Multi-Rotor System Seminar 2025

Session 1: Industry (1/2)

MRS, selected key factors

Wind Catching Demo – full scale demonstrator project

A full-size demonstration Project for the W2Power solution

Session 2: Industry (2/2)

Engineering Challenges in Monster Blades & Mechanical components

Session 3: Aerodynamics and Loads Modelling                      

Modelling aerodynamic loads on closely spaced rotors

Open-source reference rotor library for multi-rotor aeroelastic modelling and design

Enhancing wind farm efficiency by Multi Rotor Wind Turbine Systems with Lifting Devices (MRSL)

Numerical simulation of multi-rotor diffuser augmented wind turbine system using the actuator line method in PyFR solver

Literature review and preliminary actuator cylinder modelling of adjacent VAWTs

Closing words Day 1

Dinner at Rickmer Rickmers 

Adress of the location:

Museumsschiff RICKMER RICKMERS
Landungsbrücken, Ponton 1a
20359 Hamburg

Session 4: Loads, Control and Structure

Beyond Single Rotors: Enhancing Performance in Multi-Rotor Wind Turbines

Multi-rotor floating wind turbine concepts: control co-design to ensure their feasibility

MRS space frame loads and rotor interactions

Active Power Control of Multi-Rotor Turbines for Fast Frequency Reserve

Session 5: Offshore, Floating, O&M

Multi-rotor wind turbines: A review of modern research efforts and challenges

Session 6: System Design

Park scale LCOE modelling for floating multi rotor systems and its impact on turbine rating

LCoE Calculator for MRS: From Scaling Theory to Cost Evaluation

The Windbrücke and multigenerator system for alpine sites

Session 7: Looking Back and Looking Forward

Session 1: Industry (1/2)

MRS, selected key factors

Research and Innovation in multi rotor wind turbine systems (MRS) has made substantial progress over the past two decades. Research projects, such as INNWIND and X-Energy improved the design methods and knowledge on MRS, such as loads, structural design, operation, maintenance and more. The Vestas quad-rotor demonstrator revealed further insights, in particular on aerodynamic interactions and wakes. Numerous publications show the increasing interest in MRS and improved the knowledge in areas like blockage effects, wake recovery, control, loads and structural integrity. The installation and commissioning of the OceanX twin rotor as the first floating MRS, based on aerodyn's Nezzy2-concept gained a lot of interest in the wind energy community. Companies like Windcatching Systems and Myriad develop MRS with a substantially higher number of rotors.

The presentation aims to describe the state of the art in research and development of MRS and dive into selected key factors such as loads, aerodynamics, structure, O&M and cost of energy. MRS-research gaps will be identified and outlined.

Multi Rotor technology – how to enter a commercial windfarm? A developers view.

Technology development is constantly needed in order to improve offshore wind and to support the energy transition. But how to find the right focus areas? The perspective of an integrated wind farm developer and operator could give first hand support and guidance. A presentation meant to give a connecting inspiration.

Wind Catching Demo – full scale demonstrator project

In January 2025, Wind Catching Systems was awarded a 100 mEUR grant from the Norwegian grant scheme ENOVA to build a full scale multi-rotor demonstrator of about 40 MW, 20 km off the Norwegian coast. The company will present the project and the associated development work, focusing on technical developments related to the multi rotor system.

How to get multi-rotors to market: Introducing the 50kW Myriad Turbine

Until now the questions around multi-rotors have focused on feasibility and technical development paths. These have mainly been tackled as we, as a community, begin to develop the technology. Now the question is, how do we bring it to market to start making an impact?

A full-size demonstration Project for the W2Power solution

The sea-proven W2Power solution, received Design Approval for its up to 15 MW design in late 2023. This version of the innovative W2Power concept is the basis for the PRIMAVERA project, a single unit full-size project that is advancing in the permitting process, having secured the concession area and grid connection permit in the port of Granadilla in Tenerife Island (Canary Islands, Spain). The presentation will describe the conceptualization of the project, its benefits and potential to decarbonize the port community, as well as the impact into the local industry.

Session 2: Industry (2/2)

Engineering Challenges in Monster Blades & Mechanical components

During the resurgence of modern wind energy in the 1980’s, blades were typically 6m/100kg and made locally by skilled boat technicians. Today 100m/50 ton plus blades are built by semiskilled operators working under pressure in varied global locations. There’s never been a pause in the development of wind turbines to rethink how we design and make blades. We’re simply using the same processes as the challenges of multiply with scale, just using advances in digital technologies to try to control the monster.

 In operation, there are fundamental reasons of physics why very large blades are more likely to suffer problems. We’ll look at ‘black box’ mystery of blade design, how compromises have to be made between ideal aerodynamic performance, structural strength and stiffness, and high-quality manufacture. Size really matters and briefly we compare the scale challenges of blades with those of mechanical components.

