Power and Emission
An emission intensity (also carbon intensity, C.I.) is the emission rate of a given pollutant relative to the intensity of a specific activity or an industrial production process; for example grams of carbon dioxide released per megajoule of energy produced, or the ratio of greenhouse gas emissions produced to gross domestic product (GDP). Emission intensities are used to derive estimates of air pollutants or greenhouse gas emissions based on the amount of fuel combusted, the number of animals in animal husbandry, industrial production levels, distances traveled, or similar activity data. Emission intensities may also be used to compare the environmental impact of different fuels or activities. In some cases, the related terms emission factor and carbon intensity are used interchangeably. The jargon used can be different, for different fields/industrial sectors; normally the term “carbon” excludes other pollutants, such as particulate emissions. One commonly used figure is carbon intensity per kilowatt-hour (CIPK), which is used to compare emissions from different sources of electrical power.
Methodologies
- The whole life-cycle assessment (LCA): this includes not only the carbon emissions due to a specific process but also those due to the production and end-of-life of materials, plants, and machinery used for the considered process. This is a quite complex method, requiring a big set of variables.
- The well-to-wheels (WTW), commonly used in the Energy and Transport sectors: this is a simplified LCA considering the emissions of the process itself, the emissions due to the extraction and refining of the material (or fuel) used in the process (also “Upstream emissions”), but excluding the emissions due to the production and end-of-life of plants and machinery. This methodology is used, in the U.S.A., by the GREET model, and in Europe in the JEC WTW.
- WTW-LCA hybrid methods, trying to fill in the gap between the WTW and LCA methods. For example, for an Electric Vehicle, a hybrid method considering also the GHG due to the manufacturing and the end of life of the battery gives GHG emissions 10-13% higher, compared to the WTW
- Methods not considering LCA aspects but only the emissions occurring during a specific process; i.e. just the combustion of a fuel in a power plant, without considering the Up