Skip to main content

Currently Skimming:

2 Tidal Resource Assessment
Pages 27-37

The Chapter Skim interface presents what we've algorithmically identified as the most significant single chunk of text within every page in the chapter.
Select key terms on the right to highlight them within pages of the chapter.


From page 27...
... In recent years, considerable attention has been paid to the direct exploitation of tidal currents using in-stream turbines rather than a barrage, in a manner similar to the way that wind turbines work. By way of scale comparison, a current v is equivalent to a hydraulic head of 0.5v2/g (where g is gravity)
From page 28...
... . In the United States, there are multiple tidal turbine pilot projects under way, including the Verdant project in the East River in New York, which recently received approval from the Federal Energy Regulatory Commission (FERC)
From page 29...
... 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)
From page 30...
... The tidal resource assessment group calibrated the tidal models by adjusting the single friction coefficient to improve the comparison among model results, NOAA predictions of tidal elevation and currents, and limited observations of depth-averaged tidal currents. Model calibration parameters include harmonic constituents for tidal currents and water levels, maximum/minimum tidal currents, and high/low tides.
From page 31...
... Increasing the grid resolution in local areas of a ROMS model often results in a significant increase of the total model grid size, owing to the structured-grid framework. In contrast, unstructured-grid models, which have greater flexibility for high grid resolution in complex waterways, could provide an alternative, especially for areas of complex geometry with high tidal energy (see, e.g., Patchen, 2007)
From page 32...
... For example, at the site of the Snohomish Public Utility District pilot project in Admiralty Inlet, field data from the Northwest National Marine Renewable Energy Center shows a mean power density of 2 kW/m2, which can be compared to the mean power density of 0.8 kW/m2 given by the tidal resource assessment database. Field data also show a significant ebb dominance and directional asymmetry, in contrast to flood dominance and directional symmetry given by the resource maps.
From page 33...
... If the dominant tide is the twicea-day lunar tide, Pmax is equivalent to the provision from each square meter of the bay's surface of 0.3a2 watts if a is in meters. In an area with multiple tidal constituents, the potential power is greater than that available from the dominant tide alone (see, e.g., Garrett and Cummins, 2005)
From page 34...
... In theory, this back effect is allowed for in a complete tidal fence considered in the calculation of Pmax. However, other than for the case of a complete tidal fence, which results in estimates fairly close to the theoretical resource base, the tidal resource group's assessment cannot be used to estimate directly the potential power of strong currents in specific bays if more than a few turbines are considered.
From page 35...
... However, although Pmax (suitably modified to allow for multiple tidal constituents) may be regarded as an upper bound to the theoretical resource, it is an overestimate of the technical resource, as it does not take turbine characteristics and efficiencies into account.
From page 36...
... The tidal resource assessment is likely to highlight regions of strong currents, but large uncertainties are included in its characterization of the resource. Given that errors of up to 30 percent in the estimated tidal currents translate into potential errors of more than a factor of 2 in the estimate of potential power, developers would have to perform further fieldwork and modeling, even for planning small projects with only a few turbines.
From page 37...
... as noted above, even a current of 3 m/s is equivalent to a head of only 0.5 m, much less than would be available with a barrage or lagoon; (2) the construction of a lagoon should be much simpler than the installation of a large number of in-stream turbines in a region of strong currents; and (3)


This material may be derived from roughly machine-read images, and so is provided only to facilitate research.
More information on Chapter Skim is available.