Basic Energy Services - Energy Sources

Basic Energy Services in a Nutshell: Context | Basics | Energy Systems

Overview of "Energy"

The concept of energy is used to describe changes in the state of a body or system. The measure of energy is the ability to perform work. As such, it cannot be created, consumed or destroyed, it can just be transferred or converted from one form into another. An example is solar cells that do not create or consume the energy from the sun, but rather convert radiant energy to electric energy, which can later be converted to any form of energy in lighting or heating.

Thus Principle of conservation of energy, where pristine energy from the sun is still there, albeit in another form. Energy exists in different forms and not every form can be transferred into another at will. The conversion of the energy from one source to another is associated with different losses, the can either be high or low. An example is that of a solar cell where radiant energy is converted to electric energy, which is associated with considerable loss in some energy.

This can be further illustrated how different forms of energy which are encounter in different ways and used in different ways.

Type of Energy	Other Terms	Example / Occurrence	Technical Application of Energy
Mechanical Energy	Energy of motion = kinetic energy Stored energy = potential energy	Flowing water, traveling car, flywheel Dam, archer’s drawn bow	Hydro-power Storage power plant
Heat Energy	Thermal energy	Central heating radiator, hot water bottle	Heat storage tank, heater
Electrical Energy		Electric current, lightning	Generator, electric motor
Chemical Energy		Fuels, Explosives	Coal power plant, wood stove
Nuclear Energy		Atom Splitting	Nuclear Power Plant
Radiation Energy	Electromagnetic energy	Sunlight, radio waves	Photovoltaic system

Power refers to the ability of a system to perform work in a given time. Its unit of measurement is in Watts and abbreviated with the symbol "P". Output power of generators is an important figure especially in the electrical industry. Renewable energy technologies are often characterized by their "installed power", which is power obtained under optimum conditions.

Energy Use and Efficiency

The use of energy is essential in everyday life, for example, in the heating and lighting , the transport of goods and people, and in all modern communications such as telephone, computer, television and the internet. Every energy supply has to undergo a conversion processes which is described in form of efficiency. Energy balances show how efficiently the supplied energy has been used.

Some key terms that can be used to distinguish the individual stages in the energy conversion process include:

• Primary energy- This is converted from naturally available resources (e.g. fossil fuels such as coal) for human use. In the case of the solar cell, the primary energy is the solar radiation that falls on the cell.
• Secondary energy- This is the first product of the technological conversion of primary energy. It is not yet directly usable, since it first has to be transported to the user. For the solar cell this is the electrical energy generated at the cell’s location which is then fed into the electricity grid.
• Final energy- This is the directly usable part of the primary energy. In our example, this is the electrical energy, generated by the solar cell, which is now available to the user as electricity from the power socket.
• Useful energy- This is the share of primary energy that we can actually use for our desired purpose. For this, the waste heat of a lamp which is operated from solar power must be deducted from the supplied final energy.
  

The efficiency of an energy conversion process is the ratio of a later step to an earlier step i.e. useful energy to final energy, and it has an efficiency value between 0 and 1. In practice, efficiencies of 100% are never achieved since each transformation step has losses. If the overall efficiency of multiple processes is to be calculated then the total efficiency is obtained by multiplying the individual efficiencies. Example:

Source	Applied Energy	Usable Energy	Efficiency
Bicycle Dynamo	Mechanical Energy	Electrical Energy	0.20-0.60
Solar Cell	Radiation Energy (Sunlight)	Electrical Energy	0.05-0.29
Wind Energy Plant	Mechanical Energy	Electrical Energy	to 0.85
Coal Power Station	Chemical Energy	Electrical Energy	0.25-0.45
Gas Cooker	Chemical Energy	Electrical Energy	0.80-0.90
The Glowing of a glow-worm	Chemical Energy	Radiation Energy	< 0.95

Energy Sources

Energy carriers are the means of storage of the energy we use. They can be divided into two groups, non-renewable energies and renewable energies. Nearly all energy sources are created either directly or indirectly through the conversion of the radiant energy of the sun. An exception is geothermal energy which arises from radioactive decay in the Earth's mantle.

