Plug-in Economics for Prius Prime

According to Toyota, our new 2020 Prius Prime PHEV gets around 4.3L / 100km of city driving. We will use this number since it is not too far off of the combine driving number of 4.4L / 100km. This means at the time of writing this post, the current fuel price at our neighbourhood pump is at $1.15 / L. If you do some fancy math, the Prime will yield us 20.2km per dollar invested at the pump (20.2 km/$).

Ontario Electricity Costs (Fall of 2019)

As depicted by the chart on the right, in Ontario we have three tiers of charging rates. The Prime in the winter can do about 35km with a 9kWh battery. The exact numbers are 40km / 8.8kWh, but this is perfect condition, and we use some battery for heating the vehicle. This will yield us the following:

TierYield
On-Peak18.7km/$
Mid-Peak27.0km/$
Off-Peak38.5km/$

So by comparing the above numbers, it makes perfect sense to charge the vehicle during Off and Mid Peak hours, and not so much during On-Peak hours. However the On-Peak comparison is so close that if the mileage rating was at 4.5L/100km then it is a wash.

With a bit more fancy math, you can actually calculate how much does gas have to cost per Litre before On-Peak charges make sense. This turns out to be around $1.24/L.

Hopefully you find this information helpful.

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