FIGURE 2-1 Turbine designs for U.S. tidal energy pilot projects. SOURCE: Verdant Power; Ocean Renewable Power Company; OpenHydro.
Another important consideration is the large-scale far-field back effect of an array of turbines. In addition to local flow disturbance around an individual turbine, drag associated with the presence of turbines will reduce large-scale flow. Open water currents will tend to avoid and flow around a region of extra drag associated with a turbine array, while the presence of turbines in confined channels will reduce the overall volume flux through the whole channel. The potential of a single turbine may be reasonably assessed using the natural flow, but the extra power from the addition of more turbines to an array will eventually be offset by the lower power due to reduction in flow from the turbines already present. The maximum power Pmax (the theoretical resource) that can be achieved can be assessed only after taking large-scale back effects into account.
The tidal resource assessment group conducted its tidal energy assessment study by developing a set of models to simulate all U.S. coastal regions and to estimate the maximum tidal energy based on predicted