Corpower’s wave energy concept

The Wave Energy Converters are point absorber type, with a heaving buoy on the surface absorbing energy from ocean waves. The buoy is connected to the seabed using a tensioned mooring system. Novel phase control technology makes the compact devices oscillate in resonance with the incoming waves, strongly amplifying the motion and power capture. The system has improved survivability in storms, thanks to its inherent transparency to incoming wave energy in long storm waves.

The concept offers five times more energy per ton of device compared to previously known wave technologies. The high structural efficiency allows for a large amount of energy to be harvested using a relatively small and low-cost device, reducing the equipment (CAPEX) cost per MW capacity. The compact and lightweight WECs are also easy to install and maintain using low-cost vessels, bringing down operational (OPEX) costs. All together this provides competitive cost-of-energy.

Generators and power electronics are standard components known from the wind industry, enabling well known grid connection architecture. Our product concept is optimized for 10MW clusters, where the electricity is collected from an array of WECs into a collection hub. Each 10MW hub delivers grid quality electricity with standard 33/66kV electrical connection commonly used in offshore wind, with a single control and data acquisition interface over fibre and radio-link to the hub. Each WEC operate autonomously by a programmable logic controller located inside the device.

The wave farm concept is based on combining WEC clusters in arrays, connecting to a common grid export cable. The electrical architecture is chosen to allow export cables and substations to be shared with offshore wind, for projects aiming to take advantage of the complementary production profile between the wave and wind resource to deliver more continuous output from the array.

The array concept with many small units allows for mass production to drive down the cost per unit. An effective maintenance scheme is offered based on either replacing entire units or performing simple maintenance work offshore, improving farm uptime and providing overall reduction of O&M cost. The replacement scheme is enabled by the small physical size and limited cost per system, allowing simple handling and reasonable investment in spare units.

Design philosophy

Inspired by the pumping principle of the human heart, CorPower uses stored pressure to generate energy from waves in two directions. The human heart uses stored hydraulic pressure to provide force for the return stroke, thereby only requiring the muscles of the heart to pump in one direction. In a similar way, CorPower WEC uses a pre-tension system to pull the buoy downwards.

It mimics the energy storage aspect of the human heart whereby the upward force of a wave swell pushes the buoy upwards while the stored pressure provides the restoring force drives the buoy downwards. This results in an equal energy production in both directions, and a lightweight system that is naturally transparent (detuned) unless actively controlled to match the wave climate. The CorPower WEC converts energy from waves into electricity through the rise and fall as well as the back and forth motion of waves.

A composite buoy, interacting with this wave motion, drives a Power Take Off (drive train located inside the buoy) that converts the mechanical energy into electricity.  The light composite buoy is connected to the seabed through a power conversion module and a tension leg mooring system. In a conventional point absorber, the buoy follows the motion of the waves. The CorPower WEC on the other hand uses control technology to better leverage the motion of the waves by giving the oscillating motion optimal timing with each wave.

CorPower Portugal Manager Miguel Silva offers exclusive Q&A ahead of flagship HiWave-5 project

CorPower Ocean is currently laying the foundations for its flagship HiWave-5 Project in northern Portugal, representing the firm’s first commercial-scale deployment.

In a recent Q&A Portugal Country Manager Miguel Silva helps set the scene from base camp in Viana do Castelo. A hive of activity since a 16MEUR investment in summer 2020, the site will form the launchpad for HiWave-5 and further support the long-term development of supply and service capacity for commercial wave energy farms.

