In previous decades such systems were considered marginal, for two interconnected reasons:
1. Such run of the mill system are a constant source of power, not the turn on and you have electrical power, turn it off and the water is kept for later use to generate electrical power that Generators from Dams provide. Thus they competitors are coal and Nuclear power not traditional hydro dams
2. Each such electrical provider has low INDIVIDUAL power potential. Instead of one (or more) generator(s) providing all the power from the release of the water, you have to have hundreds of smaller generators. The technology for such smaller generation, prior to about 20 years ago, required as much maintenance as the large generators used in the Dams. While the larger generators produce so much power, it was worth the effort to keep them maintained, the smaller generators were generally considered to small to be cost effective. A good comparison would be comparing a bus with cars, a Bus has maybe two to three times the fuel and maintenance costs as a car, but if you compare a bus to 55 cars it is much more efficient. Thus it is worth the extra money to operate the bus compare to 55 cars.
In the last 20 years, tied in with the growth of wind turbines, the technology of water generators have improved so much that the cost of maintenance is now extremely low compared to what it was just 20 years ago. The Bus to car analogy is no longer valid, the cost to maintain the many small generators have gone down that much. It is still 55 cars or one bus, but we are looking one the equivalent of the same cost for each generators, one low cost for the large dam generator and the small small costs for maintaining the smaller run of the river generators, when both are producing electrical powers that provide more then their cost to operate.
Yes dams can still produce cheaper electricity due to the volume of water they can use to produce that electrical power, but run of the river generators are NOT that much more expensive and once installed still cheaper then coal or nuclear generation.
Some other article on Run of the River electrical generation:
http://energycentral.fileburst.com/EnergyBizOnline/2008-3-may-jun/Tech_Front_Mississippi.pdf
http://insideclimatenews.org/news/20110622/hydroelectric-power-mississippi-river-ferc-coming-boom
http://insideclimatenews.org/news/20110622/hydroelectric-power-mississippi-river-ferc-coming-boom
http://cleantechnica.com/2012/04/20/doe-finds-12-gw-of-untapped-hydro-potential-on-ol-man-river/
Now in the 1970s the Federal Government offered to municipalities along the rivers the right to install electrical powers at any of their locks and dams. Most Locks and Dams (as opposed to dams without locks) are designed solely for river navigation. i.e. to keep the river at a set range of height and restrict water flow to maintain that height. Most locks and dams even permit water to flow over the dam part of the lock and dam if the water behind the dam gets to high.
Now, in the Pittsburgh area this offer was taken up by the Clairton Borough. Clairton was able to do so for Pennsylvania law say the water is the border of all of the towns on the river, so Clairton could claim any lock and dam on the Monongahela river which it is located on. At the time it was believed by many Clairton did this as a favor to the local electrical unity, Duquesne Light, which was and is heavy invested in Nuclear plants. Thus tied all of those locks and dams up.
Now, on the Conemaugh dam, such an electrical power generator was installed. Conemaugh Dam is a hold dam, i.e. it is generally mostly empty, but in heavy rains it retains water to protect Pittsburgh from flooding. The water then is released slowly over several weeks till it is below the old railroad bridges which is now part of West Penn Trail between Blairsville and Saltsburg. a distance of 17 miles.
http://www.conemaughvalleyconservancy.org/recreation/recreation.html
In the middle of that path is the Conemaugh dam. The path works it way over the bend in the Conemaugh River where the dam is located. That bend has four tunnels through it. One for the original Pennsylvania Canal, one for the 1860 railroad that replaced the canal, a third for the 1900 railroad that replaced the 1860 era railroad and a tunnel for water to drain to the generator that was installed in the 1970s. All but the last tunnel are filled with 20 feet of concrete, so that water does not leak through them when the dam is full. The trail goes over the hill that is the bend in the river, then reconnects with the old railroad right of way (The 1900 right of way was abandoned in the 1950s, replaced by an existing railroad line that uses bridges to go around the dam. Moving existing structures is one of the reasons dams are getting harder and harder to build. On the other hand with the new technology (mostly the ability to produce very low fiction generators) run of the river system are showing themselves to be more and more a very good source of new electrical power.
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