Since 1997, The Engineering Business Ltd (EB) has been developing tidal stream generation technology. In 2002 EB designed, built and installed the worlds first full-scale tidal stream generator, the 150kW Stingray demonstrator. The Stingray concept is that the energy within tidal currents can be harnessed through oscillating hydroplanes. A full description of the concept and technology is presented in the Phase 1 and Phase 2 reports. Stingray was reinstalled in Tell Sound in the Shetland Islands between July and September 2003 for Phase 3 of the project. This report presents an overview of this phase of the project, the results obtained and outlines the implications of those results on the potential for commercial electricity generation.
The fundamental objective of the project was to demonstrate that electricity could be generated at a potentially commercially viable unit energy cost utilizing Stingray technology. In addition to this, a number of measurable targets for the Phase 3 operations were agreed with the DTI.
The aim of the marine operations was to undertake a series of tests, at slack water and on the flood tide, to reconfirm basic machine characteristics, develop the control strategy and demonstrate performance and power collection through periods of continuous operation.
A summary of the main test work findings is as follows:
- Basic machine characteristics were found to be in good agreement with previous test work.
- Power cycle development enabled significant gains to be make on the levels achieved in 2002, with further gains clearly available. Control through the cycle still remains the key issue particularly as regards the introduction of the high hydroplane actuation flows required for faster cycle times.
- Actuation power consumption was higher than expected at the cycle times achieved although much of the reason for this lies in poor control and significant efficiency gains should be realizable once this area is improved.
- Overall power generation was demonstrated on several occasions as cumulative energy collection through the course of a tide. A continuous operation period over 14 tides was also attempted - the levels of power collected would have been in excess of target values but machine downtime due to minor failures prevented operation on some of the tides.
- Useful data on the interaction of Stingray with the tidal regime was acquired and analyzed.
- A decommissioning survey and environmental review have identified that Stingray has had no identifiable impact on the seabed environment during its two operating seasons.
- The cost modeling indicates a future unit energy cost of 6.7p/kWh at the stage when 100MW of Stingray capacity has been installed.
Although compliance with the targets set by the DTI was at a lower level than would have been hoped, the broader aims were met in the majority of cases. There is evidence to suggest that the technology is capable of full compliance with all targets that remain relevant.