So I'm all excited. Our Tesla Model X is on order. I'm looking forward to charging it every night at home. So the next question is... "How much will that daily charge cost?" Well, it depends on how many miles we drive the X and how much the electricity costs to charge it. We're currently a Duke Energy Progress customer on the RES schedule which is a seasonal flat rate plan. There is a winter rate ($0.0921 Nov-June) and a summer rate ($0.1018 July-October). There is also a RES-TOU schedule. With that, the rates vary by season and time of use:
Duke Energy Progress RES-TOU rate schedule:
| Summer June-September | Winter November-May |
| 22.955¢ per on-peak kWh | 20.611¢ per on-peak kWh |
| 11.236¢ per shoulder kWh | 10.649¢ per shoulder kWh |
| 6.211¢ per off-peak kWh | 6.211¢ per off-peak kWh |
40 kWh at the off peak TOU rate is $2.50, and the same 40 kWh flat rate is ~$3.95. 40 kWh is about 100 miles which is a typical school/work day for us. I estimate we'll put 25K miles a year on the X. 25K miles is $987 flat rate vs $621 TOU rate (vs $2557 for gas at 22 mpg and $2.25/gallon). So charging the Tesla overnight at the TOU off peak rate would cost less. But what about all the other times we use electricity?
It's hard to decide without having some additional information. Maybe a neighbor switched rate plans and can provide input. You can post a question to other EV owners and ask them - I did. I posted to the Tesla Owners - NC Triangle (Tesla Triangle) G+ group. Several members replied and said the TOU rate saved them money. That was helpful, but I really wanted to know before I 'just did it.' Because once you switch, there is 1 year commitment.
It just so happens that I have the Neurio whole house energy monitor, and it's happily been sending my second-by-second energy usage to the cloud since March 2015. I've looked at the data in the past and said, "Yawn... That's nice." I got Neurio to see how much energy major appliances use. To do that, it looks at the instantaneous energy usage and tries to recognize a usage pattern. It struggles to do that well - there's just too much 'noise' in the data. It does however summarize that second-by-second data into minutes, and the minute data into hours, and the hour data into days, and the days into months and the months into years. Cool!
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| Hourly Energy usage for yesterday. |
It will also let you export the hourly data to a CSV file one month at a time. So I exported June through August 2016, and December - March 2016 (2017 was a really warm winter). I then put that data into a spreadsheet on Google docs and here is what the data showed me:
| Duke-Progress Rate values | Per kWh | kWh used | |
| Summer Flat Rate (July-Oct) | $0.09871 | ||
| Winter Flat Rate (Nov-June) | $0.08903 | ||
| Winter (Dec-March 2016) | |||
| Winter Peak 6am-9am (Oct-May) | $0.20611 | 453 | $93.28 |
| Shoulder 9-noon, 5-8pm | $0.10649 | 933 | $99.32 |
| Winter nonPeak | $0.06211 | 5315 | $330.14 |
| Bill Winter TOU | 6701 | $522.75 | |
| Bill Winter Flat Rate | 6702 | $661.60 | |
| Summer (June-August 2016) | |||
| Summer Peak 1-6pm (June-Sept) | $0.22955 | 658 | $151.08 |
| Summer Shoulder 11-1pm, 6-8pm | $0.11236 | 562 | $63.18 |
| Summer non peak | $0.06211 | 3931 | $244.18 |
| Bill Summer TOU | 5152 | $458.45 | |
| Bill Summer Flat Rate | 5154 | $508.78 | |
This table is just the energy cost and does not include service fees and taxes. The filter in the sheet separates weekends from weekdays (all weekends are off peak). However, it does not adjust for holidays which are always off peak. With those exceptions, it still strongly indicates that the TOU rate would save us some money even if we didn't have an EV. During the periods I studied, we used electricity whenever we wanted without any thought given to the time of use. If we were to be conscious of when we use appliances, I'm sure we could reduce our peak usage even further.
Time will tell. I called Duke Energy Progress, and they are going to replace our flat rate meter with a TOU meter "soon". I'll be watching Neurio data more often now that we are on the TOU rate plan. We use SmartThings to control electrical devices around our home. We have a WiFi connected Honeywell thermostat and a GE GeoSpring water heater. I plan to adjust their schedules accordingly. I suspect winter mornings could cause us the most problems since we currently turn down the temperature on the heat pump overnight and then turn it back up in the mornings.
If you are currently on a flat rate energy plan and you're even thinking about getting an EV, I'd recommend that you go on and purchase a Neurio and install it so that you will have the data you need to make an informed decision. Doing so could save you hundreds of dollars a year.
More information about the installation of our water heater can be found on my personal blog.
Get a $1000 off your Tesla by using our referral link:
https://www.tesla.com/referral/donald8803
Corresponding Video
If you are currently on a flat rate energy plan and you're even thinking about getting an EV, I'd recommend that you go on and purchase a Neurio and install it so that you will have the data you need to make an informed decision. Doing so could save you hundreds of dollars a year.
More information about the installation of our water heater can be found on my personal blog.
Get a $1000 off your Tesla by using our referral link:
https://www.tesla.com/referral/donald8803
Corresponding Video
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