# Introduction

Updated July 2023.

This page explains energy system statistics used by this site. A quick glance at the diagrams here may be all that’s needed. A national energy system can be represented by figure 11 2 3.

Measures of interest are primary energy (labelled Total Energy Supply (TES) by the IEA4 and Energy Consumption by the Energy Institute (EI)5), and final energy (labelled Total Final Consumption (TFC) by the IEA).

Final energy accounts for energy consumed by a country in its final form. For example, accounting for gas burned to produce heat separately from that burned to produce electricity. Final energy data is only available from the IEA, and so is at least two years old. Despite this, it’s arguably a more useful measure than primary energy, as explained below.

Primary energy provides a means to evaluate the energy supplied to an energy system from all fuel types. It accounts for energy supplied in its primary form, prior to any conversions such as coal to electricity.

The weaknesses of primary energy are –

• It’s a measure of how much fossil fuel electricity generation would be required to replace non-fossil fuelled, which is retrospective and unhelpful,
• it’s complicated and uninteresting for people to understand,
• the arithmetic involved is inconsistent, differing between institutions, and
• naming is inconsistent, with the EI confusingly labelling it “consumption”.

Primary energy supplied by non-combustibles (i.e. renewable and nuclear fuels) can’t be directly compared with that supplied by combustibles because non-combustibles have natural forms of primary energy (e.g. sun, wind, uranium etc). To overcome this, an equivalent quantity can be calculated for each non-combustible, using a method of ‘primary energy equivalence’. The method applied to IEA data6 on this site, and that used by BP7, is the ‘substitution method'8.

The substitution method is performed by calculating the quantity of primary energy required to be input to a thermal power station of average efficiency, in order to generate an amount of electricity or heat equivalent to that generated by each non-combustible. Primary energy values for non-combustibles are therefore the equivalent quantity of thermal generation that they have supplanted. For example, if the share of primary energy in an energy system is ‘4% solar’, then the quantity of energy from solar is equivalent to 4% of an energy system that is 100% fuelled by combustible fuels (i.e. thermal).

Values of efficiency applied to IEA data on this site are those used by the IPCC:9 38% for electricity and 85% for heat. Therefore to calculate equivalents, non-combustible quantities of electricity are multiplied by 2.63 (i.e. 1/0.38), and heat by 1.18 (i.e. 1/0.85), as shown in figure 2 below.

The EI data inherently uses the substitution method with yearly-dependant efficiency values ranging from 36% to 40%, due to efficiency improvements. Therefore this site does not apply further processing to EI data.

A shortcoming of primary energy is the measure is excessive relative to that needed in a fully decarbonised energy system solely fuelled by non-combustibles; the total energy currently supplied by combustion of fossil fuels wouldn’t be required to be generated by non-combustibles, because the inefficiency of thermal generation wouldn’t exist.

The pursuit of a solely non-combustible fuelled national energy system is not policy of any country, and a future global ‘net-zero’ energy system, as unlikely as that now seems, may continue to include substantial quantities of thermal generation, and emissions reduced using carbon capture and storage (CCS), and offset by atmospheric carbon dioxide removal (CDR).

Explanations for number prefixes and units used on this site are listed below.