Superior turbine efficiency enabled by the turning mechanism and its integration with the optimized turbine and caisson


Turret with turning mechanism

A cost effective and feasible way to turn a turbine

The rotating turret is the core of the Tidetec concept. The main intention of the turret is to turn the turbine, to enable optimal bi-directional functionality. Tidetec have a portfolio of patented turning mechanisms suited to different turbines.

Our engineering of the turret has shown that it is feasible and economical to apply this to a two-way working turbine. The cost of a complete 20 MW turbine system be more or less equal to the cost of the systems planned today. This is due to an increase in cost because of the turret (10%), and a decrease of turbine cost due to simpler turbine design. Feed engineering has been conducted for the complete turning system, to have a reliable cost estimate.

The rolling turret, is based on a cylinder rotating around a horizontal axis. It has bearings on each side of the cylinder, avoiding the need for a thrust bearing. A hollow axle (shaft) is mounted on one side of the cylinder, where all cables and cable management evacuates into a dry room in the caisson. This axle is also where the rotating movement of the turret is actuated.

Turret Dimensioning

Dimensioning and stress tests have been conducted on a 6 meter diameter turret. The turret has more than sufficient capacity to withstand the hydrostatic pressure and the axial force of the turbine during operation.


Variable speed Straflo-type turbine

As the Tidetec solution is a new conceptual way of using a low-head hydro turbine, in principle any low-head hydro turbine can be applied, however some turbines are better than others, due to their size. Tidetec in collaboration with TUM have developed a low head turbine that is capable of generating energy in both flow directions, “basin to sea” and “sea to basin” and also of pumping in those directions. This means the turbine can operate in all four quadrants of a head discharge-diagram.

A variable speed tubular Straflo turbine is used in the design of the Tidetec turbine. The variable speed turbine will be equipped with adjustable guide vanes, fixed runner blades and a turning mechanism. This design permits an optimal four-quadrant-operation. Turbine efficiency in turbining mode is simulated to be above 90%. The turbine runner and guide vanes have been optimised for 2 to 8 meter head using ANSYS and Solidworks.

The Straflo turbine is a well know turbine with almost 100 existing installations. It has also been used in tidal barrage application at Annapolis Tidal power plant.


Housing the turbine

Tidetec’s turbine solution is intended to fit into a concrete structure (caisson), which is part of a dam/barrage/lagoon. The purpose of this construction is to separate two water masses, as well as housing the turbine. The construction will consist of three elements; sluices, caisson for turbine placement in addition to a passive breakwater. The caisson is constructed with ease of maintenance in mind, so all critical areas are easily accessible.


Tidetec’s technology is covered by patents, with the latest being granted 2017

Through the PCT system, patents are valid in most countries with significant tidal power resources: UK, Russia, France, Spain, Portugal, Korea, Japan, EU, Germany, China, Canada in addition to in Norway.


Showcasing the turning mechanism

The Tidetec prototype for the turret and turning mechanism was tested in the Svelvik tidal stream during September to October 2016. The main purpose was to showcase and prove the concept, to show the robustness of the turning mechanism, the ability to keep the intended areas dry and operational in harsh sea water conditions.

The prototype consists of a polymer caisson, a steel turret with a turbine and a rotating drive and CPU to control the timing and set points of the rotation. The prototype is instrumented to make sure that all activity is logged, and to secure that the system is working as intended. Test data and additional documentation can be acquired on request .