Abstract
Wave Energy Converters (WEC) possess the potential to power systems capable of delivering sustainable potable water, helping to address the escalating scarcity of this vital resource. Moreover, these systems create a niche market avenue for the advancement of wave energy technology while addressing this critical need. There are two main ways in which WECs can produce drinking water. The first is simply using the electricity generated from a WEC to power a separate desalination system. The second is to use a Wave Driven Desalination System (WDDS), where the motion of the WEC directly drives a piston which pressurizes seawater. The pressurized seawater is then used as the feed flow into a reverse osmosis (RO) membrane, which separates the sea water into water with low salinity (permeate) and water with high salinity (brine). Due to the direct transformation of mechanical energy from the waves to pressurized seawater, WDDSs hold promise to desalinate water with greater efficiency than methods that require intermediary conversion to electricity. The potential for direct pressurization of seawater for desalination is unique to WECs as compared to other forms of renewable energy which require the intermediary conversion to electricity. This allows WDDSs to be less complex and potentially more efficient than solar or wind powered desalination systems.
Impedance matching can have a significant impact when applied to WEC power-take off (PTO) systems. Impedance matching ensures the impedance of a subsystem meshes well with the impedance of surrounding systems and the anticipated input frequencies. In one study the optimal PTO impedance increased electrical power production by 22%. It is reasonable to assume that impedance matching could have a similar impact for WDDS applications.
WecOptTool (an open-source, pseudo-spectral WEC control co-design software developed by Sandia National Lab) is a useful tool for PTO impedance optimization for electricity generation, however, it is not suited for WDDS PTOs. There are non-linear kinematics that are unable to be modeled, impedances that do not fit the assumptions made by WecOptTool, and the nature of a controller is much different in a system without electrical components.
This presentation will present a new piece of software that is an add-on to WecOptTool enabling WDDS impedance matching studies. The software consists of a class that extends the PTO class from WecOptTool but changes some features and adds extra methods that enable WDDS developers to utilize the pseudo-spectral method from WecOptTool for WDDS modeling. The software is capable of modeling and optimizing a variety of different hydraulic circuit components, including throttle valves, check valves, hydraulic accumulators, and pressure exchangers.
The software also has potential extensions to non-desalination applications where the WecOptTool PTO class fails to fully address needs. Projects involving hydraulic PTOs and more detailed PTO design (such as WEC driven carbon sequestration) may also benefit from this software and may motivate development of similar software for other niche WEC projects.