Future Offshore Wind Power Systems

Beyond the Horizon

Contents

1. Introduction

2. Overview of Existing Technology

3. Deep water Wind Power Applications Using

Microgen Technology ltd Multiple Rotor Vertical

Axis Wind Turbine (MVAWT) systems

4. The Way Forward

1. Introduction

The ongoing difficulty in producing and finding economical petroleum reserves and the need to address the influence of climate change is moving to the forefront of national policy on energy. It has been widely publicised and acknowledged that this presents a tremendous growth opportunity for renewable energy developments and will eventually lead to a proliferation of renewable energy systems competing with fossil, conventional renewable and nuclear power generation. The UK is in a unique position to exploit the market for offshore wind power as the resource is abundant onshore and offshore UK. However the UK continental shelf does cover a large acreage of deep water particularly in locations where offshore wind power is best exploited. The offshore acreage to the west of the UK presents tremendous opportunities for the development and harnessing of wind energy. However any offshore wind power installation has to meet a number of key criteria to be economically viable:

i. Power output justifies significant capital investment

ii. Facilities are accessible for maintenance in a harsh environment

iii. Reliability and availability of installation has to be much higher than current land based and near shore sites

The current design of wind power turbines utilised in large onshore and near shore wind farms employs horizontal axis wind turbine (HAWT) generators and it is our view at Microgen Technologies ltd (MGTL) that these designs have significant disadvantages for what we would term ‘true’ offshore wind farms. We believe that there are significant disadvantages in the HAWT design that requires alternatives:

i. Accessibility in far offshore locations

ii. Reliability may not be sufficient to make typical horizontal axis wind turbines (HAWT) suitable for these environments.

iii. The HAWT wind turbine technology is reaching its size limit

The purpose of this document is primarily to describe the advantages of MGTL’s own design for a multi-rotor vertical axis wind turbine (MVAWT) and to galvanise investment in the concept to develop research in to the applicability of this design leading to eventually fund a large scale prototype installation or demonstration unit in excess of 5 MW(e) capacity.

2. Overview of Current Technology

This is a brief overview of the existing technology currently employed to date primarily in the UKCS by way of example. However these models are applicable to similar marine basin environments in other countries, e.g. Denmark.

2.1 Near Shore Windfarm Current Concepts

Figure 1 illustrates a typical example of what we would term the first generation in offshore wind turbines. The turbines are mounted offshore (in fact near shore) in relatively shallow water with the turbine tower situated on a monopod structure fixed to the sea bed. The monopod structure design severely limits the water depth that these units can operate in to a maximum of about 20 m. These are not true offshore windfarms in the sense that one would expect to see in the round 3 licence awards in the UK and the monopod support structure employed in this design limits them to coastal locations. However these developments have allowed wind power development to free itself of many of the planning obstacles in onshore locations and the coastal location allows for more unobstructed wind patterns. However they still present planning issues in terms of visual impact from shore for example and while they are free of land they still do not capture all of the wind energy that could be available further offshore.

2.2 Deepwater Offshore Windfarm Current Concepts e.g. Beatrice Offshore Wind Farm

The Beatrice wind farm is an excellent model for how far offshore wind farms could in fact look and probably the best illustration of how far the current HAWT design can be employed in this type of situation. The wind turbine tower is mounted on a jacket structure (Figure 2) which is very similar to those employed in offshore oil and gas developments and the water depth that these systems can operate in is only limited by the capital cost of the jacket and its impact on the project NPV. The Beatrice wind farm was a significant development in offshore wind technology and what we would view as the intermediate step toward a true offshore windfarm development concept. This development proved that a large traditional HAWT machine can be transported and installed offshore with a conventional jacket type structure to provide a stable operating platform using offshore oil and gas construction technology to execute the installation of the facilities. This is in essence the birth of the second generation of offshore wind turbines where true deepwater application has been translated in to a commercial demonstrator reality. It is not unreasonable to expect to see this type of unit being viewed as a potential de facto standard for far offshore wind turbine developments. However they could have access limitations for far offshore locations and may become limited by the

size of wind turbines that could be available. Therefore there are two potential key parameter issues in these units:

i. Availability impacted by access difficulties

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ii. Power output limited by physical size of the turbines

This is where we at Microgen Technologies ltd see the design of wind turbine becoming important and likely to spawn concepts other than the traditional three bladed HAWT as alternatives to be located far offshore.