MRS for Offshore Wind - what needs to be done?

The idea of multi-rotor systems (MRS) has been around for more than ten years. In research a high potential has been attributed to the systems, since obvious advantages can be found. Especially for offshore wind, where the larger turbines and blade sizes pose an enormous challenge to the wind turbine manufacturers, yet larger capacities per unit would offer tremendous financial advantages. However, so far, there is no real break-through on the commercial side. The reason behind this is, that several open questions for the practical use are not answered, which are discussed in the presentation.

Session 3: Aerodynamics and Loads Modelling                      

Modelling aerodynamic loads on closely spaced rotors

Multi-rotor turbines offer the possibility of exploiting local blockage effects to improve energy yield through deploying rotors in close proximity to each other. A consequence of closely spacing rotors in such systems is increased mean and transient aerodynamic loading on the blades compared to single rotor systems. While variations in blade loading due to passing neighbouring rotors are observed in experiments and numerical simulations, mid-fidelity actuator models, such as the actuator line, may require bespoke sub-models and corrections for application to multi-rotor systems.

Open-source reference rotor library for multi-rotor aeroelastic modelling and design

The multi-rotor wind turbine (MRWT) is an emerging concept that promises benefits in aerodynamic, structural, economic and environmental performance over the existing single-rotor paradigm. This project aims to facilitate the research and development of the MRWT concept through the provision of open-source blade models aero-elastically optimised for the multi-rotor use case. The rotors generated cover a rated power range of 100kW to 1MW, and will provide greater flexibility in the generation of aero-elastic MRWT models for comparison and optimisation studies, among other uses.

Enhancing wind farm efficiency by Multi Rotor Wind Turbine Systems with Lifting Devices (MRSL)

Numerical and experimental studies have shown that adding lifting devices to a multi-rotor system significantly enhances its wake recovery. When multiple multi-rotor systems with lifting devices (MRSLs) are clustered into a wind farm, the farm performance are found to be more than doubled due to that the wake losses are substantially mitigated. Furthermore, recent results show that inflow turbulence has minimal impact on MRSL’s wake recovery, and farm layout has little influence on wind farm performance. To advance the technology readiness of MRSL, an outdoor test with its prototype is planned.

Numerical simulation of multi-rotor diffuser augmented wind turbine system using the actuator line method in PyFR solver

This study develops a high-order numerical model, AL-PyFR(DAWT), to analyze multi-rotor diffuser-augmented wind turbine (MRDAWT) systems using the actuator line method within PyFR. The model is validated against a 5-rotor DAWT experiment, accurately capturing asymmetric rotor power, wake interactions, and diffuser effects. A parametric study on a 9-rotor system shows rotor spacing and tip speed ratio strongly affect power output and efficiency, highlighting the need for system-level optimization.

Literature review and preliminary actuator cylinder modelling of adjacent VAWTs

Vertical-axis wind turbines have several interesting physical aspects when placed in pairs or rows, changing flow characteristics and often increasing power output. This presentation first summarises literature explaining the physics behind these aspects, and some illustrations of expected power gain by pairing VAWTs. Then, the Actuator Cylinder method is discussed, an extension of the actuator disk model that is capable of modelling VAWTs with relatively high accuracy for its computational speed. My own preliminary AC code, capable of modelling multiple VAWTs, is discussed and shared.

Session 4: Loads, Control and Structure

Beyond Single Rotors: Enhancing Performance in Multi-Rotor Wind Turbines

This presentation details advanced modeling and real-time control for a 23-rotor, 5 MW fixed-pitch wind turbine.
The work leverages modeling of aerodynamic interactions and dynamic inflow to develop strategies that maximize energy capture and manage structural loads through thrust reallocation and failure compensation. A central result is the introduction of a novel, efficient control algorithm that uses intentional yaw misalignment ("furling") to actively reduce structural bending moments, providing a simple, self-optimizing approach for next-generation multi-rotor architectures.

Multi-rotor floating wind turbine concepts: control co-design to ensure their feasibility

Recently, several multi-rotor floating wind concepts have been developed, ranging from 2 to dozens of generators. Starting from the simplest one, its singular design (with a single point mooring) presents a critical challenge: aligning the platform with the wind to prevent high loads, wake losses and instability, which directly impact on lifespan and revenue.

Conventional control strategies fall short. The solution lies in control co-design, an integrated approach that harmonizes the system design with its control logic from day one. The main goal of this work is to present several control co-design solutions proposed to overcome this issue, from control co-design concepts to control algorithms.

