Harvesting energy from the tides is a surprisingly old method; the technology has improved and changed through time but the general concept of using the waxing and waning of the moon and the correlating tides has remained constant.
Europe during the early Middle Ages is the one of the first recorded use of tide mills but recent archaeological information has also indicated that the Roman Era many have also used tide mills, predating the Middle Ages by about 400 years. The evidence of Roman tidal mills comes from a single archaeological site along the River Fleet in London, England; unfortunately, due to heavy continuous habitation and construction impacting the ancient site the archaeological evidence is difficult to fully interpret.
The history of tidal energy applications goes back to ancient times.
A tide mill is a dam with a sluice was constructed across a tidal inlet turning the estuary into a reservoir. At high tide sea water flowered into the reservoir through a one way gate and then it closed automatically when the tide started to fall. When the tide was low enough, the stored water was released to turn a water wheel which would then turn the millstone.
At one time there were 750 tide mills operating along the shores of the Atlantic Ocean: approximately 300 in North America, 200 in the British Isles, and 100 in France. By the mid 20th Century the use of water mills had declined dramatically. In 1938, an investigation by Rex Wailes found that of the 23 remaining tidal mills in England, only 10 were still working without modern electrical power.
Modern tidal energy dates to the 1920s in France but the first attempt was ultimately abandoned due to insufficient funds. Later, in 1966, the Rance Tidal Power Station on the Rance River in France became the world’s first tidal power station. The first (and only) tidal generating station in North America was built in 1984 and is the Annapolis Royal Generating Station in Nova Scotia, Canada.
To date, six modern tidal power stations have been constructed. The most recent is located in South Korea which has two more tidal power stations under construction. Various types of construction and concepts are currently being employed through these power stations and only the long-term will prove which concept, perhaps all, is the most sustainable form of renewable energy from the tides. -KATHY FAIRCHILD