Many web sites contain advice on how to save energy while using ovens in the kitchen. This article contains data about energy consumption and the actual saving in case these tips are applied. Surprisingly, the financial saving are pretty minimal.
The measurements were done using an energy meter for a combined microwave that is 8 years old and relatively energy efficient.
Energy saving tips on the web advise to use the preheat function only when necessary. With respect to consumption of energy, It actually does not make almost any difference on my oven, whether it gets preheated and then just maintains the temperature or whether it is heated normally. Preheating is a most energy consuming function indeed. However, it takes relatively short while. Afterwards, the oven just needs to maintain the temperature, which costs less energy.
It takes about 12 minutes to heat up my oven to 200 ºC (390 ºF) without the preheating function. The electricity consumption in this period is 1.6 kW. Thus, about 0.32 kWh is needed to warm up the oven.
My combined microwave consumes about 2.2 kW while being preheated. It takes about 5 minutes to reach the temperature of 200 ºC. So about 0.183 kWh is needed to preheat the oven. It consumes about 1 kW to maintain the temperature. To keep the oven on 200 ºC for additional 7 minutes (to make a comparison with the above case without preheating), 0.116 kWh of energy is needed. Thus during 12 minutes of operation that includes preheating, 0.3 kWh is used. This is actually less than when preheating is not used.
I have seen the instructions to preheat the oven mainly on the packagings of pre-baked pastries, which need only several minutes of baking to get ready. In my opinion, the instructions are formulated this way only to achieve repeatable results in every oven. Some ovens take longer to warm up than others. For short baking times and variable heat-up times, the total baking time differs per oven if the pastry is placed there from the very beginning.
Opening door while baking
Energy saving tips on the web advise not to open the oven door frequently because each time you open the door the oven temperature drops by 15 ºC (approximately 25 ºF). This is correct. However, it does not take much energy to restore the desired temperature.
Most of the ovens operate in two modes. The heating is either on because the temperature is below the desired level or the heating is off because the temperature is above the desired level. These two modes alternate. On my oven each mode takes about 30 seconds. After opening the oven door, the heating is on for longer period – about 2 minutes without interruption. This results in consumption of extra 0.025 kWh of energy.
Turning off the oven early
Energy saving tips on the web advise to turn off the oven about ten minutes before the food should be removed. The food should cook through anyway. This is correct. The temperature in the oven drops by 20 ºC to 30 ºC (35 ºC to 55 ºC) during this time. If a pastry is kept in the oven at 200 ºC for 30 minutes, the core temperature rises to about 90 ºC (195 ºC). The temperature drop during the last 10 minutes when the oven is off should have minimal effect on the core temperature.
The consumption is about 1kW to keep the oven on 200 ºC. So about 0.166 kWh is saved when switching the oven off 10 minutes sooner.
Read the manual for your oven. There is a fair chance that it contains energy saving tips specific to your appliance.
I pay about € 0.20 per 1kWh of electrical energy. How much can I expect to save while applying the energy saving tips above? Let’s assume that baking in the oven takes place 100 times per year, which is approximately twice a week.
- Preheating. No saving can be achieved here (at least not for my oven).
- Opening door while baking. If it happens 3 times per baking, the additional cost is
100 x 3 x 0.025kWh * € 0.20 = € 1.5
- Turning off early.
100 x 0.166kWh * € 0.20 = € 3.32
This is rather negligible saving for most of the households.
If you managed to read this far, you probably use green energy. So whether you apply those tips or not, this will not have an effect on the global warning.
In the above example, 24kWh of energy would be saved per year. The data differ regarding how much carbon dioxide is produced for generating 1 kWh of energy from fossil fuels. It is between 0.5 and 1 kilogram. So by applying the energy saving tips above, you prevent 12 – 24 kilograms (26.5 – 53 lbs) of carbon dioxide to be emitted to atmosphere.
The measurements were done for relatively small and energy-efficient oven. If you have either a large or old and inefficient oven, the saving will be greater.
Pre-baked pastries and pizzas can be put into a cold oven that will get preheated. When ready, they should be as crispy as when put into preheated oven. The baking time will be several minutes longer than what the baking instructions recommend. You will need to experiment a bit with your oven. The additional baking time depends on the time needed to preheat the oven.