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What is Energy?

The word energy has been derived from Greek word energia which refers to operation or movement. However physics associate with the attributes of objects that come under the Law of Conservation. Energy is however not an invention of science it is a natural phenomenon. Therefore the credit of development and discovery of the presence of energy in various forms goes to scientist.

History of Energy

The history of energy is centuries old when Aristotle for the first time introduced in his book Nicomachean Ethic’s energy in 4th B.C. after that in 1021 AD another Muslim scientist Alhazen introduced the concept of light and energy in his book the Book of Optics. Then the research and development in the field of physics brought many important names to the cover including Al-Khizini (who introduced the concept of gravitational energy),  Leibniz,  Isaac Newton,  William Rankie, Thomas Young (he was the first scientist who used word energy besides Vis viva) and Richard Feynman (Nobel Laureate). All these scientist analyzed energy in its various forms. It is due to their efforts and hard work that we know energy in its present form.

Forms of Energy, Types of Energy, Kinds of Energy and Uses

There are many forms,  types and sub categories of energy but few basic types are kinetic energy,  potential energy,  gravitational energy,  thermal energy,  elastic energy,  electromagnetic energy,  mechanical energy,  light energy and sound energy. Let us review all of these energy forms briefly. Potential energy is when a particular object is reverted back to its original position with some kind of force. For example the stretching of a spring. When any object or body is in the form of motion,  the extra energy that it possesses is known as kinetic energy. The energy present in the earth which holds the objects on ground is called gravitational energy. Thermal energy is produced when microscopic particles come to motion in any media like gas and plasma. The elastic energy is released by the elastic deformation in solid or liquid. Electromagnetic energy is the combination of electric and magnetic field. This kind of energy is produced when electromagnetic waves move in the vacuum. Energy is present everywhere we move. It is present in our body which we consume when a chemical reaction takes place in our body. It can be derived from the sun in the form of solar rays. The energy can be transformed from one form to another easily.

Transformation of Energy (Conversion of Energy, Change of Energy)

One form of energy can be transformed from one form to another by using any device or exerting force. Energy however can not be created or destroyed by any process; this is what Law of Conservations of energy holds. However the transformation of energy to various other forms is possible. For example thermal energy is converted into mechanical energy by using steam turbines and it can also be converted to chemical energy using blast furnace. Mechanical energy is also transformed into various forms like in thermal energy using brakes,  into electric energy making use of dynamo and into nuclear energy and into nuclear energy by particle acceleration. Energy can be derived from many sources like from natural minerals like coal,  gas,  oil,  uranium and from various chemical reactions. It can be directly transformed form one form to another purposefully like in the case of electricity (when electromagnetic radiation is transferred to electric energy using solar cells). Moreover unintentionally we transform energy from one form to another. for example when a chemical reaction takes place in our body it gives us chemical energy which is converted to mechanical ener

Energy Sources

An energy source is a system which makes energy in a certain way,  for instance a hydro-electric station. A hydro-electric station uses the current of the river for the making of electricity.  We use many different energy sources to do work for us.

Energy sources are classified into following two groups:—


In our world,  most of our energy comes from non-renewable energy sources like Coal,  petroleum,  natural gas,  propane,  and uranium are nonrenewable energy sources. They are used to make electricity,  to heat our homes,  to move our cars,  and to manufacture all kinds of products.

These energy sources are called nonrenewable because their supplies are limited. Petroleum,  for example,  was formed millions of years ago from the remains of ancient sea plants and animals. We cannot make more petroleum in a short time.


Renewable energy sources include biomass,  geothermal energy,  hydropower,  solar energy,  and wind energy. They are called renewable energy sources because they are replenished in a short time. Day after day the sun shines,  the wind blows,  and the rivers flow. We use renewable energy sources mainly to make electricity.

Nowadays we need energy-sources for electricity. Without electricity no computers,  no television,  no washers. A lot of apparatus would not work without electricity.

Sources of Energy

These are the most important sources of energy.

