|Economia & Energia
No 18 January-March 2000
|Energy Final and Equivalent -
Simplified Procedure for Conversion
Energy is the fundamental input for production. The so-called energy sources have different forms in nature, at different refinement levels from firewood to nuclear. In the global evaluation of an energy system it is convenient to express all forms of energy in a unified way.
In this work it is described in a summarized way energy conversion to useful and equivalent energy and a quick form to evaluate the equivalent energy from Energy Balance data, in the OECD (R1) format and from coefficients based on the Brazilian Useful Energy Balance (R2).
The national energy balances used in several countries as a tool for planning and evaluation classify energy sources as primary ones, which are provided by nature in their direct form, such as petroleum, natural gas, mineral charcoal, uranium ore, firewood and others.
A first accounting can be carried out from the superior calorific power of these products since in most cases this energy is in chemical form. Other forms of primary energy such as hydraulic, wind, solar and nuclear are treated in a special way, generally taking into account their capacity for generating motive energy.
A good part of primary products like petroleum undergo a transformation process that converts them into more adequate forms for different uses. The place where this process is applied is generally denominated transformation center.
In the case of petroleum, the transformation centers are the refineries where direct use products like gasoline, kerosene, diesel oil, liquefied gas and other products are obtained, and they are classified as secondary energy. In some cases, a secondary source as fuel oil obtained from petroleum goes through another transformation center where it is converted into electricity.
In any transformation part of the energy is lost in the process.
Final energy designates the energy as the consumer in the different sectors receives it, be it in the primary or secondary form. The energy balances are structured in such a way that the energy is discriminated as:
Primary ® Loses in Transformation + Final;
where the final energy includes the share of primary energy for direct use and the secondary energy.
The following figure describes the scheme of an energy balance that can be seen in a detailed form in Annex 3.
Figure 1: Schematic representation of primary, secondary, final and useful energy fluxes with indication of losses in the transformation centers in the final use. It should be mentioned that the final energy includes primary energy for direct use. In a more complete scheme it should still be considered other type of losses, exports and imports in the different phases as well as methodological or data adjustments.
The so-called final energy is final only from the point of view of the energy sector and represents roughly the form in which energy is commercialized. In each productive unit, industrial or agricultural, or in other consuming sectors, like the residential, commercial or public ones, energy has different uses such as motive, illumination, heating, etc.
To convert the so-called final energy into the form in which it is used it is necessary to submit it to a process that implies losses so it must be taken into account the efficiency of its use or yield. In the case of motive force, part of the energy is transferred to the motor's shaft and part is dissipated as heat. Yield is the ratio between this energy in the form it is used, called useful energy and the final energy, that is:
[Useful Energy] = Yield * [Final Energy]
In a general way, one can elaborate a Useful Energy Balance where:
[Final Energy] = [Useful Energy] + [Losses in use].
In useful energy balance uses are usually grouped in:
In order to elaborate a useful energy balance it is necessary to have for each sector the final energy used by energy source as in the example of Table 1. For each energy source it is necessary the distribution in the different uses and the yield in each one of these uses. Adding the useful energy values has the advantage of taking into consideration the different yields for the same use of the different energy sources.
Nevertheless, adding up the elements representing the different uses in useful energy has the inconvenient of valuing that depends on the type of use. For example, a fuel like firewood is used for generating process heat in an industry of say 75% efficiency. Diesel oil is used in the same industry for generating motive force with 30% efficiency. When added up in the form of useful energy they show a merit factor that does not corresponds to their potentialities. Actually, diesel oil could be used with a higher efficiency than that of firewood for process heat and when used as motive force it would also present an efficiency much higher than that obtained from firewood in a steam engine.
In other words, in spite of their larger potentiality or because of it, diesel final energy is shown as multiplied by 0.35 and that of firewood, by 0.75.
In order to take into account these differences we will use in the present work, besides the useful energy concept, the equivalent energy concept. In this concept, efficiency of each energy source will be compared to the efficiency of a reference source for the same use. Energy will be expressed in tons equivalent petroleum - toe - aiming at keeping the usual units used in this type of work.
In most cases natural gas was used as reference. In the mentioned example, firewood, mineral charcoal, fuel oil - and eventually diesel oil itself - would be compared to natural gas for the purpose of heat generation. For motive force purpose, diesel oil would also be compared to natural gas for the same end use.
