Hydropower- A Catalyst for Climate Change Mitigation

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Overview

Large hydropower plants make up 16% of the global energy supply, in some newly industrializing and developing countries the proportion of hydro power accounts for nearly 100% of the total energy generation of the country. In the context of there is a growing awareness towards the potential of hydro power to contribute to future energy demands by simultaneously moving economies to a lower-carbon future. The lifecycle energy payback ratios (the ratio of total energy produced during a system’s normal lifespan, divided by the energy required to build, maintain and fuel it) for well-performing hydropower plants (high energy yield pro water surface) still reach the highest values of all energy technologies.

Emissions

Nevertheless, studies show that hydropower is not always carbon neutral. Reservoirs can be sources of green house gas (GHG) emissions, such as carbon dioxide (CO₂) and methane (CH₄) resulting from the decomposition by bacteria of the biomass that was either submerged due to impoundment, that enters the reservoir from upstream inflows or that grows within the reservoir itself.

Up to date it is not clear how strong GHG emission from reservoirs contribute to the global GHG emissions. Quantification of the GHG status of a reservoir requires consideration of exchanges before and after its construction. But there has been no scientific consensus on how in fact to go about measuring the GHG status of freshwater reservoirs. The GHG Research Project.

Noting the scientific uncertainties concerning GHG emissions from reservoirs and that these uncertainties will not be resolved in the short term, a simple and transparent criteria, based on thresholds in terms of power density (W/m2), are to be used to determine the eligibility of hydroelectric power plants for Clean Development Mechanism (CDM) project activities.

The United Nations Framework Convention on Climate Change (UNFCCC) classified three categories:

1. Hydroelectric power plants with power densities (installed power generation capacity divided by the flooded surface area) less than or equal to 4 W/m² cannot use current methodologies;
2. Hydroelectric power plants with power densities greater than 4 W/m² but less than or equal to 10 W/m² can use the currently approved methodologies, with an emission factor of 90 gCO2eq/kWh for project reservoir emissions;
3. Hydroelectric power plants with power densities greater than 10 W/m² can use current approved methodologies and the project emissions from the reservoir may be neglected

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Further Information

• Barros et al. (2011): Carbon emission from hydroelectric reservoirs linked to reservoir age and latitude. Nature geosciences Vol. 4, pages: 593–596.
• Fearnside P.M. (2004). Greenhouse gas emissions from hydroelectric dams: Controversies provide a springboard for rethinking a supposedly 'clean' energy source - An editorial comment. Climatic Change, Vol. 66, Issue 1/2
• Kosten, S. et al. (2010). Climate-dependent CO₂ emissions from lakes. Glob. Biogeochem. Cycles, Vol. 24, GB2007
• St. Louis, V.L., Kelly, C.A., Duchemin, E., Rudd, J.W.M., & D.M. Rosenberg (2000). Reservoir surface as sources of greenhouse gases to the atmosphere: a global estimate. BioScience, 50, 766-775
• IPCC Special Report on Renewable Energy Sources and Climate Change Mitigation, Chapter 5 Hydropower (2011). Prepared by Working Group III of the Intergovernmental Panel on Climate Change [O. Edenhofer, R. Pichs-Madruga, Y. Sokona, K. Seyboth, P. Matschoss, S. Kadner, T. Zwickel, P. Eickemeier, G. Hansen, S. Schlömer, C. von Stechow (eds)]. Cambridge University Press, Cambridge, United Kingdom and New York, NY, USA, 1075 pp.
• UNFCCC/CCNUCC- Executive Board 23, Report, Annex 5, page
• Hydro Portal on energypedia
• Carbon Markets for Small Hydro Power