How mich is Hydroelectricity ecofriendlyby | 09-09-2015 00:06 |
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From a purely greenhouse gas (GHG) emissions based standpoint, hydroelectric has somewhat recently come under a lot of flak as not being as "green" as once believed it is still somewhat cleaner than natural gas and cleaner than coal, but only after having been deployed for a long period of time (decades). To start, hydroelectric was once applauded as being clean, renewable, and a well-understood/mature technology (we've been using waterwheels for millennia). However, the necessary flooding involved, especially for larger hydroelectric dams, results in uncontrolled decomposition of the submerged vegetation, which releases much CO2 and the more concerning GHG, methane. Fairly recent publications have investigated these emissions at a case-by-case basis [1] and at a larger scale comparing dam climate/age [2], and have revealed non-negligible GHG emissions for hydroelectric power. To compare to fossil fuels, one study estimates a global average emission profile of 92g CO2/kwh and 5.7g CH4/kwh for hydroelectric [3]. Taking CH4 as 25 times more potent of a GHG than CO2, this puts the hydroelectric average at about 234g CO2e/kwh compared to about 550 for gas and 950 for coal [4], making it somewhat cleaner but still in the same order of magnitude. However, it is important to note that these emission rates are also time dependent. The Barros paper also indicates substantially higher emissions within the first 10 years of operation of the dam, reaching as high as 20 times more CO2 and CH4 flux in reservoirs for new dams compared to those several decades older [2]. These rates put young hydroelectric dams as a far dirtier energy source than any fossil fuel, and it is important that new projects be maintained for decades if we are to reap any environmental benefits from displacing coal or gas generation. So overall, hydroelectric is somewhat cleaner than fossil fuels only if maintained for a very long time (and this doesn't even look into damages to river ecosystems). Personally, I think today's pursuit for clean energy should start with gas to kick out coal, then move towards wind, solar, and nuclear. |
