potential for misuse. Although such estimates might provide broad order-of-magnitude estimates of which resources have the greatest potential, the conceptual framework shown in Figure 1 clearly illustrates that there are many extraction filters needed to determine the technical resource. The assessment groups can only assess a few of these filters, and many of the filters require assumptions about which particular MHK technologies will be used. Moreover, a wide array and diversity of socioeconomic filters ultimately limit only a portion of this technical resource base to be representative of what the maximum practicable, extractable energy might be from MHK resources.
WAVE RESOURCE ASSESSMENT
Power in ocean waves originates as wind energy that is transferred to the sea surface when wind blows over large areas of the ocean. The resulting wave field consists of a collection of waves at different frequencies traveling in various directions, typically characterized by a directional wave spectrum. These waves travel efficiently away from the area of generation across the ocean to deliver their power to nearshore areas.
Wave power density is usually characterized as power per length of wave crest; it represents all the energy crossing a vertical plane of unit width per unit time. This vertical plane is oriented along the wave crest and extends from the sea surface down to the seafloor. To capture this orientation, wave power is expressed as a vector quantity, and accurate representation of its magnitude and direction requires the consideration of the full directional wave spectrum. Note that the wave energy conversion devices currently under development are designed to operate at different locations in the water column, and only a portion of this overall wave power may be available to these devices (e.g., devices that respond only to heave motions associated with the waves). As noted in the discussion above of the committee’s conceptual model, the considerations of the amount of power that can be extracted by specific wave power devices are incorporated in the estimation of the technical resource.
Because wave energy travels in a particular direction, care must be taken when interpreting maps that show wave power density as a function of location but do not indicate predominant wave directions. It also must be recognized that if the energy is removed from the wave field at one location, by definition less energy will be available in the shadow of the extraction device. It would not be expected that a second row of wave energy extraction devices would perform the same as the first row of devices that the wave field encountered, because any recovery of the