A lot of people quoting low rates are also just referring to their off-peak rate. This is pretty common in EV discussions. It's not exactly a fair argument there, either, because the flip side of having an off-peak rate is that the on-peak rate is usually quite a lot higher. So the true effective rate is a bit higher, somewhere in the middle depending on usage pattern.
It's easy to have your EV only charge off-peak, though. It's just a setting.
My point is that the tradeoff to get off-peak pricing is that on-peak is way, way more expensive. So you can charge the EV off-peak to maximize the savings, but everything else you do during on-peak time costs way more.
Using myself as an example:
I adjust my A/C to run outside of 5pm-9pm (peak) if at all possible, we try to avoid pointless high-draw usage during that same window, and both of our EVs hold off charging until after 9pm.
My rate from 5pm-9pm is 0.43/kWh. My rate after 9pm is 0.09/kWh. The flat rate alternative, if I did not want to worry about time of day, would be 0.21/kWh. These prices are all-in, including transmission and distribution/whatever.
It would be dishonest to say that my EVs only cost me 0.09/kWh to operate, which on it's face is a claim to paying over 50% less. In reality, time of day pricing typically saves me somewhere between 10% and 15% in an average month compared with flat rate.
If you leave the EV charging out of your consumption, does a time of day plan still save you money on the remaining usage? Or does it cost you? If it saves you money, then it would make sense to be on a ToD plan regardless of EV charging. Which means it makes sense to consider your additional EV draw as costing the marginal off-peak rate. Essentially the EV load has the valuable property of being dispatchable.
You can do the same thought experiment with say a dehumidifier in your basement. It can easily be off during peak usage and still accomplish its job, so its cost of electricity is also the marginal off-peak rate.
> If you leave the EV charging out of your consumption, does a time of day plan still save you money on the remaining usage? Or does it cost you?
It would cost me more (modestly so, less than 10%) to be on TOD without the EVs. This will vary by customer, of course, and I expect that the power company designs TOD to be a wash for the average customer. They even guarantee it won't be more than 10% more expensive over the first year or they will refund the difference.
Then yes I'd agree with you, it doesn't make sense to describe your EV charging as costing $0.09/kWh since you're presumably only on the slightly more expensive ToD plan due to the EV.
Personally I'd love to have a ToD plan, especially with the rate structure you've laid out - break even seems to be using less than 1/3 of your daily electricity usage during the on-peak hours, which is only 1/6 of the day? I've got a bunch of fixed loads (computers) plus ones that tend to run overnight anyway (dishwasher, dryer, etc).
FWIW I'd think the pricing of the ToD plan versus the fixed rate plan has more to do with how the power company themselves has to buy power and model/hedge against demand at various parts of the day, rather than simply trying to make the costs even for the consumer.
> FWIW I'd think the pricing of the ToD plan versus the fixed rate plan has more to do with how the power company themselves has to buy power and model/hedge against demand at various parts of the day, rather than simply trying to make the costs even for the consumer.
I agree, my single point of evidence to support my theory is that the power company advertises the TOD plan by presenting an average customer with their breakdown of usage throughout a typical day, and then itemizes how it would look with flat-rate versus TOD. The resulting figure is within a few pennies. I figure that is not accidental, but I could be wrong and it is entirely coincidence.
Fair point.
I guess it depends on if you would be using ToU otherwise.
It looks like about 50% of Californians use ToU plans, but the number is only 10% nation-wide.