Primary energy (PE) is an "energy form found in nature that has not been subjected to any "human engineered 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.
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.["citation needed]
PE and TPES are better defined in the context of "worldwide energy supply.
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
|Energy system component||to||"Energy carriers (main)|
|"Oil (or crude oil)||"Oil refinery||"Fuel oil|
|"Coal or "natural gas||"Fossil fuel power station||"Enthalpy, "mechanical work or "electricity|
|"Natural uranium[nb 2]||"Nuclear power plant ("thermonuclear fission)||Electricity|
|"Natural thorium||"Thorium breeder reactor||Enthalpy or electricity|
|"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||"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|
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.
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. "District heating is another example of secondary energy.
"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 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.
Site energy is 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 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 energy provides a more complete picture of energy consumption, it is harder to quantify. 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. Conversely, the New Buildings Institute uses site energy in their annual list of verified "Zero Net Energy Buildings.
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.