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Author Topic: MIcrowave vs. Stovetop  (Read 11928 times)

Offline pirunner

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MIcrowave vs. Stovetop
« on: 17/03/2008 23:33:24 »
All others things equal, which method is more energy efficient. Also, whcih actually creates less CO2? (cobmustion of methane on the stovetop, or electricty consumed by the microwave - I understand that the type of power plant would also have to be specified, but differences in this aspect would also be appreciated).


 

Offline techmind

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MIcrowave vs. Stovetop
« Reply #1 on: 18/03/2008 00:12:22 »
I did a kind of analysis on this topic some time ago - see http://www.techmind.org/energy/calcs.html

Now a microwave is not perfectly efficient, as you will find out if you compare the electric (input) power label on the back with the advertised microwave power on the front. You probably lose 30% of the energy as heat in the magnetron...

As I conclude in my analysis (linked), an electric kettle is a fairly good way to heat water. It's quick, which minimises losses. And electricity can be used to heat water with very high efficiency. All the losses are at the power-station (or elec distribution).

Heating a pan on the hob is less efficient because it usually takes longer (therefore more time to lose heat to the air) and because quite a lot of the heat creates hot air around the pan and in the room rather than heating the pan itself. Having a lid on the pan helps reduce losses... but since you can't see when it's boiling you might leave it longer than necessary.


Depending on exactly how much water you have, what power the gas hob, and how the electricity is being generated (mix of coal/gas/oil/nuclear...) the gas and hob generates roughly the same amount of CO2 (assuming UK energy mix; US electricity has slightly greater carbon impact), but with the gas hob your "losses" are as excess heat in the kitchen (good in the winter, bad in the summer) whereas with electricity the losses are in the power station and outside your control.

The microwave will generate at least 30% more losses than the electric kettle owing to the magnetron inefficiencies, and the lower power (eg 800W microwave compared to 2400W kettle) means the microwave will take longer so you'll lose more heat from the water-vessel to the body of the microwave.
 

another_someone

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MIcrowave vs. Stovetop
« Reply #2 on: 18/03/2008 00:34:31 »
I would have thought there is one aspect of your comparison of microwave efficiencies you have ignored - the human element.

Normally, when you cook in the microwave, you are only heating the food you eat.  It is almost never the case with a kettle that you only boil the water you need, although with modern flat based kettles one will often try to get close to it, there is always some excess.  With other food, it depends on the food you cook as to whether you have excess water (or other fluid) that you heat with the food.  I cannot think of anything I cook in the microwave where there is excess fluid you heat with the food.
 

another_someone

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« Reply #3 on: 18/03/2008 03:06:47 »
You probably lose 30% of the energy as heat in the magnetron...

but with the gas hob your "losses" are as excess heat in the kitchen (good in the winter, bad in the summer) whereas with electricity the losses are in the power station and outside your control.

For the 30% inefficiency in the magnetron, I'd have thought it would be exactly comparable to heat losses on the hob.

Where you do not have control is in conversion and distribution losses (from inefficiencies in power conversion, resistive losses, or gas leaks in the gas pipes, or the energy required to pump the gas).

On other aspect with the hob is that often you will open the kitchen window not merely to release excess heat (and those heat levels tend to be far greater from most cooking I do on the hob than in the microwave), but also to release smells that accumulate from the cooking.

Ofcourse, the other incomparables is whether you would be cooking like for like.  Are you boiling or frying on the hob (frying will use a higher temperature than boiling, but you cannot fry in a microwave).
 

lyner

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MIcrowave vs. Stovetop
« Reply #4 on: 18/03/2008 09:43:09 »
Quote
Normally, when you cook in the microwave, you are only heating the food you eat.
Very true - and not only that but the food is the hottest thing in the oven, whereas on a stove the element / pan etc are hotter and a lot of heat is lost. The 30% loss in the microwave oven is, at least, a known quantity.

Both the actual mass of material to be cooked and the required cooking time are relevant here. Microwaves do not actually penetrate very deeply into meat, for instance, and time is still needed for a large joint to 'cook through'. Large and multiple dishes are sometimes best cooked in an oven with less use of energy and they are ready at the same time, too.

