Like many Volt owners, I buy my electricity on a Time-of-Use basis as opposed to a flat rate. This means that as long as I charge during off-peak hours, I only pay $0.05/KwH, and a full charge on the Volt is just 60 cents.
The key to making this work is telling the Volt what times are peak and what are off-peak, and to their credit, the Volt engineers have made this pretty easy. You can set individual schedules for each day of the week, specify peak, mid-peak, and off-peak hours, and even input different schedules for Summer and Winter.
On October 1st, Progress Energy Winter hours began. During winter weekdays, in addition to the evening off-peak hours, there is also a 3 hour period in the afternoon (1-4pm) that is off-peak.
And thus my confusion began -- for I noticed that even after driving the car in the morning, it would wait until the evening to charge the car, and not take advantage of the afternoon off-peak period to top off the battery.
The Volt has 3 charging settings; Immediate (Feed me now!), Delayed Departure Time (Fill me up by a certain time), and Delayed Rate and Departure Time (Fill me up by a certain time, but try to do it during the cheap rate periods). I was using the third choice, obviously. I inquired on the GM-Volt forums, and it was suggested I change my departure time to just after the evening cheap rates started, in the hopes that this would force the car to take advantage of the afternoon off-peak.
I did this and the Volt immediately updated and said it would start during the afternoon off-peak. But it said it would end just after evening off-peak started, and so it appeared as if it would be charging right through the early evening peak period -- which was exactly what I didn't want it to do.
So I changed the time of departure back to the morning, and here is where it got doubly confusing, because the Volt still appeared to be saying it would charge through the evening peak period.
At this point, I really had to do some testing. So I unplugged the Volt until the evening to avoid any issues, and then waited a few days until I had to do some morning driving. While doing so, I watched the charge scheduling display, and as soon as I started driving, it started indicating that it would charge during the afternoon off-peak.
As I drove further, the estimated charge end time crept closer and closer to the end of afternoon off-peak, and when it finally reached the limit, it immediately jumped to the start of evening off-peak.
Aha! This meant that the Volt was only charging during off-peak, which was what I wanted and expected in the first place. And indeed, I monitored the car when I got it home and it did exactly that; it broke up the charging into two segments.
The end result of all this testing is that there are some issues that the Volt engineers ought to think about:
* There may be a bug in the way the Volt figures out when to charge immediately after a Summer/Winter change in schedule. It appears (though I am not 100% sure on this) that you need to make a change (as I did with departure time) to get things to "stick".
* There really ought to be a 4th charging option, "Charge whenever needed, during off-peak only". This would be particularly useful to those of us on Time-of-Use/Demand plans, where we really, really don't want to add extra load during peak hours (since we get hit for an extra peak demand charge).
* There is a driver confusion issue in the charge scheduling display, because it only shows charge start and end time, but does not show any periods where charging has been suspended. Part of the issue here is that the display is trying to show too much information; it shows start and stop times for both 120v and 240v, but 99.44% of the time, the driver knows what his next charge rate is going to be (and it's almost always the same as the last one).
So this display should be restructured, defaulting to show only one voltage (the last one used), with a button to select the other one. And the space freed up could be used to display a table showing start time, stop time, and estimated range for each planned charging segment.
* Special Bonus Suggestion: The Volt should automatically wait an extra 5 minutes before starting to charge during off-peak, and stop charging 5 minutes before peak rates start again. The point of this is to avoid accidentally starting during peak because of slight differences in the clocks of the power company and the Volt, and thus getting hit with a demand charge. Right now, I have my off-peak schedule set to start 15 minutes late and end 15 minutes early to avoid this issue.
At the very least, the manual should mention this issue and suggest programming in a buffer period.