Nuclear Power (Non-Renewable)

Nuclear power is a form of energy which arise from a reaction between atomic nucleï. Mostly this form of energy comes out of nuclear fission. To explain how this process works,  we give a little explanation about the structure of atomic nucleï. Atomic nucleï excist out of neutrons and protons. these little parts (neutrons and protons) are held together in the center of the atomic nucleus through a special energy,  called binding-energy. In a process in which the atomic nucleï collide whith eachother,  they fall apart and the loose parts come out of the atomic nucleus. The energy which kept the parts together is not necessary anymore and this energy comes ‘free’. At the technique of nuclear fission, atomic nucleï collide with eachother in a central boiler to become as much energy out of it as possible. The so called ‘binding-energy’ falls apart and this energy comes out of the atomic nucleus. This energy is used for heating up water and this water becomes steam. Through the steam a turbine can be driven and so electricity is a fact. The speed in which the atomic nucleï collide is controlled by special rods. These rods can pull atomic nucleï towards them and so there become less atomic nucleï which can collid and then there is less binding-energy to come ‘free’.

Fossil Energy (Non-Renewable)

Fossil energy is generated through the burning of fossil remains. At this burning the fossil fuel is used as a source of heat to make steam out of water. This steam is used for the working of a turbine. With the help of a generator,  this turbine can make electricity. Examples of fossil fuels are oil,  natural gas and coal. These fossil fuels are remains of dead materials of plants and animals. These plants and animals died over a million years ago and under the pressure of the earth’s surface and through the decay of this material their came a process of compression. Carbon is the main part of these fossile fuels,  the more carbon,  the heavier the fuel.

Renewable Energy

Alternative energy is a form of energy without waste-matters. It is also a form where the source,  which delivers the energy,  is endless. Some alternative energy-sources are sun-,  water- and windenergy. By all these forms of alternative energy, existing energy (like water, wind and sun) is used for the making of electric energy. For instance,  a hydro-electric station makes use of the fall between a lake and a river. They build a flood control dam between the lake and the river. And in the one outlet of the dam they build a turbine. This turbine activates a generator and the water energy is transformed into electric energy. More information about alternative energy you can find in the article about green energy.

Pros and Cons of different Sources of Energy

The three different kinds of energy-sources have their own pros and cons which are as under:-

Nuclear Power

For the generation of nuclear power little raw material is needed to generate a lot of electric energy. This is an advantage,  because the supply of the raw material will be enough for quite a time. A very big disadvantage is that the raw material for nuclear power,  uranium,  is very radio-active. Also the used rods en other used materials stay radio-active for ages. at a nuclear power plant as Tsjernobyl we have seen how dangerous this type of energy-generation can be. This is the major reason why environmental groups (like Greenpeace) are against this form of energy-winning.

Fossil Energy

The big advantage of fossil energy is that,  to generate the energy from the raw material is easy and cheap. Disadvantage is that during the process of combustion a lot of toxic materials comes into the air which causes extra pollution of the atmosphere,  these materials also increase the effect of global warming. Another disadvantage of fossil energy is that the supply of fossil fuels is not endless. The current supply is for approximately 50 years. That is why the USA wants to trail for oil and natural gas in Alaska. If the USA do this,  there are big consequences for the environment. For more information about this subject,  go to the article about exhaustion.

Alternative Energy

The advantage of alternative energy is that the energy source is endless and doesn’t give any pollution. Still,  there are not many alternative energy forms,  because for instance the technique to transform sun-beams into electric energy is very expensive. For more information about alternative forms of energy-winning, go to the article about green energy

Global Scenario

According to the International Energy Outlook 2011, world marketed energy consumption grows by 53 percent from 2008 to 2035. Total world energy use rises from 505 quadrillion British thermal units (Btu) in 2008 to 619 quadrillion Btu in 2020 and 770 quadrillion Btu in 2035 (Figure 1). Much of the growth in energy consumption occurs in countries outside the Organization for Economic Cooperation and Development (non-OECD nations), where demand is driven by strong long-term economic growth. Energy use in non-OECD nations increases by 85 percent as compared with an increase of 18 percent for the OECD economies.

