All the chain that goes from energy supply (extraction and exploitation of primary energy resources) to energy demand (energy-using units in industry, transport, buildings and other sectors) makes part of the energy system of a country or a region (European Environment Agency, 2015). The transformation of energy from the primary forms to forms that may be used by end-users for the performance of energy services do obligatorily involve a phenomenon designated as energy conversion (Hazen, 2021). Energy conversion represents a passage between different steps of an energy system, which may be classified mainly in (Grubler et al., 2012):

  • Primary energy: the form of energy that is found in nature and that it has not still be submitted to any conversion process, and may be of non-renewable (fossil) nature or renewable;
  • Secondary energy: the form of energy comprised by energy carriers (resulting from the conversion of primary energy), which are for instance electricity, heat and solid/ liquid/ gaseous fuels;
  • Final energy: the form of energy that is distributed to the end-users (for instance, industry, transports and buildings);
  • Useful energy: the form of energy that is comprised by energy services (resulting from the conversion of final energy) such as the one that is measured in services such as vehicle mobility, thermal comfort, manufacturing process heat and illumination.

The first step of the analysis of an energy system passes by the analysis of energy consumption. While in the context of SMEs the analysis of interest would be in terms of energy services, it is firstly necessary to understand the energy consumptions levels in the entire world, which may only be performed by analysing primary energy consumption. This analysis serves essentially to understand the resources that are being extracted from nature and the non-renewable/ renewable nature of the whole energy chain. In Figure 1, it is represented the evolution of primary energy consumption in the timeframe of 1965 – 2020.

Figure 1 Energy Consumption in the world in the timeframe of 1965 – 2020 (adapted from (Rodrigue, 2020))

As may be observed, while renewable energy resources use share have been increase in the last years, prominently since the mid-2000’s, the energy dependence of the entire world still relies on the use of fossil fuels. The decrease of the energy dependence on fossil fuels of the entire world (and thus the attainment of energy system decarbonization) and each country may be either performed by the increase of the use of renewable energy resources or the implementation of measures that allow improved energy conversion between each step of the energy system. In Figure 2, the energy use levels in and in-between each step of the world energy system are presented.

Figure 2 Energy use levels in each step of the world energy system from primary to useful energy (adapted from (Grubler et al., 2012))

As may be observed in the figure above, there are considerable energy losses parcels in the lower part of the diagram (which represents energy services, and thus useful energy). The main instrument for the decarbonization of the energy use in SMEs (apart from renewable energy integration) passes by the decrease of these losses, which passes by the implementation of measures that promote a reduced energy footprint, increased energy efficiency and improved energy management.

2.1. Energy Footprint

Energy Footprint is defined by Global Footprint Network as the sum of all areas used to provide non-food and non-feed energy. It is a measure of the area required to absorb CO2 emissions (Footprint, 2002), and thus depends on the sum of total CO2 emissions, in addition to hydropower land, forests for fuelwood, and cropland for fuel crops (Manufacturing Energy and Carbon Footprints (2018 MECS) | Department of Energy, no date).

The energy footprint allows us to better understand the spatial distribution of energy utilization as well as to compare energy consumption within different enterprise sectors. Identified areas of significant energy consumption or energy losses could indicate energy footprint enhancing opportunities by implementing appropriate energy management practices and energy efficiency guidelines, upgrading energy systems, or applying new technological solutions. Therefore, the energy footprint provides a macro-scale benchmark for the evaluation of energy consumption, and prioritization and opportunity analysis (Ewing et al., 2009).

Although energy footprint may not take at all times simple measurements, it highly depends on the measurement equivalent to carbon dioxide (CO2,eq), which is of most common and simple measurement. Each primary energy source is associated with an emission factor, and associating each of these factors to the energy consumption levels of each source it is possible to determine the total CO2,eq emissions (Penman et al., 2006). The promotion of energy efficiency and energy management reduces total GHG emissions, thus the total energy footprint. In Figure 3, it is represented the evolution of CO2,eq emissions in the most representative regions of the world.

Figure 3 Evolution of total CO2,eq emissions in the timeframe of 1960 – 2021 for each one of the most representative regions in the world (adapted from (Hausfather, 2021))

The elaboration of the international standards on energy use and consumption generally starts from the overall aim to decarbonize the energy systems, this is, reduce total CO2,eq emissions. Each policy then establishes its own strategies for such achievement, either passing by actions at the level of increasing energy conversion or either more directly using primary energy source with an associated less CO2,eq emissions levels.

2.2. Energy Efficiency

Energy efficiency is the use of less energy to perform the same task or produce the same result. Energy-efficient buildings use less energy to heat, cool, and run appliances and electronics, and energy-efficient manufacturing facilities use less energy to produce goods.

