6.4 Calculate the Cost of Electricity Consumption
Energy Efficiency
Energy efficiency is the percentage of input energy transformed into a useful output energy form.
Energy efficiency = Useful energy output × 100%
Energy input supplied
Technology which Applies the Concept of Energy Efficiency
Use of Electricity in Electrical Appliances
Electric power, P, is the rate of electrical energy, E, used by an electrical device.
The S.I. unit for power is watt (W).
The power of 1 watt (W) means 1 joule (J) of electrical energy used in 1 second (s).
Electric power can be defined as follows:
Electric current, I, is defined as the rate of flow of electric charge, Q, through a conductor.
The S.I. unit for electric current is ampere (A).
The S.I. unit for electric charge is coulomb (C).
Electric current is defined as follows:
Voltage, V, is defined as the electrical energy, E, used to move a unit of electric charge, Q, through a conductor.
The S.I. unit for voltage is volt (V).
Voltage can be defined as follows:
Calculating Flow of Current through Electrical Appliances
The quantity of current that flows through a certain electrical appliance can be calculated by using the following formula:
Current ,I (A) = Power, P (W)
Voltage (V)
Example:
Using the equation P = VI
I = P
V
= 2.2 kW
240 V
= 2200 W
240 V
= 9.17 A
Calculating the Cost of Electrical Energy Used
The relationship between electrical energy (kWh), power (kW) and time (h) is shown in the following formula:
Electrical energy (kWh) = Power (kW) × Time (h)
Example
A 2 kW electric kettle takes 10 minutes to boil water. Calculate the cost of electrical energy used to boil the water if the rate per unit is 21 sen.
Electrical energy used (kWh) = Power (kW) × Time (h)
= 2 kW × 10
60 h
= 1/3 kWh
= 1/3 unit
Cost of electrical energy used for the electric kettle = 1/3 unit × 21 sen/unit
= 7 sen
The total energy used by an electrical appliance depends on the power of the appliance and the duration that appliance is used.
Ways to Save Electrical Energy Consumption
The green building which applies the concept of energy conservation has succeeded in reducing the cost of electrical energy consumption.
The construction of green buildings is gradually expanding in Malaysia.
Among the features of a green building are as follows:
Efficient ventilation system to reduce the use of air conditioning and fans
Maximising the use of natural lighting to reduce the cost of electrical energy consumption
Installation of solar panels as a renewable energy source to replace conventional energy sources