With summer time comes my annual vacation back in my home region, Brittany, with its beautiful coast line spread with pink granite and emerald alike rocks that shine in the sunset like jewels on a crown. The frequent rains maintain a rich and colorful vegetation in-land, stage of many past legends. The dense forest of Broceliande once hosted the adventures of the Knights of the Round Table and Merlin the Enchanter…
This year trip was the occasion to re-discover the potential of an important source of alternative energy, much less talked about than sun and wind. I am talking about water. As I was driving away from Paris and entering the Breton region via the county of Rance — adjacent to the county of Broceliande and mostly known for its cider — I surprised myself to learn about the local hydraulic power plant that leverages the tidal currents into the Rance river and generate up to… 250 MW.
The Rance tidal power plant produces more energy than any solar farm today. It consists of 24 hydraulic turbines generating electricity in both current directions, and of a dam to help store energy and redistribute it on demand. The plant was built in the sixties and remains a spectacular but lone example due to the environmental impact caused by the construction of the dam. Yet, the plant operated by French energy giant EDF recouped its construction cost and provides today non polluting electricity at a lower cost than nuclear (1.8c per kWh vs. 2.5c per kWh for nuclear).
To limit the environmental impact on coastal habitat, smaller tidal plants that do not require dams are preferred today. They can be deployed along the coast or at the entry of rivers. Tidal currents also have the advantage to be completely predictable and stronger than marine currents like the Gulf stream. Last week, EDF announced the deployment of a new tidal power farm near the fortified city of Saint Malo with a capacity of 6 MW. The turbines generate each 1 MW with a conversion efficiency of 30%, above the efficiency avhieved by solar cells and comparable to wind turbines. A cable connects the generated electricity back to a station on the shore.
The idea of harnessing the power of water currents is not new. Like wind mills, tide mills spread in the late Middle-Ages, mostly along the Atlantic coasts of North America, Great Britain and France. Some remain today as the one in Brehat, near Saint Malo. My favorite? The tide mill in Ploumanach, further west and close to my home village. It is made of pink granite and kept its colorful character despite the ages.
Power plants based on combustion still dominate. Sure. Solar cell and wind turbine companies are growing fast. True. But do not discount the fourth element: water. The tidal power farms are discretely replacing the tidal mills of the past and will continue to capture our imagination…
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