ECOLOGICAL FOOTPRINT OF HYDROPOWER[*]
GENERATION CHAINS
RUAN SHIPING
Dr., engineer,Nanjing Hydraulic Research Institute (NHRI), China
XU SHIKAI
Dr., professorate senior engineer,NHRI, China
TONG ZHONGSHAN
Dr., senior engineer,NHRI, China
WANG YONG
Engineer, NHRI, China
ZHANG YING
Master, NHRI, China
- INTRODUCTION
Preserving our natural environment and mankind's development of society are complementary to each other. During the early stage of the society, due to the underdeveloped economic and small population, nature resources are in littledemand and the environmental impact of the human race on was slighter. With the development of economic and the increase of population, the contradiction of increasing energy demand with the limited bio-capacity becomes more and more evident, which has become the key factor and primary problem restricting economic and social development.
Hydropoweris an important material foundation for the development of the society. As a resource, it cycles in natural world, so its development and utilization will certainly have an impact on the ecological environment and the impact degree corresponds to the amount of nature it occupies to produce. Take China’s hydropower for example, in the period of 1980-2000, constructions of 34 high dams, its height greater than over 100m, have been/have been being finished. Since the new century, 28 dams overof height greater than 100m have been being/will be constructed, in among which arch dam of the Jinping Hydropower Station grade 1 reaches new height of 305m. They, no doubt, will play greater role in the developments of China.But on the other hand, with the raising of the environmental awareness of the whole society, many issues such as effects of hydropower project on ecological environment, establishment of eco-water resources become increasingly concerned[1].
Ecological footprint theory was employed to estimate the effects of hydropower generation chains on the needs of carrying capacity of natural resources and services, of the earth ecosphere and the results were changed into quantitative biologically productive area, i.e., ecological footprint of the hydropower generation chains.
2. THEORY OF ECOLOGICAL FOOTPRINT
Ecological footprint concept was firstly used by Wackernagel and Rees (1996), it associates human resource consumption to six different land categories (cropland, pasture, forest, fishing ground, built-up land for infrastructure, fossil fuel land to absorb anthropogenic carbon emissions)[2].Through following the tracks of consumption of energy and natural resources of a region, these consumption patterns provide information of areas, showing each type of land necessary for providing these material resources. By comparison of these different areas providing natural resources, we can quantifiable judge the scope within which that area’s capacity to provide can be developed.Ecological footprint theory has been widely used all over the world in various zone scales and various social fields and the interesting areas include the footprints of the earth[3,4],the footprints of nations and regions[5], the footprint of cities andthe footprint of industries[6].
3. ECOLOGICAL FOOTPRINT OF HYDROPOWER GENERATION CHAINS
Ecological footprint is defined as land areas to meet the needs of human being consumption and waste absorbability [7]. In this paper ecological footprint of hydropower generation chainsis defined as biologically productive areas of requirement for resources use and waste absorbability in the period of hydropower project construction.
Ecological footprint includes three functions of ecological system: space occupation of resources supply, waste absorbability and basic establishment. Ecological footprint of hydropower generation chains consists of two parts: direct and indirect biologically productive areas occupation.The former is biologically productive areas of the main structures and their accessorial permanent hydraulic structures, such as forest, cropland, fisheries area and pasture, and is transferred as built-up land. The latter is land occupation about construct facilities, equipment, construct materials,workersand the land to absorb the GHG from reservoir during the hydropower generation(shown in Fig.1). Because of the lack of energy consume data, dam retire was not ignored in this study.
Fig.1 Ecological footprint of hydropower generation chains
Ecological footprint of hydropower generation chains is the sum of ecological footprints during project construction and during project operation, and expressed as:
[1]
where is ecological footprint the hydropower chains in global hectare (gha); is ecological footprint of during project construction, gha; and is ecological footprint of during project operation, gha.
and can be calculated with following formulas:
[2]
[3]
where is the land area of the ithtype, ha; is the equivalence factor the ith type land, it represents the world average potential productivity of the ith type land relative to the world average potential productivity of all bioproductive area, gha/ha；is the yield factor the ith type land, it describe the extent to which a biologically productive area in a given country is more (or less) productive than the global average of the same bioproductive area, dimensionless。The values can be acceded fromreference[8].
Formula [2] and [3] can be simplified according to the main environmental impacts of the project during the life-cycle of the project.
During the construction stage, main environmental impact is the GHG from the generation and transportation chains of building materials such as steel and cement. So formula [2] can be written as:
[4]
where the subscript “Fossil” means fossil fuel land reserved to absorb the GHG.
