ADDITIONAL EMBODIMENTS OF AND ENHANCEMENTS TO THE GRATZER CYCLO-TURBINE

PRIORITY CLAIM AND CROSS REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority US Provisional Patent Application Serial Nos. 63/406,922 and 63/407,131 filed September 15. 2022, and this application relates to: European Patent EP 3 426 915 Bl, EP Application No. 21170310.3 filed 23 April 2021; and U.S. Patent Application Serial No. 17/349,846 filed June 16, 2021 ; the contents of which are hereby incorporated by reference in their entirety as if fully set forth herein.

COPYRIGHT NOTICE

[0002] This disclosure is protected under United States and/or International Copyright Laws. © 2023 the Estate of Ruthmarie Gratzer. All Rights Reserved. A portion of the disclosure of this patent document contains material which is subject to copyright protection. The copyright owner has no objection to the facsimile reproduction by anyone of the patent document or the patent disclosure, as it appears in the Patent and/or Trademark Office patent file or records, but otherwise reserves all copyrights whatsoever.

BACKGROUND

[0002] In this provisional patent application, based on the market potential of the original unique Cyclo-Turbine design, as invented by Louis B. Gratzer, European Patent EP 3 426 915 Bl (incorporated by reference herein in its entirety), certain additional improvements and embodiments are proposed. The co-inventors have developed and evaluated a detailed aeroelastic prototype model of the Gratzer turbine which was evaluated in "WP I : Report on the Aeroelastic Model Prototype Design of the Gratzer VAWT” [3] using the aeroelastic software QBlade.

[0003] Based on the generated performance and machine data a cost model of the Cyclo-Turbine design has been developed to identify the cost-savings and optimization potential of the Cyclo-Turbine design when compared to conventional multi-MW class horizontal axis wind turbines.

[0004] Based in part on those findings in this report a potential for at least 11% (and potentially considerably more) in cost of energy (COE) reduction, compared to common horizontal axis wind turbines, has been identified. Other potential advantages of the CycloTurbine design include, without limitation:

[0005] Large upside for floating offshore application due to lower center of gravity and system mass;

[0006] Low noise levels due to lower blade tip speed ratio, potential for installation near residential areas; and

[0007] Largely simplified maintenance and installation due to a towerless design, smaller foundation required.

[0008] These findings are based on the design details as described in the European patent referenced above and certain innovations and new embodiments, which exploit the unique design features of the Cyclo-Turbine design. This report should be considered as a preliminary investigation of the potential of the Cyclo-Turbine design. More development, considering some of the suggestions made within this report, could further improve the effectiveness and cost-competitiveness of this design, well beyond a 11% COE reduction.

[0009] The following patent application report details the machine design data, an initial comparison of the prototype that was devised in WP1 and a subsequent exploration of further innovation opportunities on which the projection of at least 11% COE reduction is ultimately based.

[0010] In the following comparison, with respect to the cost-model construction, for all machine components, current market prices have been assumed, such as for the blades, for which the market price of conventional composite structure rotor blades was assumed. Thus, the cost-saving potential of Cyclo-Turbine tailored designs of specific components, such as the rotor blades, pitch drives, gearbox or generator, was not considered in the first analysis. [0011] The Cyclo-Turbine design excels especially in the area of installation and maintenance. As the design is towerless all machine components can be easily installed and accessed close to the ground. Thus, significantly less heavy construction machinery (such as cranes or excavation equipment) is required during installation. The maintenance access is largely simplified as the major maintenance heavy components (gearbox, generator and pitch drives) are located at ground level, resulting in enormous cost savings during initial construction and ongoing maintenance.

[0012] Highlighting the potential for further innovation, based on the ideas and new embodiments discussed in this report, and the opportunity to further tailor machine components towards a low-cost, high-volume mass production, it can be concluded that the Cyclo-Turbine design is worthy of additional investigation for a potential commercial deployment.

BRIEF DESCRIPTION OF THE DRAWING FIGURES

[0003] FIGURES la - 26 illustrate multiple views of several features according to various embodiments and are inserted throughout this application adjacent the relevant descriptive text.

DETAILED DESCRIPTION

[0004] This application is intended to describe one or more embodiments of the present invention. It is to be understood that the use of absolute terms, such as ‘'must,” “will,” and the like, as well as specific quantities, is to be construed as being applicable to one or more of such embodiments, but not necessarily to all such embodiments. As such, embodiments of the invention may omit, or include a modification of, one or more features or functionalities described in the context of such absolute terms. In addition, the headings in this application are for reference purposes only and shall not in any way affect the meaning or interpretation of the present invention.

[0005] Part of the research and development to invent further enhancements and improvements to the Gratzer Cyclo Turbine was to generate a preliminary cost model for the vertical axis cyclo-turbine design to answer the question whether a finalized, matured product based on this specific design can realize significant cost benefits as compared to the widely spread conventional horizontal axis wind turbine designs.

[0006] A first prototype may be around four times more expensive [1] than the final cost that can be realized in an already established production process. It is not within the scope of this report to perform the detailed engineering that is required for a design optimization of the individual turbine components, but rather to point out and highlight the system components that exhibit the most potential for a significant cost reduction and give suggestions for the required optimization process and new embodiments to help achieve that optimization. Thus, in this report the cyclo-turbine embodiment will be judged primarily in terms of its potential cost benefit that is only achieved when it reaches similar stage of technological maturity that the common standard horizontal axis wind turbine designs.

[0007] The main metric that will be used in the following assessment is the Cost of Energy (COE), which, while not the only available metric, is the most appropriate one to evaluate an innovative system. The COE (in $ per kWh produced energy) contains all projected costs of the system for commissioning, operation, and maintenance over the turbine lifetime. By exposing the cyclo-turbine design to a direct comparison with a state-of-the-art conventional design, it is then possible to show the potential cost benefits that arise from the implementation of design changes and innovation. In this report this comparison will be performed against the well-known NREL 5MW [2] horizontal axis wind turbine design.

