Energy efficiency of pneumatic power take-off for wave energy converter

Abstract

This paper investigates the energy efficiency of a pneumatic power transmission which serves as power take-off for a small-scale, low cost, portable wave energy converter. The wave energy converter was implemented and tested as a prototype in the Eastern Mediterranean. The power transmission uses a standard cylinder as a pump with check valves for flow rectification. Air is stored in an accumulator and discharged through a vane motor coupled to a brushed DC generator which is connected to an electrical load. Numerical models are given for each component of the system which allow to calculate the component and system losses for a range of operating conditions. Experimental results are presented from laboratory tests with the power take-off system. Measurements are conducted at steady state, transient, as well as simulated wave conditions using a hydraulic wave simulator. The measurements validate the predicted losses of the numerical models. The losses in each part of the power transmission are graphically illustrated with a Sankey diagram. We conclude that even though the overall efficiency is low, the setup serves well as a low cost instructional tool to teach principles of wave energy harvesting and to demonstrate typical challenges faced in the design of wave energy converters and pneumatic power transmission. © 2015 Elsevier Ltd All rights reserved.