Standard vs net meter

[bbartmasse r]

My question is whether a standard meter will register consumption no matter which side the source of power is on? As opposed to a net or bi directional meter that knows the difference? For example, if the solar is out producing the loads in a home and the standard meter is still installed, will it register as consumption?

 

[winnie]

All meters (standard or net) register only the power flowing through the metering point.

If you have 10 kW of solar production and 11 kW of local consumption, all _downstream_ of the meter, then the meter will register 1 kW of power consumed from the grid...with some caveats.

1) If power consumption is not happening at the same time as power production (meaning that the customer with the PV array is using the grid as a virtual battery) then the power _is_ going through the meter and might be registered. In other words: If you produce 2kWh in the morning and use 3 kWh in the afternoon, then a total of 5kWh has passed through the meter and how this is registered will depend upon the design of the particular meter. (Examples that I have heard of include the meter running backward when power is flowing from customer to utility, thus the customer gets billed for 1kWh, meter not registering when power is flowing from customer to utility thus the customer gets billed for 3 kWh, and the meter always registering power consumption no matter which way the power flows, in which case the customer gets billed for 5 kWh.... This latter is possible with smart meters and is a punishment for connecting solar to the grid without telling the POCO what you are doing)

2) If the PV array is connected to the grid upstream of the meter, then the solar production looks to the meter like it is coming from the utility.

-Jon

 

[Hv&Lv]

Ours are secure forward, which means they will register energy in either direction, but the kWh totalizer only registers in the forward direction, regardless which way energy is flowing.
it’s the last example given in the post above and the reason is also stated above.

Once we know about it and have a proper interconnect agreement, the meter is changed out with a meter that is a TOU meter because we pay a premium for exporting during peak.

 

[electrofelon]

Ours are secure forward, which means they will register energy in either direction, but the kWh totalizer only registers in the forward direction, regardless which way energy is flowing.
it’s the last example given in the post above and the reason is also stated above.

Once we know about it and have a proper interconnect agreement, the meter is changed out with a meter that is a TOU meter because we pay a premium for exporting during peak.

The POCOs around me do similar where the standard meter counts up no matter which way energy is flowing. These are newer digital meters. The older mechanical meters with dials will count backwards (at least everyone I have seen and checked this).

 

[GoldDigger]

The POCOs around me do similar where the standard meter counts up no matter which way energy is flowing. These are newer digital meters. The older mechanical meters with dials will count backwards (at least everyone I have seen and checked this).

Plenty of purely mechanical meters incorporate a ratchet mechanism that drives the dials forward regardless of the direction of energy flow.

 

[Carultch]

My question is whether a standard meter will register consumption no matter which side the source of power is on? As opposed to a net or bi directional meter that knows the difference? For example, if the solar is out producing the loads in a home and the standard meter is still installed, will it register as consumption?

By the simplest design possible, a meter would function as a net meter. It would spin forward, or spin backward, depending on the instantaneous direction of net power flow.

Making the meter anything other than a net meter, is a countermeasure to tampering and unauthorized generation. It is common for such a meter to either register exported power as consumed power (called secure-forward), or it might just ignore exported power and count its energy as zero.

The term net meter means it treats all kW-hrs equally, and credits you fully for what you export. It adds to the total during instants when you import, and subtracts from the total during periods when you export.

The term bidirectional meter means it has two separate registers for import and export. You may have different rates applied to each one, such that it is likely in your interest to self-consume, instead of export.

In any case, no meter can tell the difference between 1 kW consumed, vs 11 kW consumed simultaneously with 10 kW produced. All it can track is net power flow (instantaneous consumption minus production), and the corresponding energy that accumulates with time. Graph net power vs time. Shade the area between the positive part of the curve and the time-axis blue, and likewise red for the negative part of the curve. Bidirectional means it tracks red and blue area separately. Net means it subtracts red from blue. Secure-forward means it tracks both red and blue together as if they were both positive, ignoring the fact that red is negative.

 

[electrofelon]

Plenty of purely mechanical meters incorporate a ratchet mechanism that drives the dials forward regardless of the direction of energy flow.

I don't doubt that there are mechanical meters that will always count forward regardless of energy flow direction....just not sure about the term "ratchet mechanism" . Please provide details or drawing of such a mechanism

 

[Carultch]

I don't doubt that there are mechanical meters that will always count forward regardless of energy flow direction....just not sure about the term "ratchet mechanism" . Please provide details or drawing of such a mechanism

Yeah, such a thing never happened with mechanical odometers, that would have a similar working principle to the mechanism of the digit displays in electrical meters. The countermeasures to mechanical odometer tampering were pickups on the non-drive wheels, directional clutches, and digit etching. Electronic odometers are set up to always count forward, even when driving in reverse.

 

[electrofelon]

Yeah, such a thing never happened with mechanical odometers, that would have a similar working principle to the mechanism of the digit displays in electrical meters. The countermeasures to mechanical odometer tampering were pickups on the non-drive wheels, directional clutches, and digit etching. Electronic odometers are set up to always count forward, even when driving in reverse.

