Hydropower, a renewable energy source often overshadowed by excitement about wind and solar power, is enjoying something of a global resurgence.
Huge, controversial dam projects have recently made headlines in Brazil, Chile and Laos. Many developing countries, hungry for energy to supply their growing economies over the long term, are determined to keep building more modest-sized dams too.
Record amounts of hydropower capacity came online in 2008 and 2009, the most recent years for which data are available, according to Richard Taylor, executive director of the International Hydropower Association in London.
“There has been, over the last decade, a dramatic increase in the deployment of new hydropower capacity,” Mr. Taylor said.
The private sector, he added, has become more willing to provide financing for projects, which include not only the construction of new dams but also the modernizing of existing ones in places like Europe and the United States. The biggest new dams can cost billions of dollars.
But the renewed attention to hydropower, which accounts for about 16 percent of the global electricity mix, comes with environmental red flags. More attention than ever focuses on people who face displacement, as well as the effects of new dams on land and fish.
In Chile last week, demonstrators protested against a government plan to dam two rivers that wind through a wild, remote part of Patagonia. Last month, officials from Southeast Asian countries failed to reach an agreement about a proposed dam project on the Mekong River in Laos, amid concerns from Vietnam, Cambodia and Thailand about downstream implications.
An additional environmental issue — one that has caused mounting concern in recent years — is climate change. Changes in rain or snowfall patterns can drastically affect the amount of power a dam produces and also the amount of sediment flowing through the river.
Prolonged droughts are already taking their toll. Brazil, which gets about 80 percent of its electricity from hydropower, experienced a bad drought about a decade ago, and Chile has struggled with drought, too, according to Deborah Lynn Bleviss, a professor in the energy, resources and environment program at Johns Hopkins University’s School of Advanced International Studies in Washington.
A 2009 drought took a toll on countries including Guatemala, Venezuela, Argentina and Uruguay, as well as Brazil, she said.
“All have had impacts on hydropower capacity in these countries,” Ms. Bleviss said in an e-mail.
The region around Three Gorges Dam in China, the largest hydropower project in the world, is coping with a severe drought that has closed part of the Yangtze River to shipping, according to the state-run China Daily newspaper.
Small hydropower projects are especially vulnerable to climate change, according to Leandro Alves, who heads the energy division for the Inter-American Development Bank’s infrastructure and environment department, because they may not have enough reservoir storage capacity to compensate for decreased precipitation.
However, some dams may get more water, not less, as the climate changes. In a summary report on renewable energy released last week, the Intergovernmental Panel on Climate Change said that the effect of climate change would vary depending on a project’s location.
“For hydropower the overall impacts on the global potential is expected to be slightly positive,” the report states.
“However, results also indicate the possibility of substantial variations across regions and even within countries.”
In Norway, which gets nearly all of its electricity from dams, climate change on balance may benefit hydropower plants. “The studies have uncertain results, but the main result is that climate change on average will lead to more rain and thereby better production capability in Norwegian power plants,” said Tor Arnt Johnsen, who heads the analysis section of the Norwegian Water Resources and Energy Directorate, which is part of the Ministry for Oil and Energy, in an e-mail.
However, he noted, climate change is expected to lead to substantial weather variations. Thus, in especially dry and cold years, the dams are likely to produce less electricity, which could result in high electricity prices and the need to import power.
One Norwegian study has forecast that climate change will typically cause power prices in Norway to fall, because of both increased hydropower production and also the expectation that demand for electricity will be lower in warm weather, said Gorill Kristiansen, who works for the Research Council of Norway’s climate program.
So climate change will have some kind of effect on hydropower production, but the flip side is that the case for hydropower rests partly on the desire to combat greenhouse gas emissions.
Indeed, said Mr. Taylor of the International Hydropower Association, this is among the reasons why the private sector’s interest in dam-building has revived.
Hydropower accounts for about 30 percent of the projects in the Clean Development Mechanism, he said. (The mechanism is part of the international emissions-reduction system.)
Hydropower is arguably the most reliable — and certainly the most established — renewable electricity source in the world. It is a good way to back up intermittent renewables like wind, because the dams can add power instantly when the wind dies down, and cut back when there is a steady breeze.
In Europe, according to Mr. Taylor, growth in wind power is driving increased interest in “pumped storage,” which is the concept of using excess wind power at night to pump water uphill, and then releasing it to generate power during the day when electric demand is high.
Dams will also help to control flood risks in some areas, Mr. Taylor said, noting that this is important, given the severe weather swings climate change is expected to bring.
But big hydropower projects are not free of emissions. New projects do generate greenhouse gases — less than burning fossil fuels, but certainly more than wind power, according to Mr. Alves of the Inter-American Development Bank.
This is partly because the plants and trees that get flooded when a reservoir is built eventually decompose and emit methane, a greenhouse gas more potent than carbon dioxide. The Inter-American Development Bank has undertaken a project in Brazil to find ways to process the methane emissions, which could be used to make electricity.
The bank is also emphasizing the importance of refurbishing dams, as mechanical equipment reaches the end of its useful life after decades of use. The turbines can be replaced so the dam can produce more power, without the need for a new dam. That way, “we’re not touching the environment or the ecosystem,” Mr. Alves said.On June 1, 2011, comes a report from Reuters that Brazil has given definitive approval to build the $17 billion Belo Monte hydroelectric dam on the Xingu River, a tributary to the Amazon:
The government has said the 11,200-megawatt project, due to start producing electricity in 2015, is crucial to provide power to Brazil's fast-growing economy. It will be the world's third biggest hydroelectric dam after China's Three Gorges and Itaipu on the border of Brazil and Paraguay.
The 6-km-long (3.75-mile) dam will displace 30,000 riverdwellers, partially dry up a 100-km (62-mile) stretch of the Xingu river, and flood large areas of forest and grass land.