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ELECTRICITY IN THE BRAZILIAN ENERGY BALANCE – BEB
João Antonio Moreira Patusco Approach: analysis of the relative participation of hydraulic power and electricity in the offer and consumption of energy in Brazil and comparison with other countries, taking into account different criteria for conversion factors for the common unit adopted. CONVERSION COEFFICIENT FOR HYDRAULIC POWER AND ELECTRICITY IN BEN The tonoilequivalent (toe) is the common unit used to convert the measuring units of different forms of energy used in BEN. The conversion factors are calculated based on the superior calorific power of each energy source relative to that of petroleum, namely 10,800kcal/kg. For hydraulic power and electricity offer and demand it is used the factor of 0.29 toe/MWh, resulting from the ratio between the average consumption of fuel oil in kcal/kWh in the Brazilian thermoelectric plants and the superior calorific power of petroleum (3,132/10,800). Therefore, it is the factor that represents the thermal equivalence of electrical generation. Note: 3,132 kcal/kWh corresponds to a thermal generation average efficiency of 27.5%. Should the theoretical criterion for hydraulic power and electricity be used, where kWh =860kcal (according to the first principal of thermodynamics), the conversion factor would be 0.08 toe/MWh (860/10,800), therefore 3.62 times smaller than the one used in BEN. Note: the use of the superior calorific power barely modifies the results in toe, since in order to calculate the conversion factors, the numerator and denominator are practically proportionally altered. HISTORICAL PRECEDENTS At the start of the seventies, when the first reports containing energy data consolidation were started in Brazil, the international literature on energy balance indicated for hydraulic power the preponderant use of thermal equivalence factor. This criterion was based on making comparable the offer of energy from countries with high and low participation of hydraulic generation. Therefore, hydraulic power factors varying from 0.20 to 0.30 toe/MWh were used, depending on the average efficiency of the thermal power plants. For the offer and consumption of electricity, the theoretical criterion was used, namely, 0.080 toe/Mwh. Therefore, the consolidated balances presented high losses (fictitious) by transforming hydraulic energy into electricity, due to accounting hydraulic power as thermal equivalency. By the previous reason, Brazil adopted for electricity offer and demand the same criterion of thermal equivalence (0.29 factor). As a matter of fact, from the seventies on the international energy balances have substituted the thermal equivalence criterion by the theoretical one in hydraulic power accounting, which did not occur in BEN/BR. As examples we mention the recent energy balances from the International Energy Agency, the World Energy Council, the LatinAmerican Energy Organization, etc. The thermal equivalence criterion is applied only to nuclear, solar, wind and geothermal energies. EFFECTS OF CONVERSION FACTORS FOR HYDRAULIC POWER AND ELECTRICITY ON BEB Table 1 presents 1997 data from the Brazilian Internal Energy Offer – IEO, considering both accounting criteria for hydraulic power and electricity – h&e (0.29 and 0.08 conversion factors). TABLE 1
As one can notice, the IEO changes from 242.7 million toe by the thermal equivalence criterion to 175.7 million toe by the theoretical criterion – a reduction of 28%. Still by the theoretical criterion, h&e changes its participation in the IEO from 14.6% to 38.2%, according to the other criterion – 23,6 percent points less. As a consequence, the renewable energy has also its relative participation considerably reduced, loosing 15.8 percent points. The graphic below shows the evolution indexes of the GNP and of IEO, the last one according to both criteria for h&e, taking 1970 as basic year. EVOLUTION INDEXES OF GNP AND IEO Since h&e was the energy source group that had the largest growth in the period 1970/1997, one can observe, due to the fact that its conversion factor is diminished, the IEO presents smaller growing rates, showing in the period an elasticity smaller than one, relative to the GNP.
