Is it Cheaper to Cook With Electricity Than Gas? Let’s Do The Math

What is cheaper: cooking with an electric cooker or gas? This is a question that has resurfaced recently after the Kenya Power and Lighting Company and LPG gas suppliers both reviewed and adjusted their prices.

To help answer this question, the Kenya Renewable Energy Association (KERA) developed the KEREA Energy Price Index to allow consumers see how much energy they use compared to all the other energy types sold in the country.

KEREA is an independent nonprofit association that facilitates the development of renewable energy business in Kenya. 

From its latest report, we can then look into the numbers and what they mean when it comes to settling for the cheaper and more efficient source of energy for a typical household in Nairobi.

What Do The Numbers Say?

Well, for starters, a hot-coil electric cooker is more efficient. Research shows that when using a normal flat-base sufuria, electric cookers can achieve about 70% energy efficiency. 

On the other hand, gas cookers are much less efficient as only 40% of the fire is actually used for cooking. The rest is lost to the surroundings. So, in a 13kg cylinder, only 5.2kg goes to useful cooking.

The highlights of the April 2022 KEREA Energy Price Index are as follows:

• The average cost of the grid electricity tariffs is Ksh15.30 per Kwh
• The average cost of fossil fuels sold in Kenya is Ksh15.52 per Kwh
• It is cheaper to use the 1st 100 units of electricity on domestic tariff for cooking than to use LPG in the 6,13,22.5 or even 50 kg cylinder.
• The cheapest energy source sold in Kenya today is biogas using cereal as the feedstock, which is at a levelized cost of Ksh0.13 per Kwh and the most expensive energy sold is electricity on the Interruptible tariff at Ksh25.4 per Kwh.
• It is cheaper to cook with grid electricity for domestic and small commercial users than to use the 3Kg LPG cylinder.
• By Introducing a time-of-day tariff for domestic consumers, people can be encouraged to cook during off peak hours using electricity and they can reduce their costs while increasing sales for the utility by increasing off peak sales to the domestic market.
• The cheapest source of electricity is daytime Solar Power produced in direct current (that can charge an electric car battery) at Ksh2.40 per Kwh or the equivalent of paying Ksh23 Ksh per litre of petrol.

Boiling 1 Litre of Water: Electricity vs Gas

We first of all need to assume that efficiency and other relevant factors such as convenience and environment are all held constant.

This way, we can then easily calculate how much it would cost to bring 1 litre of water to boiling point, using either electricity or gas.

1. Assuming the water at room temperature levels out at 25 degrees Celsius, it would then mean that in order for the water to boil, there needs to be a 75 degrees Celsius change in temperature, as water boils at 100 degrees Celcius.

2. Now, studies have shown that to raise 1g of water by 1 degree Celsius requires 1 calorie (the standard unit for measuring energy).

         1 Calorie = 4.184 Joules.

3. So, how many joules are required to boil one litre of water regardless of source of heat?

          To raise 1000 grams of water (1 litre) by 75 degrees requires the following joules of energy.

          1g by 1 degree = 4.184joules

          1000g by 75 degrees = ?

          1000 * 4.184 * 75 = 313,800 joules

4. The next step would be to find out how many joules we have in one kilowatt hour. 

         1 unit of electricity is equal to 1kWh

          1 joule = 1 Watt * 1 Second (There are 3,600 seconds in an hour)

          Therefore: The number of Joules in 1kWh is 1000 * 3600 = 3,600,000j

5. If so, then how many kilowatt hours do we need to boil 1 litre of water that requires 313,800 joules. 

          313,800j/3,600,000j = 0.0872kWh

Using this model, you need 0.0873 Kilowatt hours to boil 1 litre of water from a room temperature of 25 degrees Celsius to 100 degrees Celsius. 

How Much it Costs to Boil 1L of Water Using Electricity

Using Ksh15.94 as the current cost of a unit of electrical power in Kenya, we can then easily tabulate the cost of boiling water using electricity.

Ksh15.94 * 0.0872 = Ksh1.38

How Much it Costs to Boil 1L of Water Using Gas

To get a corresponding cost, we have to express gas in terms of kilowatt hours (kWh).

