LONDON — In recent months, a number of initiatives aimed at speeding up the development of the wave energy sector have been launched in the U.S. and Europe. As part of the ongoing work to establish a viable United States wave energy industry, the National Renewable Energy Laboratory (NREL) and Sandia National Laboratories (SANDIA) are working on the creation of a sophisticated open-source modeling tool known as WEC-Sim — and the U.S. Department of Energy is also enlisting the coding community to help in its development. Meanwhile, the European WavePOD project is an industry-wide initiative that aims to solve the problem of converting captured wave energy into electricity by creating a “standardised self-contained offshore electricity generator for the wave industry.”
Last year, the U.S. Department of Energy (DOE) funded NREL and SANDIA to work on a three-year collaborative project to develop a simulation tool for the wave energy sector. A little over a year into the project, the team has already released the first version of the Wave Energy Converter Simulator (WEC-Sim), a customisable open-source numerical modeling tool designed to help the wave energy community to analyse and optimise wave-energy converters (WECs) and meet device-specific modeling needs.
As Kelley Ruehl, Technical Staff Member at the Water Power Technologies Department at Sandia National Laboratories, and one of the Principal WEC-Sim Developers, explains, the tool is capable of modeling wave energy devices that are comprised of “rigid bodies, power-take-off systems, and mooring systems” with simulations “performed in the time-domain by solving the governing WEC equations of motion in 6 degrees-of-freedom.”
“The WEC industry relies heavily on numerical modeling tools during the device design and optimisation process. The existing WEC modeling tools are closed-source and cannot be customised to meet device specific modeling needs. WEC-Sim provides the WEC community with an open-source tool that will allow the industry to develop new and innovative WEC devices,” she says.
The code that underpins the tool is developed with a combination of the MATLAB (Matrix Laboratory) programming language and the Simulink data flow graphical programming language tool — using a “multi-body dynamics solver” known as SimMechanics. According to Ruehl, the code solves the “governing WEC equations of motion in 6 degrees-of-freedom” using what is known as the Cummins impulse response formulation — the equation of motion most commonly used to model the dynamics of a body in water, including ships and WECs.
Throughout 2014, NREL and SANDIA have worked to develop the first version (v1.0) of the code and have tested its capabilities through loose collaboration with several U.S. industry members. Ruehl also reveals that, in 2015, the WEC-Sim team plans to work with several device developers to demonstrate and verify the performance of the tool — and will participate in “an international code-to-code comparison and validation effort.”
“In order to ensure WEC-Sim is meeting the needs of industry, the team has reached out to several US industry members to determine features for future development of the WEC-Sim code. Based on this feedback, and the WEC-Sim Questionnaire, the WEC-Sim team has focused its code development,” she says.
For Ruehl, the key advantage of the WEC-Sim tool in the development of innovative wave energy technologies is the fact that the code is open source and allows users to “modify the code to meet their specific modeling needs.” In her view, this feature is critical for the WEC industry because the “wide range of existing technologies’ makes it ‘difficult to create a code capable of modeling them all.”
“These challenges will be overcome by opening development of future WEC-Sim features using the public development platform GitHub in order to accommodate the diversity of existing devices,” she adds.
Looking ahead, the SANDIA-NREL team plans to continue the development of the WEC-Sim code using user feedback provided via direct interaction and an online questionnaire. Ruehl says that the team will also perform experimental wave tank texts for WEC-Sim code validation in 2015.
“In 2015, we are also considering the advantages of moving to a completely open-source coding language. Although WEC-Sim is open source, it is implemented in the MATLAB environment and we are considering moving the code to a Python-based environment. This will [provide] researchers who do not have access to MATLAB [with] the ability to use the WEC-Sim tool,” she adds.
In recognition of the central role that such numerical tools will continue to play in the WEC design and analysis process, the DOE has also launched the Open Wave Analysis and Response Program (Open-WARP) Challenge to further improve the WEC-Sim tool.
As Alison Labonte, Marine and Hydrokinetic Technology Manager at the DOE explains, one “critical piece” of WEC-Sim is the boundary element method (BEM) module that “provides hydrodynamic coefficients that are needed for time-domain WEC-Sim simulations.”
“The objective of the Open-WARP project is to create a boundary element method module. To date, several competitions have been completed. The objectives of these competitions have been to create a mesh generation capability and a Graphical User Interface (GUI). Upcoming competitions will be to improve existing open-source BEM codes so they meet the requirements of WEC-Sim,” she adds.
According to Labonte, none of the models and tools developed as part of the program have yet been used in the wave energy technology sector — with the results of the contest set to be released to the public in 2015.
“The wave energy research community is relatively small and does not have expertise in all areas of coding an algorithm development. Using code competitions allows the ocean energy community to tap into the coding expertise of the online coding community to leverage expertise in specific areas of knowledge,” says Labonte.
