The turbine selected for the pathfinder tidal lagoon at Swansea Bay is a bi-directional, low head, Kaplan bulb hydro turbine which will be manufactured by Andritz Hydro. The turbines’ control systems, as well as the generators which are connected to the turbines and produce the renewable electricity, will be manufactured by GE Power Conversion. Andritz Hydro and GE, two of the world’s leading manufacturers of turbines and generators will join forces in a Consortium to safely and successfully deliver this state of the art equipment for the Swansea Bay Tidal Lagoon.

Project development has been steered by the most in-depth engagement of some of the world’s leading hydro turbine manufacturers in a tidal range market opportunity for many decades. This has involved the modernisation of established and proven turbine technology, resulting in higher plant efficiencies, higher energy yields and optimum energy outputs.

The maximum theoretical potential energy that can be captured by a tidal range power station over a year is termed the Emax.  Typically, proposals for a Severn Barrage and the existing tidal barrage projects worldwide extract approximately 20% of the Emax.  Through close engagement with manufacturers, extensive turbine R&D and development of Tidal Lagoon Power’s highly sophisticated energy modelling capability, we are now able to extract close to 60% Emax with bespoke tidal lagoon turbines.  This makes tidal lagoons a remarkably efficient form of power generation and has significantly reduced the cost of tidal power.  Our lagoon design has also increased flexibility of output, helping tidal lagoons to integrate with local ecosystems and ever-evolving grid demands.

GE Andritz TLSB ‘4 quadrant’ variable speed bulb turbine; image courtesy of Andritz Hydro.

Bulb turbines are commonly used in conventional run-of-river hydro projects which experience a low head range and varying flow conditions. Here are some useful facts about the Swansea turbines:

• The size of a turbine is measured by the runner (propeller) diameter. In the case of Swansea Bay Tidal Lagoon this will be 7.2m.
• There are numerous reference projects around the world which use similar bulb turbines including a similar scale tidal range project at Sihwa in South Korea, which uses 7.6m bulb turbines.
• Unlike run-of-river plants, tidal lagoons generate power on both the ebb and flood tides and so the turbines also need to be bi-directional (work in reverse).
• Swansea, as with all conventional hydropower plants, utilises the head difference between the upstream and downstream (inlet and tailwater) water levels to generate power.  The higher the head, the greater the potential energy.  In the case of a tidal lagoon the head difference is created from the natural tidal variation (tidal range) and through manipulating the lagoon levels using the turbine wicket gates to delay water from entering or leaving the lagoon until the optimum head difference is reached.
• Bulb turbines are normally ‘double regulated’, which means flow and therefore power can be adjusted mechanically in two ways: firstly by having variable pitch guide vanes called wicket gates (which can also completely stop the flow) and secondly by having a variable pitch propeller called a ‘Kaplan runner’.
• One of the pioneering aspects of the Swansea turbine is the use of variable speed (varspeed) regulation in the form of power electronics.  This gives very high efficiencies across the broad head range experienced by tidal range plants and also allows high efficiencies in reverse operation and pumping modes.
• The turbine has a four quadrant operation, which means it has four main, active, operating modes: forward turbining; reverse turbining; forward pumping; and reverse pumping.
• The turbine can also be used in ‘sluice mode’ at very low heads to adjust lagoon levels.
• The lower average rotational speed with varspeed technology also significantly reduces potential injury to fish compared to the conventional fixed speed turbines.  The addition of variable speed technology means the Swansea turbines are effectively triple regulated.
• The turbines at Swansea are encased in the concrete turbine housing and will always be submerged with the exception of when they are de-watered for maintenance or cleaning purposes. The efficiencies and overall energy production or Guaranteed Minimum Annual Energy Production is one of a raft of contractual guarantees which link back to a contractual scale model test.  This means we can guarantee with certainty the efficiency of the turbines and the annual electricity we will export onto the grid.

The key elements of a conventional hydro double regulated bulb turbine.