After showing a world map of all of the areas of extremely high tidal ranges, (Bristol having the third highest after two bays in Canada), he described the three types of tidal power generation. These being Tidal Flow, Barrage, and Tidal Lagoon.
He showed how Tidal Flow systems, which are like underwater wind turbines, work but that the areas of the Severn Estuary that have sufficient water flow rate are all in the navigation channel to Bristol Docks and this system cannot be used.
He went on to give the details the La Rance Tidal Barrage, near St. Malo in Britanny, which was built over 60 years ago and then the details of the proposed barrage across the mouth of the River Mersey between Liverpool and Wallasey which should start its planning approvals in mid 2026.
Dennis then showed the location and details of all of the nine barrage schemes which have been considered on the River Severn with details of their advantages and planning restrictions including the large coastal areas of special scientific interest. He showed that until 2009 all of the schemes could not compete when comparing their construction costs with those of cheap gas and oil fired power stations.
He advised that a recent Government funded study had concluded that the most likely type of Tidal Energy schemes to succeed in the River Severn were Tidal Lagoons which could be built on the side of the river away from the special scientific areas. Dennis described the two Tidal Lagoon schemes being considered at present, one in Swansea Bay and the other between Minehead and Watchet (The West Somerset Lagoon). The West Somerset Lagoon would extend along 14km of coastline and 7km out into the River Severn. At peak generation it could produce comparable amounts of electricity to a nuclear power station although the average would be about 30%. The design life of the Lagoon system would be 120 years compared with 30 years for a wind turbine and 60 years for a nuclear power station. The scheme would result in a major regeneration of the Minehead area, noting that the La Rance Barrage has over 70,000 visitors each year. Planning and environmental studies are ongoing and if successful the scheme could be generating electricity by 2036.