“The online coding community has a great deal of expertise in algorithm development and coding that has proved to be very beneficial to the Open-WARP project. However, many competitions require specific knowledge of fluid dynamics. We are therefore working to encourage the WEC code development community to participate in future Open-WARP competitions, especially those that require specific knowledge of fluid dynamics,” she adds.
Wave Energy Conversion (WEC) Prize Competition
During September, the DOE also announced that it will award $6.5 million to a Prize Administration team led by Ricardo Inc. for the “development, launch, and execution” of the Wave Energy Conversion (WEC) Prize Competition. The company will work alongside JZ Consulting in “challenge development and management expertise,’ with SANDIA and NREL contributing “engineering and technical expertise.” According to a press release timed to coincide with announcement, the WEC Prize competition “aims to attract innovative ideas from developers by offering a monetary prize purse and providing an opportunity for tank testing and evaluation of scaled WEC prototypes.”
The DOE believes that the competition will achieve “game-changing performance enhancements to WEC devices” — and help to establish a pathway to “sweeping cost reductions at a commercial scale.” Further information about registering for the WEC Prize competition will be available on the Water Power Program website in Spring 2015.
Meanwhile, in Europe, WavePOD is an industry-wide initiative that aims to solve the problem of converting captured wave energy into electricity by creating a “standardised self-contained offshore electricity generator for the wave industry” that is designed to be suitable for a number of different wave energy concepts.
The WavePOD test rig
The initiative brings together project founders Aquamarine Power and Bosch Rexroth, along with wave technology developers Albatern, Carnegie Wave Energy UK and M4 WavePower. Other partners include the Offshore Renewable Energy Catapult, the University College Dublin Electrical Research Centre and the Institute for Fluid Power Drives and Controls (IFAS) at RWTH Aachen University, as well as Irish utility ESB — which is developing the European Commission-funded Westwave wave farm off the west coast of Ireland.
As Louis Verdegem, Ocean Energy Technology Manager at Bosch Rexroth explains, individual wave device manufacturers have previously been working on the issue in isolation from each other — but WavePOD marks a “step change” in this approach by combining the collective experience of the leading wave industry developers and Bosch Rexroth to take “a system-wide approach to Power Take Off (PTO) that can be used across all devices.”
The technology is based on an oil hydraulic system that takes reciprocating motion and converts it into rotary motion to drive a generator — and Verdegem reveals that the hydraulic system itself is a “proven mature technology” that is already used in a number of industries.
“The WavePOD project is focused on adapting this technology for the specific requirements of the wave industry. If successful, it will see Bosch Rexroth provide the complete PTO system, taking responsibility for conversion, control and instrumentation from the mechanical input to the export cable — including the environmental control and enclosure ‘pod’ technology,” he adds.
Maximizing Power Capture
Once proven, Verdegem claims that the WavePOD technology will allow developers to supply “a reliable, cost-effective source of reusable energy” that will allow the individual businesses that comprise the industry “to concentrate on what they do best” — namely “maximising the amount of power that can be captured, optimising structural design and developing deployment methods.”
However, he also admits that the project team will need to rise to the technological challenge posed by the need meet the requirements of a machine “that needs to stay in near constant operation for up to five years.”
“In addition, there are a wide range of input conditions that need to be taken into account, without resulting in a solution that becomes cost prohibitive. Operationally, the biggest challenge is to ensure that the system is reliable and has sufficient redundancy to cover for the inevitable minor failures and maintain power output between maintenance. Both of these lead to the big financial challenge of making the cost of the electricity generated economical,” he adds.
The project team has already created a tenth-scale prototype, which is currently undergoing testing at the IFAS in Germany. The next step will be to scale up the prototype and begin testing and developing the technology “in more difficult conditions.”
“In the longer term, when the systems are proven, we expect to apply the lessons to any number of wave energy developers. What is interesting about the wave energy sector is that the technology solutions are so diverse, with each adapted to differing locations and positions in the water. As a result, it’s unlikely that there will be just one technology that would be used at all depths and environments. However, WavePOD will be applicable to all devices,” says Verdegem.
Developing Reliable Technologies
Commenting on the project, Sian George, CEO at pan-European trade association Ocean Energy Europe reveals that there is “substantial renewable energy potential,” estimated at around 320 GW, to be harnessed from Europe’s oceans — but the industry is “still some way away” from having commercially available wave energy devices capable of capturing this energy. For her, the key challenge at the moment is delivering technologies “that can operate reliably in the harsh ocean environment.”
“[I]f the WavePOD consortium is successful in delivering a product which can be used by wave energy companies to accelerate our progress towards more reliable and commercial technologies, then the market could be significant,” she says.
“At our Ocean Energy Europe conference in Paris we heard from a number of industry leaders the importance of increased collaboration. We have made significant strides in recent years in demonstrating the viability of ocean energy technologies and our next step is to solve some quite specific and well recognised pan-industry technology challenges. There is growing consensus that the best way to address these challenges is through a collaborative approach — and the WavePOD project is a very good example of how this can be achieved,” she adds.