What have been CorPower’s key developments since its multi-million investment in Viana do Castelo in July 2020?
Miguel Silva, CorPower Portugal Manager: “Since the investment announcement back in July 2020 we have achieved a number of our preliminary objectives including the development of a new Manufacturing, Research & Development Centre. This building is prepared for two main tasks. The first being the Composite Hull Development Programme, and later the integration of the hull with the PTO (Power Take Off) system which is being constructed in Sweden. To make this happen, we have installed a new medium voltage power line along with comprehensive systems which support the composite development and fabrication. This includes air cleaning systems and environmental control together with sufficient health and safety systems to operate all the tasks required for the composite winding cell. Meanwhile, we have also been installing and commissioning our filament winding machine. In parallel, we have developed a material qualification programme, that is informing our designers in Sweden with the necessary data to complete the design of the hull. In addition, we are gaining the necessary expertise to operate the filament winding machine, which is truly innovative in terms of its dimensions and the overall approach to manufacturing and fabrication.”

The stage is being set in northern Portugal for CorPower’s flagship HiWave-5 project. Our Composite Manufacturing Facility in Viana do Castelo has reached an important milestone of process qualification ahead of fabrication of the first full scale composite hulls.

What facilities does CorPower have in Viana do Castelo?
Miguel Silva, CorPower Portugal Manager: “CorPower has chosen the Port City of Viana do Castelo in northern Portugal as the primary base for the Composite Hull Development Programme. Our main building will have two distinct areas – the first dedicated to the composite development programme and the fabrication of four hulls, for four separate Wave Energy Converters due for deployment in the next two years. The other area is set aside for the integration, and later on the Operation and Maintenance of the devices. Later this year members from our Swedish team will arrive, together with the PTO system, to complete the integration process with the composite hull from Portugal ahead of preparations for deployment at sea. After deployment and the necessary number of hours of operations, we will be able to easily retrieve our devices from the sea due to the base location less than 50m from the water. From there we will execute our O&M tasks from inside the building making any necessary repairs and upgrades.”

What is the ‘mobile factory concept’ and the rationale behind it?
Miguel Silva, CorPower Portugal Manager: ‘The ‘mobile factory’ concept is one of the underlying principles of the Composite Hull Development Programme. Due to the dimensions of the hull it will always be a challenge to move the components through a logistics chain. However, to address this issue we have developed and continue to gather knowledge on the ‘mobile factory’ concept in Viana do Castelo. The idea is to prove and demonstrate that this mobility can be achieved, and that we can produce a high number of units near project locations. The idea is to take the factory to the deployment location where we can fabricate on-site eliminating many logistical issues, and reducing CO2 emissions related to cumbersome transportation of the hulls. We will take all the lessons learned from this first experience to complete the front-end engineering for the next mobile factories due for deployment around the world, most likely starting in Europe in the following years.”

What is happening in Viana do Castelo to prepare for the HiWave-5 deployment?
Miguel Silva, CorPower Portugal Manager: “There are three key activities taking place. The first one will be the installation of a new submarine cable in Agucadoura, Póvoa de Varzim. It will be unloaded here in the harbour of Viana do Castelo and reloaded to the installation vessel. Next and in parallel we are testing our anchoring system in field test in Aveiro. But most important for us here in Viana and connected to the composite program development is the actual manufacturing, fabrication of the first hull.”

How will the Viana site underpin CorPower’s broader expansion plans moving forward?
Miguel Silva, CorPower Portugal Manager: “As we are developing and building knowledge here in Viana do Castelo, mainly on the Composite Hull Development programme and also later on the main marine operations connected with the management of the actual devices in the wave energy array in Agucadoura, we are collecting and generating a lot of knowhow. This  knowledge will always be connected to this region and the people that are living here and working with us.”

How does CorPower’s investment in Portugal align with the nation’s wider renewables/ ocean energy strategy?
Miguel Silva, CorPower Portugal Manager: “CorPower has taken a very active role in the broader discussion on Portugal’s National Strategy for the Sea 2030. Looking at that document, CorPower is contributing to 5 of the 10 key objectives including knowledge generation, business growth and de-carbonisation. Most importantly we are involved in one of the priority intervention areas regarding ambitious marine renewable energy targets to deliver 370MW by 2030.”

