1 Statistical analysis of power production from OWC type wave energy converters L. Martinelli 1 , B. Zanuttigh 1 and J. P. Kofoed 2 1 DISTART, University of Bologna, Viale Risorgimento 2, 40136 Bologna, Italy E-mail: luca.martinelli@mail.ing.unibo.it, barbara.zanuttigh@unibo.it 2 Wave Energy Research Group, Department of Civil Engineering, Aalborg University, Sohngaardsholmsvej 57, 9000 Aalborg, Denmark E-mail: jpk@civil.aau.dk Abstract Oscillating Water Column based wave energy plants built so far have experienced a low efficiency in the conversion of the bidirectional oscillating flow. A new concept is considered here, the LeanCon Wave Energy Converter (WEC), that unifies the flow direction by use of non-return valves, into a unidirectional flow, making the use of more efficient air turbines possible. Hereby, a more steady flow is also obtained. The general objective of this note is to examine, the power take off (PTO) efficiency under irregular wave conditions, for WECs with flow redirection. Final practical aim is to identify a method that allows the choice of the optimal power generation capacity for which the device should be designed, when subjected to any given wave climate. The analysis is based on the experimental results of existing tests carried out in the 3D deep water wave tank at Aalborg University, Denmark. First, the power measured at the modelled PTO is compared with the available incident wave power in order to examine the overall system response in a scale- independent manner. Then, the power production density function is fitted to a simplified shape, whose parameters are related to the tested sea state conditions (wave period, wave height). Average performance and stochastic variability is thus obtained for any sea state and therefore also for the annual wave climate of interest. An example application of a LeanCon unit is carried out for a location off-shore Cagliari (Italy). Conclusions provide economic criteria for estimating the optimal value of power for which the PTO should be designed. Keywords: power production, oscillating water column, statistic distribution. © Proceedings of the 8th European Wave and Tidal Energy Conference, Uppsala, Sweden, 2009 List of symbols d = OWC draft g = gravity acceleration H s = significant wave height L o = wave length based on T m-1 p = pressure P = power produced by the OWC P W = wave power s o = wave steepness based on T m-1 T m-1 = spectral wave period T p = peak wave period v = air velocity t = time g = parameter of the lognormal distribution l = parameter of the lognormal distribution μ = average value of the lognormal distribution r = water density s = variance of the lognormal distribution Subscripts d = daily value e = exit i = in m = mean value y = yearly value Superscripts ′ = non dimensional value (with the average power) 1 Introduction This note addresses a class of floating wave energy converters (WEC) of the oscillating water column (OWC) type, that unifies the flow direction by use of non-return valves, into a unidirectional flow, making the use of more efficient air turbines possible. Hereby, a more steady flow is also obtained. The specific concept under investigation is the LeanCon (www.leancon.com). 295