Energy efficiency is one of the easiest and most cost-effective ways to counteract climate change, reduce the use of fossil fuels, reduce energy costs and improve the competitiveness of businesses. Energy efficiency is also a vital component in achieving net-zero emissions of CO2 through decarbonization (Department of Energy – Energy Efficiency, 2010).

The implementation of energy efficiency improvement measures passes by the increase of the energy conversion between each step of an energy system. For instance, it passes by the decrease of the ratio between total final energy use and total primary energy use (FE/PE ratio), and also the ratio between total useful energy and total final energy use (UE/FE ration). In terms of the FE/PE ratio, typical values for existing conversion technologies include (Domingues, 2021; Silva, 2021):

  • Natural gas transportation – Near 99%;
  • Electricity transportation – Near 95%;
  • Refineries – 95%;
  • Gas turbine – up to 40%;
  • Combined cycle (Gas turbine and steam turbine) – up to 60%;
  • Water turbine – up to 90% (practically achieved);
  • Wind turbine – up to 59% (theoretical limit);
  • Solar cell – up to 43%;
  • Fuel cell – up to 80%;
  • Water electrolysis – 50% – 70%;
  • Small electric motors – 30% – 60%;
  • Medium electric motors – 50% – 90%;
  • Large electric motors – 70% – 99.99%.

In terms of the UE/FE ratio, typical values for existing conversion technologies include (Domingues, 2021; Silva, 2021):

  • Electrical resistance – Near 100%
  • Electrical motor – Near 90%
  • Boiler – Near 85%;
  • Fluorescent lamp – Near 50%;
  • Internal combustion engine – Near 30%;
  • Incandescent lamp – Near 5%.

The promotion of energy efficiency may be performed by analysing potential improvements at the level of electricity use, thermal energy use and fuel consumption. At the level of electricity use, improvement measures essentially pass by the associated enhancements of electric motors, such as (Fernandes and Costa, 2016):

  • Installation of variable speed devices (VSD’s);
  • Change of conventional motors to high-efficiency ones;
  • Guarantee the maintenance of motors;
  • Avoidance of motor oversizing.

In relation to thermal energy use and fuel consumption, improvement measures essentially subsist on the use of waste heat (waste heat recovery) (Castro Oliveira et al., 2020):

  • Direct hot air recirculation as combustion air to combustion chambers;
  • Installation of heat exchangers (air preheaters and economizers);
  • Thermal energy storage (for dynamic supplies and demands).

More complex measures include power generation from waste heat (such as the one achieved by the installation of thermodynamic cycles) (Jouhara et al., 2018) and planning of water system that consider water recirculation as both as freshwater resource and recirculated heat medium (which causes savings in hot utilities to preheat water and cold utilities that cool down water to be discharged into the environment) (Boix et al., 2012).

2.3.International Standards for Energy Use and Consumption

The efficient energy use and consumption in each country of the world is secured by the establishment of several policies, that may range from regulations, directives, and recommendations. In Table 1, several international policies that are set to promote energy efficiency and a low-carbon economy are characterized.


European Environment Agency (2015) Overview of the European energy system — EuropeanEnvironment Agency, Eea. Available at:

Grubler, A. et al. (2012) ‘Energy Primer’, Global Energy Assessment (GEA), pp. 99–150. doi: 10.1017/cbo9780511793677.007.

Rodrigue, J.-P. (2020) 4.1 – Transportation and Energy, The Geography of Transport Systems.
Available at:

Footprint, E. (2002) ‘What is Energy Footprint ?’ Available at:

Ewing, S. et al. (2009) ECOLOGICAL FOOTPRINT ATLAS 2009. Oakland.

Penman, J. et al. (2006) ‘2006 IPCC – Guidelines for National Greenhouse Gas Inventories’,Directrices para los inventarios nacionales GEI, p. 12. Available at: 

Hausfather, Z. (2021) ‘Global CO2 emissions have been flat for a decade, new data reveals’, CarbonBrief, p. 22. Available at:

Department of Energy – Energy Efficiency (2010). Available at:

Domingues, T. (2021) ‘Energy, Environment and Sustainability Lecture 02 – Thermodynamics’,
Instituto Superior Técnico.

Fernandes, M. C. de C. S. and Costa, I. C. (2016) Medidas transversais de eficiência energética
para a indústria.

Castro Oliveira, M. et al. (2020) ‘Review on Energy Efficiency Progresses, Technologies and Strategies in the Ceramic Sector Focusing on Waste Heat Recovery’, Energies, 13(22), p. 6096. doi:

Jouhara, H. et al. (2018) ‘Waste heat recovery technologies and applications’, Thermal Science and
Engineering Progress, 6, pp. 268–289. doi: 10.1016/j.tsep.2018.04.017.

Boix, M. et al. (2012) ‘Minimizing water and energy consumptions in water and heat exchange
networks’, Applied Thermal Engineering, 36(1), pp. 442–455. doi:

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