Renewable Energy

Renewable energies are derived from natural sources and they are replenished at a higher rate than they are consumed. The common renewable energy sources are; Solar, wind, geothermal, hydro, and biomass. These energy sources have been the driver of much of the growth in the global clean energy sector since the year 2000. Recent years have seen a major scale up in wind and solar photovoltaic (PV) technologies. However other renewable technologies continue to grow from a strong established base adding thousands of gigawatts of capacity worldwide.

Energy security and diversification of the energy mix is a major policy driver for renewable. With the diversification caused by renewable growth in terms of technology portfolio and geographical sources. Use of renewable energies can also reduce fuel imports and shield economies from fuel prices which in the long run brings energy security. However, concentrated growth of variable renewable s can make it harder to balance power systems, which must be duly addressed.

With the renewable energy sector demonstrating its capacity to achieve cost reductions, there has to be appropriate policy frameworks in place and enacted for this to be achieved. And with deployment expanding rapidly, non hydro renewable s such as wind and solar PV are increasing at double-digit annual growth rates. Costs have been decreasing and a portfolio of renewable energy technologies is becoming cost-competitive in an increasingly broad range of circumstances. Some established technologies such as hydro and geothermal are often fully competitive whereas where resources are favorable onshore wind is almost competitive. However, economic barriers remain important as the costs need to be reduced further. Moreover, fossil fuel subsidies and the lack of a global price on carbon are significant barriers to the competitiveness of renewables.

Worldwide, renewable energy generation has grown by an average of 2.8% since 1990 which is less than the 3% growth seen for total electricity generation. While 19.5% of global electricity in 1990 was produced from renewable sources, this share fell to 19.3% in 2009. This decrease was mainly the result of slow growth of the main renewable source, hydroelectric power, in OECD countries. Achieving the goal of halving global energy‐related CO2 emissions by 2050 will require a doubling (from today’s levels) of renewable generation by 2020.

Hydropower

Hydro-power is the electrical energy derived from turbines being driven by flowing water in rivers, with or without man-made dams forming reservoirs. Presently, hydro-power is the world’s largest source of renewable electricity. It has the advantage that it is relatively continuously available, achieves high efficiencies and can store potential energy.

There are three different types of hydro-power plants:

• Run‐of‐river hydro power plants convert the potential energy of naturally falling water.
• Storage power plants convert the potential energy of naturally or artificially stored falling water.
• Ocean energy power plants use the continuous motion of the ocean waves (kinetic energy, wave energy plants), the temperature differences between cold and hot water masses (thermal energy, ocean‐thermal power plants) and the ebb and flow of tidal ranges (potential and kinetic energy, tidal generators).
  

Water turbines are classified as either impulse turbines or reaction turbines. In an impulse turbine the turbine runner operates in air and is turned by one or multiple jets of water which make contact with the runner blades on the other hand in the reaction turbine, the turbine runner is fully immersed in water and is enclosed in a pressure casing. The runner blades are angled so that pressure differences across them create lift forces, like those on aircraft wings, which cause the runner to rotate.

Solar Energy

Solar energy is available almost everywhere and is widely used for the production of heat and electricity. For heating energy production the solar system can be divided into active and passive solar system. The term active use describes the conversion of solar radiation into electricity using photovoltaic s (solar cell technology), or into heat using solar thermal collectors whereas passive use is where solar radiation is used without the active components, an example of this is the transfer of heat and light to buildings through windows and facades. These forms of solar energy are important in improving the internal lighting for example, by using light‐transmitting cladding on the building which reflects light from the outside onto the ceiling and deep into the room’s interior.

The intensity of solar radiation varies significantly in different parts of the world, both spatially and temporally. for example, spatial variation in the solar radiation in Germany is about 1,000 kWh per square meter (m2) per year and in the Sahara 2,200 kWh per m2 per year. Temporary variation can be seen all around us, they follow predictable rhythms and occur as the day‐night cycle as well as the changing seasons. However irregular fluctuations depend on weather conditions where clear weather leads to direct radiation whereas cloudy sky leads to diffuse radiation. Therefore solar systems always require some form of energy storage in order to provide a constant supply of energy.

