Details from Octopus on how they work out the energy savings.
"We’ll look at your historical smart meter data leading up to a Session, and calculate what you usually use at that time of day, on average.
If the Session is on a weekday, we’ll look at your half-hourly usage over the last 10 weekdays (excluding saving session days). If the Session is on a weekend, we’ll look at your half hourly usage over the last 4 weekend days. These half hourly averages are then subject to an ‘In Day Adjustment’ which will make adjustments based on how much energy you’ve used on the day of the session.
We then use these adjusted half-hourly averages as a benchmark – so you’ll earn points for every kilowatt hour you save during your Session."