Tides      
Tidal power density Power of horizontal tidal currents flowing through a vertical plane of unit area.
P = ½pu3
Watts per square meter (W/m2) Horizontal kinetic energy flux; applies to a single device.
Total regional tidal resource (Garrett and Cummins, 2008) Based on annual average power available from a tidal bay or channel
Pmax = 0.22pgaQmax
Terawatt-hours per year (= 114 MW) Maximum power obtainable with a complete tidal fence; equivalent to a barrage.

NOTE:

List of variables:

p = water density

g = gravitational acceleration

S = wave spectrum (sea-surface height variance, per frequency and direction)

cg = wave group speed

f = wave frequency

θ = wave direction

l = length of coastline, depth contour, or other region

u = tidal current speed

a = tidal amplitude (half of tidal range)

Qmax = maximum horizontal tidal volume flux (over tidal cycle)

The theoretical resource, shown in the left column of the conceptual framework in Figure 1, is defined as the average annual energy production for each source of hydrokinetic energy. Determining the theoretical resource requires a series of inputs (including methods, models, assumptions, and data and observations) for each source of hydrokinetic energy (e.g., waves, tides). In response to the original DOE request, some, but not all, of the assessment groups have identified paths designed to produce two key outputs for the theoretical resource: (1) overall regional or national numbers for the U.S. theoretical resource, expressed as an average annual energy resource (typically in terawatt-hours per year); and (2) a Geographic Information System (GIS) database that represents the spatial variation in average annual power density in units appropriate for each source (i.e., watts per meter for waves or watts per square meter for tides).

The technical resource (center column in Figure 1) is defined as the portion of the theoretical resource that can be captured using a specified technology. For each resource, there are technological constraints that



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