Primary energy (PE) is the energy found in nature that has not been subjected to any human engineered conversion process. It encompasses energy contained in raw fuels and other forms of energy, including waste, received as input to a system. Primary energy can be non-renewable or renewable.
World total primary energy consumption by type in 2020[1]
Total primary energy supply (TPES) is the sum of production and imports, plus or minus stock changes, minus exports and international bunker storage.[3] The International Recommendations for Energy Statistics (IRES) prefers total energy supply (TES) to refer to this indicator.[4] These expressions are often used to describe the total energy supply of a national territory.
Secondary energy is a carrier of energy, such as electricity. These are produced by conversion from a primary energy source.
Primary energy is used as a measure in energy statistics in the compilation of energy balances,[5] 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 carriers used by human society.[6] Primary energy only counts raw energy and not usable energy and fails to account well for energy losses, particularly the large losses in thermal sources. It therefore generally grossly undercounts non-thermal renewable energy sources .
Examples of sources
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Primary energy sources should not be confused with the energy system components (or conversion processes) through which they are converted into energy carriers.
| Primary energy sources | converted by |
Energy system component | to | Energy carriers (main) | ||
| Non-renewable[nb 1] | Fossil fuels |
Oil (or crude oil) | Oil refinery | Fuel oil | ||
| Coal or natural gas | Fossil fuel power station | Enthalpy, mechanical work or electricity | ||||
| Mineral fuels |
Natural uranium[nb 2] | Nuclear power plant (thermonuclear fission) | Electricity | |||
| Natural thorium | Thorium breeder reactor | Enthalpy or electricity | ||||
| Renewable | Solar energy | Photovoltaic power plant (see also Solar power) | Electricity | |||
| Solar power tower, solar furnace (see also Solar thermal energy) | Enthalpy | |||||
| Wind energy | Wind farm (see also Wind power) | Mechanical work or electricity | ||||
| Falling and flowing water, tidal energy[7] | Hydropower station, wave farm, tidal power station | Mechanical work or electricity | ||||
| Biomass sources | Biomass power plant | Enthalpy or electricity | ||||
| Geothermal energy | Geothermal power station | Enthalpy or electricity | ||||
Usable energy
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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, refined fuels, or synthetic fuels such as hydrogen fuel. In the field of energetics, these forms are called energy carriers and correspond to the concept of "secondary energy" in energy statistics.
Conversion to energy carriers (or secondary energy)
editEnergy 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 (is highly ordered) and so can be converted into other forms of energy very efficiently. District heating is another example of secondary energy.[8]
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.[6]
Conversion efficiency varies. For thermal energy, electricity and mechanical energy production is limited by Carnot's theorem, and generates a lot of waste heat. 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
editSite 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.[9]
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.[10] 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.[9] For electricity, a typical value is three units of source energy for one unit of site energy.[11] 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.[12]
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[13] but site energy for its Commercial Building Energy Consumption Survey[14] and Residential Building Energy Consumption Survey.[15] The US Environmental Protection Agency's Energy STAR program recommends using source energy,[16] and the US Department of Energy uses site energy in its definition of a zero net energy building.[17]
Conversion factor conventions
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Where primary energy is used to describe fossil fuels, the embodied energy of the fuel is available as thermal energy and around two thirds is typically lost in conversion to electrical or mechanical energy. There are very much less significant conversion losses when hydroelectricity, wind and solar power produce electricity, but today's UN conventions on energy statistics counts the electricity made from hydroelectricity, wind and solar as the primary energy itself for these sources. One consequence of employing primary energy as an energy metric is that the contribution of hydro, wind and solar energy is under reported compared to fossil energy sources, and there is hence an international debate on how to count energy from non-thermal renewables, with many estimates having them undercounted by a factor of about three.[18] The false notion that all primary energy from thermal fossil fuel sources has to be replaced by an equivalent amount of non-thermal renewables (which is not necessary as conversion losses do not need to be replaced) has been termed the "primary energy fallacy".
