Ok so this is from the Daily Mail , but I assume they have done the investigation and look into it :
Using the slow cooker instead of the oven
Just under one in five of those surveyed by GoCompare said they were switching away from their energy-draining ovens in favour of slow cookers.
They may want to reconsider, as this energy-saving tip might be the biggest myth of them all - depending on how you use your slow cooker.
On average, electric ovens have a power rating of 2.0-2.2 kWh, whereas slow cookers use 0.64 kWh of electricity on low settings and 1.65 kWh on high settings.
So assuming someone used an oven five days a week, for one hour at a time, this would cost around £150 per year.
Alternatively, if they used a slow cooker five days a week for eight hours at a time on the lowest setting it could around £370.
However, slow cookers often use heat more efficiently than conventional ovens, wasting less energy – so they may actually work out cheaper depending how they are used.
For those worried about how much energy their slow cooker is using, experts suggest they get a smart meter and monitor their energy use to work our whether it is saving or costing them money.
Myth or Magic?
Myth, as the average energy consumption for a slow cooker is more than an electrical oven in the time it would take to prepare the same meals.
Energy saving tips suggest using a slow cooker more often instead of a conventional oven, however, it could cost you more in the long-run to make the switch full time.
Food for thought perhaps ?