Current and Proposed Locations

Ideal locations for tidal generators differ depending on the type of technology which is being used. Since tidal barrages operate on similar principles as hydroelectric dams, the location must be able generate a sufficient tidal head to drive the turbines. In this instance, the current speed of the tide is not as important. Conversely, for tidal current turbines, the current speed must be sufficient to make them able to generate electricity efficiently.

Tidal Barrages

Table 1: Current and potential locations for tidal barrages (O Rourke, et al., 2010).

Table 1 provides a detailed listing of locations worldwide which have been identified as being suitable for tidal barrage construction. Currently, there are only four operational tidal barrages in operation (O Rourke, et al., 2010). The largest is in La Rance, France (Figure 7). Constructed between 1961 and 1967, it is the largest tidal barrage in the world with a generating capacity of 240 MW and an average annual power output of ~480 GWh (O Rourke, et al., 2010). Second in size, the Annapolis tidal generation plant located in the Bay of Fundy, Canada (Figure 8). This plant was constructed between 1980 and 1984 and currently has a generating capacity of only 20 MW (O Rourke, et al., 2010). Currently, the full generating potential of the Bay of Fundy is untapped. With a maximum tidal head of 16 m, it has the largest tidal range in the world. Other basins within the Bay of Fundy have been identified as suitable for tidal barrages and, if fully utilized, could have an installed capacity exceeding 5 GW (O Rourke, et al., 2010). The other two operational tidal barrages are pilot projects located in Russia and in Jangxia Creek, in the East ChinaSea. These tidal barrages have capacities of 400 kW and 500 kW respectively (O Rourke, et al., 2010).

Fig. 7: La Rance tidal power station, operational and during construction (O Rourke, et al., 2010).

Fig. 8: Annapolis tidal power facility under construction (O Rourke, et al., 2010).

Tidal Current Turbines

Tidal current turbine technology is still in its infancy and current work is focused primarily on reliability testing (O Rourke, et al., 2010). Three basic designs are currently under development for tidal current turbines: horizontal fan turbines, vertical helical turbines, and horizontal ducted fan turbines. Depending on the design, these turbines are anchored to the seafloor using pilings, utilize a mooring system where the turbine assembly is allowed to float freely and is tethered to the seafloor, or are gravity anchored (O Rourke, et al., 2010). A detailed description of some promising designs can be found here: (O Rourke, et al., 2010).

In order for tidal current turbines to be commercially viable, they should be installed in areas where tidal flows and topography constraints can generate predictable currents of at least 2 m/s (Pelc & Fujita, 2002). Figure 9 shows current speed data for the southwestern portion of the English Channel and indicates areas which would be suitable for the construction of tidal turbine farms.

Fig. 9: Tidal current speeds within the English Channel (Benelghali, et al., 2007).