2.3 The Next Generation

As stated earlier our view at MGTL is that at this point in time no one truly completely understands or has an appropriate model for how a far offshore location wind farm would look other than an extrapolation of the Beatrice wind farm concept. The model in most potential developer’s minds is of future deepwater wind farm development employing jacket type support structures. Some Norwegian concept developers have put forward floating anchored or guyed buoyant support structures as a possibility, again supporting a HAWT three blade configuration.

However this model could prove to have limitations in a number of areas:

i. Can the turbines be sufficiently large to be feasible and justify the high capital costs of such a project?

ii. Can long term reliability be assured for these units operating in a hostile far offshore location?

iii. Can these wind turbines be safely accessed by air using helicopters?

iv. Vessel offshore access systems would be useless for most of the year?

v. Are blades reaching their size limit?

There are therefore a number of issues that need to be resolved before a commercially viable offshore windfarm development in one of the round 3 licence areas can feasibly be considered. It is our view in Microgen Technologies ltd that the supporting structures required to support the wind turbine can use existing technologies e.g.

i. Fixed piled to sea bed jacket structures

ii. Guyed buoyant monopods

iii. Other floating structures, e.g. a lightweight dual hull anchored semisubmersible

Where we differ from the current views of the industry is that for the larger size of wind turbine that would be required in deepwater locations we believe that vertical axis wind turbines can have a part to play. We are also of the view that some of the limitations of this design can be overcome and make it feasible for far offshore deepwater applications. The MVAWT concept has a number of features that make it advantageous in comparison to HAWT. Figures 1 to 3 illustrate schematically and to proportionate scale how the evolution from a near shore mono pod based HAWT to the MVAWT concept developed by Microgen Technologies ltd would look.

Figure 1 Coastal/Near shore Monopod Type Structure

Figure 2 Deepwater Jacket Type Structure Supporting a HAWT

Illustrated in figure 3 is a multi rotor vertical axis wind turbine (MVAWT) where the rotors rotate around a vertical axis. In the case illustrated in figure 3 four rotors rotate around the support tower, each rotor drives an individual generator located within the tower and the tower is in essence the vertical axis of rotation in this design. Loads are balanced across the tower structure by the rotors contra-rotating to each other. As can be seen from this simplified illustration the size of facility will match the hub height for a HAWT mounted unit employing similarly sized rotor blades. The sheer size of the offshore located MVAWT (and current HAWTs) makes it feasible to mount the generators inside the support structure and allow reasonable access for maintenance and repair personnel. As can be seen from figure 3 helicopter access is unrestricted by the wind turbine blades and this allows any size of aircraft to operate and service the windfarm and meet the requirements of CAP 437 easily. As will be discussed in the next section we view unrestricted helicopter access for long range helicopters a key success factor that is required to allow operation of far offshore located wind turbines. However ease of access alone is not sufficient motivation to consider an alternative to HAWT technology and it is also the case that this concept was conceived to provide a significantly higher power output for a given hub height for a comparably sized HAWT.

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Figure 3 Far Offshore Located Unit Incorporating Multi Rotor Vertical Axis Wind Turbine

Figure 2 Deepwater Jacket Type Structure Supporting a HAWT

Comparison of MVAWT and HAWT Turbines Located on Deepwater Jacket Structures

3. Deepwater Wind Power Applications Using Microgen Technology ltd Systems MVAWT Technology

3.1 Overview

In 2008 MGTL identified the concept for a multiple rotor vertical axis wind turbine (MVAWT) for far offshore locations as it was our belief that, although the output from current designs of horizontal axis wind turbines was and is becoming more efficient there are alternatives that may have been overlooked. This view is based on the premise that current HAWT designs require significant spacing in arrays and to increase output the wind turbine becomes increasingly large. The use of ever larger rotors requires increasingly larger structures to support the wind turbine and in offshore locations helicopter access may become more difficult and create aviation safety issues, particularly in far offshore locations where a Eurocopter EC 225 or similar size aircraft would be required on grounds of crew size and particularly range to facilitate a maintenance visit for even the most basic maintenance tasks, e.g. addressing a sensor failures or condition monitoring.

