TODAY’S STUDY: NUMBERS FOR THE NEW AND OLD ENERGIES (Part 1)
Primary Energy Demand of Renewable Energy Carriers; Part 1: Definitions, accounting methods and their applications with a focus on electricity and heat from renewable energies
Alexander Stoffregen and Dr. Oliver Schuller, April 2014 (PE International)
Energy related discussions and policy making, such as defining energy saving targets or energy efficiency measures, are often based on primary energy values. These values express the energy consumption of a country, or the energy demand of a system, service or product in primary energy units. They are often published by international and national energy statistics, energy scenarios/outlooks, or environmental assessments, however there is a potential for inconsistency in how these primary energy values are determined.
Primary energy values taken from different energy statistics and studies may sometimes be compared without considering possible influences from different definitions and methodologies used for primary energy. Recent studies have raised awareness about the influence of different methods s to determine primary energy consumption from renewable energy sources in energy statistics. In Moomaw (2011) and Macknick (2011) the differences in energy statistics and energy outlooks/scenarios that occur, due to the different methods and definitions, are highlighted as well as the challenges faced in comparing these different accounting methods. In addition, Harmsen (2011) investigated the impact of different methods on energy saving targets in Europe.
The method for calculating the primary energy of fossil fuels is clear and consistent (as described in chapter 3). In contrast, primary energy factors for electricity or heat generated from renewable energies, waste, nuclear energy, or imported electricity are not calculated according to a single consistent methodology. Instead, several approaches are available and used in practice. Figure 1 presents an overview of the different energy sources used to generate electricity. Waste is a unique case as it can be considered to be either a renewable energy source, a fossil energy source, or a mixture of both depending on its specific characteristics. Heat generation uses the same energy sources as electricity generation, with the exception of hydro and wind energy.
This paper is the first part of a two paper series commissioned by the European Copper Institute. It addresses the different primary energy definitions, accounting methods, and their applications with a focus on electricity and heat generation from renewable energy. In addition to renewable energy sources, primary energy factors for electricity from waste, nuclear, and imported electricity are also discussed as these can be calculated in different ways. In the second part of the study, “Primary Energy Demand of Renewable Energy Carriers – Part 2 Policy Implications,” conducted by ECOFYS (2014), the application of primary energy factors (PEF) in the three EU Directives – Energy Performance of Buildings Directive (EPBD), Energy Efficiency Directive (EED) and Renewable Energy Directive (RED) is discussed.
In Nakicenovic (1996), primary energy is defined as:
The energy that is embodied in resources as they exist in nature: the chemical energy embodied in fossil fuels or biomass, the potential energy of a water reservoir, the electro-magnetic energy of solar radiation and the energy released in nuclear reactions.
Similar or adapted definitions of primary energy can be found in publications dealing with energy statistics, energy economics, or environmental assessments. They all define combustible fossil fuels such as coal, oil, and natural gas extracted from a stock of finite resources, as primary energy.
The conversion efficiencies for steam power plants, heat plants, combined heat and power (CHP) plants, or residential heating systems using combustible energies are determined based on the ratio between produced electricity and/or heat, and input of energy (amount of fuel multiplied with calorific value) as outlined in Formula 1. In the context of renewable energy carriers in energy statistics, the expression primary energy equivalent is used instead of efficiency…Hence, primary energy factors are the quotient of primary energy input to energy (electricity/heat) output, i.e. the reciprocal value of the conversion efficiency as shown in Formula 2…
These definitions are relatively straightforward to use if the primary energy demand or primary energy factor (PEF) of a fossil power plant needs to be calculated for the supply of secondary energy, e.g. electricity. Assuming a conversion efficiency of 40% for a fossil power plant, 2.5 MJ of primary energy is needed to provide one MJ of electricity (PEF = 2.5). Similarly, for electricity from biomass and waste, the primary energy factor can be calculated in the same way as for fossil fuels.
For electricity and heat from non-combustible renewable energy or nuclear energy, several methodologies to account for primary energy and to calculate the primary energy factors have been developed and applied. These are listed in Table 1. The same holds true for electricity and heat from co-generation, as the primary energy has to be partitioned (allocated) to two different products (heat and electricity) for which different methodologies exist.
The methodology for Option 1 is straightforward, as the primary energy is, by definition, always zero for non-combustible, renewable energy sources. Option 2 uses so-called primary energy equivalents to calculate the primary energy of the generated electricity or heat without further differentiation into renewable or non-renewable (fossil) primary energy.
For Options 3 and 4, the system boundaries are different compared to Options 1 and 2, as the primary energy that is needed, for example to produce and transport construction materials or auxiliary materials, is included. In these cases, electricity or heat from non-renewable or renewable combustible energy is considered, as well as the primary energy necessary to extract, cultivate, transform, and transport the fuels. The enlargement of the system boundaries takes into account that, depending on the energy source, the build-up of infrastructure and the supply of fuels may be of relevant from an environmental perspective.
