The effect of tidal stream power conversion on the tidal regime is studied at the estuary scale. A multi-criteria method for tidal power conversion schemes to select favorable locations and to rank them according to their suitability is developed and applied to the Georgia coast.
Wave power potential is studied in an area bounded by latitudes 27°N and 38°N and longitudes 82°W and 72°W (i.e. North Carolina, South Carolina, Georgia, and northern Florida). The available data from National Data Buoy Center wave stations in the study area are examined. Temporal trends of the wave heights, wave periods and the wave power are analyzed for seasonal variations with a time scale of weeks. The time series from the wave stations are downsampled with a 15-day moving average filter with near 50% overlapping to study the seasonal trends. Power calculated from hourly significant wave heights and average wave periods is compared to power calculated using spectral wave energy density. It is found that a factor of 0.61 needs to be applied to the wave power calculated from hourly significant wave heights and average periods in order get the same results with the power calculated from spectral wave density. The mean power within 50 km of the shore is determined to be ∼9 kW/m, whereas higher power (∼15 kW/m) is available further offshore beyond the 3500 m contour line.
The tidal stream power potential along the coast of the state of Georgia is evaluated based on the available data and numerical modeling of the currents. This region has low (<0.5 m/s) to moderate (<0.8 m/s) average tidal currents along most of the coast, but with the possibility of relatively very strong (>1.0 m/s) local currents within its complex network of tidal rivers and inlets between barrier islands. The limited number of tidal current prediction locations is not sufficient to resolve the temporal and spatial changes in the current speeds and patterns. Therefore, the currents are modeled with the Regional Ocean Modeling System (ROMS) to determine the locations with high tidal stream power potential. The modeling results show that the areas with the highest tidal power density on the Georgia coast are a part of the Intercoastal Waterway between the Altamaha and Doboy Sounds and a part of the Canoochee River. The tidal power densities based on one-month simulations at these locations are computed to be on the level of 1600 W/m2, 1400 W/m2 and 1100 W/m2, respectively. The Savannah River is also found to have areas with high tidal power density in the region. One-year time series are generated by harmonic analysis of model results, and used to calculate the annual average power and energy at selected locations in the Savannah, Ogeechee and Altamaha Rivers. Annual average power at these locations are found to be respectively, 1.3 MW, 3.0 MW and 1.9 MW, which corresponds to annual energy of 112 GWh/year, 258 GWh/year, and 162 GWh/year. The distribution of tidal current magnitudes and tidal power densities in a year is provided with histograms for each location.
The effect of power extraction on estuarine hydrodynamics is simulated by implementing an additional retarding force in the governing momentum equations in ROMS. Two different power extraction schemes are simulated in the Ogeechee River. The first scheme involves power extraction across the entire cross-section of the river, and causes considerable changes in the original currents, water levels and original undisturbed tidal power. The second extraction scheme, where power is extracted from a part of the cross-section is found to have substantially lower impact on the original flow than the first scheme, but extracts higher power from the flow despite having a smaller area to capture power. This is attributed to the recovery in the flow momentum on the unconstructed part of the river cross-section in the second scheme.
A multi-criteria assessment methodology that accounts for the physical, environmental and socioeconomic constraints is proposed to select the most suitable locations for tidal stream power converters. The proposed method is applied to the Georgia coast to find and rank the best locations for power conversion. A demonstrative ranking procedure shows that Medway River has one of the best locations for tidal power conversion on the coast of Georgia.