PV Metering

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Grouch

Grouch

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New York, NY
Hi all,
So this time I have a few metering questions:
1. With a single family residence that has a bi-directional meter on the line side of the service panel, is this also known as net metering?

2. With a single family residence that has a bi-directional meter on the line side of the service panel, does the inverter output still need its own dedicated meter before hitting the backfeed breaker? (or is this based on the local utility requirements?)

3. In a multifamily building (say 20 apartments) where you land the inverter output on a backfeed breaker on a house panel, does the inverter output need its own dedicated meter before hitting the backfeed breaker? I've seen a set of drawings where they just use an ethernet connection from the inverter to a LAN. That can be used as a substitute for a meter?

4. In a commercial building, I've seen a set of drawings where they use 2 inverters (277/480 volts output), land the inverter outputs on a combiner panel, then it goes to a step-down transformer to bring the voltage down to 120/208, then to a fused disconnect switch, then connecting directly to the service conductors (between C.T. cabinet / meter and the service switch for the building). There is no meter for the PV system, nor did i see any mention of an ethernet cable for monitoring. Is the meter or any type of monitoring missing?

Thanks again!
 
1. Not necessarily. Net metering refers to a system where energy sold to the utility is credited at the same rate as the customer pays. The meter could tally energy flowing to the utility and it could be bought or credited at a different rate than the customer pays.

Your other questions generally relate to whether there are laws that don't allow people to "offset" their usage. This is sometimes called "buy all, sell all".

There may also be utility requirements that require two meters, but aren't necessarily a "buy all sell all" scheme.
 
Grouch1980 said:
Hi all,
So this time I have a few metering questions:
1. With a single family residence that has a bi-directional meter on the line side of the service panel, is this also known as net metering?

2. With a single family residence that has a bi-directional meter on the line side of the service panel, does the inverter output still need its own dedicated meter before hitting the backfeed breaker? (or is this based on the local utility requirements?)

3. In a multifamily building (say 20 apartments) where you land the inverter output on a backfeed breaker on a house panel, does the inverter output need its own dedicated meter before hitting the backfeed breaker? I've seen a set of drawings where they just use an ethernet connection from the inverter to a LAN. That can be used as a substitute for a meter?

4. In a commercial building, I've seen a set of drawings where they use 2 inverters (277/480 volts output), land the inverter outputs on a combiner panel, then it goes to a step-down transformer to bring the voltage down to 120/208, then to a fused disconnect switch, then connecting directly to the service conductors (between C.T. cabinet / meter and the service switch for the building). There is no meter for the PV system, nor did i see any mention of an ethernet cable for monitoring. Is the meter or any type of monitoring missing?

Thanks again!
Click to expand...
1. Usually but not always.
2. Whether or not PV is separately metered is up to the AHJ.
3. The same. If PV is individually metered in a multifamily building, it is up to the AHJ whether there are separate meters for each unit or if virtual metering is allowed.
4. The same. The AHJ decides; it can be anything from no metering at all to metering with remote control of the inverters by the utility.
 
It could be, but as meters have non-zero cost, I would expect the only reason to have a separate generation meter is that the utility tariff treats all generation the same. I.e. it doesn't allow local generation to offset concurrent local usage. When local generation is allowed to offset concurrent local usage, you only need one meter.

Cheers, Wayne
 
Sorry, still trying to understand it. So the setup of the meters doesn't matter. (bi-directional or individual meters for utility and PV)... net metering has to do with getting charged for utility use at the same rate as you delivering power to the grid? If it is NOT the same rate, then it is NOT considered net metering?
 
This is all dependent on what is allowed and required by state regulations, utility rules, and financial and ownership arrangements. Ask the relevant parties where you will be installing, because peoples' experiences in other parts of the country is barely relevant. Probably what will vary the most is whether a PV production meter is required and by who. It could be required by law, or by utility rules, or by a third-party under a lease or power purchase arrangement, or it could be not required.

I wouldn't get too hung up on what is and isn't 'net metering.' It's an imprecise term that could mean slightly different things in different places and contexts. Find out the terminology that's being used where you're installing.

Also, as I've pointed out elsewhere, the NEC doesn't require meters whatsoever. So don't count on the building department to tell you what's required by a utility or a leasing provider.
 
Grouch1980 said:
Sorry, still trying to understand it. So the setup of the meters doesn't matter. (bi-directional or individual meters for utility and PV)... net metering has to do with getting charged for utility use at the same rate as you delivering power to the grid? If it is NOT the same rate, then it is NOT considered net metering?
Click to expand...
Correct. Net metering usually means your meter runs forward and backward, depending on your production and usage, and at the end of the month you pay for the net energy consumed according to the meter. Usually it's done with a single bidirectional meter on the utility side of the service disconnect.

EDIT: As jaggedben says, there are lots of different ways that AHJs deal with PV systems. Check with your local AHJ to find out how they do it where you are.
 
