Step C: Calculate on-peak / off-peak usage
- This is where things get interesting. First, you need to understand the 'split' (on- vs off-) for the different tariffs. For EDF GoElectric this is 2100 - 0700 (10hrs) plus all day Sat & Sun. For Octopus Go this is 0030 - 0430 (4hrs).
- Next, I needed to calculate how the 6,000 KwH would be split between on- and off-peak. First, I needed to understand EV charge time, which is based on a 7KwH Tesla Wall Charger and a 50KwH requirement would be c. 7hrs.
- I am now ready to calculate KwH split: I did this in two phases; first the previous 12 months (2,000 KwH) and secondly the new EV charging (c 4,000 Kwh). The key factor here is the duration of off-peak rates.
- As the EDF off-peak rate lasts 10hrs plus weekends, and average charge takes under 10hrs, I was able to allocate 100% of the 4,000 EV-related KwH charging to the off-peak rate. I also shifted some of the previous 12 months (2,000 KwH) into off-peak based on an estimated on- vs off-peak usage (excluding EV charging). This resulted in 1,200 KwH on-peak and 4,800 KwH off-peak for EDF.
- For Octopus Go, only 4hrs (57%) of the 7hrs of charge would qualify for off-peak charging. Thus, I calculated 57% of the 4,800 KwH off-peak usage from EDF (equal to 2,736 KwH) as Octopus Go's off-peak usage, and therefore a further 3,264 KwH on-peak use.
I get the impression that you are still thinking of charging as refuelling but there is a different mindset for charging.
The idea that you would charge 50kWh at a time is a bit odd. If you went for the Octopus GO tariff, you would want to maximise use of those 4 hours and so would charge accordingly. At 400 miles per week, the 4 hours per night is ample. It may surprise you but there is a subtle change of mindset when you become an EV owner and a little often is the way ahead.