In a major step forward in the search for sustainable renewable energy sources, Design Thinking Solutions (DTS), a South African-based company, has invented technologies that allow for the design and construction of large sea current and wind driven turbines, which when used in combination will provide a large base load and peak power availability.
“The DTS design allows us to manage the load bearing parts effectively,” says Anton Cordier, director for engineering and design at DTS. “This enables us to design and build very large wind turbines that are less complicated to run, and require a smaller capital investment to manufacture.”
“Current commercially available Horizontal Axis Wind Turbine (HAWT) designs reach cost and construction limitations from about 3MW upwards,” he continues. “Without these restrictions, we believe there would be much larger HAWTs on the market. As of 2010, the maximum power capacity of a HAWT design is 7MW based on very high wind speeds.”
Cordier conceived the HAWT Kite concept and, jointly with Dr Becker van Niekerk, developed the DTS wind and sea current turbines. “Our constrained flying wing HAWT Kite can sweep through a larger sky area and generate more power per unit of time than static ground-based three blade wind turbines.” According to Cordier, work commenced with 20MW at 40 kilometres per hour wind for the HAWT Kite and 400MW for the Sea Current Turbines (SCT) Kite at a sea current design flow speed of approximately 7 kilometres per hour.
The difference between the DTS HAWT Kite and those currently in operation is the use of multiple propeller-driven generators mounted on the leading and trailing edges of one or more free pitching wings, which are supported on aerofoil blades. The blades in turn are connected to a centrally mounted idler shaft capable of pivoting around a support tower. All the thrust loads generated by the wings and blades during operation are transmitted to the ground through a tether connected to a mobile mounted anchor point on the ground. This, in turn, travels in a circle around the wind turbine. Cordier has coined the design as being a “HAWT Kite”.
The design obviates the need to control rotational speed of the main rotor assembly to ensure constant alternating current frequency (RSA 50 Hz). It is also not necessary to use variable pitch controlled propeller blades to maintain electricity supply frequency. The control tail fitted to the wings ensures a lift: drag ratio designed for optimum electricity generation. Electricity is then transmitted via cables to a supply substation without having to use slip rings.
The company further proposes that by utilising pumped storage schemes in combination to their solutions it would be possible to store the extra energy available in the integrated system to adequately power the peak demands in the grid at all times.
DTS is presently developing additional types of SCT Kites, all of which fly similarly to a wind kite, but are mounted in the ocean current running steady at +/-2 metres/second with a tether anchoring the system to the sea bed.
Cordier and his team are particularly excited about two of these designs. “One option flies from side to side in the current, while the other remains stationary as prop-on wing turbine generators rotate around an idler spindle.” In all instances, large power outputs are possible, and being mounted in the sea current off-shore and submerged, power is available on a continuous basis, and not prone to the non-availability of wind supply problems associated with HAWT farms. “It is also not foreseen that the designs will harbour any major environmental concerns to sea life at this stage, and they are deemed as appropriate as ship propellers,” he adds.
“The materials and generators required for both wind and sea turbines are much the same as those currently used internationally and we are confident that the majority of our equipment can be manufactured in South Africa.
Progress on design is advancing steadily and Cordier believes that the detail design on both turbines will be completed by the end of 2011. Plans are then to build a 1.5MW prototype HAWT Kite, and a 5MW SCT Kite.
1. DTS Caption:
All the thrust loads generated by the wings and blades during operation are transmitted to the ground through a tether connected to a mobile mounted anchor point on the ground