[0008] Considering that innovation is associated with large costs and long time to market, it should be noted that the projected COE reduction are expected to be significant enough to offset the initial investment.

Figure la. Visualization of a Lattice Based Embodiment of a modified Gratzer Cyclo Turbine

Figure 2b. Visualization of the two compared designs. Left: 1.2MW cyclo-turbine design, right 5MW NREL turbine design

A. Cvclo Turbine Overview

Figure 3. Turbine dimensions and power curve of the cyclo-turbine embodiment

[0009] The cyclo-turbine embodiment (see Final Report WP1 [3]) is a towerless vertical-axis wind turbine design. A first embodiment prototype with 1.2MW rated power has a blade length (or height) of 60m. The slightly inclined, straight blades are mounted near the ground on a turntable or track which connects them to a ground-based generator. The rotor operates at variable speeds in the range of 2-12rpm. The blades are equipped with a collective pitch system, which is used for power regulation, idling and shutdown of the system. It is apparent that the most potential in cost reduction is due to:

• Towerless design -> reduction of material and installation cost

• Ground-based generator and pitch actuators -> low maintenance/installation cost

• Vertical blade orientation no periodic gravitational blade loading

A. Reference Wind Turbine Overview (NREL 5MW)

Figure 4. Turbine dimensions and powercurve of the NREL 5MW wind turbine

[0010] The NREL 5MW wind turbine [2] is a well-known reference design that is used by the research community ⁷ for wind turbine analysis of any kind. It is a conventional horizontal axis design with a hub height of 90m and a rotor diameter of 126m. Its size is representative of the current state-of-the-art (according to a study conducted by the Department of Energy in 2021, the average size of U.S onshore wind turbine installations in 2020 was 125m [4]). Thus, it is well suited as a baseline reference design against which the cost model of the cyclo-turbine can be compared. Throughout this report it will be referenced as 5 MW RWT (Reference Wind Turbine). [0011] Baseplate Embodiments

[0012] One of the key components of the Gratzer cyclo-turbine represents the base platform simply due to its sheer size, weight, and thus large share of the total CapEx (Capital Expenditures). In the digital turbine prototype, constructed in WP1 [3], embodimentual work on a baseplate system was not conducted. Since the baseplate is a major component of the cyclo-turbine design, an exploratory investigation on possible improved embodiments and solutions is conducted in the following.

[0013] While at first glance the design of such a platform seems like a straightforward task, the number of requirements the embodiments must fulfill quickly brings forth the complexity of the problem. The functions may vividly be observed from Figure 5.

1. The structure needs to support the weight of each blade throughtout the entire lifetime of the turbine. Considering the inner radius of 15 m, combined with a weight of approximately 17000kg, large bending moments act around the mounting point at the center of the platform.

2. The root bending moments (RBMs) generated by the aerodynamic loads on the blades need to be absorbed and, in case of the rotor torque, transferred along the platform to the shaft and eventually the generator to produce electricity.

3. During operation load cycles of multiple frequencies caused by the dynamic nature of the turbine itself, aerodynamic turbulence, possible earthquakes, etc. create fatigue loads that over a lifetime could potentially lead to a failure.

4. Ultimate loads that are caused by rare events like a wind gust that occurs statistically every 50 years create short peak loads that need to be absorbed by the structure.

5. The weight of the platform itself poses a challenge. A heavy platform possesses a large inertia which negatively influences the cut-in behavior of the turbine. Furthermore, the costs correlate directly with the weight of the platform.

[0014] Summing up the key requirements for the base platform embodiment it should be a lightweight structure being able to support the weight of the turbine and to transfer the generator torque while behaving insensitive to fatigue and ultimate loads and while also posing a considerable cost advantage over the cost of a tower of a conventional turbine design.

[0015] In this report we provide four embodiment embodiments expanding on the original Gratzer design, including a base platform design inspired by the brief description of the requirements in the European patent [5], The first and apparently and initially most promising embodiment (the lattice structure) has been analyzed in a first set of structural simulations and further optimized to minimize its possible disadvantages.

Figure 5. Structural Embodiment of the Gratzer cyclo-tur bine, from [5]

[0016] The just mentioned lattice structure and the second embodiment that is presented (Azimuthal Grid Structure) follow a conservative approach that represents logically a straight forward solution and replicates the assembly from Figure 5. Both approaches only differ in the embodiment of the base platform itself. The remaining parts below the platform can be set up identically, where the base structure is connected to a shaft that transmits the torque either via a transmission (classical embodiment) or directly into the generator (direct embodiment). To understand the advantages and disadvantages of both generator embodiments, a basic understanding of the composition of mechanical power is needed.

[0017] Mechanical power can be expressed as the product of the torque M and the angular velocity co (rotational speed n multiplied by In) of a rotating system. The mathematical equation is:

P = M ■ 2n ■ n (1)

[0018] The cost of a generator scales with the torque (M in the equation). Hence the idea behind the embodiment is to transform the power efficiently in a transmission so it is composed by a high angular velocity and low mechanical torque. Thereby, generator costs are substantially reduced. The potential drawback however is that the cost of the transmission itself together with the operational cost and a risk of failure somewhat compensate the cost reduction. The direct embodiment uses a variable speed synchronous generator that is directly coupled to the rotational speed of the rotor. This embodiment is very robust against failure and is compact due to very few necessary parts. The disadvantages are associated mostly with high generator costs.

Figure 6. Visualization of the bearing embodiment [0019] The bearing embodiment needs to support the axial loads that are introduced into the vertical shaft (see Figure 5). Here, the tapered roller bearings represent a viable option as they are capable of absorbing large axial loads efficiently. Either a single row- or double row- or even multiple rows of bearings could be chosen for the fixed bearing side. The floating bearing side could easily be realized by a cylinder or ball roller bearing or other configurations.

[0020] Lattice Structure Embodiment

[0021] The lattice structure relies on the structural properties of an I-beam that is supported by a lattice-tj pe construction to absorb the most outboard sections. A very basic approach is shown in Figure 7.