Key components

Pre-tensionning system

The pre-tension system provides downward force on the buoy, replacing the mass that would otherwise be needed to balance the buoyancy at midpoint. As a result, the natural period of oscillation of the WEC is reduced, providing a period of oscillation which is shorter than all ocean waves. This natural state of the machine is the detuned mode where the device has little response to incoming wave.

Waves spring phase control

WaveSpring provides a negative spring function to the system, giving it an inherently resonant response over a wide bandwidth. Optimised phase control is provided without information on incoming waves. The WaveSpring function is deactivated in storms, thereby detuning the device to give significantly reduced loading and improved survivability. In such storm protection mode the WEC is highly transparent to waves. In operational mode the WEC response is amplified and the operation is close to optimal from a hydrodynamic point of view.

Cascade gear technology

The wave energy absorbed into linear motion along the buoy axis is converted into electricity by the mechanical drive train located inside the buoy. A key component is the Cascade gearbox, which efficiently converts linear motion to rotating motion. It has a design principle similar to a planetary gearbox, and divides a large load onto a multiple of small gears which allows highly efficient and robust conversion of linear motion to rotation. The gearbox industrialisation has been done in partnership with Swepart Transmission, a major gearbox manufacturer. Their sister company Cascade Drives brings this revolutionary technology to industrial application outside ocean energy.

Structure product verification

CorPower follows a structured five-stage product verification process, established as best practice for ocean energy development by International Energy Agency-OES, ETIP Ocean and funders such as Wave Energy Scotland. It involves step-wise validation of survivability, performance, reliability and economics starting with small scale prototypes in Stage 1, continued by sub-system testing and then fully integrated WECs in increasing scales up to array demonstration in Stage 5. The purpose of this process is to address risks in a managed way early on in the product development process, while costs are still limited due to smaller device scale and team size. Prior testing of multiple prototypes has been completed during Stages 1 to 3 in Portugal, France, Sweden and Scotland between 2012 until 2018. The Stage 3 program (HiWave-3) saw a large scale (1:2) Wave Energy Converter system taken through structured verification, first by dry rig testing in Stockholm followed by ocean deployment at the European Marine Energy Centre in Orkney (Scotland). They are currently in Stage 4 designing the first full scale WEC system named C4.

Stage 1 – Concept validation using modelling, scale 1:30 tank testing (Portugal) and scale 1:10 PTO component testing (Sweden) during 2012-2013. Took the technology from TRL 1 to TRL 3.

Stage 2 – Critical systems verification through tank tests at scale 1:16 (France) and PTO dry HIL-rig test (Sweden) at scale 1:3 during 2014-2015. Took the technology from TRL 4 to TRL 5

Stage 3 (C3) – Demonstration and certification by DNV GL using a complete 1:2 scale WEC, with dry testing (Sweden) and ocean deployment (Scotland) during 2015-2018. Took the technology from TRL 5 to TRL 6.

Stage 4 (C4)– Demonstration and prototype certification of single full scale C4 WEC, dry testing and ocean deployment, planned for 2018-2021. Ongoing. Taking the technology from TRL 6 to TRL 7.

Stage 5 (C5) – Demonstration and type certification of pilot array with three C5 WECs, dry testing and ocean deployment, planned for 2022-2023. Taking the technology from TRL 7 to TRL 8.

Dry testing

CorPower has invested in advanced dry testing capabilities by developing bespoke test rigs capable of accurately simulating the loading the WEC devices will experience in the ocean, starting in a controlled machine hall environment.

The C3 device was debugged and stabilized by an extensive dry test campaign to verify functions, performance and reliability prior to ocean deployment. This allowed control and safety functions to be tested and tuned, initially with gentle loads and low velocities before ramping up the simulated sea conditions to reach full storm loads.

Operating the equipment in the high load regime allowed adjustment and verification of the machine over longer periods. Performing such dry testing in a machine hall provided ease of access to equipment and a high degree of instrumentation improved understanding of machine behaviour, contributing to an effective test and stabilization program.

Once the C3 device was installed in the ocean it operated with high reliability, much thanks to the debugging and stabilization performed in dry testing.