Hydroelectricity was one of the very first technological developments made in US energy industry. Since the first hydroelectric plant opened in 1887 in San Bernadino, California, hydroelectricity had become one of the major sources of electricity production in US as shown in figure 1, second only to coal in its early days [2]. However, the contribution to the total US electricity production from hydropower has been decreasing consistently over the last few decades. The US hydropower has never quite reached its potential.
Figure 1: Timeline of various power production plants in US (1949-2012) [1]
At large scales, hydroelectricity is the most efficient power production technique, reaching efficiency of up to 95% as shown in figure 2 [3],[4]. It is a renewable source of energy which, in fact, helps fight climate change since it does not produce harmful gaseous emissions at a rate anywhere close to what other power plants operating on coal, gas, or oil produce. The advantages of hydropower are countless. It is fueled by water and therefore, it is free and abundant. The fact that it does not rely on any other natural resources, and that water cycle around the world is capable of constant and reliable electricity production, makes it extremely reliable. It is available when needed and can be easily controlled. In addition, large dams built for hydropower plants are a huge asset at the times of flood and drought. They also help maintain the quality of water [5].
Figure 2: Efficiency of various power plants
On the other hand, there are some downsides of hydropower plants, the most problematic of which is the construction of huge dams. Expensive to build dams, not only require operation of such power plants for decades for the payback, but they also cause some alarming environmental concerns. They can cause some serious geological damage. They require accumulation of large water bodies and therefore destroy the habitat around them. Construction of large dams can also alter the natural flow of water, fish migration, and eventually the surrounding ecosystem [6]. Upstream migration of fish can be severely impacted because of this. Hence, it is obvious that most of the concerns relating hydropower are because of the dams.
But, is there a way around this whole issue of building dams? Can we take the most efficient power production system we have and turn it into an even more efficient one? The answer to that maybe a damless hydropower. Researchers have shown that hydropower can be generated without establishment of such dams and therefore negating all the concerns that arise with them.
The only difference between a dam-based and a dam-free hydropower is the presence or the absence of a dam. The same water current turns the turbines which generate electricity. As shown in figure 3, damless hydropower does not need a dam to create pressure and uses natural flow of the river or tide to produce electricity. Such turbines are low head installations that have very minimal environmental impact. The developers of damless hydropower also claim that the blades turn slow enough to allow fish to escape, and therefore do not affect the fish migration the way dams do. Another important advantage of damless hydropower is that the turbines can be site-based and optimized for performing in certain unique situations. Each power plant can be studied on a site by site basis for optimal performance.
Figure 3: A typical damless hydro turbine [7]
Damless hydroelectric production has been studied for quite a while now and researchers have found that installing electricity generating turbines under water is practical. For example, Hydro Green Energy, LLC has been testing a damless hydroelectric power plant in Hastings, Minnesota. A 2007 Electric Power Research Institute study estimated that there is a potential for adding a 300 megawatts of damless hydropower in the US by 2025. Federal Energy Regulatory Commission (FERC) could play an important role in the establishment of damless hydropower in the future since the same challenges of federal and state approvals that apply to the existing dams, apply to the new technologies as well [8].One interesting observation is that the US government is so focused at other renewable sources of energy like wind and solar, it may be overlooking the contributing potential of hydroelectricity. More investment into damless hydro is key to its development into a feasible renewable and clean alternative for power production.
References:
1. http://upload.wikimedia.org/wikipedia/en/b/b5/USHydroPower.jpg
2. http://www.hydro.org/tech-and-policy/history-of-hydro/
3. http://www.mpoweruk.com/hydro_power.htm
4. http://www.mpoweruk.com/energy_efficiency.htm#comparison
6. http://www.envirothonpa.org/documents/19bHydropowerAdvantagesandDisadvantages.pdf
7. http://sajjankumargupta.blogspot.com/2008/10/free-flow-turbine.html
8. http://www.publicpower.org/Media/magazine/ArticleDetail.cfm?ItemNumber=23169
Energy, Technology, & Policy 
A very interesting topic, one that was explored in depth in the National Renewable Energy Laboratory’s (NREL) “Renewable Electricity Futures” study: http://www.nrel.gov/analysis/re_futures/
In the study, NREL examines the resources and technologies needed to expand our renewable energy productions in the U.S. dramatically by 2050. For the higher penetration level scenarios (70-90%) NREL finds that growth is likely needed in hydroelectic resources. As the OP discusses, these new hydro resources are much more likely to be “run of river” hydro than conventional dam installations.
Damless hydropower does seem like it has a couple good things going for it, namely that it minimizes the disturbance to the surroundings and that it leaves no visible footprint. If citizens want to keep a river in its natural state for aesthetic reasons or otherwise, this does seem like an excellent way to preserve nature. You could have a multitude of these turbines beneath the surface and no one would ever know they existed.
It’s kind of funny that these turbines serve the same purpose as wind turbines, the only difference being the fluid. In fact, the good news with water based turbines is that you can expect a much more consistent flow compared to the many times temperamental behavior of wind. Droughts and flooding would affect the river flow, but it would be safe to assume that there would almost always be at least some flow.
However, I think there could be some potential nuisances or problems. If I wanted to get the most power out of these turbines, I would put them in a fast flowing river. So I would imagine that installing them would be a pain. I just think that the number of these turbines you would need to actually get a noticeable benefit out of the project would be very high. I don’t know much about installation of these things, but over water bridges use something called caissons (http://wiki.answers.com/Q/How_they_build_bridge_foundation_under_the_current_of_water) to allow workers to build the foundation, and I’m assuming something similar would have to be done for a project like this. That seems like a lot of man hours and money spent on providing a safe work environment for the workers trying to install the turbines. Perhaps those considerations are small compared to other projects, but I think it would be interesting to know how they do that.
Also, I would like to know how much power the turbines put out. If a blade rotates slow enough that it doesn’t kill a fish going through it, I just instinctively have concerns that it probably isn’t a powerhouse.
I also wonder what the costs are to transport that power from each of the turbines through under water wires, presumably buried beneath the river floor, from probably a ton of these turbines, to a location where the power can actually be used?
These turbines seem like a really interesting way of potentially increasing the amount of energy in the US that is produced by renewables. Rivers are underexploited in terms of how much power they are used to produce compared to their potential output.
I have a couple of thoughts about this, though. First of all, since there are so many existing dams that could be converted to produce hydroelectric power, I don’t think that an energy company would necessarily shy away from the idea of conversion. This would surely be an expensive and arduous process, but so is building any other kind of large-scale power plant. And the advantage here is that the technology is available and well-tested. The new turbines could certainly have their place, but it is difficult to image wide-scale adoption coming on very quickly since the technology is quite new.
Another thought I have is hits—since these are a bunch of submerged structures, how would they impact the movement of water vehicles? A lot of goods are transported via rivers, and it seems like it might be difficult to be able to reconcile the presence of a turbine farm with the path of a boat or a barge, which inevitably has some portion of its body submerged. The largest rivers are presumably the ones both most capable of producing power and allowing goods to be moved, so this seems problematic.
Dam less hydro power calls for totally new approach like this. Here is our link. Regards. Subramaniam Udhayamarthandan
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