Tide MillsTide mills operate in the same way as water mills but use ocean tidal power instead of rivers and streams. Rising tides fill a reservoir and at the peak gates are closed to prevent water from flowing out. Once the tides have gone out these gates are opened and the water turns a wheel as it flows out. Rotation provided by this wheel turned a shaft that powered grain mills. First uses of tide mills can be traced back to Ireland in 619 AD. Although increasingly rare some tide mills are still in operation mainly for historical preservation. Tidal mill technology was the precursor to tidal barrages for electricity generation as you’ll see next.
Tidal Electricity Generation
Generating electricity from tides is heavily dependent on proper location. Difference between high and low tide has to be 5 meters (16 feet) for electricity to be generated, only 40 such locations exist worldwide. Additional factors include the type of tidal system (diurnal, semidiurnal, mixed) and local ecology and energy demands.
|1. SeaGen, world’s first commercial tidal generator. Image by Fundy. License: CC BY-SA 3.0||2. Tidal power plant on estuary of Rance River in Bretagne, France. Image by Dani 7C3. License: CC BY-SA 3.0||3. Top down view of a dynamic tidal power dam, color differences represent water height. Image by UNguyinChina. License: US PD|
- Tidal Stream – This tidal electricity generation technology anchors individual turbines to the ocean floor that turn as tides come in and go out.
- Tidal Barrage – Estuaries and bays that are subject to tidal fluctuations can be dammed similar to hydroelectric dams, this is known as a tidal barrage. Turbines built into the barrage generate electricity as the tides rise and fall.
- Dynamic Tidal Power – One theoretical tidal power technique is to build a dam straight off the coast. Rising and lowering tides would be impacted by this dam creating significant water height differences between either side which could be harnessed for electricity production.