Time of Use electricity billing - my findings

mackstann · 01-30-15, 01:52 PM

I've been looking at my utility's time of use billing option, and it wasn't clear if I would save money or not. The off peak times are at night, and certain periods of the day depending on season. Here is an image (PDF) showing their schedule: https://www.portlandgeneral.com/resi...se_sticker.pdf

So, conveniently, I log my electricity use. Every watt-hour is logged in real time, and I have data going back to last August, so while it is not a full year picture, it at least does contain a pretty full range of temperatures through the year. I wrote a Python script to run through this history and calculate what I would have paid conventionally, and what I would have hypothetically paid with the time of use billing.

The results were actually pretty good. Here is a bigass image of the chart I made: http://i.imgur.com/3jQHYvR.png . The green line is the important one. When it's over zero, I save money with TOU billing. When it's below zero, I lose money. The line is almost always over zero, even during summer. The savings are more dramatic in winter but still pretty good in summer. Totalled up, over this roughly 6 month period, I would save $139. That's pretty good. That is before any intentional shifting of electricity use to off peak times.

Considering that off-peak pricing is about 1/3 of peak pricing, it makes sense to shift usage even when you might actually end up using somewhat more electricity than you would have. So, while right now it is optimal to run my (heat pump) water heater at as low a temperature as possible, with TOU billing it would make sense to run it up to 140 at night and then turn it off (or WAY down) when the morning peak time hits, coasting on the extra hot stored water and not running the WH until the peak time ends. I am able to control my GeoSpring with a Green Bean already so this would be pretty easy. Similarly, I could heat up the house a bit extra just before the morning peak (we heat with a mini split), and then let the house "coast" during the morning peak at a lower thermostat set point (I do have a programmable t-stat for it). In summer, I could cool the house extra just before the 3pm afternoon peak starts, and then crank the AC down. We just had the house air sealed and insulated, so it holds a temp for a while now, at least much longer than it used to.

There are some other things we could do, like trying to run laundry and the dishwasher after 10pm. I think I could possibly save over $300 a year with all of these changes. That's pretty big because our annual electricity cost is probably only like $1200-1300. And while it does feel like a bit of trickery to save money without saving energy... it does do some good, because peak power is dirtier and off-peak electricity is not fully utilized anyway (at least that is my understanding).

01-30-15, 01:52 PM	#1
mackstann Lurking Renovator Join Date: Jun 2013 Location: Portland, OR Posts: 21 Thanks: 0 Thanked 3 Times in 3 Posts	Time of Use electricity billing - my findings I've been looking at my utility's time of use billing option, and it wasn't clear if I would save money or not. The off peak times are at night, and certain periods of the day depending on season. Here is an image (PDF) showing their schedule: https://www.portlandgeneral.com/resi...se_sticker.pdf So, conveniently, I log my electricity use. Every watt-hour is logged in real time, and I have data going back to last August, so while it is not a full year picture, it at least does contain a pretty full range of temperatures through the year. I wrote a Python script to run through this history and calculate what I would have paid conventionally, and what I would have hypothetically paid with the time of use billing. The results were actually pretty good. Here is a bigass image of the chart I made: http://i.imgur.com/3jQHYvR.png . The green line is the important one. When it's over zero, I save money with TOU billing. When it's below zero, I lose money. The line is almost always over zero, even during summer. The savings are more dramatic in winter but still pretty good in summer. Totalled up, over this roughly 6 month period, I would save $139. That's pretty good. That is before any intentional shifting of electricity use to off peak times. Considering that off-peak pricing is about 1/3 of peak pricing, it makes sense to shift usage even when you might actually end up using somewhat more electricity than you would have. So, while right now it is optimal to run my (heat pump) water heater at as low a temperature as possible, with TOU billing it would make sense to run it up to 140 at night and then turn it off (or WAY down) when the morning peak time hits, coasting on the extra hot stored water and not running the WH until the peak time ends. I am able to control my GeoSpring with a Green Bean already so this would be pretty easy. Similarly, I could heat up the house a bit extra just before the morning peak (we heat with a mini split), and then let the house "coast" during the morning peak at a lower thermostat set point (I do have a programmable t-stat for it). In summer, I could cool the house extra just before the 3pm afternoon peak starts, and then crank the AC down. We just had the house air sealed and insulated, so it holds a temp for a while now, at least much longer than it used to. There are some other things we could do, like trying to run laundry and the dishwasher after 10pm. I think I could possibly save over $300 a year with all of these changes. That's pretty big because our annual electricity cost is probably only like $1200-1300. And while it does feel like a bit of trickery to save money without saving energy... it does do some good, because peak power is dirtier and off-peak electricity is not fully utilized anyway (at least that is my understanding).