As conscientious inhabitants of Planet Earth in the early days of the 21st century, there are a number of easy adjustments we can make to our hectic lifestyles that will ease our burden on the environment. Fitting energy efficient light bulbs, doing our recycling and eating organic food are all examples of changes we can make with minimal effort that are good for the soul and good for the planet. Another one of these ‘usual suspects’ is swapping our regular kettles for eco-kettles.
This article (which is actually more of a musing than an article) intends to address a couple of thoughts that I’ve been harbouring ever since I got a stovetop kettle for Christmas, these being: what exactly are eco kettles and are they the best option?
Why the thought?
Well, while watching my new kettle boil on Christmas Day afternoon, just before Dr Who, a thought occurred to me. That thought was: if gas is cheaper and less damaging to the environment, then why are so many people using electric kettles, and more to the point, why are ecokettles not gas powered?
So what do I have against ecokettles?
Well, nothing to be honest, I think they’re a great investment; I’m just wondering if there may be a better way of boiling water. My first inkling as to the eco kettle conundrum was in reference to the specific heat capacity of water. Specific heat capacity is the amount of energy it takes to heat a certain amount of a substance – in this case water – to a certain temperature.
Aha! I hear you say. I see what he’s talking about now … but just in case you don’t get it, what I’m saying is this: If the energy required to heat water is always the same (at sea level), surely it makes sense to use X amount of kilowatt hours (kWh) of gas rather than electricity, because it cheaper and emits less CO2. Do you see where I’m going with this now? Good.
Just for your information; the specific heat capacity of water is expressed as 4.187kJ/kg/K. That is, it requires 4.187 kilojoules (kJ) of energy, per kilogram (kg) of water, to heat it per degree Kelvin.
I was always under the impression that eco kettles used less energy to boil the water, but after looking at a lot of eco kettles it’s apparent they simply boil just the right amount of water required. Well duh! Isn’t that obvious. Haven’t we been told to do that for years? I thought they we’re far more complex than that. Nevertheless, it is widely accepted that ecokettles can save 30% off a household energy bill, which is done merely by taking the hard part out of measuring the amount water you need. Genius.
Some of the sums – time to compare kettles
At risk of this turning into a physics lesson – albeit a very basic, badly taught physics lesson – I am going to explain the maths behind some of my thinking and how I have arrived at my conclusions:
According to Which the average energy used to boil a litre of water in an electric kettle is 0.114kWh. [1] According to my meter reading the energy used to boil a litre of water on a stovetop is 0.334kWh.
The carbon emissions from gas and electricity per kWh* are as follows [2]:
Gas: 0.203kg/kWh
Electricity: 0.527kg/kWh
* Calculated to include losses on the national grid and other inefficiencies.
If we assume that an average of I litre (about 4 cups) of water is boiled per day then:
Gas: 0.334kWh x 365 days = 121.91kWh per year
Electricity: 0.114kWh x 365 days = 41.61kWh per year.
Multiplying the yearly energy usage by the carbon emissions of each energy supply gives us:
Gas: 121.91kWh x 0.203kg = 24.75kg carbon/year
Electricity: 41.61kWh x 0.527kg = 21.93kg carbon/year
Finally we subtract to get the difference;
24.75 -21.93 = 2.82kg carbon/year
Assuming an electricity price of 14p per kWh and a gas price of 7p per kWh, then the cost of using the kettle per year is:
Gas: 7p x 121.91kWh = £8.53/year
Electricity: 14p x 41.61kWh = £5.82/year
A difference of £2.71 per year.
So there it is; using a gas fired stovetop to boil an average of 4 cups a day of water will emit about 3kg more CO2 and cost about £3 more on your energy bill, per year.
The reason is this: the main difference between the two methods of boiling water is the efficiency with which the heat is transferred. With an electric kettle the element is immersed in the water so there’s very little heat loss, whereas with the gas, waste heat is allowed to escape. Of course if you’re boiling your kettle on the hob at 7am, in the depths of winter, in a cold Victorian house, believe me, there’s no such thing as waste heat.
But still, I was hoping for the stovetop to perform better, or at least on a par with an electric kettle, but it doesn’t, so there goes my argument about specific heat capacity straight up the gas flue.
A couple of other thoughts
Not content with the electric kettle having the last word, I have to quickly raise a couple of points in favour of the stovetop:
- If you have kids or if you like a LARGE cuppa in the morning, an eco kettle may not work for you. I shall elaborate: I would imagine that eco kettles use the standard 250ml measure as a cup and boil you the appropriate amount. However, my two daughter’s teacups are 180ml, while my favourite large cup is 290ml. So how do I avoid boiling too little or too much with an eco kettle? With my stovetop I pour the water into whatever vessel (small cup, large cup, teapot) I am using and thus boil the right amount of water every time. Yes I know it may sound like a bit of a pain, but with an abnormal cup size dilemma such as mine, what else can I do?
- A gas kettle has no moving parts, so if it’s well made it should outlast an electric kettle, which will also lose efficiency as the element begins to fuzz up. I would like to see these test results on a pair of 5 year-old kettles.
- It takes a little more time to boil a stovetop than a regular kettle, but hey: sometimes we need to slow life down a little, don’t we?
- If you use an Aga, stovetops are definitely the greenest and cheapest option.
In summary then…
Well, it would seem the eco kettle’s place in our kitchens is safe. It is the most efficient way of boiling water, but only just. Whether or not you go for an eco kettle or a stovetop is down to your own preference, but be aware that the eco kettle – or any electric kettle used with the right amount of water – is the easiest way to save energy, money and carbon.
So that’s it. Even though I was proved wrong (barely) I can now put this argument to bed. And when it gets up, I will make it a nice cup of green tea.
To read an article on eco kettles, use the link below:
http://www.energysavingwarehouse.co.uk/news/128/20/Eco-Kettles.html
References
[1] http://www.which.co.uk/home-and-garden/kitchen/reviews/kettles/page/faqs/
[2] http://www.carbonindependent.org/sources_home_energy.htm
