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PGE Rate calculation details

Posted: Tue Dec 03, 2013 4:08 pm
I'm writing a program that downloads PGE Green Button data and calculates the bill for each of the available tariff options, with consideration of net-metering, etc. I've yet to find any detailed algorithm published on how exactly PGE performs its bill calculations. If anyone has such a reference, please do share

Take, the daily baseline allotment vs rate computation. Is it: (1) a strict daily calculation, (2) a piecemeal calculation breaking up discontinuities when rates/seasons change, or (3) a summation of the daily allotment for the full billing cycle calculation without regard to mid billing cycle rate adjustments.?

Please humor an exaggerated example with a mid-billing cycle seasonal change to illustrate why this matters so much. Suppose the following:
Billing days: 30
Day 1-15: 10 kwh baseline per day
day 16-30: 20 kwh baseline per day
Power usage:
Day 1: 200Kwh used
day 2-29: no power used
Day 30: 300Kwh used

Method (1) -- strict daily baseline vs usage:
Calculate bill for 200 kwh at 2000% of baseline using Day1-15 rate table
Calculate bill for 300 kwh at 1500% of baseline using Day16-30 rate table

Method (2) -- piecemeal by rate period:
Day1-15: Baseline of 10*15= 150kwh. Thus, calculate bill for 200kwh at 133.3% of baseline for this piecemeal period using day1-15 rate table.
Day16-30: Baseline of 20*15= 300kwh. Thus, calculate bill for 300kwh at 100% of baseline for this piecemeal period using day16-30 rate table.

Method (3) -- baseline usage covers entire billing period:
Total baseline = 10*15 + 20*15 = 450 kwh. Total consumption is 500 kWh, therefore,
Calculate bill for 200kwH at 111.1% of baseline using Day1-15 rate table
Calculate bill for 300kwh at 111.1% of baseline using Day16-30 rate table

I believe that Method (2) is correct, but, I'm not really sure.

What is so maddeningly frustrating is that PGE Green Button data doesn't match perfectly with what shows up in my net-metering bill! Further, the net-metering summary report given each month has absolutely no mention of tiering to help reverse engineer it.

Re: PGE Rate calculation details

Posted: Tue Dec 03, 2013 4:23 pm
They don't know either, they are designed to confuse and benefit them.

Re: PGE Rate calculation details

Posted: Tue Dec 03, 2013 4:27 pm
^^^^^

Ouch! You're probably right except for the part about them not knowing...

Re: PGE Rate calculation details

Posted: Tue Dec 03, 2013 9:55 pm
foobert wrote:I believe that Method (2) is correct, but, I'm not really sure. What is so maddeningly frustrating is that PGE Green Button data doesn't match perfectly with what shows up in my net-metering bill! Further, the net-metering summary report given each month has absolutely no mention of tiering to help reverse engineer it.
I've gotten lazy recently, but I used to try to match their calculation each month. I've been on net metering for seven years, now, and while I was keeping up I came within a few cents of their cost each month. I agree that they use Method (2). It's true that they don't show tiers on the net metering statement, but I didn't find that a problem. You know your daily baseline and the number of days, so it is trivial to calculate the number of units in each tier. Perhaps what you are missing is that the tier calculation is done first on total use (broken up only by rate/season changes), and the results applied proportionally to TOU periods.

Ray

Re: PGE Rate calculation details

Posted: Wed Dec 04, 2013 11:59 am
Thanks for the confirmation.

I get the tiering usage. I didn't even consider this before your comment: take the data from the net-metering summary bill and plugging that directly into my program as a validation. "What forest, there's only a bunch of trees"

The real problem is that the hourly kwh data downloaded from PGE doesn't always match the summary kwh data provided in the net-meter bill. It sorta makes you go "hmmm".

In any case, I think I'll work on cleaning up my code and publishing on sourceforge or github so that others can review it for technical errors, but, more importantly, enable people to make informed decisions about which rate plan to use. I currently have too many dependencies to make it portable -- using sql database backend, etc...

I don't have a problem sharing, but, at the same time, I'm not so keen on dealing with supporting it...

Re: PGE Rate calculation details

Posted: Wed Dec 04, 2013 2:42 pm
Look around for pieces you can (re)use. Miimura (at the myrav4ev forum) has an Excel sheet you paste your monthly green button data into. There are others.

If you have both TOU and baseline varying rates (like E-9). It feels like you have to walk through all the hourly samples as you would have a difficult time correctly assigning kWH to the correct rate tier by just summing for all TOU periods and dividing across the tiers.

The folks at http://www.pev4me.com" onclick="window.open(this.href);return false; also have some calc's, they'll take a whole year's green button data.

You've no doubt seen the PG&E/opower rate simulations.

Re: PGE Rate calculation details

Posted: Wed Dec 04, 2013 3:06 pm
srl99 wrote:If you have both TOU and baseline varying rates (like E-9). It feels like you have to walk through all the hourly samples as you would have a difficult time correctly assigning kWH to the correct rate tier by just summing for all TOU periods and dividing across the tiers.
That's exactly what I do.

I'll look at the other references. Thanks for pointing them out!

Re: PGE Rate calculation details

Posted: Wed Dec 04, 2013 4:16 pm
Moin, moin
foobert wrote:
I believe that Method (2) is correct, but, I'm not really sure.
Up until three months I would have agreed with you. The last three month they broke it up on the 1st of the month no matter IF there was a change in season and rate or NOT. Not sure if this is a bug or if PGE sees it as a feature of their billing

Best regards

Jens

Re: PGE Rate calculation details

Posted: Sun Feb 08, 2015 2:01 am
I have done this in spreadsheet form with CSV data from the Green Button. It lines up very closely to PG&E's actual bills.

PGE Electric Rate Calculator_V1.7.xlsx