See also
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Notes
edit- ^ At the scale of earth sciences, all primary energy sources can be considered to be renewable. The non-renewable essence of resources (PES) is due to the scale of needs within human society. In certain situations, the use of resources by human society is performed at a much higher rate than the minimum rate at which it can be geophysically renewed. This is the rationale behind the differentiation between non-renewable primary energy sources (oil, coal, gas, uranium) and renewable primary energy sources (wind, solar, hydro).
- ^ Some nuclear fuels, such as plutonium or depleted uranium, are also used in nuclear fission power plants. However, they cannot be considered to be primary energy sources as they cannot be found in nature in any quantity. Indeed, there must be a consumption of natural uranium (primary energy source) in order to make these other nuclear fuels available.
References
edit- ^ "Statistical Review of World Energy (2021)" (PDF). p. 13. Archived (PDF) from the original on 15 August 2021. Retrieved 19 August 2021.
- ^ "2019 Key World Energy Statistics" (PDF). IEA. 2019.
- ^ OECD (2012). OECD Factbook 2013: Economic, Environmental and Social Statistics. OECD Factbook. OECD Publishing. p. 108. doi:10.1787/factbook-2013-en. ISBN 9789264177062. Retrieved 16 August 2021.
- ^ Department of Economic and Social Affairs (2018). International Recommendations for Energy Statistics (PDF). New York: United Nations. p. 105,137.
- ^ "Primary energy". Glossary. Washington, DC: U.S. Energy Information Agency. Retrieved 18 August 2021.
- ^ a b Giampietro, Mario; Mayumi, Kozo (2009). The Biofuel Delusion: The Fallacy of Large Scale Agro-Biofuels Production. Earthscan, Taylor & Francis group. p. 336. ISBN 978-1-84407-681-9.
- ^ "Energy and the Natural Environment" Archived 2008-10-24 at the Wayback Machine by David A. Dobson, Ph.D., Welty Environmental Center Feature Article, accessed July 9, 2009
- ^ U.S. EPA Energy STAR Retrieved 2017-11-03
- ^ a b "Measuring energy: site energy vs. source energy in ENERGY STAR Portfolio Manager". Natural Resources Canada. 28 March 2017. Retrieved November 8, 2017.
- ^ Torcellini, Paul; Pless, Shanti; Deru, Michael; Crawley, Drury (June 2006). "Zero energy buildings: a critical look at the definition" (PDF). ACEEE Summer Study. National Renewable Energy Laboratory/U.S. Department of Energy.
- ^ "Site Energy vs Source Energy". The World Bank. Retrieved November 8, 2017.
- ^ "Technical Reference: Source Energy" (PDF). Retrieved 2017-11-09.
- ^ "Total Energy - U.S. Energy Information Administration (EIA)". www.eia.gov. Retrieved 2017-11-09.
- ^ "Commercial Buildings Energy Consumption Survey (CBECS) - U.S. Energy Information Administration (EIA)". www.eia.gov. Retrieved 2017-11-09.
- ^ "Residential Energy Consumption Survey (RECS) - U.S. Energy Information Administration (EIA)". www.eia.gov. Retrieved 2017-11-09.
- ^ "The difference between source and site energy". www.energystar.gov. Retrieved 2017-11-09.
- ^ "DOE Releases Common Definition for Zero Energy Buildings, Campuses, and Communities". Energy.gov. Retrieved 2017-11-20.
- ^ Sauar, Erik (31 August 2017). "IEA underreports contribution solar and wind by a factor of three compared to fossil fuels". energypost.eu. Energy Post. Retrieved 22 April 2018.
Further reading
edit- Kydes, Andy (Lead Author); Cutler J. Cleveland (Topic Editor). 2007. "Primary energy." In: Encyclopedia of Earth. Eds. Cutler J. Cleveland (Washington, D.C.: Environmental Information Coalition, National Council for Science and the Environment). [First published in the Encyclopedia of Earth June 1, 2006; Last revised August 14, 2007; Retrieved November 15, 2007.
- Øvergaard, Sara (September 2008). Definition of primary and secondary energy (PDF). Norway: Statistics Norway. Retrieved 2016-12-17.