In the mentioned case, natural gas would be considered as having an efficiency of 85% for heat generation and 25% for motive force. The equivalencies obtained would be more independent of the form of using it.
That is, considering the yield of any energy source i and the reference yield r, one would have:
Natural gas has been chosen as the reference energy source due to its large flexibility in the industrial, residential and commercial sectors and when available, in agriculture as a heat source. For the transport sector (motive end use) it would be logical to use a liquid fuel of large use (diesel or gasoline). Gasoline presents the same yield as that of natural gas (NG) in the Brazilian Useful Energy Balance. We have chosen gasoline as the reference fuel and we express the results as "NG equivalent". In the specific use of electricity we have used the analogous procedure used in the Brazilian National Energy Balance - BEB ( R3 ) to express equivalent energy in order to account for hydraulic energy which is valued as thermal energy necessary for generating one kWh of electrical energy.
Useful Energy and Final Energy Balance
The process of obtaining the Useful Energy Balance is detailed in (R2). The economy is divided into consumption sectors linked to industrial, transport and other activities. The split terms adopted in this work, very close to that of OECD, are shown in Table 5.
Schematically, one has for each of these factors a column of final consumption for each energy source and, for the same sector, it is given a distribution of the different energy sources by end use. There is also for each end use and each energy source the yield of the energy source for this end use.
The useful energy for each energy source in the considered sector (residential in the example of Table 1) will be obtained by multiplying the final energy value (2nd column) by the corresponding distribution and yield values as indicated in the table. It is also shown on the last column the useful energy addition in their different forms.
Table 1 Simplified example for the residential sector in order to obtain the useful energy from the final energy.
In order to express in terms of equivalent energy, each energy source would be represented in terms of NG equivalent. The reference yields used would be those relative to NG, that is, in a given sector, for a determined energy source one would have:
In the case of specified uses of electrical energy it is considered the energy in NG necessary to generate the consumed electrical energy. It was considered that the electrical energy would be generated from NG with efficiency of 28%.
The equivalent energy can be calculated in a similar way to that of useful energy with help from Table 2. This table is analogous to Table 1 for useful energy where the absolute yields were substituted by relative yields.
Table 2. Simplified example of obtaining the equivalent energy value from final energy.
Note: In this table [EE(i,j) = FE(I,j) x D(i,j) x Rr(i,j), for example, for electricity the equivalent motive energy is 4,800 = 4,000 x 0.40 x 3.
In the quick process shown here, for reasons to be mentioned below, it is proposed to use the average relative efficiency for each energy source in each sector, indicated on the last column as in the table's example, in order to evaluate the equivalent energy in different countries. This average relative efficiency would be the conversion factor between the final and the equivalent energies in the considered sector.
Results for Brazil in 1993
In the simplified example of Figure 1 it was considered a closed cycle where there would be no exports and imports of primary or secondary energy. In a national energy balance it is necessary to consider these fluxes.
In Brazil the external energy trade in the form of secondary energy corresponds only (export and import average) to about 10% of the final consumption. The primary, final, useful and equivalent energies represent approximately the real relation among primary energy production, final consumption and end use in a closed cycle. As it will be shown in Annex 2, the particular form to account for hydraulic energy is not invalidated by this fact.
In Figure 2 the primary, final and useful energies are presented. Roughly, the differences between the two first columns represent the losses occurred in transformation and the difference between the second and third columns are losses due to the end use. The equivalent energy would be the quantity of (final) energy from natural gas necessary to supply to heat generation and motive force end uses added to the (primary) energy to generate from NG the electricity necessary to supply to the specific uses or almost specific such as: electrochemical, illumination and others, (such as electronic equipment).
Figure 2. Primary, final and useful energies (Brazil - 1993) and the equivalent energy that corresponds to NG consumption in order to supply to the primary energy demand necessary to generate electricity for the specific ends and to supply to further uses as final energy. In Figure 1 in Annex 3 are shown the values used as criteria for the Brazilian BEB and the calorific value.
For the 1993 practically all data necessary for evaluating the equivalent energy are available. These data are fundamentally the necessary ones for elaborating the Useful Energy Balance.
Applying the described concepts that is mentioned in the previous item we have in Brazil for 1993 the following distribution:
Table 3 - Energy distribution by Sector (thousand toe)
Figure 4: Equivalent energy values the more important end use of energy such a motive and electricity purpose. This has as a consequence that consumption in the transport, residential, public agricultural and husbandry sectors are comparatively larger in equivalent energy.
