"Much water goeth by the mill that the miller knoweth not of."
Proverb
In a tidal mill, incoming water enters and fills the millpond through sluices and is then channeled out at low tide to turn the mill wheel, thus powering the millstones, and crushing the grain to flour. The first known tidal mill, dating around 787, was built on Strangford Lough in northern Ireland, and was used by monks to grind corn for the nearby monastery.
Tidal mills were used along Europe's Atlantic coast in the Middle Ages, where the high tidal ranges ensured generous payback for the millers. The number of suitable sites was limited, and the mills could only operate for a certain period after each high tide, but their output was predictable compared to weather- dependent windmills and traditional watermills.
The popularity of tidal mills waned with the arrival of the steam engine, until in 1966 French engineers harnessed the tides to generate electricity. The Ranee estuary in northern France was dammed by a barrage housing twenty-four turbines capable of producing power from both the ebb and the flow of the tide. Other schemes have been developed since, but the specific site requirements and the environmental considerations around the tidal basin are limiting. Modern alternatives to the barrage approach are to construct underwater turbines, either on a riverbed or seabed, or to hang them from tethered surface buoys that rotate in the tidal stream.