Didnt they try to drive a jacked up car in reverse in Ferris Bueller's day off to reverse the odometer? I dont remember if it worked

 

[rainwater01]

Didnt they try to drive a jacked up car in reverse in Ferris Bueller's day off to reverse the odometer? I dont remember if it worked

Yes they did and no it didn’t work. The son ended up getting mad and kicking the car until it came off the jack and drove off wrecking it as I remember. A classic


Sent from my iPad using Tapatalk

 

[Carultch]

Didnt they try to drive a jacked up car in reverse in Ferris Bueller's day off to reverse the odometer? I dont remember if it worked

It did not work. And not just for the plot, but also for that particular car, their attempt would not work if you tried that in reality.

The pickups for the odometer on that car are on the front wheels, and the car is rear wheel drive. You could spin the correct front wheel manually and unwind the miles. Or actually drive it in reverse. Because that car was made before directional clutches where part of odometers.

 

[jaggedben]

The answer to the original question is that it entirely depends on the particular meter.

 

[electrofelon]

The answer to the original question is that it entirely depends on the particular meter.

You've got a lot of nerve providing such a short concise accurate answer....... That's not how we do things on this forum

 

[winnie]

The answer to the original question is that it entirely depends on the particular meter.

Not quite. All meters are limited to registering only that power that passes through the metering instrument.

If the poco is on the left side of the meter and the customer is on the right side of the meter with their home PV system, then any power generated by the PV system and used immediately by the customer is 'invisible' to the meter. (I believe this is the answer to the original question.)

The response to any power flowing through the metering point is particular to he meter in question.

-Jon

 

[Carultch]

Not quite. All meters are limited to registering only that power that passes through the metering instrument.

If the poco is on the left side of the meter and the customer is on the right side of the meter with their home PV system, then any power generated by the PV system and used immediately by the customer is 'invisible' to the meter.

Key word here is "power" in units of Watts. And that is precisely the way it works. The only power it can measure is net power that passes through it. And this is the case regardless of the type of meter.

Energy in kilowatt-hours is another matter entirely, because different meters are built differently to accumulate the Watts into kilowatt-hours, and keep track of directional power flow.

 

[jaggedben]

Not quite. All meters are limited to registering only that power that passes through the metering instrument.

If the poco is on the left side of the meter and the customer is on the right side of the meter with their home PV system, then any power generated by the PV system and used immediately by the customer is 'invisible' to the meter. (I believe this is the answer to the original question.)

The response to any power flowing through the metering point is particular to he meter in question.
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-Jon

I understood his original post to be asking about whether a meter can be counted on to report power flow in a certain way, not to be asking about direct consumption of solar behind the meter. He said " For example, if the solar is out producing the loads in a home and the standard meter is still installed, will it register as consumption? "

 

[winnie]

I understood his original post to be asking about whether a meter can be counted on to report power flow in a certain way, not to be asking about direct consumption of solar behind the meter.

I think you are correct. I read the op as asking if consumption balanced by PV production would still register as consumption...but upon rereading I agree the question is 'will solar export to the grid be accounted as consumption? ' which as discussed is completely meter dependent.

Jon

 

[Coppersmith]

Most of the solar setups I see are small. Most are on a 30 amp breaker and I'm fairly sure they produce a lot less than 30 amps even at peak. So is this really an issue? What percentage of solar systems export power? I suspect it's a low number. My A/C is on 24/7/365. It would probably suck up all those amps by itself.

 

[Carultch]

Most of the solar setups I see are small. Most are on a 30 amp breaker and I'm fairly sure they produce a lot less than 30 amps even at peak. So is this really an issue? What percentage of solar systems export power? I suspect it's a low number. My A/C is on 24/7/365. It would probably suck up all those amps by itself.

During the shoulder seasons when both heat and A/C are off, and the residents are out of the house all day, I suspect most would export power. Without a metering policy that allows you to benefit from exporting power, you don't get to use that credit to offset what you'd consume at night. Loads are highly variable throughout the year, and each user has their own habits of use that will vary. Predictions of consumption from statistical models of user behavior cannot guarantee that you will self-consume everything, and never export a Watt.

Plus, thermostat controlled loads such as A/C will cycle on and off. If A/C were running all day and it were the only load, the downtime between thermostat cycles will be when you would export.

It is an issue on principle, because it is a double-whammy if you export power from behind a secure-forward meter. Not only do you get no credit for exporting, you are also being charged as if you consumed it.

 

[jaggedben]

Most of the solar setups I see are small. Most are on a 30 amp breaker and I'm fairly sure they produce a lot less than 30 amps even at peak. So is this really an issue? What percentage of solar systems export power? I suspect it's a low number. My A/C is on 24/7/365. It would probably suck up all those amps by itself.

Just about every grid tied solar system exports to the grid at some point if the utility allows it. They are generally sized to offset usage on an annual basis. Which means that during the middle of the day, especially in summer, the solar will output more than the house's average need. Which will mean at some point the load is much lower than output. If you think houses always use 30A you haven't been looking into it that much. And if someone does use that much, their solar system might have a 200A breaker.