Assessment of Energy Production Potential from Tidal Streams in the United States

Abstract

Executive SummaryTidal stream energy is one of the alternative energy sources that are renewable and clean. With the constantly increasing effort in promoting alternative energy, tidal streams have become one of the more promising energy sources due to their continuous, predictable and spatially-concentrated characteristics. However, the present lack of a full spatial-temporal assessment of tidal currents for the U.S. coastline down to the scale of individual devices is a barrier to the comprehensive development of tidal current energy technology. This project created a national database of tidal stream energy potential, as well as a GIS tool usable by industry in order to accelerate the market for tidal energy conversion technology.Tidal currents are numerically modeled with the Regional Ocean Modeling System and calibrated with the available measurements of tidal current speed and water level surface. The performance of the model in predicting the tidal currents and water levels is assessed with an independent validation. The geodatabase is published at a public domain via a spatial database engine and interactive tools to select, query and download the data are provided. Regions with the maximum of the average kinetic power density larger than 500 W/m 2 (corresponding to a current speed of ~1 m/s), surface area larger than 0.5 km 2 and depth larger than 5 m are defined as hotspots and list of hotspots along the USA coast is documented. The results of the regional assessment show that the state of Alaska (AK) contains the largest number of locations with considerably high kinetic power density, and is followed by, Maine (ME), Washington (WA), Oregon (OR), California (CA), New Hampshire (NH), Massachusetts (MA), New York (NY), New Jersey (NJ), North and South Carolina (NC, SC), Georgia (GA), and Florida (FL). The average tidal stream power density at some of these locations can be larger than 8 kW/m 2 with surface areas on the order of few hundred kilometers squared, and depths larger than 100 meters. The Cook Inlet in AK is found to have a substantially large tidal stream power density sustained over a very large area. BackgroundTidal streams are high velocity sea currents created by periodic horizontal movement of the tides, often magnified by local topographical features such as headlands, inlets to inland lagoons, and straits. As tides ebb and flow, currents are often generated in coastal waters. In many places the shape of the seabed forces water to flow through narrow channels, or around headlands. Tidal stream energy extraction is derived from the kinetic energy of the moving flow; analogous to the way a wind turbine operates in air, and as such differs from tidal barrages, which create a head of water for energy extraction. A tidal stream energy converter extracts and converts the mechanical energy in the current into a transmittable energy form. A variety of conversion devices are currently being proposed or are under active development, from a water turbine similar to a scaled wind turbine, driving a...

A Tidal Hydrodynamic Model for Cook Inlet, Alaska, to Support Tidal Energy Resource Characterization

“…Overall, the differences between predicted and observed tidal phases are mostly on the order of a few degrees for major tidal constituents. The error statistics suggest that model-predicted tidal elevations match NOAA observations generally better than those (e.g., an average of 10% over-prediction in M2 amplitude) reported in the earlier study [17]. For example, in the earlier study [17], the amplitude difference for M2 constituent between model prediction and field observation at Nikiski tidal gage was 0.17 m (or 7% less than the observed value).…”

“…The inlet has long been regarded as one of the top candidates for tidal energy development (e.g., [17,27,28]) because of its extremely large tidal ranges. For instance, the Turnagain Arm near the northern end has the largest tidal range in the U.S.; it has a mean of 9.2 m. Tidal fluctuations in the main body of Cook Inlet, while not as extreme as those in the shallow and narrow Turnagain Arm, regularly reach 7 m or higher during the spring tide.…”

“…In the U.S., the first nationwide assessment of tidal stream energy production potential was released in 2011 [17]. In this assessment, the Regional Ocean Modeling System (ROMS) was applied to more than 50 individual coastal subdomains along the U.S. coastline.…”

“…Coastal circulation models have been widely used to support earlier-stage tidal energy development by providing a large-scale assessment of theoretically and practically available tidal energy resources, as well as the potential physical impact of energy extraction [5,6,8,11,[17][18][19][20][21][22][23][24][25]. In these studies, both structured-grid and unstructured-grid coastal circulation models have been used.…”

“…The objective of this study was to develop and validate an unstructured-grid, tidal hydrodynamic model framework for Cook Inlet, Alaska to support tidal energy research in this energetic tidal system. Compared to the first nation-wide tidal energy resource assessment by Haas et al [17], this study uses an unstructured-grid modeling approach. The model grid can be easily refined on an as-needed basis at local scales to provide a higher-resolution representation of tidal velocity and energy resource distributions at potential energy hotspots.…”