Spills will absorb energy waves just as readily as the cooking food. Microwaves operate more efficiently when the interior is clean.
Microwave cooking can be more energy efficient than conventional cooking because foods cook faster and the energy used only heats the food, not the whole oven compartment.
The microwave oven clock and standby function can consume a significant amount of electricity, even when the oven itself is not in use. It could be consuming most of its energy when not actually cooking, it may be better to unplug your microwave when not in use.
For smaller meals, reheating them in a microwave will save energy. It is estimated that you can reduce the energy used in cooking by as much as 80% when using the microwave instead of an oven.
About 65% of the electric energy used by a microwave oven is converted to microwave energy which heats the food. This is considerably more efficient than a conventional electric oven which may convert as little as 10%.
Defrosting food in the microwave is convenient, but with a bit of forethought you can do this using no energy at all. Just leave it in the fridge overnight and it will be defrosted the following day!
There is concern that microwaving foods in plastic containers can cause toxic chemicals to leach into the food from the plastic. Make sure you transfer your food into glass or ceramic containers labelled ‘safe for microwave oven use’.
Microwave ready meals can be energy-intensive products in terms of their food miles, the packaging used and the food processing involved. Chris Goodall, in his book ‘How to live a low-carbon life’, estimates that convenience food manufacturing may be responsible for three times as much CO₂ output as home cooking.
Microwave ovens cook food with waves of oscillating electromagnetic energy that are similar to radio waves but move back and forth at a much faster rate. According to the US Food and Drug Administration, microwave energy is changed to heat as it is absorbed by food, and does not make food radioactive or contaminated.