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Comparison of IEA and e&e/MCT results
Olga Mafra, Frida Eidelman
The International Energy Agency (IEA) is an autonomous body which was established in November 1974 i of the Organization for Economic Co-operation and Development (OECD) to implement an international energy program.
In the past few years, there was a fundamental change in the way governments consider energy issues and their connection with environmental matters, mostly the greenhouse gases emission – GEE. Therefore, the IEA started to publish data on GEE emission such as the report entitled “CO2 Emissions from Fuel Combustion” (2007) that provides statistics on CO2 emissions from fossil fuel combustion for nearly all countries worldwide from 1971 to 2005. The data presented in this publication comprise energy emissions but it does not include all the emissions from the inventory made by the countries to the UNFCCC Secretariat.
Among other data, CO2 total annual emissions, CO2 emissions/GDP and per capita CO2 emissions are provided.
The methodology utilized by IEA to estimate CO2 emission from fuel combustion is that from IPCC Guidelines (1996) that includes the Reference approach and uses the Total Energy Supply in the country (Top-Down) with IEA Energy Balances that are based on national balances of each country. Sector data are also presented taking into account the sectors in which each fuel is used (Bottom-Up). Since more detailed methodologies can be utilized by different countries to calculate their inventories, some differences in the emission values may occur.
The Economy & Energy Organization – e&e uses to calculate its CO2 emissions the same approaches (Reference and Sectoral) as those of the IEA and energy data from the “National Energy Balance” (Balanço Energético Nacional - BEN).
Besides, e&e has developed the bal_eec software that produces tables and graphics from the consolidated energy balance of the “National Energy Balance” and from carbon emission coefficients used in the first Inventory on Greenhouse Effect Sources under the responsibility of the Ministry of Science and Technology (MCT). The software, available in the web (http://ecen.com), presents various options regarding the types of values that will produce output tables. The tables are presented in toe (tonne of oil equivalent), boe (barrel of oil equivalent), carbon mass, CO2, CH4, CO, N2O, NOx and NMVOCs emissions, Bottom-Up Carbon emission, Top-Down Carbon emission and carbon values not emitted in fuel combustion.
The gases emission data are submitted to a consistency control by the calculation of the Carbon Balance to make sure that all the carbon from the fuels was taken into account as emitted or retained carbon.
It is worthwhile to say that e&e uses the Lower Heating Value adopted in BEN since 2003, year base 2002, to define the toe unit (1 tep = 104 Mcal), that was not usual when the Initial Inventory was made and in the reference studies on which it was based. Because of that, as one compares the results obtained by the software with those from the Initial Inventory, it should be taken into account that though the primary data source is the same, the Lower Heating Value conversions are slightly different.
Like IEA, the e&e program utilizes the carbon emission factors, the retained carbon factors and the non-oxidized correction for petroleum, mineral coal and natural gas (NG) recommended by the IPCC, therefore the results are directly comparable.
Comparison of Top-Down Results
In this paper, some results obtained by the IEA for Brazil are compared with those calculated by Economy & Energy using the bal_eec software. In Table 1 the CO2 emissions (millions tons/year) for some years from 1971 to 2005 are presented. These data were obtained using the reference approach (Top-Down) for non renewable energies. The consistency between the two sets may be considered quite satisfactory. Actually they are as low as 2% since 1990. The larger discrepancies refer to previous years.
Table 1: CO2 emissions (Top -Down or Reference Approach) million tons
It was not possible to know if IEA considers in the Top-Down calculations the non used Natural Gas (burnt at the extraction due to the impossibility of utilization). However, it is evident that the NG combustion emissions in the production processes were not taken into account in the total Bottom-Up approach. .
Table 1 A compares CO2 emissions obtained by IEA with those calculated by e&e without considering those emissions for non-used NG.
Table 1 A: CO2 emissions (Top-Down or Reference) - million tons
( without considering those emissions for non-used NG)
The e&e considered natural gas, coal and its products and petroleum and products (including the liquids of natural gas) and other non-renewable resources. Therefore, all the emissions that do not result directly from the combustion of mineral coal and products and from natural gas are assigned to petroleum
In Table 2, the total CO2 emissions (in millions tons) are presented from 1971 to 2005 in the sectoral approach for non-renewable energy types. These data are comparable to those obtained by the Bottom-Up through coefficients and considering the final energy consumption and that of the power plants (Public Service and Autoproducers). Coal, petroleum and natural gas were also considered here.
