In a bit of a change of pace from the normal fare, I thought I'd post some pictures from a visit today to TVA's Norris Dam. At 130 MW peak generating capacity, it is perhaps the one source out there that can truly compete with nuclear in terms of marginal unit cost as well as dispatchability: hydro.
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| Norris Dam from the western overlook |
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| Norris Dam and power station |
In other respects, hydro shares some similarities with other renewables - the energy output of a hydroelectric plant is fundamentally tied to nature - namely by the reservoir level (which in turn is influenced by rainfall levels). Unlike wind and solar however, hydro represents relatively "smooth" and predictable power output - while meteorology is far from a perfect science, rainfall patterns are generally quite predictable, meaning output levels from hydroelectric dams can also be readily planned for in advance.
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| The view from the top of Norris Dam |
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| Clinch River valley, past the impoundment |
Unfortunately, at least as far as the U.S. goes, most of the "prime" hydroelectric capacity has already been tapped - meaning we've got about as much as we're going to get from this source.
Happy Memorial Day to our U.S. readers - we'll be back to our regular scheduled programming later this week.
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It may come as surprise to some that there is still a significant amount of undeveloped traditional hydro potential left in North America. The National Hydropower Association (U.S.) river basin studies show a potential of 73,200 MW of additional U.S. hydroelectric capacity in 5,677 undeveloped sites. The situation is the same for Canada, including the Far North where eight major rivers draining into the Artic Ocean are considered ripe for exploitation. Of course this is emphasizing engineering feasibility and some economic analysis, but no environmental considerations. Despite the widespread belief that hydro is the ideal clean source of renewable energy the bald fact is that it is hugely destructive to local environments and can and does create disruptions to the hydrology of an area several orders of magnitude greater.
ReplyDeleteHydroelectric dams also produce significant amounts of carbon dioxide and methane, and in some cases produce more of these greenhouse gases than power plants running on fossil fuels. Carbon emissions are driven by seasonal changes in water depth create a continuous supply of decaying material. In the dry season plants colonize the banks of the reservoir only to be engulfed when the water level rises. For shallow-shelving reservoirs these "drawdown" regions can account for several thousand square kilometers.
In effect man-made reservoirs convert carbon dioxide in the atmosphere into methane. This is significant because methane's effect on global warming is 21 times stronger than carbon dioxide's.
@DV8XL - Entirely true that hydroelectric requires a substantial ecological disruption (something I considered but left out). But it seems like the issue of carbon dioxide, at the very least, is "baked in" to nearly any energy source one can conceive of. Concrete and steel - consumed in spades for nuclear - produce significant amounts of CO2. That being said, given the energy output of a nuclear unit, the CO2 per unit energy is still infinitessimal compared to conventional sources.
DeleteI think the calculations of emissions from hydro rely quite heavily over assumptions of its use case. Norris Dam is a bit of an interesting case - the Nebraskan Senator for whom it was named opposed prior private efforts (before the TVA) to build a dam there because he felt private entities would focus solely upon electricity generation, rather than the combination of flood control and electricity generation that Norris currently provides. Other cases, less oriented toward flood control and more toward power generation alone, would likely see more of the variability you describe, I imagine.
I'm not an expert in life cycle emissions studies, but I'd be curious to see a side-by-side comparison with the assumptions laid out clearly.
The issue with hydroelectric/water management dams producing GHG is far more acute in tropical latitudes than in temperate, however it can be significant. In a study published in Mitigation and Adaptation Strategies for Global Change, it was calculated that in 1990 the greenhouse effect of emissions from the Curuá-Una dam in Pará, Brazil, was more than three-and-a-half times what would have been produced by generating the same amount of electricity from oil due to methane/carbon dioxide pulsing caused by seasonal changes in water depth. This is continuous and over and above any contribution made from concrete curing and releases from rotting vegetation created during initial flooding during the creation of the reservoir, both of which can be significant for a large project. The National Greenhouse Gas Inventory Programme, which calculates each country's carbon budget, since 2006 has included emissions from artificially flooded regions. This raised Brazil’s emissions inventories by about 7% as one example.
DeleteWhile this is not a problem with run-of-the-river types of dam, they too have a far greater impact on the environment than one would suppose at first glance primarily due to changes in the flow of nutrients that can impact ecosystems both up and downstream and of course they interfere with aquatic wildlife migrations.
The point here being is that the selection of hydroelectric projects, particularly in underdeveloped nations (which there are many in the tropical regions) as an ecologically sound alternative to nuclear may be simply untrue.