Grouch1980 said:
Sorry, still trying to understand it. So the setup of the meters doesn't matter. (bi-directional or individual meters for utility and PV)... net metering has to do with getting charged for utility use at the same rate as you delivering power to the grid? If it is NOT the same rate, then it is NOT considered net metering?
Click to expand...
Correct.

Just note that with a single meter, you can offset your usage at the retail rate even if you are paid less than the retail rate for energy going to POCO. I think it's a crime, but some places require the two meters such that even your offset is worth less than retail.
 
electrofelon said:
Correct.

Just note that with a single meter, you can offset your usage at the retail rate even if you are paid less than the retail rate for energy going to POCO. I think it's a crime, but some places require the two meters such that even your offset is worth less than retail.
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One such arrangement is how Austin Energy compensates a customer for solar generation. AE has a tiered energy tariff based on consumption to encourage customers to conserve energy. Usage beyond some kWh threshold is charged at a higher rate, and there are more than one of these breakpoints. The output of PV systems is monitored separately and payback/offset for PV is at the same rate per kWh generated for everyone irrespective of the usage tier they are in. The customer pays for their consumption at whatever tariff they qualify for irrespective of where it comes from.
 
electrofelon said:
Correct.

Just note that with a single meter, you can offset your usage at the retail rate even if you are paid less than the retail rate for energy going to POCO. I think it's a crime, but some places require the two meters such that even your offset is worth less than retail.
Click to expand...
Two meters is commonly referred to “buy all,sell all”
Your still offsetting your consumption, just not at the retail rate.
 
ggunn said:
1. Usually but not always.
2. Whether or not PV is separately metered is up to the AHJ.
3. The same. If PV is individually metered in a multifamily building, it is up to the AHJ whether there are separate meters for each unit or if virtual metering is allowed.
4. The same. The AHJ decides; it can be anything from no metering at all to metering with remote control of the inverters by the utility.
Click to expand...

Maybe AHJ has a broader meaning in your region, but in my understanding of the meaning of AHJ, I would not expect an AHJ to care about what metering setup you have. The AHJ is the party to enforce and interpret the code, and approve products to be used. In other words, the inspector, and any organization that governs the inpsector. An installation could meet code without a single meter, and that would complete the scope of the AHJ's concern. But if you want it powered by a utility, the utility will be the one to require the meter.

In my experience, the parties who would be concerned with your metering setup are:
1. The utility
2. The incentive programs
3. The financier of the project / owner
4. The customer's preferences
 
electrofelon said:
Your other questions generally relate to whether there are laws that don't allow people to "offset" their usage. This is sometimes called "buy all, sell all".
Click to expand...
The other questions also relate to whether or not there are any applicable programs that require a revenue grade production meter.

The meter in question could be a meter that the utility owns to track your production, usually in a socket that the customer builds as a provision for the utility to add the meter globe later. It could also be a completely customer-owned meter that doesn't concern the utility, and that doesn't even look like a utility meter.
 
The best thing you can do is call the utility.
You want to buy or sell power, the utility is the AHJ as far as metering goes.
 
ggunn said:
1. Usually but not always.
2. Whether or not PV is separately metered is up to the AHJ.
3. The same. If PV is individually metered in a multifamily building, it is up to the AHJ whether there are separate meters for each unit or if virtual metering is allowed.
4. The same. The AHJ decides; it can be anything from no metering at all to metering with remote control of the inverters by the utility.
Click to expand...
In some cases the decider will not be the building official AHJ but the POCO.
 
Carultch said:
Maybe AHJ has a broader meaning in your region, but in my understanding of the meaning of AHJ, I would not expect an AHJ to care about what metering setup you have. The AHJ is the party to enforce and interpret the code, and approve products to be used. In other words, the inspector, and any organization that governs the inpsector. An installation could meet code without a single meter, and that would complete the scope of the AHJ's concern. But if you want it powered by a utility, the utility will be the one to require the meter.

In my experience, the parties who would be concerned with your metering setup are:
1. The utility
2. The incentive programs
3. The financier of the project / owner
4. The customer's preferences
Click to expand...
I take the meaning of Authority Having Jurisdiction to be just that - whomever has jurisdiction over the issue you are concerned about. It could be the utility, the building inspector, the fire inspector, or someone else, depending on the issue at hand.
 
ggunn said:
I take the meaning of Authority Having Jurisdiction to be just that - whomever has jurisdiction over the issue you are concerned about. It could be the utility, the building inspector, the fire inspector, or someone else, depending on the issue at hand.
Click to expand...
I think for most people AHJ does not refer to the utility because by default it means whatever building department or other governmental authority has jurisdiction, which is usually not the same as the utility. Also if you mean the utility then say utility. Some places there's less of a distinction but not for most of us. In the context of this discussion, usually the metering will be decided by the utility or a contractual party and not any other AHJ.
 
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