Evolution of “Daisy” Kite-ring-turbine Concepts..
The “Daisy” kite turbine concept, started from asking if the radii of an autogyro kite turbine (Such as the superturbine® by Doug Selsam) can be significantly expand to increase the torque capability and power scalability?
An initial concept proposed flying kites radially outward from a relatively small, inner tensile ring-to-ring torque transmission system. The concept would have been very difficult to control. Torsion would have crushed the transmission, twisting the lines together.
To overcome this problem, the topmost ring part was made as wide as the rotary path. Kites were then fixed directly to a wide diameter ring. Kites can now have their bridles fixed onto tethers and lower rings. The multiple fixing points help to stabilise the kite-blades.
A presumed need for high rigidity in wide ring designs, seemingly posed a severe mass scaling penalty. However, it was realised that the ring can be operated as a tensile component. The rings hold their form by exploiting inflating and centrifugal properties of multiple rotary kite blades.
The tensile kite-ring configuration stabilises individual kite motion. Similarly, a kite arch can stabilise hundreds of individual kites on a wide anchored shared line.
A cone of kite material was tested to help the kite-rings inflate. The cone material is unnecessary. In operation, compression from torque transmission is counteracted, by the inflating dynamic of multiple banked blade aerodynamic forces.
Multiple small blades are easily held apart and supported for launch and landing by a large diameter carbon ring. Normal tethering holds the kite-ring set axially. This effectively stabilises the kites into a collected rotary motion. The turbine blade path stays within the restrictions of the full set of connected network components.
Separating the tethers around the axis, allows them to transmit torque to another ring. Torque is transmitted through a series of rings. The lowest ring, at ground level, drives a generator. The kite-ring autogyro rotation is retarded by force transmission over the series of rings.
Stacking for Efficiency
Tests of kite ring stacking demonstrated modular scaling capability. Adding extra kite-ring layers on top of a turbine stack, adds little line length per turbine blade area. The stacking kite-ring-turbines improved efficiency. Stacked kite-ring-turbines contribute less line drag per kite blade area.
In tests, rigid kite blades were more efficient than ram-air parafoil kite blades.
Basic Lift and Safe Rigging
A lifting kite provides extra lift to stabilise the kite-turbine and to fix the elevation angle. The lift kite attaches to the top of the kite-turbine, via an inline bearing. The lift line has a back anchoring line, to set the elevation and provide a safety line, preventing breakaway. The back line is also used in launching, stall and recovery operations.
The tethers gradually terminate (from line to webbing strap), onto a power take off wheel rim. This removes the line wear problem of alternative kite-power designs.
The system is mechanically autonomous. Prototyping was done within a very modest budget. This mechanical “drag mode” operation significantly simplifies control and reliability. This method avoided the intense modelling and control, required by other airborne wind energy projects.
Network architecture has safety and robustness benefits. By connecting to multiple lines, no component breaks away if a single line breaks. The turbine performance degrades but stays operable even if multiple lines break.
Simple Continuous Output
Continuous rotary output allows standard power meters to be used for testing. Continuous rotary output also simplified power generation and measurement through electronic speed controllers.
This is the only airborne wind energy method which produces continuous power output.
Tests and models show how joining lifter kites together, with a top layer network and wide anchoring, smooths individual lift kite motion. Kite-turbines can likely be arrayed in a farm topology under a form reconfigurable, stabilising lift kite network. This would further maximise deployment density.
Modelling suggests, modular kite-turbines allow large scalability. Rings can be stacked. Kite numbers per ring can be increased. Further kite-rings can be added concentrically.
Kite turbines can seemingly support any number of blades in operation, as long as the blades inflate the turbine.
Each blade dynamic has to encourage a collected expansion and lift in the line, then torque can be successfully transmitted over the separated tethers.
Scaling the power by increasing the number of kites on the network has many benefits over scaling the size of single unit kites. Network kite components can be made in smaller facilities. They are more easily deployed and cheaply maintained. Their power to weight can be more easily maximised
Whereas scaling up a single kite unit, decreases power to weight ratio and increases the necessary wind speed and tether weight. Scaling a single unit kite uses more land & increases operational risk.
Scaling kite-turbine power by kite-blade numbers can optimise power density for a given volume of air, and reduce operational risk of airborne wind energy production.