Consumption monitoring not matching electric bill

[soleremy]

Hi,

I have roughly a 14.5kwh sunpower system on my roof. My online portal lets me use hourly electric usage, along with how much my system is generating. For my billing period ending February 5th the online portal says I sent 5.3kwh to the grid. My electric bill states that I took 278kwh from the grid which is totally different, I would understand a small discrepancy, but this seems rather large. Please let me know if this makes sense or if I am totally off base here,

[soleremy]

Attached are the relevant portions of the electric bill and my online monitoring system.

[bcroe]

Hi,

I have roughly a 14.5kwh sunpower system on my roof. My online portal lets me use hourly electric usage, along with how much my system is generating. For my billing period ending February 5th the online portal says I sent 5.3kwh to the grid. My electric bill states that I took 278kwh from the grid which is totally different, I would understand a small discrepancy, but this seems rather large. Please let me know if this makes sense or if I am totally off base here,

Your system would be rated in KW, not KWH. The idea of sending a bucks worth of energy (5.3KWH) from
an array of 14.5KW over much time indicates your measurement device is completely useless. My system
of similar size can generate that energy in much less than an hour in sun, sort that out first. Bruce Roe

[J.P.M.]

For starters, your system is rated in kW (power) not kWh (energy).

Next, the 278 kWh is most likely what the utility sent to you over the billing period from 01/09 to 02/05.

As for what the Sunpower monitor is doing, the best place to get answers for that is the installer. After that I'd call Sunpower and ask them.

Have you done either yet ? I'd suggest that since you paid for their product, they are the best place to start.

What the Sunpower data may be telling you is that for the period in question,the system generated 907.3 kWh of which 902 kWh were either sent to the grid or used on site, with the 5.3 kWh either used on site or sent to the grid.

[soleremy]

Your system would be rated in KW, not KWH. The idea of sending a bucks worth of energy (5.3KWH) from
an array of 14.5KW over much time indicates your measurement device is completely useless. My system
of similar size can generate that energy in much less than an hour in sun, sort that out first. Bruce Roe

I didn't just generate 5.3kwh. According to the monitoring system I generated 907.3kwh and used 902kwh hence I sent 5.3kwh to the grid.

[soleremy]

For starters, your system is rated in kW (power) not kWh (energy).

Next, the 278 kWh is most likely what the utility sent to you over the billing period from 01/09 to 02/05.

As for what the Sunpower monitor is doing, the best place to get answers for that is the installer. After that I'd call Sunpower and ask them.

Have you done either yet ? I'd suggest that since you paid for their product, they are the best place to start.

What the Sunpower data may be telling you is that for the period in question,the system generated 907.3 kWh of which 902 kWh were either sent to the grid or used on site, with the 5.3 kWh either used on site or sent to the grid.

Yes the 278 kwh is what the utility company is saying they sent to me. Sunpower is saying I should have sent them 5.3kwh over the course of the same time period. I spoke to the installer and sunpower, they cannot give me a good answer as to why there is such a discrepancy. We left things off where I would contact the electric company and see if there is a problem with my meter. I thought someone here may have a little more insight as to what may be happening since I hear faulty meters are somewhat rare.

[littleharbor]

Just out of curiosity what would your typical kwh. usage had been before the addition of solar?

[soleremy]

The year before solar I used an average of 1534 kwh per month. I am in NJ if that helps, so peak usage is in summertime with AC running. Winter months were generally less. 900kwh Jan-Feb seems pretty normal.

[bcroe]

I didn't just generate 5.3kwh. According to the monitoring system I generated 907.3kwh and used 902kwh hence I sent 5.3kwh to the grid.

Let me try again. It might say you generated 907.3 KWH, of which you concurrently consumed
902.0 KWH, the remaining 5.3KWH were temporarily sent to the grid. However overall you also
consumed that 5.3KWH (at night) and an additional 278KWH from the grid.

Your summer consumption is near 5 times mine, I am wondering how efficient it is. Bruce Roe

[soleremy]

Let me try again. It might say you generated 907.3 KWH, of which you concurrently consumed
902.0 KWH, the remaining 5.3KWH were temporarily sent to the grid. However overall you also
consumed that 5.3KWH (at night) and an additional 278KWH from the grid.

Your summer consumption is near 5 times mine, I am wondering how efficient it is. Bruce Roe

Thank you for your replies. My summer consumption was roughly between 2k and 3k KWH, we have roughly a 3700 sq ft house that was built in the mid 80s and isn't insulated as well as it could be.

Regarding the 5.3kwh at night, I don't believe that is what the online system is saying. I am almost positive it is saying that I should have sent a total of 5.3kwh back to the grid over the course of the time period. This would be taking night time consumption into account. See the attached screenshot from sunpower for a bit more detail on my daily usage.

[Superman_006]

How does the Sunpower portal know what is being used in the house vs back to the grid? If you have just a single panel and you are connected your inverter by back feeding a breaker and you put CT's on your mains then your are going to be off because CT's are not able to read to which direction the energy is going and it would just read energy.

I would think you would have to re-wire your entire house so you would have a panel with just solar in it between the meter and all the circuits then put your CT's on the "mains" going to your circuits or use something like curb or sense that would take all the devices or circuits and be able to subtract them from your solar output to figure out a net-metering type of way to get an actual grid in/out minus solar output to have something that agrees with the electric bill.

[ButchDeal]

because CT's are not able to read to which direction the energy is going and it would just read energy.

CTs certainly CAN read the direction the energy is flowing. Some equipment does not report the direction but other equipment reports it as positive or negative depending on direction.

[soleremy]

How does the Sunpower portal know what is being used in the house vs back to the grid?

I don't know the technicalities, but they offer something called a "consumption monitoring kit" which I have installed and I get reports on how much energy I am using hourly along with how much I am producing. Check the screenshot a few posts ago to see what I see.

[Superman_006]

Perhaps things have changed thing and someone has figured it out. But I was always told (and my understanding) that only DC could be measured bidirectional with the clip on CT's and that AC current could not and it would be measured as RMS value, and on that there is no directional sense with AC (alternating current) with only the use of a clamp meter. However my knowledge would be 15+ years old though my Fluke meter says bi-directional on it but it also only works on DC. When I reverse the clamp I get the same reading when dealing with AC.

[ButchDeal]

Perhaps thing have changed thing and someone has figured it out. But I was always told (and my understanding) that only DC could be measured bidirectional with the clip on CT's and that AC current could not and it would be measured as RMS value, and on that there is no directional sense with AC (alternating current) with only the use of a clamp meter. However my knowledge would be 15+ years old though my Fluke meter says bi-directional on it but it also only works on DC. When I reverse the clamp I get the same reading when dealing with AC.

I have several systems that all read AC bidirectionally. You can check out my system on PVoutput which is using TEDPro CTs (link in my signature) and they DEFINITELY measure direction of power flow. Many inverter manufacturers have the same thing.

For OP you do have to make sure that the CTs are installed correctly and that the system is configured with the correct layout of your CTs or the data will be wrong.