J1m I find this an interesting topic, and one which has caused much debate in various groups if you're on FB.
Every time there's a "free" session, a plethora of posts appear, with the same questions, and the same wrong/partial/ill-informed/regurgitated answers.
It's not helped by the poorly worded and explained info from Octopus themselves.
However, the fact of the matter is, as always, there's more than one way to skin an 🐙.
For IOG (ignoring the first session, which many users, myself included, were very unhappy about, where IOG, and especially solar/battery users were unfairly discriminated against) you've got multiple options but, in each case, you're refunded at the same rate you're charged at:
1) plug in your EV before the session, let IOG schedule the charge and don't touch it. Use as much household electricity as you dare (washing machine, dishwasher, cooking etc), charge your house battery.
All the household usage (above normal) will be billed at day rate, and you'll be refunded the same. You'll also be refunded for 1 or 2 hours (depending on how long the session was) of smart charging at cheap rate. In this instance, it doesn't matter when the car charges, as long as you're letting Octopus control it and you haven't unplugged.
If octopus happen to schedule the charging during the free session, any other use at that time will also be billed/refunded at the cheap rate.
2) say you don't trust IOG to behave, you could either switch off smart charging to schedule a charge, either through your EV or charger.
In this case, your EV/charger is effectively just seen as another houseload, so everything would be billed/refunded at day rate.
3) you panic and press "boost".
Despite everyone saying don't do this, and spewing out the Octopus T&Cs, the reality is it just doesn't matter, due to the way the sessions are billed/refunded. Just remember to stop the charge at the end of the Octopus session. The session will be billed/refunded at the day rate.
In each case the end result is the same, a net zero cost, regardless of the rate.
I've tested all three methods, and in each case I was refunded the same as I was billed, one at 7p/kWh, one at 28p, and one at a mixture. Bear in mind that my "normal" grid use at these times is zero, so it's simple to check. My only gripe is they should actually be paying me more as I'm typically exporting at these times during the summer, but that's a different argument.
