October 06, 2007

HydroPower - Is it clean or not?

Opponents of dams have long argued against putting barriers in the natural flow of a river. Dams, they point out, prevent endangered fish from migrating, alter ecosystems, and threaten the livelihoods of local communities.

Native Americans, fishing communities, and environmentalists have made these arguments in their quest to decommission four dams on Klamath River, which runs from southwest Oregon to the coast of California. But with California requiring a 25 percent reduction in the state's carbon dioxide emissions by 2020, clean energy has suddenly entered the Klamath dam debate.


However, replacing the power from these dams could result in adding combustion emissions to the environment.

Hydro-Québec, the world's biggest producer of hydropower, claims that "compared with other generating options, hydropower emits very little greenhouse gas," thus "contributing significantly to the fight against climate change."

Maybe not. Recent reports on methane emissions suggest that dams are anything but carbon-neutral.

According to recently published estimates from Brazil's National Institute for Space Research, the world's 52,000 largest dams release 104 million metric tons of methane annually. If these calculations are correct, then dams would account for about four percent of the total warming impact of human activities -- and would constitute the largest single source of human-related methane emissions.

If methane released from reservoir surfaces, spillways, and turbines were taken into account, India's greenhouse emissions could be as much as 40 percent higher than its current official estimates. But, India as a developing nation, is not required to cut emissions -- and has yet to measure methane from its 4,500 dams. And that's a problem, because while methane does not last as long in the atmosphere as carbon dioxide, its heat-trapping potential is 25 times stronger.

A Swirling Debate

In 2004, National Institute for Research in the Amazon suggested that a massive surge of methane emissions could occur when water is discharged under pressure at hydroelectric dams in a process known in the industry as "degassing."

The problem with dams is that organic matter gets trapped in them when land is first flooded, and more gets flushed in, or grows there, later on. In tropical zones, such as Brazil, this matter quickly decays to form methane and carbon dioxide.

But just how big a problem this creates is controversial. A debate has been raging for years between researchers connected to Hydro-Québec and Brazil's Electrobras, the world's largest hydropower companies, and several small teams of independent hydrologists.

According to Fearnside, if degassing emissions were factored in at several large hydropower plants in Brazil, then these dams would be larger contributors to global warming than their fossil fuel counterparts. To be precise, Fearnside suggested that during the first decade of its life, each of these dams would emit four times as much carbon as a fossil fuel plant that makes the same amount of electricity.

Fearnside's claims have triggered a firestorm. Luis Pinguelli Rosa, formerly of Electrobras but now based at the Federal University of Rio de Janeiro, claimed Fearnside had made "scientific errors," including a failure to grasp how degassing works, and so had exaggerated the emission levels.

Rosa pointed out that Fearnside had extrapolated his calculations from data taken from the Petit Saut dam in French Guyana in the years immediately following the creation of the reservoir, when organic matter, and thus methane emissions, would likely be their highest. Patrick McCully, executive director of the Berkeley, CA-based International Rivers Network, says that one of the areas of strongest disagreement among reservoir emissions researchers is how to quantify net emissions.

In a recent paper, "Fizzy Science," McCully shows that key factors influencing reservoir greenhouse gas emissions include fluctuations in water level, growth and decay of aquatic plants, decomposition of flooded biomass and soils, the amount of methane bubbling from the surface, and the amount of carbon dioxide diffusing in.

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2 comments:

Anonymous said...

I don't know where people get their facts. This nonsense is perpetuated by a media that wants to find something, anything wrong with hydropower. They continually quote McCully as if he's an expert. He is an expert at one thing, falsifying facts. He has taken a few examples of dams located in the tropics and extrapolated that information to all dams. His facts are wrong. The University of Sydney, Australia completed a report in 2006 titled "Life-Cycle Energy Balance and Greenhouse Gas Emissions of Nuclear Energy in Australia". While the focus was mainly on Nuclear power, the report provided some recent data on all forms of energy production. Here's a summary of the results (note that hydropower has the lowest greenhouse gas emissions):
"A comparable analysis has been undertaken for a number of conventional fossil-fuel and renewable electricity technologies. As with the methodology for the nuclear case, a range of literature values and current estimates have been used to examine the performance of these technologies in an Australian context, assuming new capacity is installed at close to world’s best practice. These results, together with a summary of the nuclear energy results, are presented in the table below. The figures in parentheses represent the likely range of values. It is clear from the results that the fossil-fired technologies have significantly higher energy and greenhouse intensities than the other technologies."
Electricity technology Energy intensity
(kWhth/kWhel)
Greenhouse gas intensity
(g CO2-e/kWhel)
Light water reactors 0.18 (0.16 – 0.40) 60 (10 – 130)
Heavy water reactors 0.20 (0.18 – 0.35) 65 (10 – 120)
Black coal (new subcritical) 2.85 (2.70 – 3.17) 941 (843 – 1171)
Black coal (supercritical) 2.62 (2.48 – 2.84) 863 (774 – 1046)
Brown coal (new subcritical) 3.46 (3.31 – 4.06) 1175 (1011 – 1506)
Natural gas (open cycle) 3.05 (2.81 – 3.46) 751 (627 – 891)
Natural gas (combined cycle) 2.35 (2.20 – 2.57) 577 (491 – 655)
Wind turbines 0.066 (0.041 – 0.12) 21 (13 – 40)
Photovoltaics 0.33 (0.16 – 0.67) 106 (53 – 217)
Hydroelectricity (run-of-river) 0.046 (0.020 – 0.137) 15 (6.5 – 44)
Read the full report and get some accurate facts.

profmaster said...

Dear Reader,
I also do agree with you and that was my purpose of posting it on the blog, so that we can share facts & bring those exposed who are in favor of silly things by manipulating facts.
My ethanol article was also there with the same purpose. There also I find many people who are justifying it over any other fuel, which is not true. Diversion of food grains to fuels will create a vacuum in future for society.

I would like you to invite for writing on my blog so that each one can share this table in proper readable format. Just send your Email ID & I will add you as writer, then U can directly post articles.

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