Primary energy (PE) is an

energy In physics, energy (from Ancient Greek: ἐνέργεια, ''enérgeia'', “activity”) is the quantitative property that is transferred to a body or to a physical system, recognizable in the performance of work and in the form of ...

form found in nature that has not been subjected to any human engineered conversion process. It is energy contained in raw

fuel A fuel is any material that can be made to react with other substances so that it releases energy as thermal energy or to be used for work. The concept was originally applied solely to those materials capable of releasing chemical energy b ...

s, and other forms of energy, including waste, received as input to a

system A system is a group of interacting or interrelated elements that act according to a set of rules to form a unified whole. A system, surrounded and influenced by its environment, is described by its boundaries, structure and purpose and express ...

. Primary energy can be

non-renewable A non-renewable resource (also called a finite resource) is a natural resource that cannot be readily replaced by natural means at a pace quick enough to keep up with consumption. An example is carbon-based fossil fuels. The original organic ma ...

or renewable. Where primary energy is used to describe fossil fuels, the embodied energy of the fuel is available as thermal energy and around 70% is typically lost in conversion to electrical or mechanical energy. There is a similar 60-80% conversion loss when solar and wind energy is converted to electricity, but today's UN conventions on energy statistics counts the electricity made from wind and solar as the primary energy itself for these sources. One consequence of this counting method is that the contribution of wind and solar energy is under reported compared to fossil energy sources, and there is hence an international debate on how to count primary energy from wind and solar. Primary energy is used in energy statistics in the compilation of energy balances, as well as in the field of energetics. In energetics, a primary energy source (PES) refers to the energy forms required by the energy sector to generate the supply of

energy carrier An energy carrier is a substance (fuel) or sometimes a phenomenon (energy system) that contains energy that can be later converted to other forms such as mechanical work or heat or to operate chemical or physical processes. Such carriers includ ...

s used by human society. Secondary energy is a carrier of energy, such as electricity. These are produced by conversion from a primary energy source. Total primary energy supply (TPES) is the sum of production and imports, plus or minus stock changes, minus exports and international bunker storage. The International Recommendations for Energy Statistics (IRES) prefers total energy supply (TES) to refer to this indicator. These expressions are often used to describe the total energy supply of a national territory.

Examples of sources

Primary energy sources should not be confused with the

energy system An energy system is a system primarily designed to supply energy-services to end-users. The intent behind energy systems is to minimise energy losses to a negligible level, as well as to ensure the efficient use of energy. The IPCC Fifth As ...

components (or conversion processes) through which they are converted into energy carriers.

Usable energy

Primary energy sources are transformed in energy conversion processes to more convenient forms of energy that can directly be used by society, such as

electrical energy Electrical energy is energy related to forces on electrically charged particles and the movement of electrically charged particles (often electrons in wires, but not always). This energy is supplied by the combination of electric current and elect ...

, refined fuels, or synthetic fuels such as hydrogen fuel. In the field of energetics, these forms are called

s and correspond to the concept of "secondary energy" in energy statistics.

Conversion to energy carriers (or secondary energy)

Energy carriers are energy forms which have been transformed from primary energy sources. Electricity is one of the most common energy carriers, being transformed from various primary energy sources such as coal, oil, natural gas, and wind. Electricity is particularly useful since it has low

entropy Entropy is a scientific concept, as well as a measurable physical property, that is most commonly associated with a state of disorder, randomness, or uncertainty. The term and the concept are used in diverse fields, from classical thermodyna ...

(is highly ordered) and so can be converted into other forms of energy very efficiently.

District heating District heating (also known as heat networks or teleheating) is a system for distributing heat generated in a centralized location through a system of insulated pipes for residential and commercial heating requirements such as space heating ...

is another example of secondary energy. According to the laws of thermodynamics, primary energy sources cannot be produced. They must be available to society to enable the production of energy carriers.

Conversion efficiency Energy conversion efficiency (''η'') is the ratio between the useful output of an energy conversion machine and the input, in energy terms. The input, as well as the useful output may be chemical, electric power, mechanical work, light (radi ...

varies. For thermal energy, electricity and mechanical energy production is limited by Carnot's theorem, and generates a lot of

waste heat Waste heat is heat that is produced by a machine, or other process that uses energy, as a byproduct of doing work. All such processes give off some waste heat as a fundamental result of the laws of thermodynamics. Waste heat has lower utilit ...

. Other non-thermal conversions can be more efficient. For example, while wind turbines do not capture all of the wind's energy, they have a high conversion efficiency and generate very little waste heat since wind energy is low entropy. In principle solar photovoltaic conversions could be very efficient, but current conversion can only be done well for narrow ranges of wavelength, whereas solar thermal is also subject to Carnot efficiency limits. Hydroelectric power is also very ordered, and converted very efficiently. The amount of usable energy is the exergy of a system.

Site and source energy

Site energy is the term used in North America for the amount of end-use energy of all forms consumed at a specified location. This can be a mix of primary energy (such as natural gas burned at the site) and secondary energy (such as electricity). Site energy is measured at the campus, building, or sub-building level and is the basis for energy charges on utility bills. Source energy, in contrast, is the term used in North America for the amount of primary energy consumed in order to provide a facility’s site energy. It is always greater than the site energy, as it includes all site energy and adds to it the energy lost during transmission, delivery, and conversion. While source or primary energy provides a more complete picture of energy consumption, it cannot be measured directly and must be calculated using conversion factors from site energy measurements. For electricity, a typical value is three units of source energy for one unit of site energy. However, this can vary considerably depending on factors such as the primary energy source or fuel type, the type of power plant, and the transmission infrastructure. One full set of conversion factors is available as technical reference from Energy STAR. Either site or source energy can be an appropriate metric when comparing or analyzing energy use of different facilities. The U.S Energy Information Administration, for example, uses primary (source) energy for its energy overviews but site energy for its Commercial Building Energy Consumption Survey and Residential Building Energy Consumption Survey. The US Environmental Protection Agency's Energy STAR program recommends using source energy, and the US Department of Energy uses site energy in its definition of a zero net energy building.

Outlook

Energy accidents and fatalities

Energy accidents are accidents that occur in systems that provide energy or power. These can result in fatalities, as can the normal running of many systems, for example those deaths due to pollution. Globally, coal is responsible for 100,000 deaths per trillion kWh.How Deadly Is Your Kilowatt? We Rank The Killer Energy Sources James Conca, June 10, 2012
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Notes

References

External links

The Encyclopedia of Earth: Primary energy

{{Authority control Energy Energetics Thermodynamics