A new analysis by Oakridge National Laboratory (ORNL) says that America could generate 12.6 gigawatts of
always-on peak baseload power just by adding electrical generation capacity to existing dams that don't already have it. That's 12 6 (big) nuclear reactors' worth — the average reactor at the Fukushima Daiichi plant produced only 0.78 GW.
[Update: Jesse Jenkins at The Breakthrough Institute points out that the capacity factor for most hydroelectric projects hovers around 50%. This means that on average they can only produce half the electricity they are rated for, mostly because of variability in their energy supply — water. On the other hand, hydroelectric plants are often useful for balancing out other renewables, as they can often produce more power on-demand. The headline of this piece has also been changed to reflect this.]
Much of that power-generating capacity is low-hanging fruit: ORNL estimates that even if you focused only on the country’s 100 biggest non-electrified dams, you could still generate 8 gigawatts of power. That's
four times twice as much energy as the Indian Point nuclear power plant, which provides 30 percent of the electricity used by New York City and Westchester county.
Historically, hydropower has been seen as a dead end in the race to replace fossil fuels with renewables. A 2002 analysis by the Union of Concerned Scientists says that "The impact of very large dams is so great that there is almost no chance that any more will be built in the United States," and "… hydropower is almost certainly approaching the limit of its potential in the United States." But ORNL isn’t talking about building more dams — just getting more out of the existing ones.
Whether or not the new findings from ORNL will change anyone's mind is the big unknown, but a bipartisan group of Senators headed by Lisa Murkowski (R-Alaska) is apparently ready to go to the mat to see the Hydropower Improvement Act [PDF] get done.
Environmental Impacts of Renewable Energy Technologies, Union of Concerned Scientists.