by David Hoyle

A Tide Mill Institute email subscriber recently asked TMI why historical tide mill sites are not being used to generate electricity. It’s a fair question: for an 8-foot tidal range, each acre of a tidal basin could power one typical household. The simple answer: the multiple hurdles to be overcome to implement tidal power generation seem to outweigh the benefits. In other words, there does not seem to be a need for tidal power compelling enough to motivate an individual, community, or developer to overcome those hurdles.

First, let’s remember that a historical tide mill required a dam to impound water at high tide and used the difference in head between the tidal basin and the sea to generate mechanical power. Producing electricity in this way is called tidal range generation. (Generating electricity by placing a tidal turbine in tidal currents, without a dam, is called tidal stream generation. While tidal stream generation was not common historically, it has become the de facto standard for new tidal electricity generation projects today.)

Obstacles for Tidal Range Power Generation

In cases where a historical tide mill dam has been transformed into or replaced by a causeway with culverts to permit limited water exchange, the former tidal basin has typically become a lake with little tidal amplitude. Property owners surrounding the lake would be understandably reluctant to support a power generation project that would transform their stable lake back into its original, tidal state, filling and emptying twice a day.

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