1 unit of electricity means 40 Watt Tube Light Running for 25 Hours

1 unit of electricity means 40 Watt Tube Light Running for 25 Hours
“ 1 Unit of Electricity Saved by You is 2 units of Electricity Generated “
( 1 unit of electricity means 1kW of power usage for an  hour / 860 kcal of Heat Units) 

              This is simple yet a very powerful quotation seen at many places recent days after the world started realizing the need for energy conservation. This quote is considered one among the powerful as it has a quantitative explanation embedded in it. This quotation highlights that the overall efficiency of electrical energy from generation to utilization is only 50% and hence one unit of electricity, you save at your end can save nearly double the resources required to generate that. I thought that if logic behind this is explained then this may trigger a bit more awareness towards energy conservation.

How Electricity or Electrical Energy is measured?

Unit of measurement for electrical energy is kWh ( Kilowatt Hour) and 1 unit of electricity means, using of any equipment rated at 1 kW for a continuous period of 1 hour. If we use a 40-watt tube light for 10 hours a day continuously then the electric energy consumption will be 40x10 = 400 wh or 0.4 kwh or nearly half a unit. If the same is used for one month then the consumption will be nearly 15 units. But the other side of the story is ....30 units need to be generated at supply side to give you that 15 units as the losses in the line from supply to distribution are around 50%. There are lakhs of such tube lights on the earth and hence the electrical energy consumption is such high. So switching off a light when not used will definitely create a big impact.    

What do you mean by 1 unit of electrical energy ???

One unit of electricity equals to
1 Unit of Electricity Means

 1 unit of electricity means 40 watts tube-light running for 25 hours
 1 unit of electricity means 75 watts ceiling fan running for 13 hours
 1 unit of electricity means 32 watts LED TV running for 18 hours
 1 unit of electricity means 300 Litres refrigerator running for 12 hours
 1 unit of electricity is equivalent to 860 kcal of Heat Energy 


Electrical energy need to cross through various elements in the power system from the point of generation to user end which results in multiple losses like conductor losses, switching losses, current losses, power factor related losses etc., The power source to end-user efficiency link is a key factor, which influences the electrical energy input at the supply end/source end. If we look at the flow of electrical energy from the point of generation to the user end in terms of cascaded energy efficiency, typical profile from generation to 11Kv – 33KV user industry is as follows

η: Efficiency

Electricity flow from generation to end user

1.Efficiency Ranges from 28 % to 35 % with respect to age, size and capacity utilization of a thermal   plant

2.Step up to 400/800 Kv to enable EHV transmission. The envisaged maximum loss of 0.5 % or efficiency of 99.5 %

3.EHV transmission and substations at 400 Kv/ 800 kV. Envisaged maximum losses 1.0 % or efficiency of 99 %

4.HV transmission & substations for 220/400 kV. Envisaged maximum losses 2.5% or efficiency of 97.5 %

5.Sub-transmission at 66/132 kV. Envisaged maximum losses 4 % or efficiency of 96 %

6.Step-down to a level of 11/33 kV. Envisaged losses 0.5% or efficiency of 99.5%

7.Distribution is the final link to end user at 11/33 kV. Envisaged losses maximum of 5% of the efficiency of 95 %

Cascade efficiency from Generation to end-user


= η1 x η2 x η3 x η4 x η5 x η6 x η7

= 0.995 x 0.99 x 0.975 x 0.96 x 0.995 x 0.95

= 87%

Practically after all technical losses, the standard average cascaded efficiency in India is 83%.

Now the energy after reaching the industry it again meets the secondary distribution transformer then HT distribution network, then LT distribution transformer and then via some cabling reaches to a motor or light or any other equipment. A typical distribution network efficiency including transformer is 95% and motor efficiency is about 90%. Another 30% is lost in the mechanical system which includes coupling/ driven equipment such as pump and flow control valves etc. Thus the overall energy efficiency becomes 

= 0.83 x 0.95 x 0.90 x 0.70

= 50%

If you open your current bill or electricity bill, you may find the electrical energy consumption details like No of units consumed or Billed units or kWh billed. Generally, electrical distribution companies will charge you directly based on units of electrical energy consumed but at the backend, they will also charge you for the units of electrical energy lost in transmission and distribution lines in the name of some surcharges which are relatively less are ignored by end customer most of the time.

Sample Electricity Bill - Domestic :




Hence the statement one unit of electricity saved in the user end is equivalent to two units of electricity generated at the power plant/ generating station side.



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