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Energy Types

Energy is all around us. Yet we cannot see it. So how do we know it is there?

We can observe only the effects of energy, not the energy itself. For example, energy can cause movement of masses, increase in temperature, and changes to material, such as expanding its volume.

In fact, energy has many forms. These are the main ones:

thermal energy


Energy of heat. Thermal energy moves from a hot body to a colder body, at a rate dependent on the type of material.

radiated energy


Electromagnetic radiation such as visible light, infrared, radio and microwaves.

chemical energy


Storage of energy in substances, such as carbohydrates, hydrocarbons and ions in solution, released by reactions involving changes to the energy states of atoms and molecules.

electrical energy


Energy from electrons in a current.

Uranium-235 decays through neutron bombardment to barium and krypton
Uranium-235 decays through neutron bombardment to barium and krypton


The energy released during the decay, or fission, of the nucleus of an atom, such as uranium, or the energy released during the fusion of two atoms.

kinetic energy


The energy in movement. Energy can be seen converting from kinetic to potential in simple harmonic motion systems, such as a pendulum swinging. A skier gains potential energy from electrical energy of a skilift, and this converts to kinetic energy as he skis down the piste.

potential energy


Energy that is stored in the position of a mass in a gravitational field, a charge in an electrical field, or the internal tension of a spring.

Examples of potential energy include:

  • Gravitational
  • the potential energy held by a mass in a gravitational field

  • Electrical
  • the potential energy held by a charge in an electrical field

  • Chemical
  • the potential energy held by a chemical substance by nature of its relative enthalpy

  • Elastic
  • the potential energy held by a mass under elastic strain, such as a compressed spring

Solar World

Ultimately, nearly all the energy on Earth comes from the Sun.

We often hear about 'solar energy' and fossil fuels. But ultimately, all energy derives from the Sun:

  • The physical movements of the air and water are due to solar radiation - our weather is solar powered.
  • Fossil fuels, such as coal, oil, and gas, are the residues of living matter which were created by photosynthesis - solar energy being stored in a chemical form.
  • The energy of all living things derives from photosynthesis - solar radiation stored in glucose and other carbohydrates in plants and animals.

Which energy source does not come from the sun? Nuclear decay of uranium in the Earth's interior generates the heat which keeps the core molten. This uranium, and some other radioactive metals, formed in the supernova which created the solar system, so their energy does not derive from the sun.

Law of Conservation of Energy

Energy can be stored and transferred, and converted from one form to another, but it cannot be created or destroyed. The amount of energy the universe started with at the Big Bang is exactly the amount of energy that exists today, and that will exist till the end of the universe, if such a thing occurs.

Power and Energy

We have to be careful to distinguish between energy and power. In common usage, power refers to electrical energy. Energy is converted from one form (solar, gravitational potential, thermal or chemical) to electrical. This may be used to do work in a machine (converting the energy back into kinetic, radiated or thermal energy), or stored as chemical energy (in batteries).

What is meant by a natural resource?

A natural resource is something that nature or the Earth provides and that humans need. These include minerals, metals, energy, biological systems and extracts, and environmental services.

Energy is provided by a number of sources which can be divided into two main groups: Renewable and Non-Renewable.

Renewable Sources of Energy

Renewable energy sources are called such because they can be replenished by natural processes within a timescale that humans find useful. However, despite the great need for alternatives to fossil fuels, solar, wind, and geothermal plants produce only 3% of the world's electricity. Hydropower, on the other hand, contributes 16%.

Examples are:

    Photovoltaic cells convert solar radiation energy to electricity at an efficiency of about 15-20%
  • Solar
  • The energy of the sun is used in two ways: direct heating of water, and photovoltaic electricity production.

    Rooves can be fitted with a system of pipes filled with water, and these are heated by the sun to provide the hot water a house needs. Rooves can also be fitted with rows of photovoltaic panels to produce electricity during the day.

    This electricity can be used directly, stored in batteries, or sold to the mains network of the city. Solar is still very expensive, but the price is decreasing as more people use it.

    Governments often subsidise the installations to encourage it as a green energy.

    Wind energy
    Wind turbines are a cost-effective way of exploiting the physical energy of the wind
  • Wind
  • The energy of the air used to turn a turbine and generate electricity. Wind turbines work very well at sea (off-shore wind 'farms') as well as in coastal areas.

    Wind energy is now cheaper than nuclear, oil and coal, and is a large and rapidly growing industry. However, they can cause annoyance to local residents because of noise and visibility, and can be a hazard for birds.

  • Hydropower
  • The energy of moving water. In mountainous areas, such as Switzerland, dams store water in reservoirs and release it to turn a turbine. These reservoirs can also be used to store 'energy' from other sources.

    Other hydro resources are tidal movements in and out of bays, and river flow. The largest hydropower dam in the world is on the Yangtze River in China, and generates power equivalent to more than 20 nuclear power stations.

    Hydropower produces 16% of the world's electricity, but expansion of hydropower is limited by the availability of usable water resources.

