Do you need a consumption meter to know your monthly (not real time) usage?

[Ampster]

It would depend on the wiring of your service from the PUC. The only slight difference would be equivalent to the transmission loss via the grid. I would be surprised if it were any higher than 2 or 3 percent difference from the transformer to your house.

Yes, if the OP had two meters, one for solar generation and one for consumption it would be entirely different. If those meters were on the same service drop then the electrons would still flow out one meter into the next.
Yes, the resistant of the lines is part of the physics. I don't believe it would be proportional though. I believe generation would flow to the nearest load, then to the next load, etc.

[BFW577]

I use an Efergy Engage hub with a 15 second update interval. The hub is $125 with one set of CT sensors and a extra set is like $40. I have 2 mini splits connected as well. Its probably the best inexpensive setup for monitoring live electricity consumption and solar production as well as other circuits.
It is also supported on the pvoutput solar website.
Here is a snapshot of some of the data.

Screenshot_20191220-124416_Monitor.jpgScreenshot_20191225-185054_Monitor.jpg

[petesamprs]

Cool, so is this connected to your inverter to be able to pull the actual solar production data as well? Do you just use their app to track consumption/production instead of Solaredge's monitoring app?

[BFW577]

Cool, so is this connected to your inverter to be able to pull the actual solar production data as well? Do you just use their app to track consumption/production instead of Solaredge's monitoring app?

I have a line side tap so I have one is reading the lines coming out of the inverter and one on my lines after the meter going to my panel.

I have Solaredge monitoring as well but the efergy data is more accurate and the data is in 15 second intervals. Solar edge updates every 15 mins I believe. The efergy updates live right on my phone every 15 seconds.

[DrLumen]

I use an Efergy Engage hub with a 15 second update interval. The hub is $125 with one set of CT sensors and a extra set is like $40. I have 2 mini splits connected as well. Its probably the best inexpensive setup for monitoring live electricity consumption and solar production as well as other circuits.
It is also supported on the pvoutput solar website.
Here is a snapshot of some of the data.

Screenshot_20191220-124416_Monitor.jpgScreenshot_20191225-185054_Monitor.jpg

That's pretty cool.

Brultech makes a similar system but more for whole house monitoring via ct's on most/all circuits. It is more expensive but it can monitor up to 32 channels and the data is kept within a dedicated data server onsite rather than pushed to a cloud.

https://www.brultech.com/store/index.php?id_product=132&controller=product

I'm not trying to slam your gear, It is cool and would be good for most people. My concern is the cloud based data. There is no telling when they might go out of business or decide to take their servers down. During a recent web outage, that took days for the ISP to resolve, I realized that cloud stuff is really fragile and useless without the internet. I was using some of the Samsung hub and sensors and it all came crashing down without internet connectivity. I try to keep all data onsite now.

[BFW577]

That's pretty cool.

Brultech makes a similar system but more for whole house monitoring via ct's on most/all circuits. It is more expensive but it can monitor up to 32 channels and the data is kept within a dedicated data server onsite rather than pushed to a cloud.

https://www.brultech.com/store/index.php?id_product=132&controller=product

I'm not trying to slam your gear, It is cool and would be good for most people. My concern is the cloud based data. There is no telling when they might go out of business or decide to take their servers down. During a recent web outage, that took days for the ISP to resolve, I realized that cloud stuff is really fragile and useless without the internet. I was using some of the Samsung hub and sensors and it all came crashing down without internet connectivity. I try to keep all data onsite now.

The data is also being logged by a display unit that can be also downloaded to a computer. The transmitter also l logs everything without a connection and will upload it in the event you lose your internet connection. I have had the system for 6 years and have continuous data. Never had any issues.

Here is what the reciever looks like.
41Y5jjqnv1L._AC_.jpg

[DrLumen]

The data is also being logged by a display unit that can be also downloaded to a computer. The transmitter also l logs everything without a connection and will upload it in the event you lose your internet connection. I have had the system for 6 years and have continuous data. Never had any issues.

Here is what the reciever looks like.
41Y5jjqnv1L._AC_.jpg

I guess I was looking at a different unit then. It was saying the sensors transmit to the cloud. That is when I stopped reading.

[SunEagle]

I guess I was looking at a different unit then. It was saying the sensors transmit to the cloud. That is when I stopped reading.

