Seaflow and Optcurrent

Canada is implementing a 250 kW demonstration plant[223] but Great Britain is in­stalling and grid-connecting a 300 kW horizontal axis turbine. [224] The latter is a Joule Program project code named “Seaflow”. The “Optcurrent” project is likewise a Joule Program undertaking involving Robert Gordon University and University College of Cork, besides IT Power.

The Seaflow project utilizes a Lynmouth turbine, a horizontal axis system mounted on a rigidly fixed vertical pillar. While the Stingray (see below) involves a linear lifted based device which relies on the same operational physical principles.

8.7.1 Stingray

The “Stingray” project is underway (Fig.4). A feasibility study had been started in August 2001 and a prototype generator has been immersed off the Shetland Islands in Yell Sound, in 36 m deep water. Costing close to $3 million (C 2 million), the generator weighs 180 metric tons; the 150 kW device was financed in part by the British government’s Department of Trade and Industry. It was assembled on-shore along the Tyne River.

Due to the current’s predictability the electricity can be marketed under the ex­isting pool management regime free of under – or over-provision risk.

Stingray had a predecessor, the AWCG, a tidal stream device that used the cur­rent flowing over hydroplanes to lift a chamber up, and let it down, at the surface of the water.[225] The air in the chamber was alternately drawn in and expelled through a generator driving rotating turbine affixed on top of the chamber. The oscillating hydroplane principle was retained, though the hydroplanes are mounted on a com­pletely submerged structure. Tidal current action on the hydroplanes initiates the oscillating motion that directly operates hydraulic cylinders. The cylinders act on high-pressure hydraulic oil that drives the generator. Seabed positioning protects the device from storms and insures that it does not interfere with navigation. An environmental impact assessment was conducted.

The hydroplane is 15 m wide and is installed at 20 m above the sea bottom. The structure is 24 m high. A yaw mechanism keeps the hydroplanes aligned with the flow of water through ebb and flow. A peak hydraulic power of 250 kW was matched by a time average output of 90 kW in a 1/2 m/s measured current. A repeatable 45 kW output was attained in a 1.7 m/s current speed.

Cost-wise a price of 8-30 US cents is foreseen; technological improvements will probably lower the price of the kWh.

The machine is due to get improved hydroplane control and a new configuration. Retrieved in later 2002, the newer Stingray version was re-deployed during 2003 for a longer period of operation. A correct grasp of the resource and the effects of plac­ing multiple devices in service should be known later. According to the company involved—Engineering Business Ltd—a simultaneous program to start installation of a 5 MW version, connected with local power grids, was scheduled for July 2004.

Still in the Shetlands area, Scotland benefited from the European Union Re­gional and Urban Energy Programme.[226] Small islands would be happy recipients of electricity generated from ocean sources, e. g. Vlieland (see further below). In this project actual measurements were computer fed and, for two sites, the ensuing mathematical model showed that load factors of around 50% could be reached for 15 m-200 kW turbines rated for tidal current speeds of 2 m/s. Including installation

and grid connection costs would run close to 920,000 Euros ($1.380.000[227]) for tur­bines with a minimum life-span of 15 years; electricity could be produced at a price of 0.123 Euros ($0.144) per kWh. With theoretically eight turbines with 20 m diam­eters a price of less than 0.74 Euros ($0.87) kWh would be reached.

Updated: September 26, 2015 — 9:32 am