Figure-1: World energy consumption, 1990-2035 (quadrillion Btu)

World energy markets by fuel type

In the long-term, projects increased world consumption of marketed energy from all fuel sources through 2035 (Figure 2). Fossil fuels are expected to continue supplying much of the energy used worldwide. Although liquid fuels—mostly petroleum based—remain the largest source of energy, the liquids share of world marketed energy consumption falls from 34 percent in 2008 to 29 percent in 2035, as projected high world oil prices lead many energy users to switch away from liquid fuels when feasible. Renewable energy is the world’s fastest growing form of energy, and the renewable share of total energy use increases from 10 percent in 2008 to 14 percent in 2035.

Figure-2: World energy consumption by fuel, 1990‑2035 (quadrillion Btu)

Liquid fuels

World use of petroleum and other liquids grows from 85.7 million barrels per day in 2008 to 97.6 million barrels per day in 2020 and 112.2 million barrels per day in 2035. Most of the growth in liquids use is in the transportation sector, where, in the absence of significant technological advances, liquids continue to provide much of the energy consumed. Liquid fuels remain an important energy source for transportation and industrial sector processes. Despite rising fuel prices, use of liquids for transportation increases by an average of 1.4 percent per year, or 46 percent overall from 2008 to 2035. The transportation sector accounts for 82 percent of the total increase in liquid fuel use from 2008 to 2035, with the remaining portion of the growth attributable to the industrial sector (Figure 3). The use of liquids declines in the other end-use sectors and for electric power generation.

Figure-3: World liquids consumption by sector, 2008‑2035 (million barrels per day)

To meet the increase in world demand, liquids production (including both conventional and unconventional liquids supplies) increases by a total of 26.6 million barrels per day from 2008 to 2035. It assumes that OPEC countries will invest in incremental production capacity in order to maintain a share of approximately 40 percent of total world liquids production through 2035, consistent with their share over the past 15 years. Increasing volumes of conventional liquids (crude oil and lease condensate, natural gas plant liquids, and refinery gain) from OPEC producers contribute 10.3 million barrels per day to the total increase in world liquids production, and conventional supplies from non-OPEC countries add another 7.1 million barrels per day.

Unconventional resources (including oil sands, extra-heavy oil, biofuels, coal-to-liquids, gas-to-liquids, and shale oil) from both OPEC and non-OPEC sources grow on average by 4.6 percent per year over the projection period. Sustained high oil prices allow unconventional resources to become economically competitive, particularly when geopolitical or other “above ground” constraints limit access to prospective conventional resources. World production of unconventional liquid fuels, which totaled only 3.9 million barrels per day in 2008, increases to 13.1 million barrels per day and accounts for 12 percent of total world liquids supply in 2035. The largest components of future unconventional production are 4.8 million barrels per day of Canadian oil sands, 2.2 and 1.7 million barrels per day of U.S. and Brazilian biofuels, respectively, and 1.4 million barrels per day of Venezuelan extra-heavy oil. Those four contributors to unconventional liquids supply account for almost three-quarters of the increase over the projection period.

Natural gas

World natural gas consumption increases by 52 percent from 111 trillion cubic feet in 2008 to 169 trillion cubic feet in 2035. Although the global recession resulted in an estimated decline of 2.0 trillion cubic feet in natural gas use in 2009, robust demand returned in 2010, and consumption exceeded the level recorded before the downturn. Natural gas continues to be the fuel of choice for many regions of the world in the electric power and industrial sectors, in part because its relatively low carbon intensity compared with oil and coal makes it an attractive option for nations interested in reducing greenhouse gas emissions. In the power sector, low capital costs and fuel efficiency also favor natural gas.

The major projected increase in natural gas production occurs in non-OECD regions, with the largest increments coming from the Middle East (an increase of 15 trillion cubic feet between 2008 and 2035), Africa (7 trillion cubic feet), and non-OECD Europe and Eurasia, including Russia and the other former Soviet Republics (9 trillion cubic feet). Over the projection period, Iran and Qatar alone increase their natural gas production by a combined 11 trillion cubic feet, nearly 20 percent of the total increment in world gas production. A significant share of the increase is expected to come from a single offshore field, which is called North Field on the Qatari side and South Pars on the Iranian side.

