The Starwind5 is equipped with OptiflowTM Savonius Cups mounted on each centre strut to ensure consistent fast startup at 2.5 m/sec. wind speed, efficiently trap gusts in low and medium wind speeds up to 6 m/sec, and safely regulate the top rotational speed (rpm) at 24 m/sec wind speeds and higher in order to protect the generator sub system, thus ensuring a 25 year useful life in the field. Starwind5 is mounted 25% to 35% lower than conventional 3 or 5 blade HAWT propeller turbines or 3 blade VAWT turbines because of higher solidity, that is more push and flying surface, found in the specially designed five blade Starwind5 turbine and its special airfoil shapes and blade mount telemetry.
Starwind5 began life as Darwind5 in 2011, where you can read more about this on Gizmag here: Starwind5’s predecessor Darwind5 on Gizmag
Starwind5 and Darwind5 share exactly the same aerodynamic airfoil properties with Starwind5 adding additional performance improvements via OptiflowTM, and through the use of the symmetrical rotor shape, Starwind5 can now be ordered in both clockwise and counterclockwise configurations for project sites wishing to use Starwind5 in a compact hi power/hectare foot print.
Starwind5’s OptiflowTM has a “Five fold” feature set which is the key to having the Starwind5 generating electricity at higher wind speeds over 15 m/s, doing so with lower cost generators sets equipped to handle a wider range of RPMs, thus ensuring the capture of the most useful high wind speed kinetic power for conversion to electricity, while ensuring consistent sub 3 m/s startup and low and medium wind gusts (Brief Accelerations).
All of the above are key in the efficient conversion of low speed trickle charge air flows, low and medium speed gust accelerations and continuous high speed gales into electricity needed to reach “Best in class AEP” and ultimately “Best in class LCOE”.
Starwind5 OptiflowTM is really a system of wind turbine geometry and telemetry making use of air pressure (any engineer will tell you “pressure is our friend”) to deliver 35% better AEP “Annual Energy Production” via the following 5 physical/mechanical or “Aerodynamic – Aero-elastic” attributes:
Lift Generating Darrieus “Eggbeater” Rotor Blade Profile Shape, Airfoil Shape, Rotor blade Angle, and Rotor Blade Offset contributing to positive rotation.
Push Generating Strut Integrated Savonius Scoops, Savonius Trailing Edge and Savonius Rotor Blade Offset during the Darrieus Lift “Stall” phases of the blade (1 on the windward side, 1 one the leeward side) contributing to positive rotation.
Centripetal Forward Rotation Preservation via Weighted Rotor Blade Centers , outside diameter Weighted caps, cowlings, cross flow balancing and shear control limiting center rotor blade mounted SBVGs “Sub Boundary Vortex Generators” (which keeps the rotor blade stable in accelerations, limiting vibration which will disrupt aerodynamic lift performance if allowed), and a generator set housing flywheel combined with a generator set housing driven wheel raceway, all designed to preserve forward rotation.
Wide RPM range Capable Low Cost Generator Sets with skewed magnets and/or coils to reduce cogging at early startup and in low and medium winds, yet still well within their NP “Nameplate” limits at the top speed of the wind turbine rotor.
Aerodynamic Assisted Braking Capabilities providing generator set burnout protection via regulation of the rotor system top rpm 10% within the limits of the generator set NP nameplate.
These 5 key features of Starwind5 Optiflow tm are what deliver 50-65% of the value in the LCOE equation to create best in class AEP, however none of it would be possible without Feature #5 , Aerodynamic Assisted Braking Capabilities, which we have added to Starwind5 based on what we learned from the Darwind5 Field Tests (five of them) performed in June of 2012.
The basic Aerodynamic Darrieus Lift and Savonius push features found in Darwind5 are the same in Starwind5, so at Starwind5 we know our real world field test data (see Darwind5 on Gizmag) are a key part shaping Starwind5’s evolved design and improved aerodynamic performance (Cp) and we have built on that Darwind5 break through performance discovery with improvements in Features #3 & #4, and now we have added the all new Feature #5, which finally, inexpensively and reliably solves the braking challenge (burnout protection) which all VAWTS and HAWTS have faced in the past and still face today (addressed with costly electro-mechanical braking, per our previous post).
Generally Starwind5 Optiflow tm Aerodynamic Assisted Braking is achieved as follows:
Managed Generator Set Cooling Air Intake and Exhaust – using the internal flow resistance (in the form of air pressure) to slow wind turbine forward rotation in outside wind speeds over 15 m/s by driving internal airflow through the filtered air intake which is then passed over the gensets (to meet cooling requirements) where the waste heated air flow is then passed through the genset housing exhaust blower and out the sidewall lip and the floor pan exhaust holes, assisted by he driven wheel fan spokes, where some of the same heated airflow is blown into and up the interior of the rotor blades and out through the top cowling, and also up and around both sets of bearings on the inside of the floating shaft and out through the cap.
Managed Air Cross Flow Eddies off the Rotor Blade Mounted Savonius Scoop Fairing : at high speeds starting at 15 m/s the shedding eddies coming of the surface of the flexible (formed to be concave at these +15 m/s speeds) become large and elongated, creating more turbulent and less stable airflow for the succeeding rotor blade both upstream (ino the wind) and downstream(with the wind) at TSRs (Tip Speed Ratios) higher than 2.5 (this means the rotor center is moving 2.5X faster than the current wind speed). This Savonius Scoop Fairing generated shedding eddy turbulence reduces the Darrieus Lift factor of the succeeding rotor blade airfoil shape, which dynamically slows the forward rotation of the rotor blade system, whereby 21 m/s the Starwind5 rotor system meets maximum rpm and where,
Dynamic Solidity Sizing to Throttle Air Cross Flow Pass Through the Five Blade Rotor System:reduces the amount of Darrieus lift surface exposed on each rotor blade thereby reducing forward rotation. Essentially the faster the Rotor Blade System spins, the more solid it’s 3D shape becomes on the top and bottom of what is essentially an ellipsoid (like an egg solid shape) , where the Air Cross Flow is redirected around the top and bottom of the 3D shape and now throw and over those top and bottom portions of the blade. Interestingly the horizontal load characteristics only increase marginally, which means the kN “Kilo Newton” loads which need to be supported by the tower or pole on which the Starwind5 are mounted are actually 35% less than HAWTS (which spin to become a solid disk) and straight blade VAWTS (Gyromills which become a solid can, with lots of drag on the straight vertical surfaces and on the top and bottom tips of these blades). What this means is that Starwind5 tower costs are 50% less than any other competitor producing the same amount of power. (Competitor towers must be larger, taller, with more material, and bigger foundations, with more labor costs attached.)
High Five for Starwind5!
It’s been a long design, engineering and test road we have been down as it has taken much time and $$$ to develop Starwind5’s Aerodynamic Assisted Braking Capabilities, and yes, we have indeed relied on the latest VAWT simulation tools (QBlade from TU Berlin, is worth a mention here, see our previous post on Wake management and Turbine spacing) to help us determine Cp performance and AEP layered on top of existing field data from Darwind5.
The good news is, Starwind5’s latest simulation results for Starwind5 OptiflowTM have been excellent (including our wake analysis which sees Starwind5 deliver best in class power/hectare with very tight spacing). The results have confirmed our LCOE and AEP targets, so now it’s time to bring Starwind5 to market to help our partners and end users reap the benefits of best in class AEP and LCOE.