Almost all electrical appliances come with power rating in watts, but the electricity bill has no mention of watts. This means that there is a relationship between units of electricity and watts. Don’t worry, it is easy to understand and we will make it crystal clear in this post.
What is a unit of electricity?
Units of electricity measure the amount of energy consumed. It is measured in kilowatt hours (kWh).
It means that
1 unit of electricity = 1 kWh of electricity
Now the question is what is kilowatt hours (kWh)?
1 kilowatt hour is amount of power consumed by a 1 kilowatt (1000 watt) appliance when it runs for 1 hour.
If you want to understand more, we have explained in more detail here.
What is the difference between watt and kilowatt hour?
Watt is the measurement of power, while kWh is the measurement of energy (electricity).
And we learn in 10th grade that
Energy (kilowatt hour) = Power (kilowatt) x Time (hour)
What is the difference between kWh and kVAh?
To understand the difference between the two, its important know few things about electrical appliances.
Any electrical appliance that has a motor uses magnetic field coil to rotate the motor. Such appliances use electrical energy for two purposes- rotating the shaft and generating magnetic field.
- The energy used to rotate the shaft is called active energy, which is measured in kWh
- And the energy used to generate magnetic field is called reactive energy, which is measured in kVArh
- Sum of active energy (kWh) and reactive energy (kVAh) is called total energy or total apparent energy. This is measured in kVAh
- Power factor is the ratio of active energy (kWh) and total energy (kVAh). It gives an indication about how much % of total energy is being used as active energy. This is the reason why kVaH is equal to or greater than kWh.
Hence Power Factor (PF) = kWh/kVAh
kVAh = kWh/PF
It means that if the PF decreases, KVAh will increase. Basically, if you are using many appliances or machine that use motor, then the chances of PF decreasing are high because these devices use good amount of energy to generate magnetic field. Hence is usually advised to add a capacitor bank to generate additional required magnetic field so that value of PF remains close to 1.
How to estimate power consumption by an Appliance?
Calculating the power consumption is easy. You need the wattage rating which is usually displayed on the appliance or on the packaging. Now you need to observe your daily appliance usage to get the number of f minutes or hours the appliance is used daily.
Now you can use the following formulae for calculating the daily unit.
Daily Units = (Watt-age x Number of hours appliance is used in a day) / 1000
Daily Units = (Watt-age x Number of minutes appliance is used in a day) / 60000
Monthly Units = Units x number of days in a month
This formula will give you a decent idea about the energy consumption of different types of appliances. However, appliances such as AC, Iron and other appliances used to heating and cooling may consume energy as per their wattage because they come with thermostat that change the temperature and power consumption constantly.