Hydroelectric Power Not Free of Greenhouse Gases
CAPE TOWN, South Africa, December 1, 2000 (ENS) - The reservoirs
of many large dams built to generate hydroelectric power do
produce greenhouse gases, the World Commission on Dams says in a
comprehensive report issued earlier this month. This finding is
in contrast to the widespread assumption that such emissions are
zero or negligible.
"Greenhouse gases are emitted for decades from all 30 dam
reservoirs in the boreal and tropic regions for which
measurements have been made," the commission says.
The World Commission on Dams, based in Cape Town, South Africa is
made up of an international team of 12 experts. It is an
independent think tank set up and financed by aid agencies,
industry, governments, and non-governmental organizations to look
at what the commission calls "the good, the bad and the ugly
impacts of dams around the world." Established in 1998, the
Commission's mandate is to research, peer review and write the
most independent, authoritative and comprehensive cross
examination of dams and water and energy resource development
ever undertaken.
In its final report, "Dams and Development: A New Framework for
Decision-making," presented to the United Nations on November 17,
the commission writes, "All large dams and natural lakes in the
boreal and tropical regions that have been measured emit
greenhouse gases."
"Some values for gross emissions are extremely low, and may be
ten times less than the thermal option. Yet in some cases the
gross emissions can be considerable, and possibly greater than
the thermal alternatives," the commission writes.
The commission's findings were informed by the most recent
research on this issue in Canada, Brazil, French Guyana and
Finland.
In northern boreal climates like Canada and Scandinavia available
studies so far suggest that emissions from hydropower reservoirs
are low, the commission says.
For Brazil, of ten dams studied, emissions vary from dam to dam
with a 500-fold difference between lowest and highest. The lowest
emissions are on similar levels to Canadian lakes and reservoirs,
the highest annual gross emissions reach the ranges of thermal
energy plants, although life cycle assessment, and determination
of net emissions, is needed before definitive comparisons can be
made.
The flooded biomass alone does not explain the observed gas
emissions, the commission says. "Carbon is flowing into the
reservoir from the entire basin upstream, and other development
and resource management activities in the basin can increase or
decrease future carbon inputs to the reservoir," according to the
commission's report.
The commission advises that hydropower cannot be automatically
assumed to emit less greenhouse gas than the thermal alternatives
which use fossil fuels to generate power. Net emissions should be
established on a case by case basis.
Hydroelectricity provides for 80 percent of all the renewable
power generated in the United States, and provides about
one-fifth of the world's electricity. Of the 75,000 dams in the
U.S., less than three percent have hydroelectric generating
stations, according to the National Hydropower Association (NHA),
an industry organization representing 61 percent of non-federal
hydroelectric capacity in the United States.
Ideas for generating electricity with water but without building
dams to hold back rivers in reservoirs are in development,
according to the NHA. Because no reservoirs are created, a free
flow method for generating power may not create greenhouse gas
emissions.
The NHA says an idea that is ready for field testing would use
tidal or river currents to generate electricity without
impounding water behind a dam. Requiring a current of three knots
or better, these submerged units would be clustered together to
generate from 300 kW to as much as 300 MW. They could be used
either on or off the grid, providing power that is "cost
competitive with other intermittent renewable energy sources,"
the association says.
In Canada, hydropower represents 62 percent of the electricity
production. The Canadian Hydropower Association joined with the
International Hydropower Association and the International Energy
Agency in writing a report issued on November 21, "Hydropower and
the World’s Energy Future." The report declared hydropower to be,
"the main supply of clean, renewable energy, and as an energy
that will play a key role in the future world energy mix."
"One way to reduce greenhouse gas emissions while continuing to
supply the growing energy demand is to increase the development
of clean, renewable energy sources such as hydropower," says
Canadian Hydropower Association executive director Pierre Fortin.
The World Commission on Dams does not condemn all dam reservoirs
as greenhouse gas emitters. The commission calls for "explicit
assessment of future net greenhouse gas emissions of a project"
through full life cycle assessments to compare available options.
For the hydropower option, the commission proposes guidelines to
assist in these assessments. These include measuring carbon flows
in the natural pre-impoundment watershed and assessing how these
will change following dam construction.
The commission calls for further research to improve current
understanding of how greenhouse gases cycle within existing basin
and reservoirs and to improve capacity to predict future net
emissions of new reservoir projects.
The 12 commissioners who make up the World Commission on Dams
represent a wide range of interests including commercial
engineers, academics, activists and administrators of government
agencies. To learn more about the commissioners, visit:
http://www.dams.org/about/commissioners.htm
SOURCE: Environment News Service (ENS)
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