Starwind5 Optiflow Assisted Aerodynamic Braking delivers Best in Class LCOE for small wind

Copyright Harvistor LLC 2015 All Rights Reserved., R. Reive

This is a bit of a coming out party for Starwind5, describing at a high level how Starwind5 Optiflow tm really delivers “Best in class LCOE”  via best in class AEP “Annual Energy Production”. Before we go into the how, let’s first revisit LCOE:

Best in class LCOE  Levelized Cost of Energy in the power generation world, is akin to “TCO”, Total Cost of Ownership in the IT world. So most of us old IT, factory control, mobile telecoms and software security types can easily relate to LCOE once the connection is made to TCO.

How the best Levelized Cost of Energy LCOE is realized has to do with a number of factors, the most important factor we think, per my previous post, being AEP “Annual Energy Production”. In fact we think at Starwind5, AEP contributes at least 50% and as much as 65% of the value received in getting to a “Best  in Class LCOE”, depending on what rate the utility will pay for electricity sold back to the public grid, which we knows varies from state to state or country to country. (and in some cases even country to county, given local rates and incentives).

When comparing small generation facility solutions, for sure AEP is certainly the most heavily weighted factor in the overall LCOE equation when evaluating vendor solution offerings, and directly linked to the performance capabilities of the generation components of the solution.

For buyers and implementers of small hybrid renewable generation to do a proper comparison, they need vendor transparency, and they they need the performance specifications to be real.

Unfortunately for the small wind generation component of these hybrid renewable generation solutions sees most small wind vendors provide simulator or wind tunnel generated “Co-efficient of Power” or CP “power curve” data to represent their performance under the best possible conditions extrapolated into a Cost/W NP “Name Plate” , which means how much does the wind turbine cost per generator set kiloWatt  based  on the bench tested peak continuous  output rating called “Nameplate” or NP. This method can be very misleading in that each wind site has different Weibull wind speed distributions at different times in the year for different heights, coupled with the fact most small vendors really leave it up to the end user or installer to get the siting right. The result has been many more unhappy small wind turbine owners than happy owners, and we aim to fix that at Starwind5.

Weibull Speed vs Power

A Weibull Distribution Curve for Wind:

How More Kinetic Energy in Wind occurs in less Frequently Occurring Higher Wind Speeds


Why it is important for small wind turbines to capture and convert to electricity these higher wind speeds to yield a best in class AEP Annual Energy Production number.

To make matters worse, many vendors today generate their best guess AEP Annual Energy Production by extrapolating their Cp against an average site Weibull Distribution curve, that is a bell curve of wind speed % of time occurrences over the course of 1 to 10 years for the “typical”  wind site, which for most vendors is never clearly described. Generally most vendors will take their wind tunnel and or simulator data, and assume the “mean” of the Weibull bell curve distribution is 7 m/s, where most of the % time occurrence occurs left of the mean at lower speeds, and lesser % occurs to the right of the mean. So three abstractions later we get an AEP number from the small wind vendor for a particular model which could be out by as much as 50% for a particular end user site. This type of small vendor AEP reporting makes no end user happy.

Weibull Speed Power AEP

A Big Wind Example of Weibull Curve and Power Curve used together to extrapolate AEP

Also, what most small wind vendors don’t explain is that at higher wind speeds, there is significantly more kinetic energy in the wind due to pressure loads, which increases lift factors and rotational speeds, where the latter requires braking at some point to ensure generator set burnout protection, per my earlier post.

For example, a “standard” Weibull Curve for a “typical” small wind site with a “Mean” of 7 m/s, will show wind found at 15to 18m/s occurring usually around 2-3% of the time through the course of a year. What these vendors wont tell you is that 2-3% occurrence of wind speed actually represents 5-6% at a minimum, of the total AEP Annual Energy Production, which is wind energy that is never captured and converted to useful Electricity.

At Starwind5, we have stayed out of wind tunnels. We do use simulators to assist with design and performance evaluation and as well use these simulators to cross check field test performance data, so we can adjust the simulator behaviour to be more reflective of wind turbine performance in the real world wind. Also we help our partners and end users directly to get the wind turbine siting right, given their power need and geographic location using real historical wind data when ever possible. Then and only then can Starwind5 reliably forecast within -+10% what the 20 year and annual AEP will look like for a given wind site and the wind turbine chosen in order to really deliver “Best in class LCOE” to our partners and end users.

Starwind5 Optiflow tm – How is works- Starwind5’s Advantages  Revealed!

Starwind5’s Optiflow tm  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 Optiflow tm 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:

1. Lift Generating Darrieus “Eggbeater” Rotor Blade Profile Shape, Airfoil Shape, Rotor blade Angle, and Rotor Blade Offset contributing to positive rotation

2. 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

3. 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.

4. 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.

5. 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:

1- 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.

2. 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,

3. 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 Optiflow tm 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.

Exciting times ahead!!