BUT, the Microwave oven is a terrific invention and I wouldn't be without one. I don't do any convenience foods in a microwave oven but it is great for green veg, pre-cooking baked spuds, porridge (in the bowl - no extra washing up) and many sauces. Where do people get their cranky ideas about microwaves ruining food? I can't think of a better way to preserve vitamins and taste.

You can even FRY in one if you get a browning dish (resistive strips in the base). This is very quick and 'cooks through' better than superficial frying of sausages etc.
« Last Edit: 18/03/2008 09:48:40 by sophiecentaur »
 

another_someone

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« Reply #5 on: 18/03/2008 20:18:09 »
I think the key factor is that the:

actual mass of material to be cooked and the required cooking time are relevant here.

In a microwave, the cooking times are almost proportional to the amount of material you are cooking (i.e. cooking two items of a given size will generally take about twice as long as cooking one of them - although cooking something twice as big is not the same as cooking two items of the same size because of the penetration issues).

Generally, in an over of stove top, cooking two items of the same size makes relatively little difference to the cooking time; hence indicating that most of the heat is not used in cooking the food, but in heating items that do not increase in mass as you increase the amount of food being cooked.

 

Offline neilep

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« Reply #6 on: 18/03/2008 21:09:16 »
If  ' taste ' is the method of measurement then I would expect the stove top to win hands down !! :)
 

Offline techmind

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MIcrowave vs. Stovetop
« Reply #7 on: 18/03/2008 21:51:16 »
You probably lose 30% of the energy as heat in the magnetron...

but with the gas hob your "losses" are as excess heat in the kitchen (good in the winter, bad in the summer) whereas with electricity the losses are in the power station and outside your control.

For the 30% inefficiency in the magnetron, I'd have thought it would be exactly comparable to heat losses on the hob.

Yes, you're right of course that the losses in the microwave still result in heat added to the room (which may be "useful" in some sense).
However, per unit of energy delivered to the home electricity generates roughly 3-4x as much CO2 as gas owing to the generation and distribution inefficiencies (and because coal just carbon rather than a hydrocarbon you'll get more CO2 as a combustion product than gas which also yeilds H2O). It also costs 3-4x as much at UK prices.
For a kettle with near 100% electricity-to-hot-water conversion efficiency, the CO2 emissions are still comparable to heating a pan on a gas stove with 25-30% efficiency (the rest heating the room).

Of course the amount of material to be heated is relevant. For example, heating a small amount of water in a saucepan the pan may have a similar heat capacity to the water, whereas you could heat one mug of water directly in the microwave... and get a hot mug (useful) at the same time.


In the grand scheme of things its not really very significant when you consider that every single time you decelerate a car to rest from 30mph (eg at traffic lights) it dumps enough energy in the brakes to boil half a litre of water!
(Kinetic energy = 1/2 m v^2    30mph = 13.4m/s, M=1500kg ...)

I saw some figures recently that road transport accounts for 25% of the UKs total CO2 emissions.
« Last Edit: 18/03/2008 21:53:00 by techmind »
 

another_someone

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« Reply #8 on: 18/03/2008 23:12:38 »
I saw some figures recently that road transport accounts for 25% of the UKs total CO2 emissions.

Is that road transport, or all transport?  Anyway, I would imagine that goods delivery consumes as much energy that transporting people (lorry drivers are squealing about the cost of fuel for a very good reason - they use so much of it).

But the largest consumer of energy is still space heating (i.e. heating home and office costs more than driving your car to work).
 

another_someone

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MIcrowave vs. Stovetop
« Reply #9 on: 18/03/2008 23:14:41 »
If  ' taste ' is the method of measurement then I would expect the stove top to win hands down !! :)

Depends on what you are cooking.

