Microwaves: Switching from cooking using conventional methods to cooking using the 
microwave oven could save energy. Internet sites, such as local council websites, often make claims that microwave cooking is more energy efficient than traditional methods. There is however, little reliable, publicly-available research and the results appear highly dependent on how much is being cooked. Initial conclusions would appear to indicate that cooking small quantities in a microwave will be more energy efficient than in a conventional oven.
Microwaves are estimated to be in 91% of UK homes due to the ease of use and speed at which they cook food. Discovered in the 1940s they have gone on to revolutionise the way we cook food, however controversy surrounds how safe they are and whether they are more energy efficient than traditional convectional ovens. An investigation by Energy Star (the American Energy Efficiency Certification) concluded that when cooking or re-heating small quantities of food microwaves can be up to 80% more efficient than a traditional oven. (source: Energy Star Certification Scheme).
More detailed information on microwave energy use can be found here.