Rotor–Rotor Interactions in Multi-Rotor Arrays: Insights from Aerodynamic Simulations and Open Questions

Multi-rotor wind turbines promise lighter structures and higher capacity, yet operating experience remains scarce. This talk reviews rotor–rotor interaction across three scales—blade-to-blade, rotor-to-rotor and array flow—drawing on lifting-line vortex, actuator-line RANS/LES and actuator-disk CFD studies. Focus is on aerodynamic interactions shaping performance and load distributions, with brief reference to implications for structures, fatigue and control. Consistent findings, open questions, and future directions for aerodynamic research on multi-rotor arrays are outlined. 

MRS space frame loads and rotor interactions

The presentation will focus on the latest results of MRS structural investigations. Prior HAW research focusing on floating MRS space frames has been extended to include fatigue analysis. The influence of designs choices such as row and column configurations as well as the number of rotors will be shown for 20 MW systems. Rotor-rotor and rotor-structure interactions and the influence on blade root loads will also be investigated based on HAW conducted aerodynamic load simulations and external, published CFD simulations.

Active Power Control of Multi-Rotor Turbines for Fast Frequency Reserve

Fast frequency reserve is a dynamic ancillary service for the power grid. In previous grids, this was provided by power plants with synchronous machines and dispatchable primary sources. In systems of the near future, this must be provided as far as possible by converter-based regenerative resources. The requirements for wind energy systems are high. According to existing grid codes, output must be reduced by 60–80% within 1–2 seconds to provide so-called negative inertia. Positive inertia, i.e., an increase in power to emulate the inertia of conventional synchronous machines, results from the power reserve of a derated wind energy system. To be able to provide this with a multi-rotor wind turbine, i.e., the primary energy system of a wind energy system, the established control concepts must be significantly modified. This article presents a decentralised control concept in which each rotor contributes to the active power fed into the grid. A theoretical and systematic controller design method is proposed, which allows the dynamic adaptation of the power generated by wind power plants. The focus is on the dynamic tracking control of the primary power. Finally, simulation results are presented, along with a concept that enables active power generation also by turbine rotors without pitch control via stall operation.

Session 5: Offshore, Floating, O&M

Some thoughts on multi rotor wind and its interaction with curtailment

Curtailment is growing in European power markets, in part due to negative prices becoming more prevalent. In the UK in 2024, 1.8% of all operational hours (155 in total) were negative - which means that offshore wind farms on recent CfD contracts would self-curtail (so-called economic curtailment). Economic curtailment (unlike geographic curtailment) is not usually financially compensated, it is an ‘opportunity cost’. As well as lost production, curtailment could have an impact on component life, the coupling of which is not well understood.

This talk will explore some early thinking on how multi rotor wind turbines could have some advantages when compared to conventional machines with respect to economic curtailment. In particular, we will explore the idea that the modular nature of MRS turbines could mean that periods of curtailment could be forecasted and used for opportunistic servicing, owing to the simpler and quicker nature of maintenance interventions on MRS machines.  

Operation and Maintenance of Multi-Rotor Wind Turbines: Insights from a Case Study and a Startup Simulation Solution

Multi-Rotor Systems (MRS) present promising opportunities for enhanced energy capture, modularity, and redundancy, but they also introduce unique operation and maintenance (O&M) challenges. With increased component counts, interdependent failure modes, and complex maintenance logistics, effective O&M strategies are critical to ensuring system reliability and cost-effectiveness. This presentation shares key insights from a case study on the O&M of multi-rotor wind turbines at FINO-1 site in the North Sea. Quantitative results are presented to illustrate the impact of maintenance strategies on downtime, availability, and overall lifecycle cost.

Building on these findings, the session introduces a startup-developed simulation solution designed to support data-driven decision-making for O&M planning. Developed by Ventarion, the simulation tool (Ventarion Sim) enables scenario analysis and strategy evaluation for both multi-rotor and conventional wind turbine systems. By combining technical analysis, case study results, and applied innovation, the talk bridges the gap between academic research and real-world practice, offering valuable perspectives for researchers, operators, and technology developers seeking to advance wind turbine O&M.

Multi-rotor wind turbines: A review of modern research efforts and challenges

The rising capital and operational costs associated with scaling up single-rotor wind turbines have the potential to offset the energy gains of larger rotors, making their impact on levelised cost of energy uncertain. Multi-rotor wind turbines show great promise in reducing LCoE through their advantageous scaling laws. Their smaller individual rotors enable the use of more sustainable materials and streamlined operations and maintenance, addressing many shortcomings of single-rotor designs. This work reviews recent MRWT research spanning numerous disciplines, including aerodynamics, structures, and maintenance, amongst others.

