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Microwave Ovens: Science behind it; comparison with gas stove; and some myths/realties

By on April 22, 2016 with 4 Comments  

Microwave ovens are there in Indian market since quite some time, but it is only in the last few years that they have caught the fancy of Indian kitchen. We at Bijli Bachao get several requests asking for suggestions for buying microwave ovens and thus we picked it up as a topic to research about. The Bureau of Energy Efficiency in India currently does not have any star rating or standards for Energy Efficiency of Microwave Ovens and thus none of the microwave models in India are star labeled. Interestingly ovens are not rated for their energy efficiency in most countries in the world. So a model level comparison is not available anywhere. But we still went ahead with some research and found some interesting facts, which we have listed in the content below.

How does a microwave work?

The core to working of a microwave oven is a “Magnetron” that generates waves of electromagnetic energy. This electromagnetic energy, when it reaches water molecules, charges them, thus in turn heats them. On the contrary when it reaches a metallic surface, the metallic surface reflects them. For all “microwave friendly” containers, the waves pass through them without heating the container itself, but heating only the food kept in it.

Energy Efficiency of microwave and comparison with gas stove

As a microwave heats only the food and not the container & surrounding air, one would assume that microwave would be quite efficient in using energy/electricity. Add to that the microwave consumes very less time to heat the food as compared to a gas stove, so this should build a strong case for energy efficiency of microwave ovens. As one would believe that quick bursts of electricity would heat the food.

To make a comparison of gas stoves with ovens, US DOE (Department of Energy), did some tests to evaluate energy efficiency of various cooking methods, and what they found out was interesting:

Gas

Microwave Oven

Electric Heating

Induction Cooking

Heating Efficiency

40%

55%

74%

84%

Although slightly more efficient in using energy as compared to Gas, microwave technology is not as efficient as electric heating or induction cooking. The “Magnetron” that generates the electromagnetic waves does consume a lot of electricity, which makes microwave less efficient as compared to other electric cooking methods.

In a previous article on Cooktop Comparison (link), we compared Gas Stoves with Electric Heating and Induction Cooking on heating costs, and we found that all these cost almost the same. So if Microwave ovens are less efficient as compared to Electric Heating, then it will certainly be costlier to use them than using Gas stove.

Other research around myths and realities related to microwave ovens

Although it may be slightly costlier to use microwave ovens, but one cannot take away the benefit of ease of using microwave ovens. There are certain myths about using microwave ovens, which we would like to clarify on:

  1. Microwave ovens destroy nutrients in food: As per Harvard Medical School (link), this does not happen on using microwaves. The electromagnetic waves only heat up the water molecules in food causing the whole food to heat up. But they do not destroy nutrients in food.
  2. Standing near a microwave is injurious to health: People believe that microwave ovens produce radiations that are harmful. Considering how long microwaves have been in the market, one would think that any concerns about their safety would have been resolved long ago. Microwaves have metallic body all around and a metallic mesh on the door that reflects the microwave radiations to keep them inside. As per US FDA there is no documented case of radiation injury due to microwave ovens (link)

Certain things to take care of while using microwave ovens:

  1. Only use microwave friendly containers in microwave oven: Certain plastics release harmful chemicals when exposed to microwave radiation. So it is always better to use “microwave friendly” containers with a microwave oven.
  2. Avoid using metallic containers in microwave oven: Although metals deflect microwave radiations and in general do not get heated up, but at times microwaves can cause electric field at the corners of a metallic container, causing occasional sparks. Thus it is better to avoid using metallic containers in microwave.

References

http://www.health.harvard.edu/fhg/updates/Microwave-cooking-and-nutrition.shtml

http://www.princeton.edu/~achaney/tmve/wiki100k/docs/Microwave_oven.html

http://www1.eere.energy.gov/buildings/appliance_standards/residential/pdfs/cookgtsd.pdf

http://www.health.harvard.edu/fhg/updates/update0706a.shtml

http://oes.tamu.edu/guidelines/Tips_on_Safe_Microwave_Oven.pdf

About the Author:
Abhishek Jain is an Alumnus of IIT Bombay with almost 10 years of experience in corporate before starting Bijli Bachao in 2012. His passion for solving problems moved him towards Energy Sector and he is keen to learn about customer behavior towards Energy and find ways to influence the same towards Sustainability. .

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