The September 2010 issue of Power Electronics Technology (page 18) described Aquamarine Power’s system in Scotland that converts ocean wave energy into electricity. The system performs hydrodynamic-to-mechanical, mechanical to hydraulic, hydraulic-to-mechanical and mechanical to electrical energy. Key to the system is the Oyster wave energy converter shown in Fig.1. Fig. 2 shows a typical system configuration.
Aquamarine Power provided details of planned improvements to the Oyster 800 wave energy device, together with some recent production figures. The improvements, known as the Oyster 800 Product Improvement Programme, involve shutting down the Oyster 800 – which has been operating since February at the European Marine Energy Centre in Orkney.
During the summer work will take place in five specific areas on the machine – with the overall goals of improving performance, reliability and availability of the nearshore wave technology.
“Since the Oyster 800 flap was raised from the seabed on February 14 this year, we have learned a tremendous amount about how Oyster operates in real sea conditions,” says Aquamarine Power Chief Executive Officer Martin McAdam.
“This year the Oyster 800 has been operational in significant wave heights of 5.3 metres* and peak waves of 9 metres. The concept works, and our onshore hydroelectric plant is operating well. The Oyster 800 structure has performed well in the most arduous storm conditions.
“We are now starting to see some very promising power production figures – including sustained generation of 1MWh in a five hour period. Normally the system operates on two power production cylinders, but since February Oyster 800 has been operating on only one functioning cylinder – a capability we included in the original design – which makes the figures even more encouraging.
“Although Oyster 800 operated intermittently during summer 2012, the initial challenges and commissioning difficulties resulted in minimal electrical output, so this year is the first time we have generated significant power and operating data.
“We have been as open as we can about the challenges we face, particularly in this hostile offshore environment. Many components, including control and instrumentation cable connectors, hydraulic hoses, non-return valves and accumulators have performed much less reliably than expected.
“For example, Oyster uses four non-return valves on each of its two hydraulic cylinder modules. As part of the Oyster 800 test programme we installed four from one manufacturer on one cylinder and four from a different manufacturer on the other cylinder.
“Whilst the valves on one cylinder have operated perfectly since installation, the other set of non-return valves failed from the outset. We've spent time with the manufacturer of the failed valves to understand the failure and design upgraded valve components. This way we are both learning, and developing expertise within the supply chain. It is a similar story with our hydraulic hoses, accumulators and control and instrumentation systems. Most of the components that have failed are used regularly in the deep water offshore oil and gas industry; however they have failed in the highly turbulent, highly oxygenated nearshore wave environment. We are now working with the supply chain and are testing new components. Already we have redesigned many of them to cope with these conditions.
“As a result of these equipment failures the volume of our power production and availability figures have been lower than they could be, but we believe it is important to take a measured, long-term view.
“We are now implementing our Product Improvement Programme. This is a planned shutdown that will allow us to install significant upgrades in five key areas:
1. Installation of enhanced cylinder and accumulator modules with upgraded hoses, non-return valves and instrumentation.
2. Installation of an enhanced control and instrumentation architecture with upgraded cable connectors.
3. Implementation of reliability-enhancing measures following general feedback and learning to date from technical subsea issues.
4. Analysis of all data generated on the machine to improve operating procedures and overall machine efficiency
5. Increasing the performance of the on-shore header tank, filtration plant and accumulator plant.
“We believe this is the best and most cost-effective way of using what we have learned so far to improve the Oyster 800’s performance and reliability. Our goal is to have the Oyster 800 operating with increased reliability through the coming winter.
“The Oyster concept is now proven. I’d like to thank our investors for their ongoing support and patience and the team at Aquamarine Power for their commitment and endurance. Our focus is now on improving the reliability, performance and reducing the cost of the technology. Our ultimate goal is an industry in Scotland producing commercially competitive wave energy machines in the years ahead,” McAdam concludes.
Key Operational Data
February 14 – Oyster 800 flap raised from seabed and placed in operational mode
February 27 – Commences electrical power generation
February 28 – First continuous 24 hour generation
April 29 – 1 MWh generated in 5 hours on a single power cylinder (we believe this to be the highest sustained power output of any wave energy machine in the world)
April 29 – 2 MWh generated in 13 hours and 50 minutes (single cylinder operation)
July 1 – While testing onshore performance enhancement options 1 MWh generated in 9 hours
Total – Around 10 MWh generated in 144 hours of operation
* The significant wave height (SWH or Hs) is defined as the mean wave height (trough to crest) of the highest third of the waves.
To see video footage of the Oyster 800 in high waves please go to the Aquamarine website.