Wind Power

Wind energy is kinetic energy of wind exploited for electricity generation in wind turbines.In the past years there have been advancement in wind farms and they have been intensively developed and different types of convertors used. Modern wind turbines mostly have rapidly rotating horizontal axis converters with three rotor blades. They have a short energy payback time of only a few months: during their lifetime of approximately 20 years they produce 40‐70 times more energy than was used in their manufacture.

Due to the fluctuations in wind level, electrical energy obtained with wind turbines can only be used in combination with other energy sources in the network, or in very small electric grids with storage to provide a continuous energy supply. A distribution network operator is important in matching the fluctuating power generation from wind to the fluctuation in consumption. Wind generators can, in principle, be used in all climates, at sea and on all types of land (coastal, inland, mountains).

Energy production from wind turbines depends especially on some of the following perimeters; mean wind speed at hub height, the selling price of power, and system and infrastructure costs. Higher wind speeds generate higher power yields thus are preferred for wind generators however guaranteed price from feed‐in tariff makes even inland sites viable in most countries. and with the growth in the wind energy technology, some firms are even building windmills at sea (offshore).

Geothermal Energy

Geothermal energy is stored in rock and in trapped vapor or liquids, such as water or brine; these geothermal resources can be used for generating electricity and for providing heat.

In the near‐surface geothermal processes (depth 10 ‐ 500 meters) heat pumps are used to raise the temperature of low grade heat to a higher, usable level. Near-surface processes are generally very good for localized production of hot or warm, heating water for households and small consumers.
Deep borehole heat exchangers are used at depths of 500 to 2000 m where the temperatures are up to 70°C. Water circulating in the boreholes is heated up and is used at the surface either directly or via heat pumps to provide heating and hot water for large heat consumers.
Hydrothermal geothermal describes the use of heat from thermal water which is either naturally escaping or is tapped by boreholes. Hydrothermal geothermal energy has been typically applied to supply hot water or for greenhouses.

In the hot‐dry‐rock method, water is forced at pressures of up to 150 bar into hot rocks at a depth of a few thousand meters. In this way an underground geothermal heat exchanger is formed through a system of natural and artificial fissures. Geothermal power plants use this process to generate power using steam turbines.

Biomass

Biomass is any organic, i.e. decomposing, matter derived from plants or animals available on a renewable basis. Biomass includes wood and agricultural crops, herbaceous and woody energy crops, municipal organic wastes as well as manure. Bio-energy is energy derived from the conversion of biomass where biomass may be used directly as fuel, or processed into liquids and gases. Bio-fuels are fuels derived from biomass or waste feed-stocks; includes ethanol and biodiesel.

Since time in memorial the use of biomass has been evident among mankind and is currently the most important renewable energy source in the world. It has a great advantage that it is easy to store and energy can be extracted at relatively high efficiencies, but before it can be used as a conventional energy source, various customized conversion technologies are required depending on the respective solid, liquid or gaseous starting materials. The production of heat and electricity can be achieved through this bio-conversion process. For this bio-conversion process, micro organism convert the biomass which is organic waste to energy through the “aerobic” process where the micro‐organisms use the oxygen from the air. More interesting for energetic use are, however, two fermentation processes which don’t require oxygen; theformation of biogas, and the formation of ethanol.

Biogas is comparable to natural gas and can be used in the same way, the calorific value is however about 30% less than that of natural gas. Ethanol on the other hand can be used as industrial alcohol and fuel alcohol without further conversion in a wide variety of applications.

Non Renewable Sources of Energy

Non‐renewable energies include fossil fuels and radioactive heavy metals. Unlike renewable energies, fossil fuels will be exhausted in the foreseeable future, and the same applies to naturally occurring radioactive nuclear fuels such as uranium.

Fossil Fuels

Besides being non-renewable, fossil fuels have the further disadvantage, they release greenhouse gases, especially carbon dioxide (CO2), during combustion. The intensive use of fossil fuels in the past hundred years has influenced the global climate significantly in this way. It is therefore regarded as a necessity to reduce fossil fuel consumption in order to limit climate change and the negative impacts thereof.

Peat occupies an intermediate position between coal and biomass. It is sometimes considered as a renewable energy, but because of its relatively long formation period ‐ a few thousand years (averaging about 1 mm of peat deposition per year), it is more realistically counted as a fossil fuel.

