Calculate how much it costs to run the oven per hour.
An oven's nameplate rating is its power while the element is actually energised, not its average draw. Once the cavity reaches temperature the thermostat cycles the element, and a well-insulated oven holding 180 C typically runs its element only forty to sixty percent of the time — so a 2.4 kW oven consumes closer to 1.3 kWh an hour than 2.4. Preheating is the exception: the element runs continuously, which is why twelve minutes of preheat costs about as much as twenty-five minutes of baking. This is also why batch baking is so much cheaper per dish, since the preheat is paid once regardless of how many trays follow.
Oven running cost with thermostat cycling
Energy per hour = rating in kW x duty cycle / 100; cost per hour = energy per hour x rate; preheat cost = rating x preheat minutes / 60 x rate
Because the thermostat switches the element off once the set temperature is reached and only pulses it to replace heat lost through the door and walls. Holding temperature costs far less than reaching it.
Yes, typically 15-20% cheaper for the same dish. Circulating air transfers heat faster, so you can cook 20 C lower and for slightly less time — set a lower duty cycle to model it.
Each opening dumps most of the hot air and pushes the element back to full power for a few minutes. Frequent checking can add ten percent or more to a bake, which is what the higher duty cycles here represent.