[0022] The structure is built from conventional construction steel and singular components that allow for straight forward purchasing and production. The fact that it consists of modular components also allows it to be assembled either on site or close to the final installation location of the turbine, potentially reducing erection costs considerably in comparison to a tower. Results of preliminary structural simulations demonstrate promising performance with regards to the capability to absorb the weight of the blades. The presented structure weighs around 45t.

Figure 7. Lattice structure Embodiment [0023] The von Mises stress is often utilized to determine if a material will yield or fracture under a given load. Simply put, it is a parameter that may be understood as an equivalent stress, taking the geometric properties and the loads acting in the three spatial directions on a structure into account. If the resulting stress stays below the yield limit of the material, no failure is to be expected. In Figure 8, the von Mises stress is visualized and never exceeds 4.0 E+7N/m ² . The yield limit of steel sits one order of magnitude above at 1.75E+8N/nr. The deflection caused by the gravitational force of the blades is shown on the left side of Figure 9 , never exceeding 5mm.

[0024] This embodiment promises to fit the requirements of the base platform with a low level of uncertainty regarding cost and operational strategy. However, once the aerodynamic loads were introduced to the simulation, the yield limit was surpassed. Additionally, due to the edgewise moment (tangential direction) the torsion of the beam can potentially became a critical issue. Thus, further development and innovation may be advantageous to enhance the lattice design. One embodiment is made in section "Optimized

Lattice Structure” .

Figure 8. Von Mises stresses caused by the gravitational force of the blades

Figure 9. Deformation caused by the gravitational force of the blades

A. Azimuthal Grid Structure

Figure 10. Azimuthal grid structure

[0025] The azimuthal grid embodiment, that is presented here, is inspired by the description of the structural embodiment for the base platform in the European patent [5]: “the invention includes a mechanical system comprising a circular rotor-platform rotatable about a vertical axis... '\ This structure, exhibiting rotational symetry, is positioned azimuthally around the rotating vertical axis and is interconnected with circular elements along various radii for stability pruposes.

[0026] Possible advantages of this design would be similar characteristics as the lattice embodiment, but significantly higher potential for mass production of the identical azimuthally distributed sections, while increasing the torsional stability of the platform dramatically through the circular interconnection of each cross-section. The presented structure would need to be build out of light weight material with favorable structural properties, such as fiber glass composite, to save weight.

[0027] Rail Embodiment

[0028] So far, the presented embodiments somewhat resemble the general structure presented in Figure 5. While they represent the most straight forward solutions that could be realized without major investments in technology ⁷ development or research, they will continue to contribute notably to the CapEx costs simply by sheer size and weight. More innovative solutions that are being or have been deployed in other non-analogous industry sectors with relative success could lead to a notable improvement regarding costs and potentially even performance. Due to the non-availability of off-the-shelf solutions more investment in these embodiments is advantageous to be able to perform a cost analysis with conclusive results regarding operational and investment cost of the respective embodiment.

Figure 11. Rail embodiment. Each blade is placed on a sled that runs on a circular rail system attached to the ground.

[0029] An embodiment that combines possible upside while already being utilized successfully at smaller scales is the rail embodiment. The task of absorbing the acting loads at the blade roots and transferring the driving forces to the generator are split up in two separate ones. The embodiment provides that a rail is placed on the ground along the outer diameter of the blades. Three sleds are mounted on the rails. Finally, each blade is placed on a sled that, to transfer the diving moment to a generator, is interconnected by a lever-type structure to the rotating axis. An embodiment of this model is visualized in Figure 11.

[0030] In this embodiment, no heavy structure is needed to withstand the large moment that is initiated by the weight of the blades. Furthermore, the root bending moments would be absorbed by the interconnection of the rail and the sled. Only the driving forces are transmitted via the three lever elements to the center of the structure. Aside the structural advantages this system could provide, several other aspects are influenced positively as well. Since the rails are mounted on the ground, the cavity that needs to be dug is smaller. The remaining elements, i.e., shaft, bearings, generator and possibly transmission might still be needed with this embodiment. However, it might also be possible to place them, if aerodynamic interferences are kept at an acceptable level, on top of the central structure, making any need for a cavity redundant altogether.

[0031] Some preferred embodiments will have the following features:

[0032] The rail system total length equals or exceeds the outer perimeter of the turbine - approximately 90 m.

[0033] The load range of the sled-rail combination is high enough to withstand the weight load ¹ (-170000N) plus aerodynamic loads.

[0034] A suspension between the sled and the blade might be advantageous.

[0035] The maximal speed of the sled aligns with the rotational speed of the turbine at rated conditions - approx. 18.85m/s.

[0036] Maglev Embodiment

[0037] The embodiment of magnetic levitation has never been employed in the context of a VAWT such as the Gratzer Turbine. This embodiment utilizes the enormous potential that arises from the disappearance of friction (suspension of shafts) and the efficient way of propelling a moving object (e.g., from the non-analogous field of cars or trains) [6],

[0038] The potential of such a system in the context of the Gratzer cyclo-turbine is enormous. The high loads that are induced by the weight and aerodynamic load on the blades could be absorbed by the repulsion of magnets, thus making a large and heavy supporting structure redundant. Due to the levitating characteristic, friction would be vanished from the system, increasing the efficiency and improving the cut-in behavior of the turbine. Since the

The Company HepcoMotion provides a system that conceptually matches the requirements of the Gratzer turbine however on a smaller scale. Load range 0 - 220 000N system can easily be used to propel objects, the start-up behavior of the turbine could further be improved through the overcoming of the inertia. More potential benefits of the embodiment lie in the fact that many of the components visualized in Figure 5 are not required for operation. Thereby, the already mentioned structural platform, the shaft and thus the bearing system as far as potentially the generator would all be replaced by components belonging to the magnetic levitation system.

[0039] The embodiment of magnetic levitation is based on the repulsion of two opposite or the attraction of two likewise magnetic poles. In the non-analogous rail industry- two technologies have carried through so far, but have never been applied in the wind turbine context. Both are briefly described in the following.