In our design the rotor rotates around the vertical support structure and multiple rotors can be mounted on the structure in a stacked configuration preferably with the rotors contra rotating to each other. The contra rotating rotors both balance torsional loads across the structure and can reduce spacing requirements between turbine installations in an array. The vertical support structure employed in this design of turbine is virtually identical to the ‘pole’ type structure to support a HAWT nacelle and hub. On an individual rotor basis when compared to a similarly sized HAWT the individual rotor on the MVAWT is naturally less efficient, however we believe that the efficiency could be certainly 35-50% on a P90 to P50 basis and potentially up to 70% of the power output of a similarly sized HAWT rotor at the P10 range with correct design of blades. We believe that there is value in research funding to develop knowledge of this range in equipment performance evaluation and sizing.

The MVAWT proposed design utilises a four blade rotor, this ensures that the wind turbine will always have a uniform force distribution across it and that it will not stall through sub optimal attitude to the oncoming airstream. The configurations we would expect to be employed on an offshore location would typically involve four or six rotors each driving an individually coupled generator unit to each rotor. The generators would be mounted within the ‘pole’ type vertical support structure with the final drive connecting to the wind turbine rotor via openings in the structure wall to allow the gear meshing. The MVAWT unit can be mounted on a wide variety of offshore structures either fixed jackets or floating structures that have been proposed for conventional

horizontal axis wind turbines by a number of companies involved in wind turbine manufacture and general offshore engineering.

For far offshore locations the economic penalty of extra blade and generator costs can be easily absorbed into the overall cost as the offshore installation and support structure construction make up a sizeable portion of the project capital costs.

We also believe that the through life costs through increased availability of the MVAWT concept versus a HAWT unit makes it much more economically attractive when the availability is modelled on a probabilistic basis.

3.2. Principles of Operation

The MVAWT system presents a highly efficient large scale power generation system for use in offshore environments. The system operates in a mode where the blades utilise both drag and lift forces to provide motive force to a coupled generator in a constant rotational cycle. If one considers how a wind speed anemometer behaves then each rotor in the MVAWT behaves similarly but much more efficiently as it utilises lift forces in combination with drag forces as opposed to an anemometer which is purely an inefficient drag device.

3.2.1 Rotor Design

The rotor consists of a four bladed design where the blades are connected to a central rotor hub via a blade root hub. The blade material an root construction being almost identical to current HAWT technology.

The blades auto pitch in to the wind with predominant drag force application applied when the blade is moving along with the wind direction, this is when the blade is being acted upon and transmitting torque to the generator via the gear drive. As the blade approaches the oncoming wind in the opposite direction the blade is lifted by the lift forces applied by the oncoming airstream and the blade acts like the wing of an aircraft in level flight and produces minimal resistance to the diametrically opposite blade being pushed on by the wind and in fact this blade acts like the wing of an aircraft during take-off in terms of its aerodynamic resistance and performance.

As referred to in earlier sections the minimum efficiency is 35% upwards compared to a HAWT rotor this is because over 135°of the rotational cycle the blades are acted on positively by the oncoming airstream directly driving the rotor. Whilst we say this efficiency is a minimum of 35% however we believe this can be greater due to the higher torque applied to the generator through the blade also acting like a large lever and the force vectors being more complex as forces are also transmitted and captured down the

length of the blade as well as across it in a HAWT being a purely crossflow device. Therefore for a large diameter HAWT compared to a 4 rotor MVAWT of the same or similar hub height we would expect a power output some 40% greater than the HAWT unit as a minimum.

On an individual rotor basis this type of wind turbine can never compete with a HAWT. However for the same hub height in an HAWT more MVAWT rotors can be accommodated. This is particularly of value in exposed offshore locations where the foundation and platform are of considerable expense and limit the size of HAWT and hence power output achievable.

3.3 Reliability

The MVAWT has a number of key components omitted that are key requirements in a HAWT design, namely:

Nacelle: The generators and drive train are all completely contained within the cylindrical steel support structure. Therefore there is no need for a nacelle as employed on HAWT designs.

Yaw Drive: The MVAWT does not need yaw control or correction as it is optimal whatever the wind direction as it presents a uniform profile around its vertical axis to the oncoming airstream.

Pitch control: No direct pitch control mechanism is required. However a driven pitch adjustment mechanism can be employed for parking the blades by moving them to a neutral pitch angle, say in situations where wind speed is too high.

Multiple generators may be viewed as potentially presenting a reliability issue, however in fact this configuration acts in the opposite fashion. As an analogue one could think of a single versus multiple engine aircraft, therefore if one unit fails reduced overall system performance can still be maintained from the units that remain online. When looking at a single HAWT if one component where to fail the entire unit would be offline. In the MVAWT unit should a rotor and generator combination sub unit have a failure the other units rotating around the main structure will continue to operate effectively. This means in effect that should a single generator unit shut down within the MVAWT configuration only 16-25% capacity would be lost either in a six or four rotor configuration.

