OWCs can be located on the shoreline, near-shore or offshore. Incoming surface waves induce an oscillating flow of air within the chamber which, in turn, flows backwards and forwards through an air turbine installed in a duct connecting the chamber to the atmosphere. The turbine converts this air movement into electrical energy.
The challenge of OWC technology is to achieve satisfactory efficiency over a wide operating range. The airflow not only varies between zero and 100 percent, but also changes direction. At the same time, the shaft rotation must be maintained in one direction (i.e. clockwise rotation).
Dresser-Rand patented a variable radius turbine (VRT) called the HydroAir™ turbine. Constructed to withstand the rigors of a marine environment, it uses a combination of corrosion-resistant stainless steel, aluminum and reinforced composites. In addition, it offers the following benefits when compared to other turbines being used for wave energy capture —
- Superior efficiency
- One moving part (the rotor)
- Lower rotational speeds than competing turbines (reduces friction losses)
- Currently designed up to 1MW
- Wide operating range
- Reduced noise
Simply put, the HydroAir product makes the most of the impulse turbine design which has a broad operating range, uses the VRT principle to increase the efficiency, and has minimal moving parts (no moving guide vanes or rotor blades) to ensure high reliability and reduced maintenance.