Contributing to the strong competitive position of natural gas among other energy sources is a strong growth outlook for reserves and supplies. Significant changes in natural gas supplies and global markets occur with the expansion of liquefied natural gas (LNG) production capacity and as new drilling techniques and other efficiencies make production from many shale basins economical worldwide. The net impact is a significant increase in resource availability, which contributes to lower prices and higher demand for natural gas in the projection.

Although the extent of the world’s unconventional natural gas resources—tight gas, shale gas, and coalbed methane—have not yet been assessed fully, a substantial increase in those supplies, especially from the United States but also from Canada and China. An initial assessment of shale gas resources in 32 countries was released by EIA in April 2011. The technically recoverable shale gas resources in the assessed shale gas basins and the United States amount to 6,622 trillion cubic feet. To put the shale gas resource estimate in perspective, according to the Oil & Gas Journal world proven reserves of natural gas as of January 1, 2011, are about 6,675 trillion cubic feet, and world technically recoverable gas resources— largely excluding shale gas—are roughly 16,000 trillion cubic feet.

Rising estimates of shale gas resources have helped to increase total U.S. natural gas reserves by almost 50 percent over the past decade, and shale gas rises to 47 percent of U.S. natural gas production in 2035 in the IEO2011 Reference case. Adding production of tight gas and coalbed methane, U.S. unconventional natural gas production rises from 10.9 trillion cubic feet in 2008 to 19.8 trillion cubic feet in 2035. Unconventional natural gas resources are even more important for the future of domestic gas supplies in Canada and China, where they account for 50 percent and 72 percent of total domestic production, respectively, in 2035 in the Reference case (Figure 4).

Figure-4: Natural gas production in China, Canada, and the United States, 2008 and 2035 (trillion cubic feet)

World natural gas trade, both by pipeline and by shipment in the form of LNG, is poised to increase in the future. Most of the projected increase in LNG supply comes from the Middle East and Australia, where a number of new liquefaction projects are expected to become operational within the next decade. Additionally, several LNG export projects have been proposed for western Canada, and there are also proposals to convert underutilized LNG import facilities in the United States to liquefaction and export facilities for domestically sourced natural gas. The world liquefaction capacity more than doubles, from about 8 trillion cubic feet in 2008 to 19 trillion cubic feet in 2035. In addition, new pipelines currently under construction or planned will increase natural gas exports from Africa to European markets and from Eurasia to China.


In the absence of national policies and/or binding international agreements that would limit or reduce greenhouse gas emissions, world coal consumption is projected to increase from 139 quadrillion Btu in 2008 to 209 quadrillion Btu in 2035, at an average annual rate of 1.5 percent. Regional growth rates are uneven, with little growth in coal consumption in OECD nations but robust growth in non-OECD nations, particularly among the Asian economies (Figure 5).

Figure-5: World coal consumption by region, 1990‑2035 (quadrillion Btu)

Strong economic growth and large domestic coal reserves in China and India lead to a substantial increase in their coal use for electric power and industrial processes. Installed coal-fired generating capacity in China nearly doubles in the Reference case from 2008 to 2035, and coal use in China’s industrial sector grows by 67 percent. The development of China’s electric power and industrial sectors will require not only large-scale infrastructure investments but also substantial investment in both coal mining and coal transportation infrastructure. In India, coal-fired generating capacity rises from 99 gigawatts in 2008 to 172 gigawatts in 2035, a 72-percent increase, while industrial sector coal use grows by 94 percent.


