The "ΡC" WEC in "Offshore Wave and Wind Together; Afloat" –3 Years' Progress
Brown, Neal A.
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Offshore wind and wave power can be remarkably complimentary. Given an extended, stable floating platform to share, important economies of renewable power production and energy storage are possible. The Pneumatically Stabilized Platform (PSP) embodies such a platform. Developed with DARPA support and proved in model scale, the PSP will achieve its at-sea motion stability and structural loads mitigation by decoupling the "hull" from ocean wave pressures through the partial use of air buoyancy. In addition to supporting an array of WTs, the PSP deploys along its seaward edge the "Rho-Cee" WEC, termed the "Impedance-Matched Terminator"; comprising a nested set of tuned OWC absorbers, resonant across a selected frequency band. By means of impedance matching, highly efficient wave energy absorption may be achieved, and has been demonstrated in tests. Procedures and results of those tests are summarized. However, attempts to optimize the design for minimum cost, per unit of delivered energy, show that the "efficiency" of absorption is largely dictated by economics, rather than physics, and is typically smaller than that attainable. Three PTO types are considered The PSP and Rho-Cee WEC are constructed, modularly, in pre-stressed reinforced concrete, which is found degradation-free in long term exposure to sea water – and only concrete touches sea water in the platform, WEC or WT systems. All equipment subject to maintenance, replacement or inspection is "in-the-dry"– fully accessible to platform-resident personnel on foot, dry-shod. As an effective breakwater, the WEC-lined PSP ensures ready access by personnel and equipment in high sea conditions. The reduced cost and enhanced availability for such maintenance should yield significant economies. With integral foundations, WTs deployed upon such a floating platform can be located offshore in more favorable winds (and less visibility); avoiding prohibitive foundation/installation costs, and in the greater water depths favorable to the WECs;