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Primary energy (PE) is an energy form found in nature that has not been subjected to any conversion or transformation process. It is energy contained in raw fuels, and other forms of energy received as input to a system. Primary energy can be non-renewable or renewable.
Contents
- Usable energy
- Conversion to energy carriers or secondary energy
- Energy accidents and fatalities
- References
Total primary energy supply (TPES) is a term used to indicate the sum of production and imports subtracting exports and storage changes.
The concept of 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 carriers used by human society.
The use of primary energy as a measure ignores conversion efficiency. Thus forms of energy with poor conversion efficiency, particularly the thermal sources, coal, gas and nuclear are overstated, whereas energy sources such as hydroelectricity which are converted efficiently, while a small fraction of primary energy are significantly more important than their total raw energy supply may seem to imply.
PE and TPES are better defined in the context of worldwide energy supply.
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, 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)
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 (is highly ordered) and can be converted into other forms of energy very efficiently.
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 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 wind turbines do not capture all the wind energy, but 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 frequency ranges, whereas solar thermal is also subject to Carnot efficiency limits. Hydroelectric power is also converted very efficiently. The amount of usable energy is the exergy of a system.
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.