Development of a Horizontal-Axis H-Darrieus Turbine as a Wave Energy Converter: Semi-Analytical Study on Coastal Wave Characteristics for Conceptual Design

A horizontal-axis H-Darrieus turbine has been developed as a wave energy converter (WEC) to harness energy from coastal waves. In this paper, a semi-analytical method is presented to quantify the wave power contributing to power generation by the H-Darrieus WEC and to assess the distribution of wave power resources. Furthermore, the semi-analytical method incorporating insights from the rotational mechanisms of the H-Darrieus turbine is applied at the Seragaki littoral zone (Okinawa, Japan) and provides the rationale for determining the conceptual design, including installation site, underwater velocity, turbine diameter, rotational speed, and power output. Under a typical swell condition at Seragaki, wave power density of 25 kW/m was calculated right before wave breaking. Given the water depth and underwater flow velocity at this location, a turbine diameter of 2 m, a rotational speed of 120–180 rpm, and a power generation per unit turbine-swept area of 2 kW/m2 were determined as the conceptual design.