[0040] The system developed in Germany (Transrapid) uses the technology of electromagnetic suspension (EMS) for levitation. The track is made of ferromagnetic plates, C-shaped arms surround the track so that an electromagnet may be placed directly under the ferromagnetic plate of the track. When a current is induced to the electromagnet, an attraction force between the magnets causes the train to levitate [7], A different system that was developed in Japan, the electrodynamic suspension (EDS), relies on twisted coils that are placed at the outsides of the track. Inside the train, superconducting magnets inducing a strong electromagnetic field are placed. Once the train passes, the coil will encounter a magnetic flux, inducing offsetting electromagnetic fields within the coil according to Faraday's law. If now the magnetic field passes the coil off-center, a current is induced due to differences in the magnetic fields at the top and bottom of the coil, letting it behave like an electromagnet itself temporarily [8], The repulsive force from the bottom pole together with the attractive force from the top pole cause the levitation of the train. Both suspension methods are displayed in Figure 12.

Figure 12. Dominating magnetic levitation technologies -EMS (left) [7] and electrodynamic suspension - EDS (right) [9],

[0041] A potential disadvantage of the EDS system lies in the necessity for superconducting magnets. To achieve the state of a superconductor, the magnet needs extensive cooling and heat isolation. Also, since the levitating force is caused by the movement of the superconducting magnets, wheels are necessary ⁷ for low velocities.

[0042] The propulsion of the trains is achieved when the magnets within the train and the track overlap to a point where two equal poles retract and two opposing poles attract each other, causing the train to move (see Figure 13). The speed may be increased by increasing the frequency, with which the polarity is changed. Braking on the other hand is realized by changing the poles, so the forces act in opposite direction.

[0043]

Figure 13. Propulsion mechanism of a magnet levitation train [10] [0044] In the context of the Gratzer cyclo-turbine the kinetic energy ⁷ of the rotor could be transferred into electrical energy following the breaking strategy ⁷ of the magnetic levitation trains. Using an axial flux design generator where the coil is situated below the track, the changing magnetic field caused by the motion of the turbine would induce a voltage. This principle has been successfully implanted in an initial micro-scale experiment on a Darieus type VAWT design in [11], but never in the context of a Gratzer Turbine.

[0045] Certain embodiments of the Gratzer cyclo-turbine rotor provide enough levitation force to withstand the loads. Novel control techniques handle the unsteady aerodynamic. A design study of the Gratzer cyclo-turbine on a magnetic levitation track is displayed in Figure 14.

Figure 14. Study of a Gratzer cyclo-turbine on a magnetic levitation track.

[0046] Cost Model for various embodiments

[0047] Figure 1 gives a good overview of the main contributions when estimating the cost of energy (COE) of a wind turbine system. On one side are the lifetime capital costs that are associated to the plant investment, such as component costs, installation and decommissioning costs and maintenance costs. On the other side is the energy that is produced by the plant over the course of its lifetime. This energy production is directly correlated with the plant’s efficiency and its availability.

Figure 15. Cost of Energy (COE) overview, reproduced from [12]

[0048] When converting Figure 15 into the form of a simplified equation one obtains: [0049] Equation (2) above is formulated as a yearly balance; the used abbreviations are briefly explained below:

[0050] We assume a 20-year plant lifetime, a common value for modem wind energy systems, which allows us to set the Fixed Charge Rate (FCR) at -0.1 (or 10%). This leaves us with the task of obtaining values for the Annual Energy Production (AEP), Total Plant Investment (TPI) and Operation and Maintenance costs (O&M).

[0051] AEP Evaluation

Figure 16. Power curve of the Cyclo-Turbine and the NREL 5MW RWT

[0052] The energy output of a wind turbine is the result of its power performance over a period. Thus, to address energy capture, the wind turbine power curve characteristics (Figure 16) need to be considered, which already have been obtained in [3], Energy can be considered the prime value and energy capture the purpose of the wind turbine system. Thus, any increase in energy has a direct proportional effect in reducing COE. Reliability- and availability also impact directly on energy produced and are therefore also prime values. Elimination of any component in a wind turbine system always has added value in COE terms beyond the removal of its capital cost as associated issues of reliability disappear.

[0053] For the AEP evaluation we first generate the windspeed probability distributions for the three wind turbine classes, according to the standard IEC 61400-1 :2019. Table 1 shows the mean windspeed for each class.

Table I. Mean windspeeds for wind classes according to IEC 61400-1:20019 [0054] The Weibull distribution is defined as:

[0055] In formula (2) k is a shape factor. In this case k=2 is used. V is the windspeed for which the probability is to be evaluated. The mean wind speed, shown in Table 1 is related to the scale parameter^ as:

[0056] These relationships allow us to estimate the probabilities for the occurrence of any windspeed. Multiplying these probabilities with the combined hours of a year (365*24h=8760h) gives us the hours per year during which a certain windspeed occurs.

Figure 17. Windspeed distribution graph for three windclasses Table 2. Windspeed probability distribution

Combining the Power Curves (Figure 16) and the yearly hours of the windspeed bin from Table 2 allows the evaluation of the AEP for the three Wind Classes I, II and III. The AEP is evaluated for both turbines, the reference NREL 5MW and the cyclo-turbine.

[0057] Table 3 shows the evaluated AEPs for the cyclo-turbine and the 5MW RWT. It is expected that the 5MW turbine generates more energy than the 1.2 MW cyclo-turbine, as the maximum rated power of the cyclo-turbine is only at 24% of the 5 MW RWT. For the cyclo-turbine an availability of 98%, so around 7.5 days downtime per year due to maintenance, has been assumed. This is a slightly lower value than the downtime that is assumed for the 5MW RWT (11.3 days), mostly due to the larger part-count and complexity of the conventional design. One of the advantages of the cyclo-turbine is that this system does not require a tower nor a nacelle and is easier and faster to maintain, so a slightly larger availability reflects this difference. The values for the AEP, obtained herein, will be used in the COE evaluation, after equation (2).

