Ever wondered which is the most energy efficient way to boil a cup of hot water?
I've done a comparison using several methods:
Induction cooktop with kettle +375ml water
Gas burner with same kettle +375ml water
Ceramic electric jug + 375ml water
Microwave oven with 375ml water in a large mug
Immersion heater in same large mug with 375ml water
Water temp was 12C
I dont have any sort of electric hotplate, so that is not included in the comparison, however, it is considered to be less efficient than induction heating.
I've used my Graphtec data logger to extract the details of energy used from the battery/PV panels, ie this is a gross measure of the power used in my off grid situation, including inverter inefficiencies.
The electric power used, I can define precisely, but for the gas burner I searched online and Primus Australia specify that the burners on the GB300 use 416g/hr of gas. The label on the cooktop says 750g/hr which is 37.26MJ/h, I assume that is for all 3 burners running simultaneously, since the burner near the gas inlet uses significantly more gas than the far end, with the middle gas consumption being intermediate. I used the middle burner and took the 416g/h as being not too far from reality.
I've converted MJ to Wh for this comparison.
I adjusted the element position in the jug and ran it tilted back, so the element was well covered by the small volume of water in it.
Results:
Immersion heater ....118sec____ 48.3Wh .... @1473W
Electric jug ............115sec____ 51.6Wh .....@ 1615W
Induction cooktop ...101sec____ 63Wh ...... @2246W
Microwave oven ......171sec____ 89.5Wh .... @1884W
Gas burner ............167sec____ ~270Wh ..... @~5700W
The ~40 year old immersion heater is the most efficient, closely followed by the (old) electric jug, then the new induction cooktop, then the microwave. Gas was by far the least efficient, and in my off-grid situation the only method producing CO2 and other combustion gases. The microwave heating was done in 3 stages with a finger dip test to see how hot it was, the loss of heat during the 2 short breaks resulted in an insignificant increase in the amount of time required to boil the water IMO.
Traces from the data logger below- other loads were minimised when testing, to prevent fridges etc starting during the water heating test.