Introduction to Energy

Chapter 1 – Introduction to Energy

1.1 Energy and its unit

1.1.1 Energy

It is something, which is needed to do work. Hence energy can be converted into work and work can be converted into energy. In physics work is defined as

W = F.d

i.e., work is product of force and displacement in the direction of force.

The unit of work is Joule and unit of energy is calorie. They are interrelated as;

1 calorie = 4.184 Joule.

When work is done, it is required to know about the capacity of doing work, known as power. So power is defined as, work done per unit time.

 P = W/t

The unit of power is Watt (= 1 Joule/second)

In terms of power, energy is defined as,

Energy = Power X Time = Watt Hour

According to first law of thermodynamics

dQ = dU + dW

i.e., heat supplied to any system goes into increasing the internal energy of  the system and work done on the system.

1.1.2 Units of Power

The basic unit of power is Watt. But it is too small for use it in terms of rate of energy production and consumption in our life. So many others units are in use defined as under:

W        = watt (1 Joule per second)

kW      = kilowatt ( 1 Watt X 10³ )

MW     = Megawatt ( 1 Watt X 10⁶ )

GW     = Gigawatt ( 1 Watt X 10⁹ )

TW      = Terawatt ( 1 Watt X 10¹² )

PW      = Petawatt ( 1 Watt X 10¹⁵ )

XW     = Exawatt ( 1 Watt X 10¹⁸ )

1 horsepower = 746 Watt

1.1.3 Units of Energy   

kJ        = kilojoule ( 1 Joule X 10³ )

MJ       = Megajoule ( 1 joule X 10⁶ )

GJ        = Gigajoule ( 1 joule X 10⁹ )

TW      = Terajoule ( 1 joule X 10¹² )

PJ        = Petajoule ( 1 joule X 10¹⁵ )

XJ        = Exajoule ( 1 Joule X 10¹⁸ )

Energy is also defined as, power X time.

Another unit of energy is Watt-second

1 kilowatt hour = 1kWh (1 unit of electricity)

1kWh = 1000 X 3600 Joule =  3.6 X 10⁶  Joule = 3.6 Megajoule

1 Calorie = 4.184 Joule

1 Joule = 0.23884 calories

Calorie is defined as amount of energy when completely converted to heat will raise the temperature of 1 gm of water by 1°C.

1.1.4 Other units of Energy

British Thermal Unit = BTU

1 BTU is defined as amount of energy when completely converted to heat will raise the temperature of 1 pound  of water by 1°F. (1 pound = 454 gm)

1 kcal = 4184 Joule

           = 3.968 BTU

So, 1 BTU = 1054.44 Joule

1 quad (quadrillion BTU = 10¹⁵ BTU) Q = 1054.44 X 10¹⁵ Joule = 1054 Petajoule

One million tonnes of oil equivalent (MTOE) = 41.87 Petajoules of energy

                                                                          = 11.6 Billion kWh

1.2 Types of Energy

1.2.1 Primary and secondary Energy

Energy can be broadly classified into two groups, depending on its conversion form source to usable form, which can be delivered to consumer.

1.2.1.a  Primary Energy

Energy, which can be derived directly by extracting it from its natural source, is known as primary energy. For example, coal can be directly burned to release energy, just after extracting it from its natural environment. Other sources of primary energies are oil, natural gas, wood, nuclear fuels, the sun, the wind, tides, geothermal, river (to produce hydroelectricity).

1.2.1.b  Secondary Energy

When natural source of energy is transformed into another form of energy, so that it can release energy to consumer, it is known as secondary form of energy.  For example, electricity, which can be generated by converting mechanical energy into electrical energy. The source of mechanical energy may be primary, like water (river), coal, nuclear etc.

1.2.2 Renewable and Non-renewable Energy

1.2.2. a Renewable Energy

Energies, whose sources are replenished after repeated use, are called renewable source of energy. Solar energy, wind energy, hydroelectricity, ocean energy, tidal energy are examples of renewable energy.

1.2.2. b Non-renewable Energy

On the other hand, some sources of energies get exhausted after repeated use, these are known as non-renewable source of energy. Coal, oil, natural gas, geothermal energy (if used in unlimited way), biomass energy are example of non-renewable energy sources.

1.2.3 Conventional and Non-conventional Sources of Energy

1.2.3.a Conventional sources of energy

The energy sources which are being used for many times are known as conventional energy sources. Fossil fuels and hydroelectricity are examples of conventional energy sources. The technologies of conventional energy sources are well established. They may be renewable or non-renewable. Hydroelectricity is renewable, while fossil fuels are non-renewable.

1.2.3.b Non-conventional sources of energy

The energy sources, which are new and are not in trend for application at large scale, are known as non-conventional sources of energy. Nuclear energy, solar energy, wind energy, ocean energy, geothermal energy, biomass energy etc. Although biomass has been used for ancient time to produce heat, electricity generation from biomass is new option and its refined use to produce less pollutant is also new concept. Non-conventional energy may also be renewable or non-renewable. Solar, wind, ocean energy are renewable, geothermal, biomass has limited renewability and nuclear energy is non-renewable.

1.3 Terms Related to Energy

1.3.1 Feasibility and viability

Sometimes the methods of extracting energy from source are theoretically correct, but in practice it is not possible to derive energy. Such energy sources are not feasible. If feasible, they must be checked for their viability. They may need extra efforts in comparison to already existing sources of energy in form of large amount of input energy/ big change in social structure or transport problem for energy distribution. Such type of energy sources may be feasible, but not viable on the economic basis or on the social basis. Hence, those energy options may be adopted, which are feasible and viable for use.

1.3.2 Sustainable use of Energy

The energy demand is growing day by day; however, energy production is limited. If production is increased up to some extent, the source of energy may be limited. When the utilization of source exceeds the threshold limit, the energy source will be finished after some time and the source will not sustain.  Hence for sustainable use of energy, the amount of energy derived from the source must be under threshold limit, so that many generations can take advantage energy sources. If the method of production/ transportation/ mean of consumption or by-product is not feasible in long-term, that source of energy will also not sustain.

1.3.3 Qualities of Good Energy Source

A good energy source has following desirable characteristics:

• Abundant availability & Renewable nature
• Environmentally clean
• High energy content
• Low cost
• Easily storable
• Economically transportable
• Conveniently usable
• Socially compatible

1.4 Conservation, Efficiency and Cogeneration

Energy conservation means to minimize the loss of energy. That is, to accomplish a given task in minimum amount of energy. This also includes the change in habit to use energy and refers to a moderation in energy demand of society. Efficiency is related to the designing of equipment, such that it can transfer more amount of power with given amount of energy wasting minimum energy as heat. Cogeneration refers to the processes which lead to energy generation from by-product of other process. For example, electricity can be generated from steam, which is produced in any industry as by-product. Sometime large amount of heat is produced in industry and is released into atmosphere. This heat can also be used for generation of electricity.