[0058] TPI Evaluation Table 4. Typical cost split for a variable horizontal axis wind turbine, obtained from [13]

Component f Total Cost

Blades 17.7

[0059] After [12], the capital costs of a wind turbine constitute two main items - the cost of the turbine components in their finished form ready for system assembly at site and other costs described as “balance of plant costs”. Balance of plant costs for a land-based project include costs associated with assembly at site, erection, and commissioning, installing turbine foundations, access road construction, grid connection, site services such as buildings for site management and maintenance and permissions charges associated with the complete establishment of the turbine.

[0060] The approach taken in this top-level COE analysis is to consider available information on installed cost of turbines of relevant sizes. Using relative cost split information such as given in Table 4, the costs of components can be extrapolated. The component cost can often be related to mass; and while this is not ven,' useful in making any initial estimates of the cost of a wind turbine component, it can be useful in assessing the impact of innovations such as that saving 20% of mass of some components could equate to 20% cost reduction if a linear relationship is assumed. [0061] Data on the costs of materials is publicly available. Also, the estimated costs of finished product types depending on the complexity of manufacture, for example cast, fabricated, machined, or highly engineered can readily be obtained from global market data.

[0062] Despite the complexity and variability of some industrial processes, such as blade manufacturing, there is often useful convergence with a reliable average cost per kilogram - being established at least for individual manufacturers obtained from market data collected over several years. The input cost and the cost split information are never absolute and need to be refreshed periodically from whatever sources are available. In this context of evaluating innovation, such data can then provide the basis of the cost comparison of a system that may have several common components with a baseline system (in this case the

NREL 5MW RWT) but also some other innovative ones.

35000

30000

25000

“S

~ t 20000 tn ran

5 w 15000 o

10000

5000

0

0 10 20 30 40 50 50 70

Rotor Radius (m)

Figure 18. Nonlinear relationship between blade length and blade mass, based on different manufacturing technologies

[0063] NREL has developed a cost and scaling model (CSM) [14], which received the latest update from market data in 2015. The CSM is intended to provide reliable cost projections for wind-generated electricity. The cost estimation is based on turbine rating, blade length, tower height and other key turbine components. Moreover, cost scaling functions have been derived from market data that allow to model the impact of up- or downscaling different components or other design changes. In the CSM the cost is directly related to component mass (in kg) by nonlinear curve fits. Figure 18 shows exemplary curve fits, where blade mass is related to blade length for different technologies implemented in the design of the blades.

[0064] NREL’s CMS has been employed herein to construct a detailed cost/mass split for the 5MW RWT. Table 5 and Table 6 show the estimated cost per kW installed capacity for both the NREL 5MW RWT and the Cyclo-Turbine.

[0065] The detailed cost-split of the 5MW RWT results in a total cost of 3.54M USD, or around 710 USD per kW installed power output of the system. This value should not be confused with the COE, since it does not yet include installation costs, maintenance, or power production - it is merely a reference value which can be the basis for a high-level comparison of both systems on a turbine component level.

[0066] All the required components of the 5MW RWT are still listed in the cost split of the cyclo-turbine that is shown in Table 6. This serves the main purpose to highlight which of the components are not required for the novel cyclo-turbine. As can be seen in the Table 6, all components related to the turbine tower, nacelle and hub are not required. Thus, the hub, spinner, yaw drive, nacelle- platform, bedplate and cover have been removed from the list (the respective rows are marked in red). Additional components for the cyclo-turbine are the baseplate, for which the lattice structure is used in this example, and the axial bearing (which replaces the main bearing at almost equal costs of -10000 USD, obtained from a manufactures catalogue). Table 5. Estimated cost and mass split for the 5 MW RWT

Table 6. Estimated cost and mass split for the cyclo-turbine

[0067] The total component cost for the cyclo-turbine amounts to 1.3M USD in this example, resulting in a cost of 1080 USD per kW installed capacity. This cost / kW is around 50% larger than that of the conventional 5MW RWT. Looking at Table 6 can help to clarify what is causing this cost increase and which components have the largest impact on the total cost - and are promising subjects for a further optimization of the system.

[0068] As mentioned before, with linear scaling the totals cost of the 1.2MW cyclo- turbine should be at around 24% of the costs of the 5MW RWT. This also holds true for the individual sub-components of the cyclo-turbine. If we look at the last column in Table 6 (cost ratio) we find information on how the sub-component cost scales against the 5MW RWT. The least favorable scaling is exhibited by the blades, their cost is at 75% of the cost of the 5 MW RWT's blades. The reason is that both systems, despite their large difference in power rating, use the same blade length. Since the blades of the cyclo-turbine experience slightly lower dynamic (and no varying gravitational loads) a cost reduction of 25% has already been considered. However, since the rotor blades make up around 40% of the total cyclo-turbine cost - their optimization should be one of the primary goals during a prototype design.

[0069] The second component with potentially unfavorable scaling is the pitch drive. However, for this system it has been assumed that off-the-shelf pitch drives for conventional turbines will be employed. This leaves some room for improvement of this component to be specifically designed and integrated within one of the baseplate embodiments. The pitch drives contribution of -10% to the total turbine cost easily justifies such an effort.

[0070] Regarding the gearbox and the generator. While both components potentially scale unfavorably there is a little remaining room for cost reduction through an optimization since both components scale proportional to the torque, and the large torque of the cycloturbine is a direct result of its operational characteristics and low tip-speed operation.

[0071] This leaves us with the Lattice Base structure embodiments. As mentioned previously the costs assumed for this component are based on a single design loop. So, there is still a large potential for improvement and cost reduction. The current contribution of the baseplate towards the total system cost is again in the range of 10% which makes such efforts worthwhile.

[0072] Balance of Plant Costs

[0073] Besides the component cost the TPI also includes the balance of plant costs, that are associated with assembly at site, erection, and commissioning, installing turbine foundations, access road construction, grid connection, site services such as buildings for site management and maintenance and permissions charges associated with the complete establishment of the turbine.

