Its time for another of those blog posts that is a bit “out there”. In this case I would like to propose a new use for an ancient technology.
I recently returned from a vacation in France and while there I saw a few things that came together in my mind as a possible source of base-load electrical generating capacity.
First, in Normandy, I saw some current generation wind turbines spinning in unison along several of the ridges in the region. What struck me was how slowly these turbines were spinning – about 1 revolution every 4-5 seconds. And yet I know that each turbine was producing at least 1 MW of electricity. It crossed my mind that the technology has advanced to the point where relatively slow revolutions of a generator can produce a significant electrical output.
Later that week we moved to Avignon in Provence and I had the chance to walk along the Pont d’Avignon which used to be one of the most important bridges in Europe. Looking down at the Rhone as it swirled around the piers of the bridge I thought about the power of all that moving water. Even though there were no rapids or waterfalls nearby clearly there was a great deal of untapped energy in the flow of that river.
Finally, in the old part of Avignon, I saw a number of very old water wheels along a man-made canal fed by the Rhone. These water wheels used the flow under the wheel rather than having water drop onto the wheel – basically the reverse of how a paddle-wheeler works. The interesting thing was that there were 4-5 of these wheels in series along the canal.
Putting these observations together it occurred to me that perhaps a very large water wheel, 30-50 meters or more in length and 2 meters in height, could be placed in a river to tap into the stream flow. Based upon a typical stream current of 1-2 m/sec it would take about 6 seconds to spin the water wheel through 1 revolution, about the same amount of time as it takes a modern wind turbine to spin through one revolution. By connecting this water wheel to a wind turbine it would be possible to generate between .5 to 2 MW of output per water wheel. Many of these units could be placed at intervals down a river in order to multiply the aggregate amount of electricity produced.
One of the other interesting aspects of this concept has to do with the large number of older wind turbines that are going to be retired from service in the next few years. The largest example is the refurbishment of the Altamon Pass wind farms in California which will involve the replacement of several thousand older, smaller turbines (in the 200 KW - 500 KW range) with current generation turbines. What can be done with these older turbines, most of which are in perfect working order? Perhaps next generation water wheels would provide a good re-use of these units.
The only problem I can see with this concept is the need to allow river traffic to continue without being interrupted by the water wheels. Here again an ancient tactic might work.
During the seige of Rome in 537 AD the aquaducts used to supply water to drive the mills in the city were blocked. The Roman leader Belisarius anchored two boats in the Tiber River and suspended a water wheel between them allowing for the continued production of flour. A modern version of this could involve suspending a much larger waterwheel between two floating supports so that only a portion of a river's channel would be blocked allowing river traffic to continue.
A new generation of water wheels has the potential to add a relatively inexpensive reliable and renewable energy source which can be deployed on all major rivers. Definitely may be a "Black Swan" worthy of consideration.