I was interested to find an article posted by Richard Mudhar from earlier this year regarding sustainability issues surrounding boiling water - is it better to use an electric kettle or a gas stove-top kettle?
I have included details of his UK article below for interest, and have then adapted his calculations for an Australian (Victoria) perspective.
An electric kettle is often used to heat the small amounts of water for tea and coffee, because they are convenient. However, in earlier times people heated water using a kettle on the gas hob or solid fuel stoves, and for most domestic heating applications gas is cheaper. It is usually considerably cheaper in the UK (about 33%) per kilowatt-hour, and as an added advantage has a lower carbon footprint (200g/kWh for gas against about 500g/kWh for the UK). (1,200g/kWh in VIC!)
Surprisingly, it is in fact cheaper to boil water with an electric kettle (in the UK). The reason for this is that an electric kettle is much for efficient at transferring energy to the water than using a gas hob. The increased efficiency of the electric kettle outweighs all the other advantages that favour gas.
How the Efficiency of an Electric Kettle Was Compared with a Gas Kettle
For both cases, 1 UK pint of water (0.568 litres) was heated to boiling point with the water starting from 12 C. One pint of water is a typical amount needed for two mugs of tea or drip filter coffee. A mug is typically a third of a pint but some excess water is need either for the filter or grounds, or remaining in the teabags.
In an ideal world it would take 0.568 * (100-12) * 4187 Joules of energy to boil the kettle, this is established by multiplying the volume by the rise in temperature and the specific heat capacity of water, resulting in about 209 kJ. Expressed in more familiar units of electrical energy this is 0.058 kWh.
Electric Kettle Efficiency and Speed Results
Boiling a pint of water (0.568l) starting at 12C using a Krups 2.4kW electric kettle of 1.6l capacity gave the following results:
- Time - 85 s
- Energy - 0.067 kWh
- CO2 - 33 g
- Efficiency - 87 %
Gas Kettle Efficiency and Speed Results
Repeating the experiment using a Judge gas kettle of 2l capacity on a regular size mains natural gas ring resulted in these readings:
- Time - 275 s
- Energy - 0.2kWh (from the 0.0175 m3 gas used and the calorific value of about 11kWh per m3 provided by the gas company)
- CO2 - 40 g
- Efficiency - 30 %
Electric Kettles are Convenient, Efficient and Cheap to Run
Compared to the alternatives, boiling small amounts of water is one of the few heating applications where using electricity beats mains gas on performance and cost all round. This result is surprising, and seems to be largely the effect of the poor efficiency of getting the heat from the gas ring into the water. In the UK gas is approximately half the cost of electricity per kWh. The loss of 2/3 of the energy from the gas ring compared to the loss of just over 1/10 of the electrical energy means that the cost of gas is about a penny, compared with about 0.7p of electricity to do the same job.
Other ways to save energy in the kitchen include not overfilling the kettle when making tea or coffee.
Sources
A Victorian Perspective
In Victoria (AUS), the results are somewhat different. Firstly, gas is relatively cheaper here, and secondly electricity in VIC has a famously high carbon footprint thanks to the brown coal providing most of the electricity generation as well as some aged generation infrastructure.
Victoria Electricity – Gas Cost #
$0.645 / m3 or $0.0605/kWh
Victoria Electricity – Electricity Cost
$0.19/kWh
Gas Kettle per Boiling
0.0175m3* $0.645/ m3 = $0.011 and 40 g CO2
Electric Kettle per Boiling
0.067 kWh * $0.19/kWh = $0.013 and 84g CO2
# Calculated using $73/(112*1.0109) m3 (1,206kWh) based on Victoria Electricity bill
Co-Generation or Free Home Heating!
One aspect that is ignored is the issue of the waste heat, which has some interesting sustainability aspects to it. In the generation of electricity the substantial amount of waste heat (about 66% of energy input) is lost at the source as process inefficiency. In contrast, although the stove top kettle only has about the same heat transfer efficiency as an average VIC power station (a rather embarrassing statistic considering the rudimentary design of a stove top kettle), the waste heat is liberated directly into your house a free, 100% efficient heating. This is a basic type of co-generation, whereby the waste heat is utilised for a secondary benefit.
So in Victoria using a gas kettle will save you a few dollars a year, halve the emissions from your kettle use, as well as provide 100% efficient residual heating to warm your home in cold weather!