World net electricity generation increases by 84 percent from 19.1 trillion kilowatthours in 2008 to 25.5 trillion kilowatthours in 2020 and 35.2 trillion kilowatthours in 2035. Although the 2008-2009 global economic recessions slowed the rate of growth in electricity use in 2008 and resulted in negligible change in electricity use in 2009, demand returned in 2010, led by strong recoveries in non-OECD economies. In general, in OECD countries, where electricity markets are well established and consumption patterns are mature, the growth of electricity demand is slower than in non-OECD countries, where a large amount of potential demand remains unmet. Total net electricity generation in non-OECD countries increases by an average of 3.3 percent per year in the Reference case, led by non-OECD Asia (including China and India), where annual increases average 4.0 percent from 2008 to 2035. In contrast, net generation among OECD nations grows by an average of 1.2 percent per year from 2008 to 2035.

In many parts of the world, concerns about security of energy supplies and the environmental consequences of greenhouse gas emissions have spurred government policies that support a projected increase in renewable energy sources. As a result, renewable energy sources are the fastest growing sources of electricity generation at 3.1 percent per year from 2008 to 2035 (Figure 6). Natural gas is the second fastest growing generation source, increasing by 2.6 percent per year. An increase in unconventional natural gas resources, particularly in North America but elsewhere as well, helps keep global markets well supplied and prices competitive. Future generation from renewables, natural gas, and to a lesser extent nuclear power largely displaces coal-fired generation, although coal remains the largest source of world electricity through 2035.

Figure-6: World net electricity generation by fuel type, 2008-2035 (trillion kilowatthours)

More than 82 percent of the increase in renewable generation is in the form of hydroelectric power and wind power. The contribution of wind energy, in particular, has grown swiftly over the past decade, from 18 gigawatts of net installed capacity at the end of 2000 to 121 gigawatts at the end of 2008—a trend that continues into the future. Of the 4.6 trillion kilowatthours of new renewable generation added over the projection period, 2.5 trillion kilowatthours (55 percent) is attributed to hydroelectric power and 1.3 trillion kilowatthours (27percent) to wind. The majority of the hydroelectric growth (85 percent) occurs in the non-OECD countries, while a slight majority of wind generation growth (58 percent) occurs in the OECD. High construction costs can make the total cost to build and operate renewable generators higher than those for conventional plants. The intermittence of wind and solar, in particular, can further hinder the economic competitiveness of those resources, as they are not operator-controlled and are not necessarily available when they would be of greatest value to the system. However, improving battery storage technology and dispersing wind and solar generating facilities over wide geographic areas could mitigate many of the problems associated with intermittency over the projection period.

Electricity generation from nuclear power worldwide increases from 2.6 trillion kilowatthours in 2008 to 4.9 trillion kilowatthours in 2035 as concerns about energy security and greenhouse gas emissions support the development of new nuclear generating capacity. In addition, world average capacity utilization rates have continued to rise over time, from about 65 percent in 1990 to about 80 percent today, with some increases still anticipated in the future.

There is still considerable uncertainty about the future of nuclear power, and a number of issues could slow the development of new nuclear power plants. Issues related to plant safety, radioactive waste disposal, and proliferation of nuclear materials continue to raise public concerns in many countries and may hinder plans for new installations. High capital and maintenance costs also may keep some countries from expanding their nuclear power programs. In addition, a lack of trained labor resources, as well as limited global manufacturing capacity for certain components, could keep national nuclear programs from advancing quickly. Finally, although the long-term implications of the disaster at Japan’s Fukushima Daiichi nuclear power plant for world nuclear power development are unknown, Germany, Switzerland, and Italy have already announced plans to phase out or cancel all their existing and future reactors. Those plans, and new policies that other countries may adopt in response to the disaster at the Fukushima Daiichi plant, although not reflected in the IEO2011 projections, indicate that some reduction in the projection for nuclear power should be expected.

75 percent of the world expansion in installed nuclear power capacity occurs in non-OECD countries (Figure 7). China, Russia, and India account for the largest increment in world net installed nuclear power from 2008 to 2035: China adds 106 gigawatts of nuclear capacity over the period, Russia 28 gigawatts, and India 24 gigawatts.

Figure-7: World nuclear generating capacity, 2008 and 2035 (gigawatts)