Point of Interconnection - Solar

[jaggedben]

Anything AFTER the metering is up to the electrician/designer.
In a CT can, as long as it's after the metering do whatever you want.
But taps before the metering is a no no with us

You don't do services with multiple meters either? I agree with both of the others, a 'line side tap' is usually after the meter, but can sensibly be before it if it goes to a new additional meter and makes sense under the tariff.

You would be amazed at home many people ask us if they can tap ahead of the meter. Especially homeowners and small solar companies.

And I don’t understand why they ask. When they export they are paying for what they are producing because it's on the wrong side of the meter. We don’t net meter, but we do bill by TOU, and a different rate for export.
I have at least two to three conversations a year regarding this very thing. Some of these solar companies popping up really have no clue of how to interconnect.

Salespeople. The actual designers and installers would almost never make such a mistake. Or, perhaps it's a company coming in from Texas where some places do it differently.

There are different ways to interconnect, and the rules for doing so vary from jurisdiction to jurisdiction. There is a POCO near here where connecting on the utility side of the revenue meter is the only way to do it.

You know FWIW, you are always saying things like this more than the rest of us and I'm realizing it must be because Texas doesn't really regulate net-metering at the state level. Whereas in California, the basic net-metering law applies statewide, so here it really is basically the same everywhere. It took a few years in the 2010s for some places to get over their local interpretations about supply side connections but I don't really hear about that anymore.

Trying to think about it but getting a "server busy, please try again later" message from my brain

It all depends on the tariff. If you get paid a flat rate for producing solar regardless of consumption, as some places do, then the solar meter can be on either side of the regular meter as long as billing knows how it's set up. Another case would be "virtual net metering" in California, where the solar credits go to multiple customer meters.

 

[wwhitney]

If you have two meters, as long as their accumulating intervals are synchronized, then for any tariff, it doesn't matter whether one measures X and the other Y, or one measures X and the other X+Y. As in the latter case you can recover Y as the difference between the two meters readings, interval by interval.

Cheers, Wayne

 

[jaggedben]

If you have two meters, as long as their accumulating intervals are synchronized, then for any tariff, it doesn't matter whether one measures X and the other Y, or one measures X and the other X+Y. As in the latter case you can recover Y as the difference between the two meters readings, interval by interval.

Cheers, Wayne

Hmmm. For any net metering tariff. I don't think for a net billing tariff, unless I need to think harder about what you mean by 'accumulating intervals'.

 

[wwhitney]

Hmmm. For any net metering tariff. I don't think for a net billing tariff, unless I need to think harder about what you mean by 'accumulating intervals'.

If the meters measure X and X+Y, and you recover Y as their computed difference, that's the same information as if the meters measured X and Y directly. So I see no difference in capabilities.

Cheers, Wayne

 

[jaggedben]

If the meters measure X and X+Y, and you recover Y as their computed difference, that's the same information as if the meters measured X and Y directly. So I see no difference in capabilities.

I'm more interested in the case where the meters measure X and Y, and the tariff wants to compute X+Y. For a net metering tariff this can be done at the end of any interval, be it 15mins, an hour, or a month. For a net billing tariff with instantaneous netting, I believe the two meters would need to be constantly communicating either with each other or a third device, to compute and record the sum. Which I don't believe is practical with real-world metering technology.

 

[wwhitney]

If the meters measure X and X+Y, and you recover Y as their computed difference, that's the same information as if the meters measured X and Y directly. So I see no difference in capabilities.

To be clear, I'm assuming smart meters that will transmit the kWh per measurement interval directly to the POCO billing software, which can do the further computation on a per interval basis.

I'm also assuming each of X and Y is unidirectional, e.g. X is a load and Y is production. If you have loads L1 and L2 and production P, and you are supposed to meter P separately from L1+L2, but instead you meter P+L1 separately from L2, you are out of luck.

Cheers, Wayne

 

[wwhitney]

For a net billing tariff with instantaneous netting

What is "instantaneous netting"? I'm assuming all billing tariffs take as their basic input data kWh over each interval, possibly with production separately measured from consumption.

