Embodied energy
Embodied energy refers to the total energy consumed throughout the life cycle of a material, product, or service, from extraction to disposal. It includes all the energy required for activities such as mining, transportation, processing, and installation, providing a comprehensive measure of environmental impact. For example, the embodied energy of an aluminum window frame encompasses the energy used from the raw material stage through to its installation and eventual decommissioning. This concept is often quantified in megajoules per kilogram (MJ/kg) and serves as a comparative metric against alternative materials or products.
Evaluations of embodied energy can vary widely based on factors such as geographical location, methodology, and lifecycle boundaries, which can range from cradle-to-factory to cradle-to-grave assessments. Additionally, cultural and economic contexts may influence energy consumption patterns, with wealthier societies potentially having higher embodied energy due to lifestyle factors. The presence of recycled materials can significantly reduce embodied energy values, highlighting the importance of considering the source of raw materials.
With growing concerns about climate change, there is an increasing interest in measuring embodied energy in relation to carbon emissions, providing insights into a product's carbon footprint throughout its life cycle. Understanding embodied energy is crucial for making informed decisions about sustainability and environmental impact in various industries.
Embodied energy
Summary: The energy that is used in the entire process of producing a material, a product, or a service is known as embodied energy.
Embodied energy can represent the energy used up to produce a construction material, a household appliance, a consumer good, or a less tangible service, even an energy fuel itself. It is one measure of an environmental impact arising from the processing of the material or product or the activities involved in delivering the service. In the case of an aluminum window frame, for example, the embodied energy would be all the energy used to mine, extract, refine, and process the materials constituting the frame; manufacture the frame; transport and install the frame to an end user; and decommission the product at the end of its use.
The values of embodied energy are often expressed in megajoules per kilogram (MJ/kg) or the equivalent and are a comparative measure of the energy used to provide the product, compared to available alternative products. The embodied energy bears no relationship to the calorific value of a finished product or its ability to provide energy as a fuel. Embodied energy is, rather, an accounting concept to describe a material’s, product’s, or service’s consumption of energy during its process of being transformed from its initial raw state to finished article. Embodied energy may be considered to be the energy use or energy debt that a material, product, or service has consumed during its life.
Different lifecycle assessments are used for the calculation of embodied energy, depending on the boundary conditions that are relevant to the study of the material, product, or service. The lifecycle starts from birth (cradle) and ends at an appropriate accounting gateway, such as the factory, the point of use (site), or at death (grave). These lifecycle assessment periods may be cradle-to-factory, cradle-to-site, or cradle-to-grave, depending on what position in the life cycle the energy consumption is truncated.
Embodied energy figures should be used as a relative comparator rather than an absolute figure, as they are variable across different studies. Embodied energy methodologies vary and may consider process, input-output, or hybrid methods, and both vertical and horizontal system boundaries and assumptions are an important attribute in determining the results and applying data from embodied energy tables or spreadsheets.
Analyses are dependent on time period, geographical location, boundary conditions, assumptions, methodologies, and the rigor of the lifecycle assessment. Different periods of time have different energy technology availability, and different cultures have different energy uses to sustain their cultures. Studies may be related to a particular country (such as Australia, Canada, the United Kingdom, or the United States), and transportation energy may be an important factor (for example, stone from Brazil shipped to Europe may have greater embodied energy than indigenous, locally produced stone hewn and used in Europe).
The assessment of human services in support of materials, products, and services is also an area of debate and uncertainty. A product manufactured in a wealthy society by workers with a high standard of living may include a proportion of energy used to support the lifestyle. For example, whether workers travel to and from work by a motor vehicle, with excessive fuel consumption, or by bicycle may need to be taken into account. One would expect greater embodied energy in a service provided by energy-intensive societies. Some materials, such as aluminum, may have increasing proportions of recycled material that dramatically cut embodied energy; hence, knowledge of the proportion of recycled versus raw material is necessary when comparing studies.
In the special case in which the material, product, or service is itself an energy technology system (such as oil, gas, coal, nuclear, wind, hydro, tidal, solar, photovoltaic, or biofuel), the embodied energy used to extract, refine, process, and transport the energy can be expressed as an energy burden on the resulting fuel. The gross energy of the energy product is reduced by the embodied energy to give the residual net energy available.
For example, where it takes two buckets of coal to power the technology to mine nine buckets of coal, there is an energy burden (embodied energy) of two buckets of coal and a net energy resulting of seven buckets of coal.
When the coal is so deep or difficult to extract that 3 buckets’ worth of embodied energy are required to deliver 2 buckets of coal, the net energy is minus 1 bucket, a negative return that suggests the venture is no longer a sensible energy investment. This net energy accounting may be clear when a single energy resource is considered but is more difficult when numerous energy source types subsidize the energy system.
Some analysts are concerned that different energy resources are not easily aggregated using heat equivalence, economic price-derived factors, or physical thermodynamic analysis, as these aggregations lose information about the quality of an energy resource. Howard T. Odum promoted a system of energy and ecological analyses in terms of solar energy equivalents using transformity factors to bring all energies used to a common solar base, measured in a unit he termed emjoules. He used a special term emergy (with an m) to denote a special accounting of embodied energy using the embodied solar energy equivalent. International Standard 13602-1 attempts to describe a set of rules by which input and output and boundary conditions can be prescribed for technical energy systems.
With increasing interest in climate change and environmental concerns, there is a move to measure embodied energy in terms of the amount of carbon dioxide (CO2) released in the use of the embodied energy. Measures of embodied energy are cited in terms of carbon released into atmosphere (in kilograms of carbon dioxide per kilogram). This is analogous to the material’s, product’s, or service’s carbon footprint over its lifetime.
Bibliography
Cleveland C. “Energy Quality, Net Energy, and the Coming Energy Transition.” Massachusetts Institute of Technology, web.mit.edu/2.813/www/2007%20Class%20Slides/EnergyQualityNetEnergyComingTransition.pdf. Accessed 30 July 2024.
Costanza R. “Embodied Energy and Economic Valuation.” Science 210, no. 4475 (December 12, 1980).
Dixit, M. K., J. L. Fernandez-Solis, S. Lavy, and C. H. Culp. “Identification of Parameters for Embodied Energy Measurement: A Literature Review.” Energy and Buildings 42 (2010).
"Embodied Energy." California Office of Historic Preservation, ohp.parks.ca.gov/pages/1054/files/embodied%20energy.pdf. Accessed 30 July 2024.
International Standards Organization. “Technical Energy Systems: Methods for Analysis, Part 1: General.” ISO 13602-1 2002. http://www.iso-standard.org/13626.html.
Odum, Howard T. Environmental Accounting: Energy and Environmental Decision Making. New York: John Wiley and Sons, 1996.
Spreng, Daniel T. Net-Energy Analysis and the Energy Requirements of Energy Systems. New York: Praeger, 1988.