  • Geothermal
  • The heat of the Earth provides a source of power. Water is pumped down into the crust, where it is heated by the hot rocks, and the resulting steam turns a turbine on the surface.

    Geothermal energy utilises the heat differential between the surface and underground rock strata to power a turbine by superheating water to steam
  • Biomass
  • Energy from organic matter. Wood can be burnt directly, or plant material, such as sugar cane and corn, can be converted chemically into an alcohol fuel, which substitutes oil. Biomass is renewable because its inputs and outputs are part of the natural cycle. Nature does the rest.

Non-Renewable Sources of Energy

Non-Renewable energy sources are those which have been created by natural processes over a long period of time, and which will not be replenished within a timescale that humans find useful.

Examples are:

  • Coal
  • Solid carbon residues of long-dead organic matter. Available in many places of the world in large quantities. It is a very dirty fuel, causing of the world's worst air pollution, and contributing very much to the Greenhouse Effect, responsible for climate change. Coal is used to produce 41% of the world's electricity.

    In one second, a coal-burning power station burns 2 GJ of energy. This is about 80 tonnes of coal per second! The 3.4 billion tonnes of coal burnt in the world in 2002 produced 23% of the world's total energy needs.

    It takes about 500 kg of coal to power a computer for one year. Google alone uses the equivalent electrical output of a whole power station to power its network of servers around the world.

  • Oil
  • A liquid hydrocarbon, which provides many fuel products, and is the base material for plastic. It is being phased out as a fuel for electricity production, due to its decreasing availability and increasing price.

    Oil causes serious damage to sensitive ecosystems when it is accidentally released, from ships or undersea wells. Oil is a major contributor to city smog, acid rain, and global warming. The use of shale oil from rock strata will increase the environmental damage caused by oil even more.

    Oil is used to produce 5% of the world's electricity.

  • Natural gas
  • A hydrocarbon gas, methane, which is used for heating and cooking. This is the cleanest and most efficient of the fossil fuels, but, like oil, its reserves are being depleted rapidly. Europe imports nearly all of its gas from Russia and North Africa via enormous pipeline networks. Gas is used to produce 21% of the world's electricity.

    CO2 Emissions

    The biggest problem with fossil fuels is the emission of pollutants. Along with sulphur and nitrous oxide, which produce acid rain, and several other nasties, all fossil fuels produce CO2 in large quantities. CO2 is responsible for global warming and the loss of stable climate around the world.

    CO2 emissions: 0.963 kg CO2/kWh for coal power, 0.881 kg CO2/kWh for oil, or 0.569 kg CO2/kWh for natural gas. From these statistics, you can see that coal is much less efficient than the other fossil fuels, and methane gas is the most efficient.

  • Nuclear
  • Fukushima prior the accident
    Fukushima nuclear power station, Japan, commissioned in 1971, and rated at 4.7 GW, was one of the largest nuclear powerplants in the world

    Uranium can be caused to decay at higher than natural rates in nuclear reactors. This releases huge amounts of heat which can be used to generate electricity. Uranium does not release pollution of the type fossil fuels do.

    But nuclear power is expensive and its waste product, depleted uranium fuel, must be stored for tens of thousands of years till it is 'safe'. Accidents can cause leaks of radiative material which leave large areas of land uninhabitable due to contamination, as well as spreading through the groundwater and sea, entering the human foodchain through fish.


    Ticino, Switzerland, received a lot of radiation from the Chernobyl nuclear accident in 1986, from a contaminated raincloud. Japan, Russia, Ukraine, and the USA have all suffered serious nuclear accidents, releasing deadly radiation which will contaminate land, water, and food for thousands of years.

    It is being phased out in Germany and Switzerland, but France still makes 75% of its electricity from nuclear power. Italy does not use nuclear power at all. Nuclear reactors produce 13% of the world's electricity.

Future Trends

Traditionally, fossil fuels have been the main resources for human energy needs, but gradually cleaner renewable alternatives are replacing them. This is for environmental, economic, and political reasons.

In 2008, the price per barrel of oil went up to over 100 dollars. As the wars in the Middle East and conflicts and tensions in other oil-exporting countries, such as Libya and Russia, increase, the security of supply of oil is threatened. It is possible to store only a limited amount of oil (about 150 days worth), so economies are very dependent on continuous supplies for fuel, but also for industries like pharmaceuticals, plastics, fertilisers, all of which are based on mineral oil.

In the second half of 2014, production around the world slowed considerably. Factories were producing less, because consumers were not buying as much as they were before, because of the economic downturn. With less production, there is less oil consumed by industry. This causes the market to be swamped with cheaper oil supplies, and the price came down to less than 100 dollars, for the first time in 6 years.

One reason for the over-production of oil is the exploitation of oil and gas resources found in strata of rock, usually shale, which previously had been too expensive to use. This shale oil and gas extraction is extremely damaging to the environment, and effectively reverses any gains that had been achieved in the past decades to reduce fossil fuel dependency and convert economies to environmentally-friendly alternatives.

For more information on shale oil, see the article on Fracking.

Content © Renewable.Media. All rights reserved. Created : September 17, 2013 Last updated :November 14, 2016

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