In the transition to renewable energy, harvesting the power from oceanic waves is often mentioned to be next step after the deployment of wind energy technology. Although many different solutions for wave energy conversion (WEC) are being developed and financial support schemes exist, commercially extracting this energy seems however to be rather challenging. Major troubles are over-priced first projects and incapability to endure year-round oceanic conditions. While the costs are expected to reduce once a successful WEC-device enters large scale production, it is unclear what device type would be the most viable. This study presents a combination of available methods and tools that together allow to assess viability of WEC-devices in early stage of development. Prior to including economic factors, the most important aspect that defines viability is power performance. Comparing simulated power performance of different concepts for WEC is complicated by their different level of optimization of control strategies. Renowned studies that compared the power performance of various device types have been extended by calculating the viability for one particular promising device type: the quasi-rigid, submerged pressure differential device. This device appears promising being protected by its submerged position, while performing as if it was placed in the high intensity waves at the surface. The diffraction software tools commonly used for hydrodynamic calculations, could not be applied to calculate quasi-rigid (volume-changing) objects. For this problem a method is suggested which adds the functionality of panel selection to exclude surface areas of a body design for hydrodynamic calculation. In this thesis both the average power performance in time-domain simulations and the maximum power limits were calculated in order to compare the submerged pressure differential device to other point absorbing WEC-devices. The suggested methods contribute to defining a generic way of comparing future concepts for WEC to converge towards a single approach and select WEC-devices for investment.