Table 2 presents a comparison between data obtained by e&e (considering or not the emissions from non-used NG) and those by obtained by the IEA. From this comparison it is clear that, at least in the so-called sectoral approach, the IEA does not consider this kind of emission. See, for example the values for 1971 and the next years.
Table 2: Comparisons of the results of Natural Gas emissions
(million CO2 tons/year)
obtained by e&e and by IEA
(considering or not the emissions from non-used NG)
Table 3 presents a comparison between CO2 emission values obtained by e&e and IEA in millions tons in the sectoral approach (or Bottom-Up). It was observed a good data consistency throughout all the period, since the results by e&e and IEA are quite close, with differences not higher than 3%.
Table 3: CO2 emission
(Sectoral Approach, not including the emissions from non-used NG)
Tables 4, 5 and 6 present the sectoral results sorting out CO2 emissions from Coal, Petroleum and Natural Gas.
Table 4: CO2 emission from Mineral Coal and its derivates
(Sectoral Approach) million tons
Table 5: CO2 emission from Petroleum and its products
(e&e values include NG products and a small portion of other non-energy use)
For Coal, the e&e values are always higher than those of the IEA and for Petroleum they are always lower, a fact that makes us assume that when considering Coal, Petroleum and their products different allocation of products were considered by the two organizations.
Table 6 compares Natural Gas emissions.
Table 6: CO2 emission from NG in million tons
The Figure below compares the emission values by fuel calculated by both institutions using the sectoral method.
Figure 1: Comparison between CO2 emissions obtained by e&e and IEA for the various fuels source.
The Carbon Balance indicates the carbon emitted in the energy activities in Gigagrams. To make a comparison with the IEA data, it is necessary to convert the data in CO2 mass (C mass x 44/12) and divide it by 1000. Table 7 shows the CO2 mass obtained from Carbon mass, by subtracting the non-used NG that is not considered directly by IEA.
Table 7:Conversion of Carbon mass to CO2 mass for the year 2000
(*) Without considering the non-used NG fraction that was not included by IEA.
The values shown in the table correspond to the total amount of emitted carbon. In fact, there is a small fraction of carbon that is emitted in the form of other carbon compound gases. So, the whole amount of carbon from fuels is not emitted as CO2. To avoid double counting, e&e calculations take into account also the carbon emission from other gases involved in the greenhouse effect so as to maintain the carbon balance. The emitted CO2 value is, thus, slightly lower than those shown in the table presented above. Table 8 presents the values of greenhouse effect gases mass, the carbon emitted and the corresponding CO2.
Table 8: Values of the of GE gases shares for the year 2000 million tons
In the IEA data, heat generation is calculated together with co-generation what prevents the comparison of data corresponding to industry and electricity generation.
As an example, the values obtained by e&e are compared with the values obtained by IEA for Brazil in 2005: in Table 9, for the transport sector, in Table 10, for road transport sector and in Table 11 for Residential Sector. Only fossil fuels were considered.
Table 9: CO2 emission for the Transportation Sector (Total)
for the year 2005 - million tons
Table 10: CO2 emission for the Road Transportation Sector
for the year 2005 - million tons
Table 11: CO2 emission for the Residential Sector
for the year 2005 - million tons
As one can observe in the tables, the data consistency is quite good. The conclusion one can arrive at through data comparison is that the values obtained by e&e concerning Carbon Balance are consistent with the expected error percentage (about 5%). It should be remembered that both evaluations utilize mainly carbon emission values from IPCC and energy data obtained in the National Energy Balance. These facts make especially useful the comparison made in this paper that enables detection of eventual discrepancies and constitutes a valuable consistency test. The consistency between the values was found in the total (throughout the years) as well as in the several energy sources and in the sectoral activities.
Some discrepancies pointed out, though, should require attention later. It must be stressed that in the e&e case, sectoral coefficients are being generated for the Second Brazilian Inventory, based on the type of energy use in each sector to improve the evaluations available at the moment. From these new results, the comparisons shall be repeated, including also non-CO2 greenhouse gases emissions.
 It should be noted that for these years the difference of the two IEA calculations is larger.
 It may be separately calculated as fugitive emission..
 It is considered fuel consumption in each sector and the emission coefficients (carbon mass in each GEE/energy), as evaluated in the First National Inventory, between 1990 and 1994.
 Evaluated by IEA.
Graphic Edition/Edição Gráfica:
Monday, 16 February 2009.