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Old 01-30-15, 01:52 PM   #1
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Join Date: Jun 2013
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Default 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:

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: . 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).

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Old 01-30-15, 03:37 PM   #2
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Damn. I realized that the per-kWh number I was using for standard billing was too high. Re-running the corrected number turned the equation around and it looks like I'd pay more (~$70 more during the ~6 month time span). I'd have to shift a significant amount of use to off-peak times in order to benefit, and trying to estimate how much I could do that is very speculative.
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Old 01-30-15, 07:39 PM   #3
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You could put your hot water tank on a timer to only heat during the off peak hours.
I don't get metered by peak hours so I don't use one but if I did I would buy a timer.

Do all laundry in the off peak hours.

You can tune your TV to consume less watts by adjusting Picture mode , I can set my LCD tv setting to 2 out of 10 on the picture mode and save 100 watts. I turn up the brightness level to compensate , it works great.

Buy LED replacement bulbs in the few lights you use most often. Not sure if you use electric heat but if you do like I do keep the temperature at 68 and wear indoor shoes to offset the temperature.

Super heating the hot water just to later add cold water to make it useable is a exercise in wastefulness and futility IMO

So I keep my hot water tank at a nice hot bathing temperature , but no hotter then I can stand without the need to add cold water, I think this is the best energy hack as hot water tanks use about 6000w

Doing extensive draft sealing should not be overlooked.

Installing poly plastic over the window frames is effective at increasing the windows R value and will cut down on heating costs.

I have low electric bills due to my efforts , my house is heated by baseboard electric heat and my electric bill is lower then some people I know who use geothermal heat pumps but don't bother to conserve.

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Old 01-31-15, 02:21 AM   #4
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Our electricity price also varies (though not in a fixed manner like yours) and I have been working on various ways to take advantage of that. Maybe some of these ideas would also work for you.
I always start the dishwasher just before I go to bed rather than during more expensive times. Same for clothes washing.
Previously we didn't use a setback period on the GSHP with which we use to heat the house, but now I have it set to run at a lower temperature during generally expensive times. This is not ideal with a heat pump, and the setback period can need occasional adjustment as the season changes, but it does save.
Put your freezer on a timer so it only runs a few minutes per hour during peak times. Run it at a lower temperature during cheap times and at a higher temperature (but still cold enough) off peak. With the combination of these two it will run rarely, if at all, during peak times.
When I remember I move some ice blocks from the freezer to the fridge at the start of expensive periods, and move them back again at the start of cheap periods. Typically this means breakfast time and bed time. This reduces the electricity used by the fridge during peak times.
I work from home, and I use my laptop on its battery as much as possible during peak times, and plug it in during off-peak periods.
Charge things like mobile phones only at night.
Some dishes like stews can be cooked off-peak and just heated through if you need to eat during peak times. Avoid running the oven during peak times as much as possible.
Oh, with your heat pump that heats your water, be sure that it doesn't operate its resistive heating when the timer starts it up and it finds the water is a lot cooler than the target temperature. If the heat pump were working 24/7 this is less of an issue, but when it has a setback period it can be a problem when it comes back on line.

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