Energy Footprints An Overview

Not all energy sources are currently accounted for in footprint modeling. Energy footprinting typically accounts only for the major primary energy sources. Fossil fuels (coal, oil, and natural gas), hydropower, and nuclear power are handled through a direct accounting. Energy crops and fuelwood are accounting as part of total crop and forest products. Other sources, like solar energy, geothermal, and waste energy are neglected, partly because their footprints are small compared to the primary sources and partly to avoid double counting footprints.

This concept of double counting footprints bears further mention. Consider solar collectors (for electricity generation or heating), most of which are currently being installed on buildings or in parking lots. Given that buildings and parking lots are already accounted for in the models as built areas, counting them again for energy provisioning would imply that their presence in these locations appropriates yet more biocapacity, which is false. In the case of passive solar design of buildings, the building itself is the collector (or rejection of heat) and again, the footprint is already accounted for the fact that the building heats itself in winter and rejects heat in summer in no way adds to the building's footprint. The only thing it does is reduce the energy footprint associated with that building's use, but that effect is accounted for in the energy footprinting. Thus, it is better to simply leave passive solar design out of the footprinting process entirely.

As indicated in the pie chart below, the sources currently accounted for in footprinting analysis--fossil fuels, hydro, nuclear, and fuelwood-- constitute about 94% of the total world commercial energy supply. (Fuel wood yields about half of total biomass energy.) We note that non-commercial (traditional) biomass energy not shown here (from trees, agricultural wastes, and dung) constitutes about 15% of total world energy use.



Data for this chart were found on the Energy Information Administration website of the US Department of Energy. Biomass data were taken from the World Energy Council website. The biomass data have significantly higher uncertainty than the other data as the majority of biomass energy use occurs outside of commercial markets

The first task in energy footprinting therefore is to figure out how much of each of the major energy sources is used by the population of interest. The following table summarizes how the footprints of the different sources are typically estimated.The details and variations in assessment methods are discussed in the links.

The footprint of	Is based on...
Fossil fuels (coal, natural gas, oil and derivatives)	the amount of land needed to absorb the carbon emissions generated by fuel combustion
Hydropower	the land area submerged by the reservoir
Biomass	the land area required to grow fuelwood or other energy crop
Nuclear power	equivalent fossil fuel emissions

In some cases these data are already compiled, for example for many nations, and much of that data is posted on the Internet. In other cases, for example for institutions, you may have to figure it out yourself. To do so, you must consider all of the ways that energy is being used and then determine how this breaks down into the primary sources listed above.