Designing multi-rotor wind turbines: Standards, practicalities, and developments

We all know the theory and the potential advantages of the multi-rotor, but the real question is: how do you actually design one? Here, we will talk through some considerations of multi-rotor design in the real world. We will discuss design standards, practicalities and their impacts on design, modelling approaches, and what all of this means for scaling up to larger systems.

Session 6: System Design

Park scale LCOE modelling for floating multi rotor systems and its impact on turbine rating

Based on a generic 500 MW floating wind park, the presentation will discuss how LCOE modelling and turbine rating selection impacts a multi rotor system design. Which parameters impact LCOE the most, and what is the optimal turbine specification to minimise LCOE?

Perpectives of Offshore Wind and Hydrogen Economy

To decarbonize certain sectors of society, that are particularly difficult to electrify, climate-neutral produced Hydrogen provides an important future perspective. Green Hydrogen and it’s derivatives can thus provide an important decarbonization pathway for metallurgy, chemical industry, shipping, logistics and aviation. The electricity needed to produce the Hydrogen through electrolysis, is abundantly available in the coastal areas of North Germany provided by onshore and offshore wind farms. In future, with large upscaling of offshore wind, the green power resource will grow even further in the region. This makes the Hamburg Metropolitan Area predestined to become a hub for green Hydrogen production, import, transportation and offtake. This presentation will give an overview on current developments.

LCoE Calculator for MRS: From Scaling Theory to Cost Evaluation

This presentation summarizes the findings of a master’s thesis that developed a techno-economic model to evaluate the levelized cost of energy (LCoE) for 20 MW multirotor wind turbines. The study places a particular focus on mass scaling laws to assess how key component costs evolve with system size. The results offer insights into the economic viability of multirotor concepts compared to conventional single-rotor systems of equal rated power, particularly in offshore applications.

Accelerating the Future of Offshore Wind: Ramboll’s End-to-End Capability in Floating Wind Development combined with System Design Expertise 

Ramboll offers comprehensive services for floating multi-rotor system projects, spanning from conceptual design to final delivery. Leveraging our extensive experience in commercial floating wind project development, we possess the tools necessary to efficiently manage the numerous interfaces unique to floating wind projects. This capability is complemented by Ramboll’s profound technical expertise, ensuring seamless integration throughout the project lifecycle.

Using parametric design-space exploration, fully coupled integrated load analysis and digital twins, Ramboll benchmarks and refines concepts through pre-FEED and FEED, optimizing integration, structural layout, platform mass, moorings and maintenance. Ramboll has broad experience in delivery of offshore wind projects with primary steel, secondary steel designs, system integration, operation and maintenance design and owners engineering enabling a wide view on the full product lifecycle.

The Windbrücke and multigenerator system for alpine sites

Wind turbines with multirotor systems are a technical response to a rapid expansion of wind power in the Swiss Alps. Several structural and economic advantages of such turbines have been identified in the literature. Previous studies have shown a cost reduction of more than 25% for a multi-megawatt multirotor turbine compared to a single-rotor turbine with the same rated power. It is equally known from published scientifically supported measurements that an additional 2% extra yield can be achieved than a comparable single-rotor turbine with the same harvest area.

The idea shall be tested on a 1:10 full scale small tower (1:10 scale model of a 15MW full turbine size), with three nacelles and a maximum height of 35m (MR30).

This demonstration wind turbine will demonstrate the technical and commercial feasibility of this new multirotor wind turbine. With three individual machines rated each 30kW, the loads in the support structure are measured, the information is implemented in the control system and optimized in a load-saving way. This relieves the critical parts of the large structure and allows smaller and thus more economical dimension for the alps.

The entire wind turbine for the alps and the test can be erected on site without a large crane footprint. This possibility is achieved by limited component weight and new lifting techniques for both, structure, and nacelle. In addition, the total height of the test turbine of 35m can fill a possible product gap for small wind turbines in Switzerland. The appearance of the MR30 turbine has been very consciously optimized to a conspicuous appearance similar to a power pole patina, suggesting the feeling that this wind turbine has been part of the landscape for a long time.

Session 7: Looking Back and Looking Forward

Could multi-rotor historic experiences be blueprint for future pathway?

This presentation evaluates experiences with historic multi-rotor designs as potential blueprint for current initiatives with few and many rotors, other key variables, and what could prove the best way forward. Multi-rotor thereby must in a highly competitive environment always compete with single-rotor on scale (MW, W/m2), track record, risk & risk perception, time-to-market, bankability, and LCoE.

The cumulative track record encompasses four prototype concepts - four-rotor 300kW Lagerwey Quadro (1980’s) & 900kW Vestas MRT (2016), plus twin-rotor floating 16.6MW OceanX MingYang MySE 16.6T (2024) & 12MW EnerOcean W2Power (2025). Semi-commercial: 6x ~40kW Lagerwey Twin (1980’s).