Immediately after power-dams are filled, carbon dioxide and methane form during the decomposition of organic matter. In dams, the source of organic matter may be submerged pre-existing biomass, dissolved organic carbon and particulate organic carbon (DOC and POC) swept down from neighboring onshore areas, as well as biomass generated within the dam itself. At the oxic water level, CO2 is produced through aerobic decomposition of DOC and POC, with methane oxidization generated at lower water levels. For organic matter in anoxic sediments, bacterial decomposition takes place through methanogenesis, resulting in CH4 and CO2.Simplified formula [3] can be expressed as:
[5]
where the subscript “Build” meanssubmersedbioproductive area; and the subscript “Fossil” means fossil fuel land reserved to absorb the GHG from reservoir.
4. Estimating the ecological footprint of hydropower Generation chains in China
Tab.1 presents statistics data of steel and cement consumption and the embodied GHG of more than 100 hydropower stations in China.
Tab.1 Steel and cement consumption and the embodied GHG of hydropower stations in China[9]
Items / Earth-rock dams / Concretedams / Building materialconsumption / Embodied CO2
Installed capacity / 1.81×103MW / 2.428×104MW
Steel / 90kg/kW / 90 kg/kW / 90 kg/kW / 90×3.63kg/kW
Cement / 680kg/kW / 810 kg/kW / 800 kg/kW / 800×0.925 kg/kW
Footprint calculation of fossil fuel adopted waste assimilation and the ocean absorbs C of 1/3[10]. The absorbability rate of average forest was 5.2t/ha.yr to CO2, and 1.42t/ha.yr to C [6].
Due to a high variation in the productivity of land inundated by hydropower reservoirs and the lack of data documenting their distribution, this area receives a world average equivalence factor of 1.0 and a yield factor of 1.0[8].
Take the generation chain of 1kW.h hydropower for example (assuminga lifetime of 100 years). The ecological footprint can be calculated as follows:
where =1.1; =1.0.
The average value of inundated area of large and medium-scale hydropower stations in China is 1.1×10-2m2/kW.h, the CO2 emission is 7.63gCO2-equiv./kW.h; the CO2 emission of small-scale power stations is 180.3gCO2-equiv./kW.h, and the weighted average CO2 emission is 173.3gCO2-equiv./kW.h[9].
where =1.0; ＝1; ＝1.
So the ecological footprint of 1kW.h hydropower is 0.2071gha. If we assume a load factor of 0.6, the value will be 0.3452gha, i.e, and the generation of 1kW.h hydropower needs 0.3452gha bioproductive land for the nature service to supply the demand of space occupationof resources supply, waste absorbability and basic establishment.
5. CONCLUSIONS
This paper qualified the indirect environmental impact of hydropower generation chains, gave the value of China 0.3452gha/kW.h. The result shows that the GHG emission during the operation stage is the main factor on environmental impact and which during the building stage is negligible.
REFERENCES
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[3]Wackernagel, M., Onisto L., Bello P. National natural capital accounting with the ecological footprint concept [J].Ecological Economics. 1999, 29(3):375-390.
[4]WWF. Living planet report 2004 [EB/OL]. publications/general/livingplanet/lpr04.cfm, 2004.
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[6]Barrett, J., Vallack, H., Jones, A., Gary, H. A Material flow analysis and ecological footprint of York [EB/OL]. footprint.html. 2004.
[7]Lenzen, M., Lundie, S., Bransgrove, G., Charet, L., Sack, F. Assessing the ecological footprint of a large metropolitan water supplieris lessons for water management and planning towards sustainability[J]. Journal of Environmental Planning and Management. 2003, 46 (1): 113-141.
[8]Monfreda, C, Wackernagel, M.,Deumling, D.Establishing national natural capital accounts based on detailed Ecological Footprint and biological capacity assessments [J]. Land Use Policy. 2004, 21(3): 231-246.
[9]Ma Zhonghai. Study on GHG emission of some main energy resources in China [D].China Institute of Atomic Energy, 2002.
[10] Wackernagel, M., Monfreda, C., Moran, D., Goldfinger, S., Deumling, D. and Murray, M., National footprint and biocapacity accounts 2004: the underlying calculation method[EB/OL]. 2004.
Abstract: Hydropower, which is a clean energy, plays an important part in the national economy and the society development. However, over the past decade, the effects of hydropower generation chains on ecological environment have been paid good attention to from project research to project practice and have greater advances so that the functions of hydropower projects have greatly changed.
In this paper, ecological footprint theory and life-cycle assessment were introduced to account for the environmental burdens associated with the creation of 1 kW.h of energy by taking into account mass and energy flows at each step of the procedure, the ecological footprint concept and model of hydropower generation chains were developed. Such an analysis quantifies the indirect emissions attributed to the different economic sectors that contribute to the creation of the hydropower.
Key words: hydropower generation chains, ecological footprint, life-cycle assessment
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[*]Supported by Key Projects in the National Science & Technology Pillar Program during the Eleventh Five-Year Plan of china (Grant No: 2006BAC14B03).