Problems interpreting Utility API information for Max Demand

[pv_n00b]

Well it is peak in the sense of the highest of all the demand readings, but each reading is a 15 minute average not a peak.

Demand meters record the peak kW in a given interval. It's not an average kW over the interval. This is why PV can't be depended on to reduce demand load. All it takes is a cloud passing over during a peak in the interval.

 

[electrofelon]

Demand meters record the peak kW in a given interval.

That is just not correct.

 

[ggunn]

That is just not correct.

I don't know, myself, if it is or isn't, but why should such a thing not be possible? Or is it that the POCO will tolerate transient spikes in demand without charging a customer for them?

 

[electrofelon]

I don't know, myself, if it is or isn't, but why should such a thing not be possible? Or is it that the POCO will tolerate transient spikes in demand without charging a customer for them?

I don't know the specific history of why a 15 minute average was chosen (most of the time). I would just conjecture that that amount of time is most meaningful to grid operators .

 

[jaggedben]

Demand meters record the peak kW in a given interval. It's not an average kW over the interval. ...

But apparently it is average kW over a 15 min interval. Or at least in some cases. That was discussed in one of the other threads.

If you have clear sources that show exactly how utility demand data is actually generated (especially for PG&E) then I'm plenty interested in finding out if you are right about this or just making assumptions. But also, a reminder that I'm hanging my hat on the language in the exception to 220.87, which mentions 15 mins. Not the main section you quoted above.

 

[wwhitney]

But also, a reminder that I'm hanging my hat on the language in the exception to 220.87, which mentions 15 mins. Not the main section you quoted above.

One of my PIs for the next cycle is to move that language to the main section to resolve this ambiguity.

Cheers, Wayne

 

[pv_n00b]

But apparently it is average kW over a 15 min interval. Or at least in some cases. That was discussed in one of the other threads.

If you have clear sources that show exactly how utility demand data is actually generated (especially for PG&E) then I'm plenty interested in finding out if you are right about this or just making assumptions. But also, a reminder that I'm hanging my hat on the language in the exception to 220.87, which mentions 15 mins. Not the main section you quoted above.

Right, there are over 3000 utilities in the USA, I'm not going to do an exhaustive study of them all to show how all their demand meters work. Maybe some of those utilities average the demand. None of the ones I have worked with do.
I can point you to the definition of Demand Charge from PG&E here: https://www.pge.com/en_US/small-med...anage-your-usage/usage-terms-definitions.page
It would seem to indicate that they do not average but look at the peak in a given period.

 

[wwhitney]

I can point you to the definition of Demand Charge from PG&E here: https://www.pge.com/en_US/small-med...anage-your-usage/usage-terms-definitions.page
It would seem to indicate that they do not average but look at the peak in a given period.

I reach the opposite conclusion from that definition. It says "Maximum Peak Demand: The highest electric use, in kilowatts (kW), during any 15-minute period during hours when peak energy pricing is in effect. "

By referring to the 15 minute period, they are talking about an average over 15 minutes. If the average was over a shorter period (could be any period down to one cycle or maybe one half cycle), then there would be no reason to mention 15 minutes in the definition. And the shorter period would be specified.

Now if you show me a bill or report that has 15 minute data, and different data for "usage" and "peak demand" for the same 15 minute period, then I would agree that the peak data uses a shorter averaging period. But the definitions or PUC regulations would specify that averaging period.

Cheers, Wayne

 

[wwhitney]

Here's a different definition from a PG&E page (emphasis mine):

Important definitions for Business section

We want to make it easy to understand your energy statement.

www.pge.com

Demand Charge: Many non-residential rates include a demand charge. Demand is a measurement of the highest usage of electricity in any single fifteen (or sometimes five) minute period during a monthly billing cycle. Demand is measured in kilowatts (or kW). High demand is usually associated with equipment start-up. By spreading equipment start-ups over a longer period of time, you may be able to lower demand and reduce your demand charges.

That explicitly says it's usage over a 15 minute period. I.e. a 15 minute average power usage.

Cheers, Wayne

 

[electrofelon]

Right, there are over 3000 utilities in the USA, I'm not going to do an exhaustive study of them all to show how all their demand meters work. Maybe some of those utilities average the demand. None of the ones I have worked with do.

I am quite certain you are mistaken. Demand is a pretty standardized concept in the utility world, and if they were measuring an instantaneous peak, it probably wouldn't be called "demand" and certainly wouldn't have a time interval . That definition you linked to is not the clearest one I have seen, but I also read it the way Wayne does.

 

[don_resqcapt19]

Right, there are over 3000 utilities in the USA, I'm not going to do an exhaustive study of them all to show how all their demand meters work. Maybe some of those utilities average the demand. None of the ones I have worked with do.
I can point you to the definition of Demand Charge from PG&E here: https://www.pge.com/en_US/small-med...anage-your-usage/usage-terms-definitions.page
It would seem to indicate that they do not average but look at the peak in a given period.

The following is from PG&E's E19 tariff.

Definition of Maximum Demand: Demand will be averaged over 15-minute intervals for customers whose maximum demand exceeds 499 kW. “Maximum demand” will be the highest of all the 15-minute averages for the billing month.

 

[RumRunner]

That is just not correct.

This type of sampling is a valid approach in conducting studies on how to arrive at an outcome whose result we don’t know about.

To say that it is not correct is too judgmental.
If none of those previous comments, has any thing to do with what you expect –it’s not because they are a bunch of “yahoos” who don’t know any better.

They (their comments) don’t jibe with your agenda or simply because you are biased or misinformed.
We’re here to discuss … and not be judged by anyone.

 

[electrofelon]

This type of sampling is a valid approach in conducting studies on how to arrive at an outcome whose result we don’t know about.

To say that it is not correct is too judgmental.
If none of those previous comments, has any thing to do with what you expect –it’s not because they are a bunch of “yahoos” who don’t know any better.

They (their comments) don’t jibe with your agenda or simply because you are biased or misinformed.
We’re here to discuss … and not be judged by anyone.

?. I don't really understand what you are saying or even know how to respond, sorry.