Table 4: Energy Distribution by End Use (million toe)
In Table 4 and Figure 5 one can notice that the relative distribution among the energy forms changes substantially by end use in the several criteria when energy is globally expressed, as it has been previously mentioned.
In the present case, one can observe that the low average efficiencies for electricity in the "others" end use (mainly illumination) reduces to a great extent the participation in this end use when expressed in useful energy.
As to the participation in the heat form, also in useful energy, it is increased because the yields considered are relatively high. The participation of heat (process heat plus direct heating) is higher than 50% when represented as useful energy.
Simplified Process for Evaluating Equivalent Energy in Other Countries
The values of relative efficiency among energy sources for each end use present less dispersion than that referring to useful energy as can be seen in Table 5 for the Food and Beverage Industry (Brazil 1993).
In Table 5 are presented the main energy sources involved (98% in final energy) and there is competition among the different sources for end uses like process heat and direct heating. We have indicated also the absolute coefficients used to obtain the useful energy and the relative coefficients used to obtain the equivalent energy.
In the third column of each sector the deviation in useful energy or equivalent energy is represented. These deviations were calculated for a hypothetical situation where 100 units of final energy initially equally distributed (50 for PH and 50 for DH) were distributed in the form of 60 PH and 40 DH. An eventual allocation error or a different technological situation in other countries that would cause a different energy allocation would cause larger alterations in the useful energy than in the equivalent energy when globally calculated for each sector. But a change in the electricity end use profile between motive force and heat generation would cause deviations in the two ways of calculating the energy.
Table 5: Examples for the Food and Beverage Sector (Brazil 1993) with variations caused by change in energy allocation between heat process (HP) and direct heating (DH).
(*) Energy deviation between a distribution of 50 PH and 50 DH and that of 60 PH and 40 DH.
This makes attractive to use the average results for each sector of final and equivalent energy for obtaining conversion factors to be used as a first approximation when the end use distribution and the efficiency for each energy source and use type are unknown.
The process has been previously described (e&e No 17 http://ecen.com) for a split in 3 macro sectors (industry, transport and others). In the present work we suggest coefficients to be used for obtaining an evaluation of equivalent energy using energy balances presented in the economic sectors split used by OECD. The concepts used are described in Annex 1.
The Useful Energy Balance 1993 (MME/Brazil) presents for each economic sector an efficiency matrix for each energy source and for each end use which represents the situation in the country in that year. It presents as well another efficiency matrix corresponding to the technologies already existent in other countries. The objective of that publication was to evaluate the potential of energy conservation in Brazil.
Since it is intended to use the average efficiencies to compare different countries, this second efficiency matrix was considered as most significant than those now used in Brazil where the efforts concerning energy conservation are much limited.
It should be emphasized that the option for another efficiency set does not introduce important alterations on calculating the equivalent energy. Actually, the variations of the relative coefficients are less important than the absolute ones since some energy source efficiency increments are possible both for any fuel and for the reference fuel (natural gas in the present case).
The final energy distribution for the end use of each energy source and in each sector was taken from BEU/MME, corresponding to the evaluated distribution for Brazil in 1993.
Heat as a by product of cogeneration, given in some OECD's balances was converted to equivalent NG using a factor of 1.
The data conversion of the OECD's energy balances from final energy to equivalent energy can easily be calculated from Table 6. An example for Germany is shown in Annex A4. It should be noticed that due to questions concerning correspondence between Brazil's Energy Balance and those published by OECD it was necessary to handle as a set four industrial sectors included as "others".
Table 6: Coefficients for converting final energy into equivalent energy for each economic sector in the form of OECD's balances.
(*) Others (industrial ones): Transportation Equipment, Mechanics, Wood
and Wood Products, Construction and those not specified in industry.
(R1) - Energy balances of OECD Countries 1995-1996 - International Energy Agency - OECD - 1998 Edition 349 page. Energy Statistics and Balances non-OECD Countries 1995-1996 - IEA - OECD
(R2) - Balanço de Energia Útil - Ministério de Minas e Energia MME - Electronic Version 1994
(R3) - Brazilian Energy Balance - Ministry of Mines and Energy - BEB - MME - Electronic Version 1999
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