Cheers, Wayne

 

[jaggedben]

What is "instantaneous netting"? I'm assuming all billing tariffs take as their basic input data kWh over each interval, possibly with production separately measured from consumption.

Cheers, Wayne

Instantaneous netting (which might better be thought of as no netting at all) means that imports and exports are added up whenever they happen, and never netted for any interval for billing purposes, because they may always be charged/credited at different rates. It is, by the way, how the new 'Solar Billing Plan' a.k.a. NEM3 works in California.

'Net Metering', or non-instantaneous netting, by contrast, means that we just look at imports minus exports for the entire interval.

So for example if I have regular/consumption meter X and production meter Y, and I have a matching interval in which X report 7kWh total consumption and Y reported 10kWh total production, and I'm billed/credited on consumption and production, then as you said above it doesn't matter if meter Y is parallel or series with meter X because I can figure out total consumption and production either way.

However, if I have net billing with instantaneous netting that is supposed to cover the sum of both meters, then I can't do the operation above using merely an interval such as 15min. Because I don't know for sure if the consumption all occurred in the first 5 minutes and the production all occurred in the last 10 minutes, or if they occurred simultaneously and to what extent. The actual values could be anywhere from 7kWh imported and 10kWh exported to 0kWh imported and 3kWh exported. Which if I'm paying/earning different amounts for imports and exports means a big difference.

There is really no need for a production meter with net billing and instantaneous netting, but at the same time a production meter cannot practically (I think) be added in parallel to a consumption meter to achieve the netting.

 

[wwhitney]

OK, so if over a 15 minute interval, the production is 6 kW from minutes 0-10, and 0 kW from minutes 10-15, while the consumption is 0 kW from minutes 0-5, and 6 kW from minutes 5-15, then:

Net metering (interval based): no net charge or credit. Can do this with a single meter that just reports a single number per interval, positive or negative.

Buy All / Sell All : credit for 1 kWh produced, charge for 1 kWh consumed. Can do this with two meters, each of which produces a single positive number per interval.

Instantaneous Netting: credit for 1/2 kWh net exported during minutes 0-5, and charge for 1/2 kWh net imported during minutes 10-15. Can do this with one meter that reports two positive numbers per interval. Presumably internally the meter uses some faster sampling time, like once per second, and if during that second there is net consumption it gets added to one register; if there is net production, it gets added to another register.

So I agree that if you have metering set up for Buy All / Sell All with separate production and consumption meters, you can't regenerate the Instantaneous Netting numbers from the two separate interval data series. I hadn't realized that CA's NBT was Instantaneous Netting, I thought it was still based on just the single signed interval consumption, with a low, highly variable reimbursement rate if you are a net exporter during that interval, and a high, less variable cost if you are a net consumer during that interval.

Cheers, Wayne

 

[wwhitney]

Instantaneous netting (which might better be thought of as no netting at all) means that imports and exports are added up whenever they happen, and never netted for any interval for billing purposes, because they may always be charged/credited at different rates. It is, by the way, how the new 'Solar Billing Plan' a.k.a. NEM3 works in California.

Just to double check, I understand that NBT's "no netting" aspect means that you can't determine your bill just from the hourly net usage/production data, but are you sure that it is implemented by the meter keeping two separate registers for imports and exports using some internal very fine grained measuring interval? Versus just switching to 15 minute interval data from the meter, where each interval is still netted?

Cheers, Wayne

 

[jaggedben]

Just to double check, I understand that NBT's "no netting" aspect means that you can't determine your bill just from the hourly net usage/production data, but are you sure that it is implemented by the meter keeping two separate registers for imports and exports using some internal very fine grained measuring interval? Versus just switching to 15 minute interval data from the meter, where each interval is still netted?

Yes, I'm sure. Mainly from hearing about a fair amount of controversy on this fine point during the hearings of the CPUC decision making. The pro-solar parties were advocating for interval netting (hourly, I think), and were demanding that the utilities share examples of the two data streams so that all parties could analyze the impact of instaneous vs interval netting. The utilities refused to do that but assured the CPUC their meters could do it and asserted a certain typical percentage difference. And got what they wanted.

Also I recall at some point I saw a meter data readout with the multiple channels listed, although I can't recall why and when.

