then be partially extracted by the second row, leaving a further reduced fraction to the third row, and so on). To estimate the fraction of recoverable power at a given point, the assessment group compared the power carried by the incident wave field to the estimated recoverable power assuming a priori a deployment of multiple devices, defined by their combination of rated power and density. This ad hoc approach prescribes such an array using a capacity packing density, specified as 10 kW, 15 kW, and 20 kW per meter. The capacity packing density is defined as “the maximum extractable power by the array of devices,” similar in concept to the rated power (maximum extractable power by a single device). The range of values chosen is based on characteristics of the Pelamis (Pelamis Wave Power) and Powerbuoy (Ocean Power Technologies) extraction devices.
Their results indicate that 29-93 percent of the theoretical resource could be captured. The assessment group assumed that the devices could be packed in a series of parallel rows perpendicular to the main incident wave direction. Such a packing process alters the wave field because of the extractive characteristics of the device and the interaction of the wave field with the device, and the quantification of those interactions and resulting wave field constitute an active field of research. A focus of this research is optimizing the device layout to maximize the fraction of power extracted by an array or multiple arrays of n devices compared to the power extracted by n independent devices. This ratio is known as the q factor and represents the interaction of the wave field with the specified device(s) (Borgarino, 2011). This q factor is not explicitly included in the group’s recoverable power estimate; however, its estimation could be implicit in the concept of capacity packing density.
One theoretical study on wave-device interaction modeled the Wave Dragon Energy Converter deployed in the highly energetic North Sea (Beels et al., 2009). It concluded that capturing 1 GW of power would require the deployment of either a 200-km-long single row of devices (5 kW/m) or a five-row staggered grid about 3 km wide and 150 km long (7 kW/m). Such capacity packing density values are significantly lower than those assumed by the assessment group. Furthermore, this result does not take into account that the recovered power must be transformed into electricity and then transmitted.
Figure 3-1 further clarifies the difference between the concepts of recoverable power and technical power. A wave energy facility will consist of many elements, such as the wave-motion absorber, the machinery to convert that motion to electrical energy, power conditioning, and power transmission. The wave-motion absorbing part of the device is unlikely to absorb more than a single-digit percentage of the incident wave energy for a typical point absorber (Falnes, 2007), but that limitation can be overcome by adding many devices, as described above. This is not