[0074] The values shown in Table 7 have also be obtained through NRWL’s CSM. It is noteworthy that the scaling of these cost contributions is favorable for the cyclo-turbine - the reason being that the installation costs can be dramatically reduced for a towerless system, where all heavy components are installed close to the ground and thus the requirement for heavy construction equipment is significantly reduced. Depending on the choice of baseplate design the foundation costs might be affected, but for the sake of this simple comparison the unmodified scaling laws were applied, whereas a hub height of 10m was assumed for the cyclo-turbine.

Table 7. Balance of plant costs, comparison

[0075] Overall TPI

[0076] The TPI can now be established by summing the contributions from component costs and balance of plant costs, evaluated in the previous sections.

Table 8. TPI of the NREL 5MW and the cyclo-turbine

[0077] O&M Evaluation

[0078] Operation and maintenance is a particularly difficult cost item, not only because (as with other proprietary wind turbine data) much information is held confidential but also because it takes time to build up significant statistics, even if such data is available.

[0079] Furthermore, wind technology has been constantly evolving. Thus, the recorded performance of 20-year-old wind turbines has restricted relevance for predicting the performance of current installations. Usually, the innovations to be evaluated are in the turbines themselves so that it is enough to have a lifetime fraction associated with O&M that is appropriate relative to the turbine cost. If an innovation eliminates a component, a rough estimate of the impact on O&M is to consider the component’s importance in the cost split and reduce at least the replacement part’s cost fraction in proportion. This impact can be factored accordingly if the innovation does not eliminate a component but reduces its cost. In general, in top-level analyses, it is a matter of approximate judgement how O&M costs may be affected by an innovation.

[0080] Following a high-level approach one can split up O&M into the following two categories:

[0081] Operations: These are constant, known operational cost, such as scheduled, replacement of parts or planned/predictive maintenance, utilities or rent and land lease costs

[0082] Maintenance: These are variable costs, commonly related to the generated electricity' and environmental (wind, rain, dust, frost etc.) conditions.

[0083] A recent report [15], based on NREL’s "'Jobs and Economics Development Impact ModeE estimated project-level annual operations costs for onshore wind turbines to be at 15 USD/kW/Y ear, excluding the costs of land lease. Land lease costs were estimated at 8 USD/kW/Year in the same report. Costs projections for annual maintenance have been evaluated in a report by Wiser and Bolinger [15] based on wind turbine projects installed since 2010. The reported pre-tax average maintenance value is 28 USD/kW/Year and includes the cost for materials as well as labor. In this report it is highlighted that, due to the scarcity and unpredictable quality ⁷ of the data on which these findings are based, the real-life O&M cost can vary substantially from project to project.

[0084] To reflect the lower part count and the fact that the cyclo-turbine system is tower-less we assume a reduction in maintenance and operations costs of 25%, as compared to the data predicted in [15],

Table 9. O&M Cost Projection for the NREL JMW and the Cyclo-Turbine

[0085] The total projected O&M cost per year results in 255,000 USD for the 5MW RWT and in 60,375 USD for the cyclo turbine design. This reflect a 21% cost reduction (in USD / kW /year) for the cylco-turbine design, resulting from its lower part count and better accessibility.

[0086] COE Evaluation

[0087] Recalling equation (2) we can now proceed to calculate the overall COE for both turbine designs:

[0088] Table 10 shows the COE predictions for the 5MW RWT and the cyclo- turbine. We find that on average (over wind classes 1, 11 and 111) the electricity generated with the cyclo-turbine at 0.0461 USD /kWh is around 34% more expensive than the electricity- generated by the 5MW RWT at 0.0340 USD/kWh. Table 10. COE prediction for the 5MW RWT and the cyclo-turbine

[0089] Design Optimizations for certain embodiments

[0090] In the following section two key components, the baseplate structure and the rotor blades are further optimized through simple design modification and the potential impact of these modifications on the COE is briefly addressed. This represents a preliminary optimization and highlights the potential that further detailed engineering has on the overall system cost-effectiveness.

[0091] Optimized Lattice Structure Embodiment

[0092] The lattice structure, being one of the most promising structures to build a cyclo-turbine prototype, was selected to try to mitigate some of the problems that were observed in the initial design presented in section “Lattice Structure"'. As mentioned, the flapwise moment acting in radial direction causes a large deflection at the end of the beam element downwards. This point has been addressed with an evolution of the design which is presented in Figure 19.

Figure 19. Lattice structure, optimized embodiment.

[0093] First, the I-beam (Figure 20) has been strengthened by doubling the thickness of the top and bottom plates of the beam from 5 cm to 10 cm, the middle spar was thickened from 5 cm to 25 cm and the overall width was also increased from 25 cm to 60 cm. 25 60

Figure 20. I-beam modifications. Original version (left) and optimized version (right). Dimensions in cm.

[0094] Additionally, a truss style framework similar to the ones found at non- analogous construction cranes was introduced on top of the beam to increase the stiffness while maintaining the structure as light as possible. When the initial structural simulations mentioned earlier were repeated on the optimized design with the addition of the aerodynamic loads, the modifications proofed to have improved the design regarding the structural requirements. The von Mises stresses (Figure 21) largely align with the yield limit with local spikes at the outboard sections that supersede it. Furthermore, the flapwise moment is not causing worrisome results regarding deflection. Instead, the edgewise moment continues to twist the beam structure leading to a maximum deflection of around 45cm.

Figure 21. Von Mises stresses caused by the gravitational force plus the aerodynamic loads of the blades.

Figure 22. Deformation caused by the gravitational force plus the aerodynamic loads of the blades.

[0095] In a following optimization iteration, three critical areas have been considered. On the one hand, torsional stiffness likely needs to be increased to better withstand the edgewise root bending moment. On the other hand, the truss structure at the outboard section of the beam better mitigates the loads to stay below the yield strength of steel. Once the key structural requirements are matched, in this embodiment the focus lies on minimizing material used to reduce weight as the optimized structure may weigh around 170t. The inner region provides even more room for material reduction as the stresses and deflections are minor. An assembled embodiment of the Gratzer turbine with the optimized lattice structure is rendered in Figure 23.

