Report: Hydro emissions can rival those of natural gas

The Seven Sisters Dam in Manitoba. (Photo by Miss Barabanov via Creative Commons)

As states grapple with the question of whether to count hydropower as renewable energy, a recent report says dams can emit greenhouse gases at a rate far greater than wind and solar, and can nearly reach those of natural gas combined-cycle plants in their first years of operation.

Cambridge, Mass.-based Synapse Energy Economics, Inc. found that large scale hydropower using reservoirs have lifecycle emissions, as measured over a 100 year span, in excess of wind, solar, and run-of-the-river hydro. Reservoirs in northern climates can add substantially to GHG emissions if they cover land that is filled with boreal forests that serve as carbon sinks.

Commissioned by the Conservation Law Foundation, “Hydropower Greenhouse Gas Emissions: State of the Research” does not suggest hydropower pollutes more than traditional fossil sources such as coal, natural gas or diesel. But in the short term the GHG emissions from hydro – in at least three of the first 10 years of operation – exceed those of a natural gas combined-cycle plant, said Christophe G. Courchesne, staff attorney for the CLF’s Concord, N.H. office.

“In the short term, hydro is less impressive than had been assumed,” he said. “There are more short-term impacts in new projects than we expected.”

Synapse collected data from recent scientific research looking at hydro’s impact, much of it conducted in Canada, which receives a greater percentage of electricity – 59 percent – from hydro than all but two other countries.

Reservoirs are the main culprit behind high GHG emissions, which are especially intense in a plant’s first decade. A study of a Hydro-Quebec’s Eastmain 1 facility and reservoir, which produces 480 MW, found that newly flooded areas increase emissions due to the decomposition of organic material, he said.

Over the lifecycle of a large hydro plant – about 100 years – GHG emissions are still more per megawatt hour than wind, solar, nuclear and run-of-the-river hydro, the report claims.

Because flooding for dams takes out forest reserves “you eliminate a lot of carbon sinks” that absorb pollution, added Courchesne.

An imprecise science

However, there’s little consensus on hydropower’s climate impact, and both reports concede the science on some of the issues is relatively new, and novel.

In a response to the report published on the CLF website, Alain Tremblay, environmental advisor for Hydro-Quebec Production, said GHG emissions from 60 different generating stations differ greatly. Hydropower emissions are similar to those from wind power, one quarter of photovoltaic facilities, 40 times less than a gas-fired plant and 100 times less than a coal-fired one, he wrote.

The Center for Climate and Energy Solutions – formerly the Pew Center on Global Climate Change – wrote in a summary of data on hydro that its GHG emissions were less than energy from biomass and solar and about the same as emissions from wind, nuclear, and geothermal plants. The research cited, however, was more than a decade old.

The CLF’s report comes with political implications. The organization has been a vocal opponent of Northern Pass, a $1 billion proposal to build transmission lines from Hydro-Quebec’s operations to New England along a route in New Hampshire.

But it’s not the only report published recently to look at hydro’s impact. Edmonton-based Global Forest Watch Canada released in January a large, in-depth study that showed Canada reports just one figure for the GHG impact of hydro to the Intergovernmental Panel on Climate Change, and it tends to be low.

“Those numbers are relatively low within the scientific range of possibility,” said Peter Lee, executive director. “What we learned is that there is a range of possible emissions and within that range it’s probably a lot higher than governments are reporting.”

For example, Environment Canada, a government agency, estimates the country’s hydropower plants emit 1.5 megatons annually for reporting purposes. The Global Forest Watch report suggests that may be as high as 17 megatons, and as low as 0.2 megatons. 

“Our understanding of the cumulative watershed impacts of large dams is still poor,” the report says.

The CLF hopes the reports and other efforts will bring into question the claims of Northern Pass supporters who see Canadian hydro as a green alternative. Courchesne also fears Canadian hydro could stymie the growth of other renewable energy sources in New England, especially wind and solar. Locally, the Minnesota Legislature has debated whether to allow utilities to use Canadian hydro for the state’s RPS while Wisconsin allows it.

“There has been an active movement to qualify these projects (for RPS),” Courchesne said. “But we believe there is no justification for qualifying large-scale hydropower for RPS treatment. The RPS statute was meant to incentivize new technologies and not economically mature technologies that are viable without subsidy. That’s where large hydro is.”

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