Session 1: Industry (1/2)

MRS, selected key factors

Wind Catching Demo – full scale demonstrator project

A full-size demonstration Project for the W2Power solution

Session 2: Industry (2/2)

Engineering Challenges in Monster Blades & Mechanical components

Session 3: Aerodynamics and Loads Modelling                      

Modelling aerodynamic loads on closely spaced rotors

Open-source reference rotor library for multi-rotor aeroelastic modelling and design

Enhancing wind farm efficiency by Multi Rotor Wind Turbine Systems with Lifting Devices (MRSL)

Numerical simulation of multi-rotor diffuser augmented wind turbine system using the actuator line method in PyFR solver

Literature review and preliminary actuator cylinder modelling of adjacent VAWTs

Closing words Day 1

Dinner at Rickmer Rickmers 

Adress of the location:

Museumsschiff RICKMER RICKMERS
Landungsbrücken, Ponton 1a
20359 Hamburg

Session 4: Loads, Control and Structure

Beyond Single Rotors: Enhancing Performance in Multi-Rotor Wind Turbines

Multi-rotor floating wind turbine concepts: control co-design to ensure their feasibility

MRS space frame loads and rotor interactions

Active Power Control of Multi-Rotor Turbines for Fast Frequency Reserve

Session 5: Offshore, Floating, O&M

Multi-rotor wind turbines: A review of modern research efforts and challenges

Session 6: System Design

Park scale LCOE modelling for floating multi rotor systems and its impact on turbine rating

LCoE Calculator for MRS: From Scaling Theory to Cost Evaluation

The Windbrücke and multigenerator system for alpine sites

Session 7: Looking Back and Looking Forward

Session 1: Industry (1/2)

MRS, selected key factors

Research and Innovation in multi rotor wind turbine systems (MRS) has made substantial progress over the past two decades. Research projects, such as INNWIND and X-Energy improved the design methods and knowledge on MRS, such as loads, structural design, operation, maintenance and more. The Vestas quad-rotor demonstrator revealed further insights, in particular on aerodynamic interactions and wakes. Numerous publications show the increasing interest in MRS and improved the knowledge in areas like blockage effects, wake recovery, control, loads and structural integrity. The installation and commissioning of the OceanX twin rotor as the first floating MRS, based on aerodyn's Nezzy2-concept gained a lot of interest in the wind energy community. Companies like Windcatching Systems and Myriad develop MRS with a substantially higher number of rotors.

The presentation aims to describe the state of the art in research and development of MRS and dive into selected key factors such as loads, aerodynamics, structure, O&M and cost of energy. MRS-research gaps will be identified and outlined.

Multi Rotor technology – how to enter a commercial windfarm? A developers view.

Technology development is constantly needed in order to improve offshore wind and to support the energy transition. But how to find the right focus areas? The perspective of an integrated wind farm developer and operator could give first hand support and guidance. A presentation meant to give a connecting inspiration.

Wind Catching Demo – full scale demonstrator project

In January 2025, Wind Catching Systems was awarded a 100 mEUR grant from the Norwegian grant scheme ENOVA to build a full scale multi-rotor demonstrator of about 40 MW, 20 km off the Norwegian coast. The company will present the project and the associated development work, focusing on technical developments related to the multi rotor system.

How to get multi-rotors to market: Introducing the 50kW Myriad Turbine

Until now the questions around multi-rotors have focused on feasibility and technical development paths. These have mainly been tackled as we, as a community, begin to develop the technology. Now the question is, how do we bring it to market to start making an impact?

A full-size demonstration Project for the W2Power solution

The sea-proven W2Power solution, received Design Approval for its up to 15 MW design in late 2023. This version of the innovative W2Power concept is the basis for the PRIMAVERA project, a single unit full-size project that is advancing in the permitting process, having secured the concession area and grid connection permit in the port of Granadilla in Tenerife Island (Canary Islands, Spain). The presentation will describe the conceptualization of the project, its benefits and potential to decarbonize the port community, as well as the impact into the local industry.

Session 2: Industry (2/2)

Engineering Challenges in Monster Blades & Mechanical components

During the resurgence of modern wind energy in the 1980’s, blades were typically 6m/100kg and made locally by skilled boat technicians. Today 100m/50 ton plus blades are built by semiskilled operators working under pressure in varied global locations. There’s never been a pause in the development of wind turbines to rethink how we design and make blades. We’re simply using the same processes as the challenges of multiply with scale, just using advances in digital technologies to try to control the monster.

 In operation, there are fundamental reasons of physics why very large blades are more likely to suffer problems. We’ll look at ‘black box’ mystery of blade design, how compromises have to be made between ideal aerodynamic performance, structural strength and stiffness, and high-quality manufacture. Size really matters and briefly we compare the scale challenges of blades with those of mechanical components.

