Further insight with regard to the comparison of intensity changes by sector can be gained by looking at how they differ with respect to different definitions of energy use. Source energy attributes all the energy used for electricity generation and transmission to the specific end-use sector, addition to the direct consumption of electricity and fuels. Delivered energy excludes these "losses" in its definition of total energy. A third concept is an adjusted version of source energy, but holds the electric power (utility) sector intensity (ratio of losses to sales to end users) essentially constant (see methodology in 2014 comprehensive report – Section 2.6, or Terminology and Definitions. The percentage changes in energy intensity by sector between 1985 and 2011 using these various measures are shown in Table A1.
From the first column in the table, it is clear that there is no significant difference between transportation energy intensity whether calculated on a delivered energy basis or on a source energy basis. Because the transportation sector uses so little electricity, there are virtually no electricity system losses allocated to transportation. On the other hand, for the buildings sectors, a large fraction of delivered energy is in the form of electricity (in 2011, 43% for the residential sector, 52% for the commercial sector). As shown in the table, for these sectors, the difference between the (2011) indexes computed on either a delivered or source definition of energy is substantial.
The last row of table A1 shows the percentage changes in the source intensity indexes after taking account of changes in the efficiency of electricity generation. These measures provide a more accurate indicator of the source energy intensity change that can be attributed solely to efficiency improvements within the end-use sector itself. The last column shows the improvement in energy efficiency in the electricity utility sector measured as the percentage change in the ratio of losses to sales between 1985 and 2011 (9.3%). (Note: this measure of electric utility intensity is appropriate when its intensity is integrated with the other sectoral measures pertaining to source energy. In the specific discussion of the electricity power sector intensity indexes, the intensity is measured in a more conventional manner – showing total energy [i.e., including the generated electricity itself and not just losses] used by the utilities per unit of energy (electricity) delivered to final customers. This more conventional measure shows about 2/3 of the improvement indicated in Table 1.)
The difference between the unadjusted and adjusted source intensity indexes is most apparent for the most electricity-intensive (in terms of electricity share of delivered energy) end-use sector—commercial buildings. Removing the influence of utility sector improvements, the 1985-2011 change in the adjusted source energy intensity index for the commercial sector is about 5.5 percentage points higher than that shown by the unadjusted intensity index (+9.0% vs. +2.5% when converted to percentage changes from 1985).
Table A1. Percentage Changes in Various Measures of Energy Intensity, 1985-2011
Summary of Intensity Changes - Delivered vs. Source Energy, 1985-2011
|Source Energy (Adjusted for Electric Utility Improvement)||-16.8%||-13.5%||-14.9%||7.9%||n/a|