One kilogramme of gas (LPG) has an equivalent of 13.6 kWh of energy.

We know from the calculations above that we need 0.0872kWh of energy to boil one litre of water regardless of the source of energy. 

So, if 1kg of gas has 13.6kWh of energy, how many kilograms of LPG gas are needed to produce 0.0872 kilowatt hours of energy?

0.0872kWh / 123.6kWh = 0.0064kg

Then, how much would that cost you?

1. The current cost of 6kg LPG gas is Ksh1,500
2. What is the cost of 1kg?

          1,500 / 6 = 250

     3. So what’s the cost of 0.0064kg

           0.0064 * 250 = Ksh1.6

CONCLUSION: As far as comparing the cost of boiling to 100 degrees a litre of water at a room temperature of 25 degrees with all other factors held constant is concerned, using electricity is 16% cheaper than using gas i.e. Ksh1.6 versus Ksh1.38

NOTE I: Although the math shows that it’s cheaper to use electricity in the kitchen, the biggest problem is that electricity is still unreliable in Kenya.

NOTE II: It is important to remember that due to the inefficiency of the gas cooker (60% of gas is wasted), out of the 6kg of gas in a Ksh1,500 cylinder, only 2.4kg goes to useful cooking. Therefore, the effective cost is actually Ksh625 per kilogram of gas - which brings up the cost of boiling one litre of water to Ksh4.

Energy Sector in Kenya

In Kenya, charcoal is bought in tins, firewood in bundles or meters cubed, LPG and coal in kg, petrol, diesel, kerosene and fuel oil in litres, biogas in meters cubed, solar and wind in watts, solar hot water in litres and grid electricity in Kwh. 

Only the grid electricity is sold in an actual unit of energy, which is kilowatt hours and that is the SI unit for energy in the metric system. 

The fact that all the others are not sold in energy terms, means that the consumer, investor and government face a major challenge when trying to get a price and immediately compare this to other energy sources. 

This is what informed KEREA’s latest report as it summarizes the actual costs of all energy types sold in Kenya The Energy Index also generates summary of the renewable sources of energy, fossil fuels energy and grid electricity costs into rolling averages that are updated any time there is a change in prices.

Practical Energy Saving Tips

Is there a way to save cooking LPG? The answer is yes. Global LPG suppliers often publish tips on how to make your cooking gas last longer. Little adjustments in your cooking style here and there will do the trick.

Here are a few that stand out:

• Soaking: Soaking some foods will reduce extra fuel usage. For example, soaking peas or beans overnight-reduces fuel consumption by 22%.
• A visible flame touching the sides of sufurial wastes fuel since it gives out heat to the surroundings. However, if you cover the flame as much as possible by using a broad vessel, you will make notable savings.
• Use Lids: It is a good practice to cover sufurias and pans with a lid, as an open cooking pot loses heat to the atmosphere.
• It is important to clean the burner of your gas range regularly. Soot clogged gas burners increase fuel consumption.
• Clean the vessels: Undissolved salts are commonly found on the insides of kettles and cookers. Even a millimetre-thick coating can reduce heat transfer to the vessel's contents. This can increase your fuel consumption by up to 10%.
• Defrost at night: Defrosting overnight is very important to your gas savings. It reduces the amount of time your gas cooker will have to heat through the ice.

On the other hand, because the kitchen uses the most electricity in most homes due to the large number of major appliances, it is a good place to concentrate your efforts on lowering consumption.

Some tips on how to save electricity in the kitchen are:

• Use energy-saving appliances. To save electricity in the kitchen, choose an energy-efficient appliance over an older, less-efficient one whenever possible. When it's time to replace a major appliance, go with the one with the highest EnergyStar rating.

• Bring only as much water as you require to a boil. Do you boil the entire kettle of water just to make a cup of tea? To save electricity and time, only fill the kettle to the minimum fill level.
• Keep your refrigerator and freezer at least 12% full. Cool foods keep the temperature more stable than air. This is primarily due to the fact that cool air easily escapes when the door is opened, causing the fridge and freezer to work harder to bring the temperature back down.

Being conscious about one’s energy usage in the kitchen goes a long way in finding ways to make significant savings on the same..