MRS for Offshore Wind - what needs to be done?

The idea of multi-rotor systems (MRS) has been around for more than ten years. In research a high potential has been attributed to the systems, since obvious advantages can be found. Especially for offshore wind, where the larger turbines and blade sizes pose an enormous challenge to the wind turbine manufacturers, yet larger capacities per unit would offer tremendous financial advantages. However, so far, there is no real break-through on the commercial side. The reason behind this is, that several open questions for the practical use are not answered, which are discussed in the presentation.

Session 3: Aerodynamics and Loads Modelling                      

Modelling aerodynamic loads on closely spaced rotors

Multi-rotor turbines offer the possibility of exploiting local blockage effects to improve energy yield through deploying rotors in close proximity to each other. A consequence of closely spacing rotors in such systems is increased mean and transient aerodynamic loading on the blades compared to single rotor systems. While variations in blade loading due to passing neighbouring rotors are observed in experiments and numerical simulations, mid-fidelity actuator models, such as the actuator line, may require bespoke sub-models and corrections for application to multi-rotor systems.

Open-source reference rotor library for multi-rotor aeroelastic modelling and design

The multi-rotor wind turbine (MRWT) is an emerging concept that promises benefits in aerodynamic, structural, economic and environmental performance over the existing single-rotor paradigm. This project aims to facilitate the research and development of the MRWT concept through the provision of open-source blade models aero-elastically optimised for the multi-rotor use case. The rotors generated cover a rated power range of 100kW to 1MW, and will provide greater flexibility in the generation of aero-elastic MRWT models for comparison and optimisation studies, among other uses.

Enhancing wind farm efficiency by Multi Rotor Wind Turbine Systems with Lifting Devices (MRSL)

Numerical and experimental studies have shown that adding lifting devices to a multi-rotor system significantly enhances its wake recovery. When multiple multi-rotor systems with lifting devices (MRSLs) are clustered into a wind farm, the farm performance are found to be more than doubled due to that the wake losses are substantially mitigated. Furthermore, recent results show that inflow turbulence has minimal impact on MRSL’s wake recovery, and farm layout has little influence on wind farm performance. To advance the technology readiness of MRSL, an outdoor test with its prototype is planned.

Numerical simulation of multi-rotor diffuser augmented wind turbine system using the actuator line method in PyFR solver

This study develops a high-order numerical model, AL-PyFR(DAWT), to analyze multi-rotor diffuser-augmented wind turbine (MRDAWT) systems using the actuator line method within PyFR. The model is validated against a 5-rotor DAWT experiment, accurately capturing asymmetric rotor power, wake interactions, and diffuser effects. A parametric study on a 9-rotor system shows rotor spacing and tip speed ratio strongly affect power output and efficiency, highlighting the need for system-level optimization.

Literature review and preliminary actuator cylinder modelling of adjacent VAWTs

Vertical-axis wind turbines have several interesting physical aspects when placed in pairs or rows, changing flow characteristics and often increasing power output. This presentation first summarises literature explaining the physics behind these aspects, and some illustrations of expected power gain by pairing VAWTs. Then, the Actuator Cylinder method is discussed, an extension of the actuator disk model that is capable of modelling VAWTs with relatively high accuracy for its computational speed. My own preliminary AC code, capable of modelling multiple VAWTs, is discussed and shared.

Session 4: Loads, Control and Structure

Beyond Single Rotors: Enhancing Performance in Multi-Rotor Wind Turbines

This presentation details advanced modeling and real-time control for a 23-rotor, 5 MW fixed-pitch wind turbine.
The work leverages modeling of aerodynamic interactions and dynamic inflow to develop strategies that maximize energy capture and manage structural loads through thrust reallocation and failure compensation. A central result is the introduction of a novel, efficient control algorithm that uses intentional yaw misalignment ("furling") to actively reduce structural bending moments, providing a simple, self-optimizing approach for next-generation multi-rotor architectures.

Multi-rotor floating wind turbine concepts: control co-design to ensure their feasibility

Recently, several multi-rotor floating wind concepts have been developed, ranging from 2 to dozens of generators. Starting from the simplest one, its singular design (with a single point mooring) presents a critical challenge: aligning the platform with the wind to prevent high loads, wake losses and instability, which directly impact on lifespan and revenue.

Conventional control strategies fall short. The solution lies in control co-design, an integrated approach that harmonizes the system design with its control logic from day one. The main goal of this work is to present several control co-design solutions proposed to overcome this issue, from control co-design concepts to control algorithms.

