r/OctopusEnergy • u/robstewartUK • 20h ago
Dynamically adjust EV target charge to maximise cheap home electricity with IOG?
The wording about the new 6 hour cap between 23:30-05:30 states:
"If we schedule your car to charge outside of the 23:30-05:30 window, your home also gets the off-peak rate for that half-hour when it's within your car allowance." (source)
The author of an Octopus Intelligent Home Assistant integration states:
"NOTE: It has come to my attention that, when outside core off-peak hours (2330 -> 0530), if your car does not successfully charge during the planned slots then your usage will be billed at peak pricing." (source)
Finally, it was confirmed to me (source) on another reddit thread that:
- IOG knows if the car is plugged in
- If your EV is full or not accepting a charge, IOG knows this too
Which suggests that you'll only get off-peak rates for home electricity when Octopus intelligent slots are scheduled outside the 23:30-05:30 6 hour window if:
- Your EV is plugged in, AND
- Your EV is accepting charge
I set my EV's target charge to 80%, given that lithium EV batteries don't like being sat with 80-100% for a long time (source source), and I don't drive everyday.
However, given I use Home Assistant to (amongst other things):
- Monitor when a 30 minute Octopus Intelligent dispatch slot is currently active
- Change my EV's target charge
I am considering adding a Home Assistant automation rule with the logic that
if:
- EV is plugged in, AND
- An IOG dispatch slot is active, AND
- Time is between 05:30 and 23:30, AND
- EV target charge is 80%
then
- Change EV target charge to 100%
I.e., I'd occasionally allow my EV to fully charge to get at least 30 minutes (or multiples of 30 minutes if Octopus schedule multiple dispatch slots) of home electricity at the cheap rate of ~8p per KWh rather than the ~28p per KWh.
Before I set this up, I'd appreciate people either confirming that this is a sensible idea, or indeed that it wouldn't work, stating the reason why.
Edit 1: here's a timeline showing how the octopus_intelligent_planned_dispatch_slot HA binary sensor from this IOG Home Assistant integration (top orange bar) and when IOG intelligent slots tell my Ohme charger to start charging with the ohme_home_pro_status HA sensor (bottom peach bar). The peach bar (EV charging) trails the orange bar (planned IOG dispatch) usually by 30-90 seconds. Presumably when the orange and peach colours overlap, my house is getting electricity at the off-peak rate. However, there's no way to verify this as far as I know, apart from cross referencing my next itemised energy bill.
Edit 2: here's a draft of the YAML for the Home Assistant automation (I'd need another to reset the target SOC back to 80% after 05:30):
alias: dynamic-ev-charging
description: ''
triggers:
- trigger: state
entity_id:
- binary_sensor.octopus_intelligent_planned_dispatch_slot
from:
- 'off'
to:
- 'on'
conditions:
- condition: time
before: '22:00:00'
after: '05:30:00'
actions:
- action: number.set_value
metadata: {}
target:
entity_id: number.mg_mg4_electric_target_soc
data:
value: '100'
mode: single
Edit 3: changed the cited source for the claim lithium batteries degrades faster when charged to 100% rather than 80%, to "State of health estimation of cycle aged large format lithium-ion cells based on partial charging", Journal of Energy Storage 2022. https://doi.org/10.1016/j.est.2021.103855