EVOLUTION OF ENERGY AND GNP An analysis of the effects on the final energy consumption can be made through the data from table 2 where it is also introduced the concept of useful energy, namely the calculation of the relative participation considering the use efficiency of the energy sources in the final use equipment such as boilers, furnaces, dryers, motors, etc. TABLE 2 FINAL ENERGY CONSUMPTION – 1997
It can be noticed that electricity has its participation abated by using the theoretical criterion but recuperates part of the participation when calculated in useful energy. This is due to the larger efficiency of the equipment used in electricity relative to the national average. Compared to other countries and considering the theoretical criterion, the data of table 3 show that Brazil presents electricity participation in the final energy consumption similar to that of the developed countries, between 15% and 20%. Nevertheless, from the point of view of the offer, when one analyses the origin of electricity for the different countries, it is noticed that in Brazil, due to the high hydroelectricity, only 16.8% of the internal energy offer – IEO – is intended for electricity while other countries have this value between 32% and 40%. As a consequence, these countries present high loses in transformation – energy quantities between 18% and 28% of the IEO ( themoelectric generation losses). TABLE 3 ELECTRICITY IN SOME COUNTRIES
CONCLUSIONS In the energy prospective studies, where the competition possibilities among energy sources are analyzed, the end use, the equipment efficiency and captive uses are the variables used and therefore, for electricity, the theoretical criterion is valid. Therefore, from the technical point of view, there is no restriction on using one or the criterion for representing the figures of hydraulic power and electricity in Energy Balances. Advantages of maintaining the 0.29 toe/MWh factor:
Disadvantages of maintaining the 0.29 toe/MWh factor:
AUTHOR’S SUGGESTIONS Gradual introduction of the theoretical criterion in BEN, initially with simultaneous presentation of both criteria in some tables of chapter 1 (including that of useful energy) and extensive distribution of this Technical Note in BEN itself and via Internet. SOME CONCEPTS Measurement Units (Commercial) – units that usually express the commercialized quantities of energy sources, for example: for solids, ton (t) or pound (lb), for liquids, cubic meter (m^{3}) or barrel (bbl), for gases, cubic meter (m^{3}) or cubic foot (ft^{3}) and for electricity, watt(W) for power and watthour (Wh), for energy. Common Unit – unit to which the measurement units used for different forms of energy are converted. This unit allows for adding different energy quantities in the Energy Balances. According to the International Unit System – IS, joule or kilowatthour are the regulated units used as Common Unit but other units are currently used by different countries and international organizations such as equivalent tonoilequivalent (toe), toncoalequivalent (tce), calorie and its multiples, British thermal unit (Btu), etc. Conversion Factors (coefficient of equivalence) – coefficients that permit transforming quantities expressed in measuring quantities to quantities expressed in a common unit. For example, in the case of Brazil, in order to convert tons of wood into toe, the 0.306 coefficient is used, which is the ration between the calorific power of wood and that of petroleum (3,300 kcal/kg/ 10,800 kcal/kg), that is 1t of wood = 0.306 toe. Calorie (cal) – quantity of heat in kcal necessary to raise the temperature of one gram of water from 14.5^{o }C to 15.5 ^{o }C at normal atmospheric pressure (760 mm Hg). Calorific Power – heat quantity in kcal produced by 1kg or 1m^{3} N of fuel after complete combustion. Note: the fuels that produce H2O in the combustion products (derived from combustion or from impregnated water) have a superior calorific power and a lower calorific power. Since most of the time H2O escapes through the chimney as vapor, the inferior caloric power is the one that is practically significant. watt (W) – Power unit – watt is the power of an energy system in which the energy of 1 joule is uniformly transferred during 1 second. watthour – (Wh) – energy uniformly transferred during 1 hour. 1 Wh = 1 ´ 3,600 s ´ J/s= 3,600 J = 3,600 ´ (0.239 cal) = 860 cal Therefore, in the theoretical concept 1kWh = 860 kcal Note: watt, watthour and their multiples are measurement units used for hydraulic power and electricity, for power generation and distribution. joule (J) – Work unit for energy and quantity of heat. Joule is the work produced by a force of 1 newton whose application point moves 1 meter in the force’s direction. 1 J = 1 N. m newton (N) – Force unit. Newton is the force that, when applied to a body with 1 kilogram of mass, transmits the acceleration of 1 meter per second squared. Considering the acceleration of gravity as 9.806 m/s2, one has 1 N = 0.102 kg Internal Energy Offer is the quantity of energy available for transformation and/or final consumption. Therefore it gives the energy before the transmission and distribution processes. Final Energy Consumption is the energy consumed by the different sectors of the economy to satisfy the needs of different uses such as heat, motive power, illumination, etc. It does not include quantity of energy used as raw material for the production of any other form of energy. Note: except for statistical adjustments, the difference between Internal Energy Offer and Final Energy Consumption correspond to adding the losses in distribution and storage to losses in the transformation processes (refineries, distilleries, electrical power plants, coking, etc.).
