Tidal Stream Power Web GIS Tool

The GIS tools allow the user to view the full spatial distribution of the pre-calculated available power density and then to enter bathymetric constraints and energy converter specific parameters to tailor the output for particular regions.

The GIS model consists of a database containing results from the tidal model and several computational tools which extract useful information for the user. The database consists of the tidal constituents for the water level, depth-averaged currents, and the MLLW depths at a high resolution (10-500m spacing). These tidal constituents are used to derive velocity, power density and other parameters of interest as requested by the user in near real time.

Overview

The GIS tools allow the user to view the full spatial distribution of the pre-calculated available power density and then to enter bathymetric constraints and energy converter specific parameters to tailor the output for particular regions.[1]

The GIS model consists of a database containing results from the tidal model and several computational tools which extract useful information for the user. The database consists of the tidal constituents for the water level, depth-averaged currents, and the MLLW depths at a high resolution (10-500m spacing). These tidal constituents are used to derive velocity, power density and other parameters of interest as requested by the user in near real time.[1]

The interactive, web-based GIS system has been developed by the Center for GIS at Georgia Tech[2] in order to facilitate dissemination of the tidal data to interested users. The presentation of the data and results has been designed in a manner equally accessible and useful to both specialists and a lay audience. The published maps and the database provide the distribution of the existing kinetic power density of tidal streams in the undisturbed flow conditions.[1]

Data Layers

The web application consists of multiple layers that can be turned on and off through the data layers widget. The widget allows the transparency of each layer to be adjusted with a slider. The color mapped raster layers include the water depth, the mean current speed (one month average of depth integrated tidal current speed) and the mean kinetic power density (one month average of kinetic power density based on depth integrated tidal current speed). These layers are generated by interpolating the model results from computational grids onto an ArcGIS raster grid with 0.003° resolution and are useful for a quick visual examination.[1]

Developing the Tidal Stream Power GIS Tools

The GIS tools allow the user to view the full spatial distribution of the pre-calculated available power density and then to input power density and bathymetric constraints to tailor the output for particular regions.

• Depth Filter - Tidal stream energy converters are currently limited in their variety and are primarily classified in vertical and horizontal axis devices with open or shrouded rotors. Independent of their design all the devices have depth requirement based on their dimensions. The first step for assisting in site selection is to determine which locations meet the minimum depth requirements. Generally these requirements are based on minimum height of the prototype above the bed (hb), the minimum clearance of the prototype below the surface (hs) and the device dimensions (dp). The minimum depth (hmin) would then be given as $h_{min} = +h_b +h_s +d_p$.[3]
• Velocity Histograms - The model runs produce time series of the velocity which are 32 days long. The first 2 days were neglected for the computations of the tidal constituents. For the 32 day simulations, these constituents were used to create a new time series of the velocity for an entire year. The one year of hourly data was then be used to create a probability histogram of the velocity magnitude. The tool computes the histograms for sections of the coast as specified by the user. The user can also view or extract the resulting histograms or other statistics at any particular location.[3]
• Compute Available Power Densities - The histograms of distribution of annual tidal current velocity were used to compute a histogram of total available power density. These histograms can be used to compute the annual average available power at all locations. Similar to the velocity histograms, the user can view or extract the histograms and statistics of the available power density. In addition, the spatial distribution of the average annual available power was computed and displayed as the pre-calculated available power for the webpage. This can be filtered by the depth constraint previously specified.[3]
• Compute Total Available Power - Based on the feedback from a project workshop in Atlanta with outside experts, the Garrett and Cummings method for calculating the tidal stream energy potential was applied to the 4-5 regions with the most potential to provide an initial estimate of the available resource with a gamma value of 1.[3]
• Web Based Interface - Results from this study have been made available via an internet web site. An interactive, web-based GIS system has been developed to facilitate dissemination of the tidal data to interested users in a manner equally accessible and useful to both specialists and a lay audience.[3]