 

[electrofelon]

I am still a bit confused on the second load side meter thing. The difficulty is I see multiple scenarios: net metering, TOU rates, different PV and utility rates, buy all sell all..... I guess I would need to go thru all of them to feel comfortable with every scenario. If the meters can communicate or keep a time stamp of everything then sure anything is possible, but it seems like it could be complicated, although I admit with modern computers and software, perhaps "complicated" isn't an issue

 

[ggunn]

We used to do that a few years back. We had a "buy all export" meter and another house meter that was import only. We realized we were ripping the consumer off (in a way)..
The customer has the right to offset their energy bill with their own solar.
It's like you have a heat pump and you add a wood stove... you get the benefit of those savings in heat.

That's not exactly true and it's why that jurisdiction structures PV the way they do. A PV system behind the meter is connected to the POCO's grid, but your wood burning stove is not. They pay full retail for the kWh the customer pumps into the grid, the same as if it were net metered, but they can change their mind.

Austin Energy does something similar; they meter PV production, charge the customer for every kWh they use no matter where it comes from, and pay the customer for every kWh they produce. AE charges customers a tiered rate per kWh dependent on their usage and pays everyone the same for PV produced kWh.

I am not arguing over what should or should not be; I am only stating what is.

 

[ggunn]

You know FWIW, you are always saying things like this more than the rest of us and I'm realizing it must be because Texas doesn't really regulate net-metering at the state level. Whereas in California, the basic net-metering law applies statewide, so here it really is basically the same everywhere. It took a few years in the 2010s for some places to get over their local interpretations about supply side connections but I don't really hear about that anymore.

You are correct that Texas does not regulate PV metering statewide, but I have designed commercial PV systems for installations in Idaho, Kentucky, Florida, New Jersey, Pennsylvania, and a few other states that I can't think of at the moment besides Texas, and the rules for interconnecting PV to the grid vary with every AHJ.

 

[Hv&Lv]

That's not exactly true and it's why that jurisdiction structures PV the way they do. A PV system behind the meter is connected to the POCO's grid, but your wood burning stove is not. They pay full retail for the kWh the customer pumps into the grid, the same as if it were net metered, but they can change their mind.

Austin Energy does something similar; they meter PV production, charge the customer for every kWh they use no matter where it comes from, and pay the customer for every kWh they produce. AE charges customers a tiered rate per kWh dependent on their usage and pays everyone the same for PV produced kWh.

I am not arguing over what should or should not be; I am only stating what is.

? What's not exactly true?
The wood stove was an analogy, that's all. You produce heat, you don’t use heat pump. You produce solar, you get that benefit.
We do not pay full retail for exported solar. We pay avoided wholesale cost. Ours is also a tiered rate for export AND import.
I’m only stating what is..

 

[ggunn]

? What's not exactly true?

Your analogy. POCOs can and frequently do have a say in what sources you can connect to their grid, irrespective of which side of the meter or service disconnect the connection would be. In the jurisdiction I have been talking about, you cannot connect a PV system on "your" side of the revenue meter at all. As for how they would know, all they would have to do is look at your roof.

Apparently you have full net metering that tracks your tiered usage. Good for you; it's not universal.

 

[electrofelon]

You are correct that Texas does not regulate PV metering statewide, but I have designed commercial PV systems for installations in Idaho, Kentucky, Florida, New Jersey, Pennsylvania, and a few other states that I can't think of at the moment besides Texas, and the rules for interconnecting PV to the grid vary with every AHJ.

But some states have a statewide net metering law, such as NY. A POCO or AHJ can all have their own requirements, but net metering is the law of the land (with size limitations) in NY so they cant change that.

 

[ggunn]

Apparently you have full net metering that tracks your tiered usage. Good for you; it's not universal.

As long as you are not a net exporter, that is. It also depends on how often they "true up" your meter. I know of jurisdictions where it is yearly and at least one where it is instantaneous.

 

[ggunn]

But some states have a statewide net metering law, such as NY. A POCO or AHJ can all have their own requirements, but net metering is the law of the land (with size limitations) in NY so they cant change that.

True enough, but some states don't. I don't know which do and which don't, but Texas definitely does not.