Coal

Coal is a variety of solid, combustible, sedimentary, organic rocks that are composed mainly of carbon and varying amounts of other components such as hydrogen, oxygen, sulphur and moisture. Coal is formed from vegetation that has been consolidated between other rock strata and altered by the combined effects of pressure and heat over millions of years. Many different classifications of coal are used around the world, reflecting a broad range of ages, compositions and properties.

Coal currently provides 40% of the world’s electricity needs, this makes it the second source of primary energy in the world after oil. It is also considered as the first source of electricity generation, since the beginning of the 21st century it has been the fastest growing global energy source. The last decade’s growth in coal use has been driven by the economic growth of developing economies, mainly China. Irrespective of its economic benefits for the countries, the environmental impact of coal use, especially that coming from carbon dioxide emissions, should be addressed as a global issue. Carbon capture and storage (CCS) is the most promising technology to reach near-zero CO2 emissions from large CO2 sources. Although it is developing it is far from the required deployment-level to keep CO2 emissions at acceptable levels.

Oil

Oil includes crude oil, condensates, natural gas liquids, refinery feed stocks and additives, other hydrocarbons (including emulsified oils, synthetic crude oil, mineral oils extracted from bituminous minerals such as oil shale, bituminous sand and oils from coal-to-liquids (CTL) and gas-to liquids (GTL) and petroleum products (refinery gas, ethane, liquefied petroleum gas (LPG), aviation gasoline, motor gasoline, jet fuels, kerosene, gas/diesel oil, heavy fuel oil, naphtha, white spirit, lubricants, bitumen, paraffin waxes and petroleum coke)

Gas

Natural gas is a mixture of several hydrocarbon gases, including methane (between 70% and 90%), ethane, propane, butane and pentane, as well as carbon dioxide, nitrogen and hydrogen sulphide. The composition of the natural gas can vary widely depending on the gas field. Natural gas is referred to as “wet” when hydrocarbons other than methane are present, “dry” when it is almost pure methane, and “sour” when it contains significant amounts of hydrogen sulphide.

Natural gas is considered as a good source of electricity supply for a number of reasons which range from economic, operational and environmental, these include;

• it is low-risk (technically and financially);
• lower carbon relative to other fossil fuels; and
• gas plants can be built relatively quickly in around two years, unlike nuclear facilities, which can take much longer.
  

Gas plants are flexible both technical and economic terms, they can also react quickly to demand peaks and are ideally twinned with intermittent renewable options such as wind power.

Nuclear Fuels

Atoms make up all the elements in the universe, an atom is composed of a nucleus and electrons, a nucleus is composed of neutrons and protons. Some nuclei are stable, and some undergo spontaneous radioactive decay, this decay can also be induced by interaction with neutrons or other particles. Nuclear power is generated in a process called fission which is a reaction that occurs when the nucleus of an atom, having captured a neutron, splits into two or more nuclei, and in so doing, releases a significant amount of energy as well as more neutrons. These neutrons then go on to split more nuclei and a chain reaction takes place. This chain reaction produces heat, via radiation, and the slowing down of fission products as they impact the fuel around them. Nuclear reactors are designed to convert this heat into electricity, like in any other thermal power plant. To avoid overheating, the plants incorporate cooling systems.

Nuclear fusion is another type of nuclear reaction in which extra energy is released when light nuclei are fused together. This type of reaction produces heat in the sun and other stars. Unlike the nuclear fission process, extreme temperatures and pressure are needed to initiate and sustain the fusion reaction. Because of this, it is challenging to maintain fusion reactions in laboratory conditions. However, research and development aimed at achieving controlled fusion has been pursued for many years with significant advances in recent decades. Fusion offers important advantages: no carbon emissions, no air pollution, unlimited fuel, and is intrinsically safe. While fusion technology is not at the deployment stage, the potential is substantial. The fusion reaction is about four million times more energetic than a chemical reaction such as the burning of coal, oil or gas.

Further Information

• International Energy Agency (IEA), 2013.
• Renewables Academy (RENAC) AG, 2009. TREE - Transfer Renewable Energy & Efficiency. Energy Economics- An introduction.