A second aspect considered within Option 3 and 4, is that the usage of renewable energy sources for electricity or heat supply should be assessed, or accounted in a different way than finite, non-renewable energy sources. An aggregated primary energy factor that includes renewable and non-renewable primary energy has no value for the assessment of the consumption of finite energy resources. A comparison of such primary energy factors may even be misleading, as the absolute magnitude of primary energy factors, especially for electricity from renewable sources, can be much higher due to lower technical conversion efficiencies or assumed primary energy equivalents.
For that reason, Options 3 and 4 split primary energy into primary energy from renewable sources (e.g. hydro, wind, solar, geothermal and biomass) and non-renewable sources (nuclear and fossil fuels). For municipal solid waste, energy statistics often account 50% of the primary energy that is converted in the waste incineration plant as non-renewable (fossil) energy, and 50% as renewable primary energy. In addition, primary energy associated with the construction of the incineration infrastructure and the production of operating materials is accounted for as non-renewable (fossil) primary energy.
In Option 3, only the non-renewable (fossil) primary energy that is needed to supply the necessary infrastructure to produce electricity from renewable sources or to produce biomass (e.g. diesel for machinery or energy for infrastructure) is accounted for by standardized methods following a life cycle thinking approach, such as life cycle assessment (ISO 14040/44). Numerous studies and databases exist, from which the primary energy demand can be taken.
Option 4 also includes, in addition to Option 3, the primary energy of the renewable sources themselves that are used to generate the electricity, i.e. primary energy equivalents or conversion efficiencies are used to determine the renewable primary energy for electricity generation from renewable energy sources. For biomass, the calorific value is used to determine the renewable primary energy of the combusted fuel, i.e. photosynthesis of solar energy into biomass is not accounted for (as in all options and methods described within the paper). In the case of nuclear power, the primary energy is accounted for as non-renewable (fossil) primary energy. Finally, for electricity from waste, the primary energy is often accounted with the 50:50 approach for the conversion as described above.
Unlike biomass plants where the input of fuel and the generated electricity are measured similarly to fossil fuel plants, only the output of electricity is measured in non-combustible power plants using renewable energies (e.g. hydro power stations, wind turbines, photovoltaic cells etc.) or nuclear energy. In theory, the primary energy equivalence for electricity from technology such as wind turbines can be determined by using a technical conversion efficiency for the generator that converts the kinetic energy of the wind into electricity. In practice, several conversion efficiencies would have to be determined for renewable energy carriers and nuclear energy that would depend upon climatic conditions, technologies used, and overall system integration. Instead, standardized (not technology, climate specific etc.), primary energy factors are used for electricity or heat generation. The methods for the conversion from primary energy to electricity are described in the following chapter.
Methods to calculate primary energy equivalents or conversion efficiencies…Application of methods in practice…Example primary energy factors using different methodologies…
The paper has summarised the existing definitions for primary energy, efficiency and primary energy factors, as well as the different options to account for primary energy in energy statistics, environmental assessments or other applications. The usage of different types of primary energy y— total primary energy, non-renewable (fossil) energy, or the division of non-renewable and renewable primary energy— is important to understand because of the effect different options and methods may have on statistics and policy targets. All commonly used accounting methods to calculate primary energy equivalents or efficiencies have been discussed, including the impact of different methods on the calculation of primary energy factors.
There are different ways to account for primary energy which makes it difficult to compare primary energy values or primary energy factors. Depending on the type of primary energy and the method, which mostly depends on the type of application and the publishing institution, primary energy factors can distinctly vary for the same renewable energy source. As shown in Moomaw (2011), Machnick (2011) and Harmsen (2011), the primary energy consumption of a country or a system is influenced by the accounting method. A distinction between renewable and non-renewable primary energy, as normally used in life cycle assessments (LCA), could avoid misleading interpretations of energy consumption over time. This distinction has the advantage that finite energy sources are not added with infinite energy resources. Life cycle assessment and the division of primary energy into renewable and non-renewable sources is therefore, a robust and suitable way to understand the energy consumption of a system or country.
Nonetheless, a distinction of primary energy does not necessarily reveal the energy efficiency of a system or product. The electricity consumption of a system, supplied by a renewable source with a high primary energy factor (e.g. solar photovoltaic), can be explicit lower although the overall renewable primary energy consumption is higher than for an alternative system supplied by e.g. hydro power.
The separation of primary energy into non-renewable and renewable components is therefore especially useful when comparing primary energy factors for renewables with those for fossil fuels.
The non-renewable primary energy necessary to generate electricity from renewable sources gives a clear understanding of the energy intensity of the manufacturing, installation and operation of the infrastructure (hydro power station, wind turbine, photovoltaic cells etc.). Results can be compared between electricity from different renewable energy sources but also with electricity generation from fossil fuels.
In the second part of the study “Primary Energy Demand of Renewable Energy Carriers – Part 2 Policy Implications” the use of primary energy factors in EU legislation is presented. The impact of primary energy factor calculation on greenhouse gas mitigation targets and renewable energy targets is discussed, and possible policy outcomes of using different primary energy factor calculation methods in three different policy areas - Energy Performance of Buildings Directive (EPBD), Energy Efficiency Directive (EED) and Renewable Energy Directive (RED) - are provided.