More Than Living

How much electricity does a microwave oven use in a week?

We’ve taken a break from test­ing how much elec­tri­city wash­ing machines use to answer a ques­tion about microwaves.

Sandra Storr asked us to look at the one-​​time ovens of the future, as she’d heard that they used as much power on standby as they did during cook­ing. We’re relieved to find out that’s not the case.

We tested a 10-​​year-​​old Sharp microwave with a group E cook­ing power rating. Des­pite its age, we found that it only used one Watt when totally idle, which isn’t too bad. Like most microwaves, open­ing the door turns on the oven light, which added another 21 Watts, so it’s a good idea to make sure it stays closed when not in use.

Half-​​baked

Things got a little more inter­est­ing once we star­ted cook­ing, though. Our microwave’s 850-​​Watt rating refers to the amount of microwave energy it can pro­duce for cook­ing, rather than how much power it requires during the pro­cess. We found that it drew almost twice as much power – 1.6 kilo­watts (kW) – when run­ning at its max­imum set­ting. Wiki­pe­dia says that a modern microwave oven should con­vert around 64% of the energy it con­sumes into microwaves, but ours man­ages only 53%.

Even so, using our microwave for some tasks, such as baking a single potato or reheat­ing chilled food, is still likely to be more effi­cient than using a con­ven­tional oven. A typ­ical elec­tric oven draws 3kW or more for sev­eral minutes as it heats up, and does so again peri­od­ic­ally to stay hot. That’s even more than a kettle, which is why most ovens are wired dir­ectly into a heavy-​​duty cir­cuit in your home – unfor­tu­nately, that’s also why we can’t test them with our power meter.

On the other hand, the way that microwaves heat food means that bigger servings require pro­por­tion­ately longer cook­ing. This is less pro­nounced in a con­ven­tional oven, so it’s likely to be more effi­cient if you’re cook­ing many pota­toes. Of course, it’s also a better bet if you prefer them with a crispy skin.

Hot potato

Return­ing to Sandra’s ques­tion, although her microwave isn’t using as much power on standby as she feared, her habit of turn­ing it off at the plug is still saving her elec­tri­city and money. In a week of heat­ing up por­ridge and defrost­ing the odd frozen meal – waste­ful com­pared to defrost­ing in the fridge overnight – our microwave used exactly 2 kilo­watt hours, cost­ing around 22p.

IMAGE Weiser Farm Pota­toes by

Flickr user ExperienceLA

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Ori­gin­ally posted 2008-​​03-​​07 04:04:00. Repub­lished by Blog Post Promoter

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