1.1 Understanding Various Terms and Conversion Factors
3
• Calorie
• Joule
• Watt
• BTU (British thermal unit)
• TOE (Tons of oil equivalent); and
• TCE (Tons of coal equivalent)
Almost every science student is conversant with the term ‘calorie’ and ‘joule’. The
term ‘calorie’ indicates the quantum of energy required to raise the temperature of 1 g
of water by one degree centigrade or Celsius (i.e. from 14.5 to 15.5 °C) (Parr 2011),
whereas ‘joule’ is a measure of quantum of energy (or work) required to generate one
watt of power for one second (Chen et al. 2017). ‘Watt’, on the other hand, is used to
determine power and is equivalent to the rate at which one ampere of current flows
through a circuit with potential difference of one volt. Another difference between
‘Joule and Watt’ is that the former is a unit of energy and the latter is a unit of energy
transfer in joule per second. In other words, ‘Joule’ is the amount of energy and
‘Watt’ measures the rate at which energy is used. For example, when a light bulb
(sold in Indian market as 10, 20, 40, 60, 100 watts) of 100 watts glows for 10 seconds,
it will consume 100 × 10 = 1000 Joules of energy.
We can also express the relationship between joule and watt as follows:
i. Joule = Watt × seconds
ii. Watt = Joule/second
In many scientific as well as non-science literature, the words ‘energy’ and ‘power’
(Box 1) are interchangeably used. For example, we use the term thermal power or
nuclear power plant/s but not thermal energy plant or nuclear energy plant. Whereas
at the policy level, we invariably use the word ‘energy’. Nevertheless, there is a clear
distinction between these two words. Power means the rate at which energy is either
generated or consumed in a power station and is measured in watts (or kilowatts or
megawatts or gigawatt or terrawatt), which in turn means energy per unit time. For
example, all power stations have a rating in terms of megawatt or gigawatt. This
rating indicates the maximum power output a station can achieve at a given point in
time. For example, 1000 gigawatt or 5000 megawatt, and so on. On the other hand,
the annual energy output of a power station is mentioned in terms of megawatt-hour
or gigawatt-hour or terrawatt-hour. For example,
Power output of 1 terrawatt-hour per year = 1 × 10
12 watt-hour/(365 days × 24
hour per day) = 114 megawatt of constant power output for one year.
3
• Calorie
• Joule
• Watt
• BTU (British thermal unit)
• TOE (Tons of oil equivalent); and
• TCE (Tons of coal equivalent)
Almost every science student is conversant with the term ‘calorie’ and ‘joule’. The
term ‘calorie’ indicates the quantum of energy required to raise the temperature of 1 g
of water by one degree centigrade or Celsius (i.e. from 14.5 to 15.5 °C) (Parr 2011),
whereas ‘joule’ is a measure of quantum of energy (or work) required to generate one
watt of power for one second (Chen et al. 2017). ‘Watt’, on the other hand, is used to
determine power and is equivalent to the rate at which one ampere of current flows
through a circuit with potential difference of one volt. Another difference between
‘Joule and Watt’ is that the former is a unit of energy and the latter is a unit of energy
transfer in joule per second. In other words, ‘Joule’ is the amount of energy and
‘Watt’ measures the rate at which energy is used. For example, when a light bulb
(sold in Indian market as 10, 20, 40, 60, 100 watts) of 100 watts glows for 10 seconds,
it will consume 100 × 10 = 1000 Joules of energy.
We can also express the relationship between joule and watt as follows:
i. Joule = Watt × seconds
ii. Watt = Joule/second
In many scientific as well as non-science literature, the words ‘energy’ and ‘power’
(Box 1) are interchangeably used. For example, we use the term thermal power or
nuclear power plant/s but not thermal energy plant or nuclear energy plant. Whereas
at the policy level, we invariably use the word ‘energy’. Nevertheless, there is a clear
distinction between these two words. Power means the rate at which energy is either
generated or consumed in a power station and is measured in watts (or kilowatts or
megawatts or gigawatt or terrawatt), which in turn means energy per unit time. For
example, all power stations have a rating in terms of megawatt or gigawatt. This
rating indicates the maximum power output a station can achieve at a given point in
time. For example, 1000 gigawatt or 5000 megawatt, and so on. On the other hand,
the annual energy output of a power station is mentioned in terms of megawatt-hour
or gigawatt-hour or terrawatt-hour. For example,
Power output of 1 terrawatt-hour per year = 1 × 10
12 watt-hour/(365 days × 24
hour per day) = 114 megawatt of constant power output for one year.