Monday, April 26, 2010

Cost to make a cuppa in using an electric kettle versus the microwave

As I was drinking a cup of coffee I started to wonder, is it cheaper to boil the water for a cup of coffee in a kettle or the microwave!

The maths behind boiling water is quite fascinating, but I'll leave that for another day. Instead I decided to use the power meter and simply measure the result.

It's a bit tricky, but with the power meter you can set your electricity rate and let the power meter do the calculation for you. Our electricity is currently 20.1 cents per kWh. I've noticed some electricity companies charge more, and I'm sure, others probably charge less. This also doesn't take into account the early payment discount I receive.

With the meter set, I filled a mug with water and boiled it in the microwave for 1 minute 45 seconds. This is the length of time I calculated using the maths, plus additional time for heat escaping into the surroundings, such the the mug itself. This brings the water close to boiling. For the kettle I filled the kettle half full as I normally would.

Now what is really interesting is the microwave is an 800 watt unit, but uses about 1200 watts. So it loses about a third in the process.

The kettle on the other hand is rated at 2400 watt, but actual usage is closer to 2200 watts. The kettle is more efficient at boiling water than the microwave, but there's a big catch with the kettle. You can't boil a single cup of water in the kettle. In fact, from what I observe, most people simply fill up the kettle. For example I fill up the kettle so the water is half way up the scale. I never thought about that before, but really, I'm boiling close to 1.4 litres of water when I really only need about 200 ml. With other kettles I've used I've filled the kettle up to the mark in the kettle. That means it is boiling the maximum amount of water. So whilst the kettle is more efficient than a microwave, the problem is we boil more water than we need.

The good thing is if you are looking for a new kettle, look at the minimum amount of water it takes. The minimum is often enough for two cups of water, which is sufficient for a lot of people. Others start at 500 ml, so go for the kettle which boils the least. If you are like me, I often have a cuppa by myself during the day, and make two cups for my wife and myself at night.

The outcome of the measurement.

The kettle costs 2.6 cents to boil the water.

The microwave is the clear winner costing 0.8 cents to boil a single mug of water.

This amount of money is really so small you'd think it is hardly worth thinking about. But if you boil the kettle three times a day, everyday over the year, the cost of using the kettle is nearly $30, whereas using the microwave is around $9. That's a saving of $21 a year, just for using a different appliance.

The best option to me is when you buy a kettle, buy one which has the smallest minimum water level, then you can boil the amount of water you really need and save money in the process. I really don't like to throw out old appliances that still work well, but the payback on getting a new kettle which makes it easier to measure the desired amount of water versus the current kettle is a little over a year. Kettles often last years, so a new kettle will pay for itself many times over during its life.

If you are interested in how much your appliances are costing you, and you know the power the appliance uses, you can use the Electricity Cost Calculator. Measuring each device is great, particularly if a device is run for a while and switches itself on and off over time. The best part is you don't have think. you just plug the power meter in and it shows you the cost. If you are interested in obtaining the power meter you can order it from the Electricity Cost Calculator page.

- Kelvin Eldridge

Tags: electric kettle, electric kettles, tea kettles, cordless kettle, sunbeam kettle, rusell hobbs kettle


Des @ CVC Studios said...

great article and very interesting.. totally impressed with your skills.. Can you tell me which cup of tea tasted better :)))
Des - Doncaster East

JustLocal said...

Hi Des,

Great question.

Whilst not relating to taste, I found with the microwave the cup gets much hotter which can be uncomfortable.

With instant coffee the microwaved water creates a foaming effect, which I thought was pretty neat.

I also had a feeling the microwave water doesn't seem to keep the heat as long. Possibly because the hot container is already losing heat to the surrounding air. Whilst the water did start to boil I can't be certain if there was perhaps a uniform distribution of heat in the water or whether it was non-uniform. It may also simply be just be my imagination.

Overall my preference however is to boil the water in the kettle. Once I was able to get a kettle where I could easily measure smaller amounts of water, I found it much easier to use the kettle than a microwave and it is more efficient.

Kelvin Eldridge