Figure 23. Render of the cyclo-turbine installed on the optimized lattice structure base platform embodiment

[0096] Blade Tip Interconnections Embodiments [0097] As shown in the TPI evaluations, the rotor blades are the single component with the largest contribution (of 40%) towards the total TPI. Thus, optimizing bade design, and reducing blade cost, has the largest impact on overall component cost reduction (it is more than 4 times more effective than reducing baseplate costs).

[0098] The main driver of blade costs are the dynamic loads that the blades are experiencing during their lifetime (see Final Report WPI [3]). Any reduction in blade loads will therefore have a direct, positive impact on the blade cost. Due to the unique and towerless design, the blade root, where all blade loads are transferred into the base structure, is experiencing the largest loads - which is in turn requiring a tapered blade design with thickened sub-optimal aerodynamic profiles in this region.

[0099] One distinct difference between horizontal and vertical axis wind turbines is that the blades of vertical axis rotors are in much closer vicinity to each other that horizontal axis rotor wind turbine blades of comparable length. Certain VAWT designs leverage this geometric distinction by interconnecting the blades and the torque tube with the help of struts therefore alleviating loads at the blade root by distributing them along the blade over the strut supports.

Figure 24. Interconnection of blade tips by means of cables

[00100] While it is not usually possible with the towerless design embodiments of the cyclo-turbine to utilize struts, it is proposed here to interconnect the blade tips of the rotor with cables, or other parts, such as rods or even aerodynamically shaped support structures (see embodiment visualization in Figure 25). The main purpose of the blade-tip connection is to reduce the large blade deflection at the tips and to alleviate the large bending moments at the baseplate-blade connection by providing an additional support point at the free blade end.

Figure 25. Visual difference of blade deflections at rated operating conditions

[00101] The aeroelastic model that was investigated in WP1 [3] was outfitted with three blade cables, interconnecting the blade tips as seen in in Figure 24, and aeroelastic simulations have been performed at the rated operating condition.

[00102] In this preliminary study, it was found that the blade cables lead to:

[00103] Reduction of the blade tip-deflection by 95%

[00104] Reduction of the blade root bending moment by 50%

[00105] At the same time no negative impact on the rotor power production was found. These are highly promising results which point out the advantages of such blade- to-blade interconnections.

[00106] The potential benefits are:

[00107] Increased energy output through longer blades with lower or equal load envelope

[00108] Large reduction of blade loads allowing for simpler blade cross section design, reducing complexity of manufacturing (possibly utilizing extrusion process) [00109] Lower requirement for composite and high-cost materials (such as carbon fiber)

[00110] Reduction of blade self-weight allows for lighter base-plate structural design

[00111] Reduction of weight reduces inertia and increases self-start capabilities

[00112] In some embodiments, interconnecting blade cables might introduce frequency response problems (cable-galloping or resonance), which can be attenuated with dampers or averted by programmatically modifying the frequencies. For some operating conditions the blade will operate under very low tension, for some operating conditions the tension will be very high. Therefore, in some embodiments rods or aerodynamically shaped beams with more rigidity are a more efficient and practical solution. Blade interconnections have a very high potential for cost reduction. Also, these blade interconnections can be placed just below the tips such that they can still be used in conjunction with winglets for aerodynamic drag reduction and related improvements as set forth in, e.g., European Patent EP 3 426 915 Bl.

[00113] Cost Model: Results Considering Optimized Scenario

[00114] The potential impact of the optimized solutions for the baseplate and for the tower will now serve as the basis of an updated cost projection. The optimized component cost-split of the cyclo-turbine is shown in Table 11. We project the optimized lattice structure to result in a cost of 80.000 USD, based on material cost.

[00115] The impact of the blade cables is at least threefold. We assume that a 10m extension of the blades is possible (73m vs 63m), at the same time we project a blade weight and material reduction. Furthermore, a lower blade weight allows to use less material in the base-plate construction, further reducing this cost factor.

[00116] The projected cost reduction for the blades, as compared to the baseline 5MW RWT, is deemed at 55%. Such a reduction could be realized by changing to a simpler blade production process such as extrusion, but also by using different, non- composite materials and not requiring carbon-fiber. The blade elongation effectively increases the rotors energy yield by -40%. If we compare Table 11 with Table 5 we see that with the projected optimizations the TPI is already cost competitive, and surpasses the 5MW RWT baseline at only 646 USD/kW installed capacity, which equates to a -10% cost reduction.

[00117] Continuing the evaluation, including the O&M and AEP into equation (2), we arrive at a mean predicted COE of 0.0305 USD/kWh, which equates to a reduction in COE of at least -11%, thus demonstrating the potential of the cyclo-turbine to be cost competitive with existing conventional wind energy designs. Again, it should be stressed that the cost competitiveness with a matured technology is made possible in part by exploiting the benefits of a towerless design and those of a self-supporting blade structure.

[00118] Vertical axis wind turbines that have been designed in the past have attempted to leverage the possibility of simple and cheap blade designs, thus a projected reduction of blade cost by 55% is deemed to be appropriate. See as an example the extrusion manufacturing of a Troposkien shaped blade (a blade shape where only tensile forces, and no bending moments, are acting on the blade) for a typical Darrieus style vertical axis wind turbine in Figure 26, allowing the blades to be manufactured in a single step aluminum extrusion process, followed by an in-shape bending process. The Gratzer cyclo turbine, especially as modified as described herein can better leverage simpler and cheaper blade designs even compared to previous vertical axis wind turbines.

Figure 26. A Troposkien aluminum blade manufactured by extrusion (from [16])

Table 11. Estimated cost and mass split for the optimized cyclo-turbine

[00119] Further Innovation Opportunities

[00120] Some of the key preferred features of the cyclo-turbine are: its towerless design, its ground baseplate, and the geometrical uniqueness of its blade arrangement. Thus, the focus of any further development will exploit these unique features as much as possible.