Most of the energy measuring devices send their data to a website so you can review it historically. IMO all websites really keep their data stored in a server or "cloud".

[DrLumen]

Yes, if the OP had two meters, one for solar generation and one for consumption it would be entirely different. If those meters were on the same service drop then the electrons would still flow out one meter into the next.
Yes, the resistant of the lines is part of the physics. I don't believe it would be proportional though. I believe generation would flow to the nearest load, then to the next load, etc.

I'd like to see your source for that theory. None of the electrical laws or functions I was taught had a 'nearness' variable.

[Ampster]

I'd like to see your source for that theory. None of the electrical laws or functions I was taught had a 'nearness' variable.

It is not a theory. It is an opinion derived from observation of power flow by various CT clamps. I think our disagreement is about the flow of power to a load behind the meter. You said it was proportional and I sad it was not. Every Watt meter I have near my service meter reads the same as the service meter. The only time that the power to the load would be proportional is when solar generation is lower than the load and the load would be driven by the solar and the grid. The sevice meter would show net consumption equal to the solar output plus power from the grid. If the solar was generating more than the load any excess solar would be measured by the service meter using the same formula. Is that not how it works?

[Mike90250]

It is not a theory. It is an opinion derived from observation of power flow by various CT clamps.....

Opinions are nice enough, but have no effect on power distribution. Power distribution occurs by resistance/voltage differential.. If there is a load present, the power goes to it, as regulated by the resistance of the load. If the grid has a lower potential, the power goes there.
or other phrasing
If there is a local load, PV inverter power goes to that load(s), and any remaining not consumed by that load, goes on to the grid.

Throwing meters into the mix, well, you have to look at the schematic to determine what meter reads which, and figure it out from there. Don't forget you need to measure L1 and also L2

[Ampster]

Opinions are nice enough, but have no effect on power distribution. ........
PV inverter power goes to that load(s), and any remaining not consumed by that load, goes on to the grid.
........

Yup, that is my understanding. I think it is more than an opinion but I can't find any reference to the science so I expresses it as an opinion. The Inverter power goes to that load and there is no proportional usage of grid power when the inverter is generating more power than the load. I believe it to be a scientific fact.

[foo1bar]

It is not a theory. It is an opinion derived from observation of power flow by various CT clamps.

drlumen is pointing out that electric current never considers "nearness".
A current doesn't all go to the next nearest load, and then to the next closest, and so on.
This misstatement is similar to the statement "Current follows the path of least resistance" - people say it, but it isn't actually true.
Current flows through ALL paths in proportion to their conductivity. So a very conductive (low resistance) path gets a lot of current, maybe even >99% of it. But when there are multiple paths, every path still gets some current as well.


I think drlumen is trying to point out that it isn't that the power would go out a production meter and always go directly to a consumption meter that's nearby.
So your statement/opinion that it does is incorrect.


However, this is not really important for the OP's question.

The OP has a single meter that measures power flowing to/from the grid.
They have their inverter and their loads on the customer side of that meter.
And they're trying to figure out "How much benefit am I getting from my solar install?"

The simple answer is - they can't just use the data from that meter.
Instead they should use the meter that's built into their inverter.
That meter shows how much was produced.
Some of that power gets consumed by their local loads, some goes out through the meter to the POCO.
Whether it's consumed locally or goes out to the POCO may or may not even effect the calculations.

Some important factors are:
1> Is it same rate per kwh for production and consumption? (ie. always $.11/kwh being charged for consumption and $.11/kwh being credited for production sent to POCO?)
2> Is it flat rate for all hours of the day? (ie. always $.11/kwh as compared to $.22/kwh from 2PM-6PM and $.08/kwh for other hours and weekends)

*IF* it is same rate for production and consumption, AND it's same rate for all hours it's simply the number of kwh produced * price_per_kwh.
And the inverter will almost certainly have a built in meter that tells you the number of kwh produced. (although it may be off by a few % if it's not a "revenue grade" meter)

If the rate varies depending on time of day, then you have to look at what time of day those kwh were produced and apply that to your calculations.
If the rate isn't the same for production and consumption (ex. production sent to POCO gets you $.04/kwh and reduced consumption saves you $.12/kwh) then you have to take that into account since self-consumed kwh are worth more than ones sent to the POCO.