Rotor–Rotor Interactions in Multi-Rotor Arrays: Insights from Aerodynamic Simulations and Open Questions

Multi-rotor wind turbines promise lighter structures and higher capacity, yet operating experience remains scarce. This talk reviews rotor–rotor interaction across three scales—blade-to-blade, rotor-to-rotor and array flow—drawing on lifting-line vortex, actuator-line RANS/LES and actuator-disk CFD studies. Focus is on aerodynamic interactions shaping performance and load distributions, with brief reference to implications for structures, fatigue and control. Consistent findings, open questions, and future directions for aerodynamic research on multi-rotor arrays are outlined. 

MRS space frame loads and rotor interactions

The presentation will focus on the latest results of MRS structural investigations. Prior HAW research focusing on floating MRS space frames has been extended to include fatigue analysis. The influence of designs choices such as row and column configurations as well as the number of rotors will be shown for 20 MW systems. Rotor-rotor and rotor-structure interactions and the influence on blade root loads will also be investigated based on HAW conducted aerodynamic load simulations and external, published CFD simulations.

Active Power Control of Multi-Rotor Turbines for Fast Frequency Reserve

Fast frequency reserve is a dynamic ancillary service for the power grid. In previous grids, this was provided by power plants with synchronous machines and dispatchable primary sources. In systems of the near future, this must be provided as far as possible by converter-based regenerative resources. The requirements for wind energy systems are high. According to existing grid codes, output must be reduced by 60–80% within 1–2 seconds to provide so-called negative inertia. Positive inertia, i.e., an increase in power to emulate the inertia of conventional synchronous machines, results from the power reserve of a derated wind energy system. To be able to provide this with a multi-rotor wind turbine, i.e., the primary energy system of a wind energy system, the established control concepts must be significantly modified. This article presents a decentralised control concept in which each rotor contributes to the active power fed into the grid. A theoretical and systematic controller design method is proposed, which allows the dynamic adaptation of the power generated by wind power plants. The focus is on the dynamic tracking control of the primary power. Finally, simulation results are presented, along with a concept that enables active power generation also by turbine rotors without pitch control via stall operation.

Session 5: Offshore, Floating, O&M

Some thoughts on multi rotor wind and its interaction with curtailment

Curtailment is growing in European power markets, in part due to negative prices becoming more prevalent. In the UK in 2024, 1.8% of all operational hours (155 in total) were negative - which means that offshore wind farms on recent CfD contracts would self-curtail (so-called economic curtailment). Economic curtailment (unlike geographic curtailment) is not usually financially compensated, it is an ‘opportunity cost’. As well as lost production, curtailment could have an impact on component life, the coupling of which is not well understood.

This talk will explore some early thinking on how multi rotor wind turbines could have some advantages when compared to conventional machines with respect to economic curtailment. In particular, we will explore the idea that the modular nature of MRS turbines could mean that periods of curtailment could be forecasted and used for opportunistic servicing, owing to the simpler and quicker nature of maintenance interventions on MRS machines.  

Operation and Maintenance of Multi-Rotor Wind Turbines: Insights from a Case Study and a Startup Simulation Solution

Multi-Rotor Systems (MRS) present promising opportunities for enhanced energy capture, modularity, and redundancy, but they also introduce unique operation and maintenance (O&M) challenges. With increased component counts, interdependent failure modes, and complex maintenance logistics, effective O&M strategies are critical to ensuring system reliability and cost-effectiveness. This presentation shares key insights from a case study on the O&M of multi-rotor wind turbines at FINO-1 site in the North Sea. Quantitative results are presented to illustrate the impact of maintenance strategies on downtime, availability, and overall lifecycle cost.

Building on these findings, the session introduces a startup-developed simulation solution designed to support data-driven decision-making for O&M planning. Developed by Ventarion, the simulation tool (Ventarion Sim) enables scenario analysis and strategy evaluation for both multi-rotor and conventional wind turbine systems. By combining technical analysis, case study results, and applied innovation, the talk bridges the gap between academic research and real-world practice, offering valuable perspectives for researchers, operators, and technology developers seeking to advance wind turbine O&M.

Multi-rotor wind turbines: A review of modern research efforts and challenges

The rising capital and operational costs associated with scaling up single-rotor wind turbines have the potential to offset the energy gains of larger rotors, making their impact on levelised cost of energy uncertain. Multi-rotor wind turbines show great promise in reducing LCoE through their advantageous scaling laws. Their smaller individual rotors enable the use of more sustainable materials and streamlined operations and maintenance, addressing many shortcomings of single-rotor designs. This work reviews recent MRWT research spanning numerous disciplines, including aerodynamics, structures, and maintenance, amongst others.

