directly to provide the next steps within the next 24 business hours.

If you have any questions in the meantime, please do not hesitate to reach out to us.

Thanks,
Aravindh
Sense Support

Stay tuned……

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They have some protective grease in them as well.

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From Sense Support:

Hello:

Thanks for your patience. We have a couple of options for you:

1. To fix the corrosion, we have created a short extension cable that includes slightly larger pins and a bit of protective grease. We have found that in most cases, simply inserting this cable between the monitor and sensor corrects the problem and prevents future connection issues.
1. Have you send in your unit which will allow our lab tech to do a health check and pair new current sensors. This will be a free service but will require you to send in both your monitor and current sensors.

Please let me know how you would like to proceed.

Thanks,

We requested the extensions. I will also clean off, contact cleaner, etc., the plugs for the sensors when I add the extensions.

So our data is corrupt, I will assume?

Should I reset our monitor and start anew? Thoughts?

Bob

Are your going to reinstall the solar after the new roof is on ? If so, I would wait on reset and subsequent solar calibration until after the reinstall.

I would not reset, you would loose all your usage/production data.
Technically it just should get better after installing the extensions.

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Already reinstalled! And because of a weird dry spell here in Brevard County, FL, we are hitting all time highs!

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I am really impressed with the Sense Support Team! Today, Sunday, 08072022, I received a FedEx package with two new cables to plug the sensors, including the solar sensors, into the monitor, from Sense!

Easy peasy!

Turn circuit breaker for the monitor to off. Unplug the sensors from the monitor, plug the new, short cable into the sensors, then plug the cables into the monitor, and turn the circuit breakers back on.

It took some time to reboot and I did have to find my network again, but no big deal!

Up and running.

I will keep you all posted of any issues/messages, etc. And let’s see if the accuracy improves.

Thank You Sense Support for your quick communications and your VERY fast response for a fix!

Bob