Assuming that the efficiency and other costs/factors (environmental, convenience) are held constant, this is how much it would cost to boil one litre of water in Kenya as of April 2021.
Assuming that water’s room temperature before boiling is 250C and since the boiling point of water is 1000C, you would need to raise the temperature of water by 1000C-250C=750C.
The amount of energy needed to raise the temperature of 1g of water by 1 degree Celsius or (1 Kelvin) equals 1 calorie. A calorie is a unit of measuring energy.
One calorie equals 4.184 Joules.
So to raise the temperature of 1 litre of water (1 litre=1000g for water) by 75 degree Celsius, how many Joules would you need?
For commercial purposes, for comparison purposes, a unit of energy can also be measured in terms of kWh. So when you buy tokens from KPLC, a unit of electricity is equal to 1kWh.
One Joule is also equal to 1 Watt x 1 Second.
How many seconds are in 1 hour? 3600 seconds.
k denotes a kilo or 1000 in the metric system.
W denotes a unit or measuring power.
So how many joules do we have in 1kWh?
1000×3600=3,600,000 Joules
How many kWh do we have in the 313 800 joules needed to boil one litre of water?
Cost Analysis
Using Electricity (KPLC)
Assuming that one unit of electricity (1kWh) costs= KSh.15.80
0.0872kWh will cost=15.80×0.0872=Ksh.1.377
So, it costs Ksh.1.377 to boil one litre of water using electricity.
Using Gas (LPG)
One KG of LPG (gas) has 13.6 kWh of energy
How much gas is needed to boil one litre of water?
Remember, we need 0.0872kWh to boil one litre of water regardless of the method we are using.
So if, One KG of LPG (gas) has 13.6 kWh of energy
Then, how many KGs are needed for 0.0872kWh?
Assuming 6KG of gas retails at KSh1000,
What is the cost of 0.0064KG?
So, it costs Ksh.1.067 to boil one litre of water using gas.
From the above analysis, it seems cheaper to use gas to boil one litre of water than electricity, the difference being (1.377-1.067=0.31). So, it costs extra 31 cents to boil one litre of water if you use electricity.
References
- LPG (propane) Gas Unit Conversions: Gas in kg, Litres, MJ, kWh & m³
- KPLC token prices – Prepaid charges calculator
- Total Gas prices cylinders & accessories
PS. This post is in response to a query raised by a Twitter user, Mr Mugendi, at Twitter. Note that there are a lot of assumptions made and thus this is not a definitive guide.
Efficiency CANNOT be held constant in such a comparison since both sources of energy are vastly different in how they heat water. For instant, the efficiency of a gas cooker is around 40% (just to be generous. EPRI shows that in reality it is 30-40%). Conversely, the efficiency of an electric kettle is around 80% (might be higher or slightly lower depending on the implementation; again, sourced from EPRI).
Now, applying 40% efficiency to your math, we find that you need 0.01603 KG of gas to boil a litre of water, which translates to Ksh2.672.
For electric kettle, applying 80% efficiency translates to 0.108958kWh, translating to Ksh1.721.
So you need Ksh0.95 more to boil a litre of water using gas compared to electric kettle.
Thank you for pointing out that.