Designing multi-rotor wind turbines: Standards, practicalities, and developments

We all know the theory and the potential advantages of the multi-rotor, but the real question is: how do you actually design one? Here, we will talk through some considerations of multi-rotor design in the real world. We will discuss design standards, practicalities and their impacts on design, modelling approaches, and what all of this means for scaling up to larger systems.

Session 6: System Design

Park scale LCOE modelling for floating multi rotor systems and its impact on turbine rating

Based on a generic 500 MW floating wind park, the presentation will discuss how LCOE modelling and turbine rating selection impacts a multi rotor system design. Which parameters impact LCOE the most, and what is the optimal turbine specification to minimise LCOE?

Perpectives of Offshore Wind and Hydrogen Economy

To decarbonize certain sectors of society, that are particularly difficult to electrify, climate-neutral produced Hydrogen provides an important future perspective. Green Hydrogen and it’s derivatives can thus provide an important decarbonization pathway for metallurgy, chemical industry, shipping, logistics and aviation. The electricity needed to produce the Hydrogen through electrolysis, is abundantly available in the coastal areas of North Germany provided by onshore and offshore wind farms. In future, with large upscaling of offshore wind, the green power resource will grow even further in the region. This makes the Hamburg Metropolitan Area predestined to become a hub for green Hydrogen production, import, transportation and offtake. This presentation will give an overview on current developments.

LCoE Calculator for MRS: From Scaling Theory to Cost Evaluation

This presentation summarizes the findings of a master’s thesis that developed a techno-economic model to evaluate the levelized cost of energy (LCoE) for 20 MW multirotor wind turbines. The study places a particular focus on mass scaling laws to assess how key component costs evolve with system size. The results offer insights into the economic viability of multirotor concepts compared to conventional single-rotor systems of equal rated power, particularly in offshore applications.

Accelerating the Future of Offshore Wind: Ramboll’s End-to-End Capability in Floating Wind Development combined with System Design Expertise 

Ramboll offers comprehensive services for floating multi-rotor system projects, spanning from conceptual design to final delivery. Leveraging our extensive experience in commercial floating wind project development, we possess the tools necessary to efficiently manage the numerous interfaces unique to floating wind projects. This capability is complemented by Ramboll’s profound technical expertise, ensuring seamless integration throughout the project lifecycle.

Using parametric design-space exploration, fully coupled integrated load analysis and digital twins, Ramboll benchmarks and refines concepts through pre-FEED and FEED, optimizing integration, structural layout, platform mass, moorings and maintenance. Ramboll has broad experience in delivery of offshore wind projects with primary steel, secondary steel designs, system integration, operation and maintenance design and owners engineering enabling a wide view on the full product lifecycle.

The Windbrücke and multigenerator system for alpine sites

Wind turbines with multirotor systems are a technical response to a rapid expansion of wind power in the Swiss Alps. Several structural and economic advantages of such turbines have been identified in the literature. Previous studies have shown a cost reduction of more than 25% for a multi-megawatt multirotor turbine compared to a single-rotor turbine with the same rated power. It is equally known from published scientifically supported measurements that an additional 2% extra yield can be achieved than a comparable single-rotor turbine with the same harvest area.

The idea shall be tested on a 1:10 full scale small tower (1:10 scale model of a 15MW full turbine size), with three nacelles and a maximum height of 35m (MR30).

This demonstration wind turbine will demonstrate the technical and commercial feasibility of this new multirotor wind turbine. With three individual machines rated each 30kW, the loads in the support structure are measured, the information is implemented in the control system and optimized in a load-saving way. This relieves the critical parts of the large structure and allows smaller and thus more economical dimension for the alps.

The entire wind turbine for the alps and the test can be erected on site without a large crane footprint. This possibility is achieved by limited component weight and new lifting techniques for both, structure, and nacelle. In addition, the total height of the test turbine of 35m can fill a possible product gap for small wind turbines in Switzerland. The appearance of the MR30 turbine has been very consciously optimized to a conspicuous appearance similar to a power pole patina, suggesting the feeling that this wind turbine has been part of the landscape for a long time.

Session 7: Looking Back and Looking Forward

Could multi-rotor historic experiences be blueprint for future pathway?

This presentation evaluates experiences with historic multi-rotor designs as potential blueprint for current initiatives with few and many rotors, other key variables, and what could prove the best way forward. Multi-rotor thereby must in a highly competitive environment always compete with single-rotor on scale (MW, W/m2), track record, risk & risk perception, time-to-market, bankability, and LCoE.

The cumulative track record encompasses four prototype concepts - four-rotor 300kW Lagerwey Quadro (1980’s) & 900kW Vestas MRT (2016), plus twin-rotor floating 16.6MW OceanX MingYang MySE 16.6T (2024) & 12MW EnerOcean W2Power (2025). Semi-commercial: 6x ~40kW Lagerwey Twin (1980’s).