Cooking with Less Gas

Microwave ovens, when they're on, stack up well against traditional ovens.

May 01, 2001
May/June 2001
A version of this article appears in the May/June 2001 issue of Home Energy Magazine.
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        In today’s fast-track society,more and more people are eating out, buying prepared foods, or converting conventional recipes for quick cooking in the microwave oven.Modern times require modern cooking devices like the microwave oven, and it turns out this modern approach to cooking is often the most energy-efficient way to make dinner.
        Cooking four medium potatoes takes about 15 minutes in the microwave oven. In a conventional gas or electric oven, it would take about an hour. In addition to saving time, microwaves save energy because they are much more efficient than traditional ovens. Cooking potatoes in a microwave uses about 10%–25% of the energy used by a conventional oven, and results in much smaller heat losses (see Figure 1). Furthermore, a microwave does not require preheating.
        Not all foods are microwave friendly,but many foods are. Manufacturers of packaged foods often leave the cooking method up to the customer.When it comes to using a microwave versus an electric oven, this choice is easy. Cooking a frozen dinner in a microwave rather than in an oven saves almost 1 kWh of electricity. Choosing to microwave four boneless breasts of chicken, four potatoes, and stuffing for the family can save 2 kWh a day (if you can tolerate the taste and texture).Over a year, these savings can add up. If the average price of electricity is 10¢/kWh,saving 2 kWh per day will mean $73 in energy savings per year.
         A microwave wins on energy use but what about energy cost? When comparing a microwave to a gas oven, differing fuel costs can make the decision a trickier one. Although a microwave is much more efficient and will cook foods faster, the price of gas is usually about one-fifth of the price of electricity. (These figures do not take into account current regional energy shortages.) One hour in a gas oven costs approximately the same as 30 minutes in a microwave. In the case of the four potatoes, therefore, it’s still both more energy efficient and cheaper to choose the microwave.
         Microwaves can also be used in place of an electric or gas cooktop. Instead of frying an egg or boiling water on a burner,many people turn to the microwave. An electric stove, however, is much more efficient than a microwave—70% compared to 55%—because the heat is applied directly to the container that is being used for cooking (see Figure 2).For example, when boiling water for a large mug of hot chocolate, an electric stove uses about 25% less electricity than a microwave oven. A gas stove is less efficient (40%) and requires more energy than a microwave;however, gas ranges usually cost less to use, due to the lowerally cost less to use, due to the lower price of natural gas (see Figure 2).
        Even when the stove looks like a better option than the microwave, consumers can sometimes save more energy by using the microwave,since they tend to heat smaller portions in a microwave.Consider, for instance, boiling water for tea. A tea drinker would be likely to fill a single mug of water to heat in the microwave,but might fill a kettle to boil water on the stove (then go away and leave it until the water had boiled off).
         Microwaves are also frequently used for defrosting.Here,thinking ahead is the key to saving money. Although defrosting is done at a lower power than cooking,putting that frozen steak in the defrost compartment of the refrigerator won’t cost a cent.

                 The Most Efficient Microwave Is Easy to Find
         To find out just how efficient microwave ovens are,we tested ten different models using a procedure that closely resembled the International Electrotechnical Commission’s standard method for measuring microwave oven performance.We borrowed the ovens from local households so that we could test a microwave population representative of those currently in use (see Table 1).
         We found that the microwaves’ average efficiencies (the ratio of the electricity that went to heat food or water in the microwave divided by the total electricity used) ranged from 49% to 57%. These results were comparable to those from a 1994 study by Lawrence Berkeley National Laboratory (LBNL) which measured microwave efficiencies at 48%–60%. While we did not specifically test for the effects of size on efficiency,we noticed that the two largest microwaves were the least efficient. We also found that the newer ovens were generally more efficient than the older ovens,although our sample size was too small to determine if this finding was statistically significant.
         Almost all of the power required by a microwave oven goes to the magnetron—a special electron tube that produces the microwaves. A combination of small components, such as a fan,a turntable,an electronic panel,a clock,and a light,draws a much smaller amount of power. Note, however,that small components such as the clock may end up consuming more energy over time than the magnetron, since the small components are on all the time (see “Your Microwave May Be Using More Energy Off Than On,”p.36). Microwave efficiency,therefore,is mostly dependent on the efficiency of the magnetron,which is generally pretty high—usually above 70%.offers the promise of improvements in the future.

                See the Savings
        Between reheating food,microwaving dinners,boiling water,and defrosting, the typical residential microwave oven consumes about 110 kWh of electricity per year,and costs about $11.00 a year to operate.Relying more on the microwave may increase this cost,but it can cut down on cooking energy costs overall.
        To streamline your kitchen’s energy consumption,bear in mind these five tips:
• Limit the amount of food being cooked to the portion that will be consumed.
• Always consider using a microwave oven rather than an electric or gas oven.
• Think ahead and defrost in the refrigerator rather than in the microwave.
• Don’t worry about which brand to purchase,since the range of microwave efficiencies tends to be small.
• Consider pulling the plug when your microwave is not in use for long periods.

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