I just now had some pork and rice.  I cooked the pork on the hob, and it certainly tastes better that way; but I would challenge you to tell whether the rice was cooked in a microwave or on the hob.
 

lyner

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MIcrowave vs. Stovetop
« Reply #10 on: 19/03/2008 11:23:02 »
If  ' taste ' is the method of measurement then I would expect the stove top to win hands down !! :)
I would agree that, for items which need to be cooked at high temperature for their taste- i.e. browning/ frying- you are right. I wouldn't ever cook chicken or chops on a microwave oven.
Boiling or even steaming green veg causes a lot of leaching of 'taste' into the water (to wit, I would use water from 'the greens' in gravy. What comes from the microwave has virtually no 'juice' so you get all the taste on the plate.
It's also great for par-cooking (but not washing out flavour by boiling), prior to roasting. You get the benefit of roots etc. being cooked through without being dried on the surface when roasting.

Are you just suspicious of the effect of 'science rays'?
 

Offline neilep

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MIcrowave vs. Stovetop
« Reply #11 on: 19/03/2008 11:26:56 »
If  ' taste ' is the method of measurement then I would expect the stove top to win hands down !! :)

Depends on what you are cooking.

I just now had some pork and rice.  I cooked the pork on the hob, and it certainly tastes better that way; but I would challenge you to tell whether the rice was cooked in a microwave or on the hob.

Yes yes yes...there is always the exception....I use the M/wave to do vegetable more than the hob.....and fish can be done nicely too....

...hang on ?...have i just been invited to dinner ?
 

Offline neilep

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« Reply #12 on: 19/03/2008 11:30:26 »
If  ' taste ' is the method of measurement then I would expect the stove top to win hands down !! :)
I would agree that, for items which need to be cooked at high temperature for their taste- i.e. browning/ frying- you are right. I wouldn't ever cook chicken or chops on a microwave oven.
Boiling or even steaming green veg causes a lot of leaching of 'taste' into the water (to wit, I would use water from 'the greens' in gravy. What comes from the microwave has virtually no 'juice' so you get all the taste on the plate.
It's also great for par-cooking (but not washing out flavour by boiling), prior to roasting. You get the benefit of roots etc. being cooked through without being dried on the surface when roasting.

Are you just suspicious of the effect of 'science rays'?

Agree Agree Agree.....

Suspicious ?...always !..LOL !!.....I remember about ten-fifteen years ago when there was a lot of hoo ha about the potential for microwave leakage and that one would not want to keep their head too close to the oven door. To this end, a microwave engineer I knew, invented a microwave oven leakage tester......I don't know if he ever made any money from it but I've never seen any others since !!.......so...I guess.....I should be more aware of my own mind to create the fears eh ?
 

Offline Soul Surfer

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MIcrowave vs. Stovetop
« Reply #13 on: 21/03/2008 22:20:08 »
There is another method of cooking that puts the heat directly into the material and that is radio frequency cooking  but it only really works well for nicely cylindrically shaped lumps of meat like rolled joints.  They are stuck between flat plates like a capacitor and a few hundred watts of short wave radio signal tuned into them.  It's even faster than microwave cooking, cooks evenly all the way through and produces meat with a fantastic taste.

We researched it for a while at CRL.  The innovation lab where I spent most of my working life.

Needless to say most experiments were finished just around lunchtime.  :)
« Last Edit: 21/03/2008 22:22:21 by Soul Surfer »
 

lyner

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MIcrowave vs. Stovetop
« Reply #14 on: 23/03/2008 01:39:10 »
But RF heating things, efficiently, involves good matching of the source to the load. This is very hard to achieve over the range of sizes and types of food. Mostly you could expect a bad mis-match and a lot of energy loss in the RF source (a transmitting transistor or valve with an intrinsic efficiency of worse than 60%, probably, even in the best case).
I can't believe that RF heating can result in a better taste than a Barbie!
 

Offline Soul Surfer

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« Reply #15 on: 23/03/2008 12:46:48 »
I agree that it doesnt produce the nice brown bits but the flavour of the meat is excellent.  I can't remember the precise chemical reaction but the rf currents flowing through the meat created a slightly different chemical reaction.  As I said the meat has to be formed into neat cylinders and put between parallel conducting plates like a capacitor and then tuned up in the RF circuit.
 

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MIcrowave vs. Stovetop
« Reply #15 on: 23/03/2008 12:46:48 »

 

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