[00121] Typically, vertical axis wind turbines employ vastly simpler blade designs which can allow for cheap manufacturing solutions. Finding an optimal blade shape. in terms of energy yield, structural integrity, aerodynamic control authority and manufacturability is the prime focus of ongoing design and engineering efforts. A simple, low-cost modular straight blade design with the potential for mass production may be the optimal solution for this purpose. One possible embodiment would be to arrange the blades in a self-supporting arc as depicted in Figure 27. While such an embodiment modifies from the original patent application embodiments in some respects, [5] it would take advantage of the strong cost reduction potential of the rotor blades with respect to the total TPI.

Arc Concept

Generator

Figure 27. Possible "arc" embodiment with self-supporting rotor blades [00122] Challenges associated with a generally softer, interconnected blade structure might arise in the frequency domain, where rotor mode shapes might interfere with IP, 2P or 3P excitations. A careful structural design of all components for the preferred embodiments herein consider such interferences and thereby realize a structure insensitive to such excitations.

[00123] A further upscaling of the proposed technology would increase the advantage of constant gravitational self-weight loading that vertical axis wind turbine designs have over conventional horizontal axis designs. Upscaling also linearly reduces the rotational rate of the rotor, reducing fatigue loading cycles that occur during every rotor revolution.

[00124] Another preferred embodiment includes a stall regulated rotor. A stall regulated rotor can remove the necessity for pitch drives altogether (in case of the cycloturbine around 5% of the total component cost). In this embodiment, a second rotor brake mechanism is added as the rotor ordinarily could not be controlled exclusively aerodynamically without a pitch system. A possible replacement for the large and expensive pitch drives and bearings would be the distribution of local aerodynamic control elements (such as flaps) along the rotor to fulfill the purpose of rotational speed control and breaking.

[00125] Another inherent advantage of the cyclo-turbine design that has been exploited is its comparatively lower center of mass, when compared to conventional wind turbines. Especially for an offshore application in deep waters, a lower center of mass has profound advantages when designing floater embodiments for the offshore wind turbines. The share in total costs for the floating support structure is in the same range (-25%) as the cost of the turbine itself, thus any potential reduction in support structure cost will have a strong impact on the economics of the whole power plant. Furthermore, for an offshore application the baseplate structure could be replaced by buoyant devices that are supporting the rotor blades - another potential for cost reduction. [00126] Further exploration of the baseplate embodiments (azimuthal grid structure, rail embodiment, maglev embodiment) presented in this report might also result in considerable cost-savings.

[00127] Conclusion

[00128] This report details the construction of a simplified cost-model for the Gratzer Cyclo-Turbine design and various improved embodiments. For the baseline version of the cyclo-turbine, based on the V15 prototype that was investigated in WP1 [3], the cost model projects a COE of around 0.046 USD / kWh, which is about 34% higher than the COE projected for the 5MW RWT.

[00129] By introducing two design modifications of the turbines core components, namely an optimized lattice structure embodiment for the turbine base and blade tip interconnections embodiment, a projected COE reduction of -50% could be achieved.

[00130] Appendix A - Includes citations for the references cited in the detailed description above and are incorporated by reference fully herein.

[00131] Although the foregoing text sets forth a detailed description of numerous different embodiments, it should be understood that the scope of protection is defined by the words of the claims to follow. The detailed description is to be construed as exemplary only and does not describe every possible embodiment because describing every possible embodiment would be impractical, if not impossible. Numerous alternative embodiments could be implemented, using either current technology or technology developed after the filing date of this patent, which would still fall within the scope of the claims.

[00132] Thus, many modifications and variations may be made in the techniques and structures described and illustrated herein without departing from the spirit and scope of the present claims. Accordingly, it should be understood that the methods and apparatus described herein are illustrative only and are not limiting upon the scope of the claims. Appendix A - Citations to References

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[2] J. Jonkman, S. Butterfield, W. Musial, and G Scott. Definition of a 5-MW Reference Wind Turbine for Offshore System Development. NREL Technical Report, February’ 2009

[3] D. Marten. WP1: Report on the Aeroelastic Model Prototype Design of the Gratzer VAWT. Technical Report. Gratzer Family Trust, 2022

[4] U.S. DOE. Land-Based Wind Market Report, 2021

|51 European Patent Specification EP 3 426 915 BL Wind-Powered Cyclo-Turbine. 12.05.2021.

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[7] T. D. F. Cabral and F. R. Chavarette: Dynamics and control design via LQR and SDRE methods for a maglev system. International Journal of Pure and Applied Mathematics. Volume 101. No. 2 (289 300). 2015.

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[9] A. Sibilska-Mroziewicz, S. Czubaj. E. Ladyzynska-Kozdras and K. Sibilski: The use of hall effect sensors in magnetic levitation systems. Applied Mechanics and Materials. 817. 271- 278. I .4()28. 2016

[10] Z. Qadir, A. Munir, T. Ashfaq, H. S. Munawar, M. A. Khan, and K Le: A prototy pe of an energy -efficient MAGLEV train: A step towards cleaner train transport. Cleaner Engineering and Technology. Volume 4. 100217. 1 0.1016/j.clet.202L 100217.

[11] D.S. Preetham and M. S. Shashikala: Experimental Study on miniature fabricated model of maglev wind turbine. World Journal of Engineering Research and Technology. Volume 4. Issue 1 (428-436). 2018.

[12] Jamieson, P. Innovation in Wind Turbine Design. Book. John Wiley & Sons, 2018

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[14] Fingersh, L., Hand, M. Laxson, A. Wind Turbine Design Cost and Scaling Model. Technical Report NREL/TP-500-40566, 2006

[15] Mone, C., Hand, M., Bolinger, M., Rand, J., Heimiller, D. Ho, J. 2015 Cost of Wind Energy Review. Technical Report NREL/TP-6A20-66861

[16] Johnson GL. Wind Energy Systems, Prentice-Hall, 1985.