40 JUNE 2014 • WORLD AQUACULTURE • WWW.WAS.ORG Projected Performance We have made a series of performance projections using the estimated loads for a typical aquaculture application and projected power output from a scaled-up version of the Lifesaver WEC. Figures 3-5 below show projected performance in three different weeks, in three different wave conditions. The calculations were made using power output data and projected energy consumption, battery charging and diesel operation for a notional hybrid wave/ diesel system over a 24-hour period. Figure 3 shows performance of the system in a week with relatively low wave energy. For this scenario, the diesel provides a substantial amount of the required ily accommodate the difference in housekeeping and feeding power requirements, at the cost of lower efficiency for housekeeping. Any alternative energy source must demonstrate high levels of reliability (which implies simplicity of design), high operational availability to produce energy in the design sea states, survivability in the ocean environment, and longevity. Because the peak power requirement is about a factor of four times the housekeeping requirement, alternative energy sources will require some form of storage. Technology An attractive alternative energy source for offshore aquaculture operations is wave energy conversion. There are and have been many concepts for wave energy conversion (WEC) devices in both deep and shallow water. Most of these have been intended for large, grid-scale (megaWatt plus) applications. An exception to this is the Lifesaver technology developed by Fred. Olsen Wave (Fig. 1). This design is simple, robust, and scalable. The Fred. Olsen Lifesaver WEC technology has been developed over the past 12 years. This unit has been installed and operating at the Falmouth Bay wave energy test site off Falmouth, UK for the past 24 months. The Lifesaver unit has been in continuous operation and has demonstrated exceptional reliability in service. Each Lifesaver can support three to five 15-kW (depending on wave conditions) power takeoff units (PTOs). The system is very scalable both in size of the buoy and number of PTO units, down to a single PTO. The unit is modular in design, and each element of the system is over-the-road or standard 40-ft ISO container transportable. It is easily assembled and tested at a port with limited facilities and can be towed to the operational location with relatively small vessels (tugs or offshore support vessels). Concept Description A conceptual system consists of the following components: • Surface Wave Energy Conversion (WEC) buoy using Fred. Olsen Lifesaver PTO technology, with a “virtual bottom” for mooring and reaction forces for the WEC (if required by water depth) • Battery energy storage for power conditioning and backup power • Mooring system for appropriate water depths • Sensors as determined by operator requirements • Local processing with reprogrammable event recognition and reporting • Event alert transmission, via RF (extended WiFi or other). The conceptual system (Fig. 2) includes the wave energy converter buoy and power takeoff system; a “virtual bottom” (if required for the water depth); and the mooring system. The virtual bottom is a buoyant subsurface float supported by the main mooring system and providing the reaction force for the WEC. In addition, the virtual bottom increases efficiency because the the mooring system of the WEC is not moving through the water. The system continuously generates electricity that is stored and conditioned on an aquaculture support systems float. The system is moored with conventional or Marine MicropileTM anchors. The energy storage system is sized to provide peak power when required and to accommodate the base load power as needed during periods of low waves. For most applications, a small auto-start diesel provides additional backup power. TOP TO BOTTOM. FIGURE 3. Performance of a hybrid wave/diesel operation in a week with low wave energy. FIGURE 4. Performance of a hybrid wave/diesel operation in a week with moderate wave energy. FIGURE 5. Performance of a hybrid wave/diesel operation in a week with high wave energy.
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