[petesamprs]

However, this is not really important for the OP's question.

The OP has a single meter that measures power flowing to/from the grid.
They have their inverter and their loads on the customer side of that meter.
And they're trying to figure out "How much benefit am I getting from my solar install?"

The simple answer is - they can't just use the data from that meter.
Instead they should use the meter that's built into their inverter.
That meter shows how much was produced.
Some of that power gets consumed by their local loads, some goes out through the meter to the POCO.
Whether it's consumed locally or goes out to the POCO may or may not even effect the calculations.

Some important factors are:
1> Is it same rate per kwh for production and consumption? (ie. always $.11/kwh being charged for consumption and $.11/kwh being credited for production sent to POCO?)
2> Is it flat rate for all hours of the day? (ie. always $.11/kwh as compared to $.22/kwh from 2PM-6PM and $.08/kwh for other hours and weekends)

*IF* it is same rate for production and consumption, AND it's same rate for all hours it's simply the number of kwh produced * price_per_kwh.
And the inverter will almost certainly have a built in meter that tells you the number of kwh produced. (although it may be off by a few % if it's not a "revenue grade" meter)

If the rate varies depending on time of day, then you have to look at what time of day those kwh were produced and apply that to your calculations.
If the rate isn't the same for production and consumption (ex. production sent to POCO gets you $.04/kwh and reduced consumption saves you $.12/kwh) then you have to take that into account since self-consumed kwh are worth more than ones sent to the POCO.

Thanks for bringing the discussions back on track. I think in my service area (northern NJ, serviced by Rockland Electric) there is no time-of-use difference in rate, and it is the same rate for production and consumption due to net metering in NJ. Given that, I think you are right that my "savings" can just be calculated based on whatever I produce (assuming I am not producing more than I am consuming during my annual net metering period, since excess production is credited at a much lower wholesale rate)

[Ampster]

drlumen is pointing out that electric current never considers "nearness".
A current doesn't all go to the next nearest load, and then to the next closest, and so on.
This misstatement is similar to the statement "Current follows the path of least resistance" - people say it, but it isn't actually true.
Current flows through ALL paths in proportion to their conductivity. So a very conductive (low resistance) path gets a lot of current, maybe even >99% of it. But when there are multiple paths, every path still gets some current as well.

I agree with the stathments above as far as single sources of power are concerned. However in the question as posed by the original poster there are two sources of power. One, the grid, which comes through the meter to serve the loads. The other, the solar generation, is behind the meter and also serves the loads. If that generation is greater than the loads then the grid power does not flow to the loads and any excess power is exported to the grid.

That is where I disagreed with DrLumen, who said, "Mechanically, when you are producing power and using it, you are pulling from your array and the grid simultaneously as they are set in parallel in a typical system. You just aren't pulling as much from the grid. It is likely half-and-half if your consumption is equal to what you are producing at that moment. But, in that instance, the other 'half' is going to the grid."

That would be inconsistent with what I have observed. If your consumption is equal to your production then there is nothing going to the grid or anything flowing to the grid.

I think drlumen is trying to point out that it isn't that the power would go out a production meter and always go directly to a consumption meter that's nearby.
So your statement/opinion that it does is incorrect.

I didnt intend to imply that. The nearby meter in the original example was a service panel meter that measured the net consumption. What I thought I stated was the power that is generated by the inverter is used by the loads behind the meter before any is exported to the grid. That is what @Mike90250 also stated. I think it was misleading of DrLumen to imply that the grid was supplying some of the power to that load when the solar production covered that load and had enough excess to sell to the grid.

However, this is not really important for the OP's question.

The OP has a single meter that measures power flowing to/from the grid.
They have their inverter and their loads on the customer side of that meter.
And they're trying to figure out "How much benefit am I getting from my solar install?"

The simple answer is - they can't just use the data from that meter.
Instead they should use the meter that's built into their inverter.
That meter shows how much was produced.
Some of that power gets consumed by their local loads, some goes out through the meter to the POCO.
Whether it's consumed locally or goes out to the POCO may or may not even effect the calculations.

I agree they should use the production meter. That has always been the issue. I regret that I let the misstatement of DrLumen or my faulty understanding of what he said side track this thread. This is not the only thread where there have been misunderstandings about how Net Energy Metering works.