Is electricity cheaper than gas? Here is the proof

By MUNGAI KIHANYA

The Sunday Nation

Nairobi,

13 August 2006

This is a question that has troubled many people for a long time: what is cheaper - cooking gas or electricity? To find the answer, I did an experiment here are the results:

I heated half a litre (500ml) of water in an electric kettle and a similar amount in a sufuria over a medium size gas burner. The kettle took one minute and 33 seconds to boil the water while the gas cooker took 4 min, 48s.

In order to compare the costs of the two, we need to find out how much of each energy source was consumed and multiply that by the unit cost. Electricity is sold in kilowatt-hours (kWh) and one kWh is the energy consumed when a one-kW appliance is operated for one hour.

One minute and 33 seconds is equal to 0.0258 of an hour. The kettle is rated at 2,200W (2.2kW) thus it consumed about 0.057kWh in boiling the water (2.2 times 0.0258). How much did that energy cost? To get the answer, we need to know the cost of one unit of electricity.

My most recent electric bill was Sh3,495.50 (inclusive of all taxes, levies and “adjustments”) for a consumption of 346kWh. Thus the current net price per unit is about Sh10.10. At that rate, it cost about 58 cents (10.1 times 0.057) to boil the 500ml of water in the kettle.

The corresponding calculation for the gas cooker is quite convoluted: first need to work out the quantity of gas consumed in the process. From the manufacturer’s manual, I found that the medium-sized burner consumes 146 grams per hour. This is equal to 0.041g per second and therefore in four minutes and 48 seconds (288s), the burner consumed about 11.8 grams of gas.

I have a 13-kg gas cylinder costs Sh1,500, which works down to Sh115 per kilo, or about 12 cents per gram. Therefore, 11.8g costs Sh1.40. This is almost two-and-a-half times the cost of using electricity (58 cents). Is gas then really cheaper than electricity?

The manufacturer’s manual states that the medium size burner produces heat at the rate of 2,000 watts (2kW). Now, if it is left on continuously until a full cylinder is emptied, it would run for almost 90 hours (13kg divided by 146g/h). At 2kW, this is equivalent to 180kWh. If this was electrical energy, it would cost about Sh1,800 while the gas cylinder goes for Sh1,500. The difference is not very large: electricity is only 20 percent more expensive. Indeed, if VAT was removed (gas is not taxed) the two prices would be the same!

Why then is the cost of boiling the water with gas more than double that of using the kettle? The answer is in efficiency of energy utilisation. The gas flame is open to the surroundings and a big proportion of the heat is absorbed by the air – this is why the kitchen warms up when you are cooking. The kettle’s heating element is in direct contact with the water thus very little heat is lost.