3.4 Offshore Access

For a wind turbine to be mounted in a far deepwater offshore location it would have to be serviced by maintenance personnel transported to the site either by helicopter or a vessel. Both of these options are discussed in the context of the MGTL design and its advantages over a HAWT unit.

3.4.1. Helicopter Access

Where helicopters service an offshore location it is essential that the helideck must be clear of obstructions for aircraft approach and landing on the helideck area. A large HAWT wind turbine blade when in rotational state may not allow a helicopter to make a landing approach due to the air turbulence created by the blades and further complicate the aircraft approach by its impact on the ambient wind direction. It is therefore likely that even if a helicopter was able to make a landing that the wind turbine would have to be stopped and confirmed stopped before the aircraft could land in most cases. Reference to CAP 437 for helicopter operations on offshore wind turbines current requires this for helicopters dropping of crew by winch. Additionally the blade of a large turbine can present a variable obstruction to a helideck mounted on a wind turbine nacelle. The MGTL view that it is best to completely remove the hazard and this was a key rationale in the MVAWT concept. For helicopter access to a large offshore HAWT wind turbine, a helideck of sufficient size could be mounted, but this would add significant weight to the nacelle and requirements of the yaw drive to slew the hub and nacelle in yaw correction.

The MGTL design of stacked rotors rotating around a vertical axis allows a helideck to be mounted at a safe distance above the rotors. This configuration allows a helicopter to land a crew onboard the installation while the wind turbine remains on operation if it is a routine maintenance visit involving running checks on the wind turbine generators.

Additionally this configuration also presents a uniform obstruction location that is mounted well below the approach flight path to the installation helideck. The rotors mounted below the helidecks on the MVAWT units allows a helicopter to approach the wind farm at a height in excess of any of the helidecks and whatever MVAWT unit is being landed in the windfarm the flight and landing approach will not need to take into account any other installations.

For a given size we expect that the MGTL design will give a significantly lower overall structure height for a given power generation capacity and not much greater if at all than for the hub height of a HAWT installation employing similar sized rotors. The reduced structure height offers significant advantages when considering installation, visit strategy and general operations in a far offshore deepwater location. Further design detail refinement of the MVAWT unit also allows for adequate structure projection marking lights to alert passing aircraft.

3.4.2 Vessel Access

Access to any offshore structure in a far offshore location requires a specialist vessel with dynamic positioning capability similar to North Sea platform support vessels. However the transfer of personnel from vessel to an installation is fraught with difficulty and it is only recently that access systems involving motion compensated booms and bridges mounted on a platform supply mono hull vessel have become available. However even these systems have limitations that do not offer anywhere close to the availability of helicopter operations for transferring personnel to and from an offshore installation. Sea state limitations defined usually by significant wave height currently limit these system operations to around 2-2.5m excluding current/swell direction in relation to the structure being serviced. Additionally for far offshore locations the sailing times to these windfarms would require the maintenance crew to reside on the support vessel. This is not a barrier to this type of support operation but it does give rise to the need for servicing crews to work rotational cycles similar to those on an offshore oil and gas installation. If maintenance crews were offshore resident it would require a highly mobile twin hull semisubmersible vessel with dynamic positioning capability that is far superior to vessels currently available. Vessel access from sea to either a horizontal or vertical axis wind turbine would be similar and therefore no particular advantage is offered by any particular wind turbine configuration in this regard.

The economics of a vessel that is capable of operating in deepwater far offshore locations may be prohibitive when compared to helicopter operations as a means of support, particularly for routine maintenance visits and light repairs to equipment that could cause a shutdown, e.g. instrumentation and hydraulics.

It is therefore clear that helicopter access offers significant advantages in servicing a far offshore windfarm. However it may be feasible to have in addition to helicopter access a highly capable field support vessel incorporating the capabilities of a twin hull semisubmersible and excellent dynamic positioning capability, e.g. DP 2/3 dynamic positioning capability. The vessel could be employed for maintenance support activities that could not be serviced by a helicopter based crew. Such a vessel could also act as an infield based service and accommodation vessel and support helicopter transits within the winfarm and from the shore base for transfer of personnel. However even if a vessel could become economically viable as a windfarm support infrastructure, it is highly likely that helicopter access would still be pivotal to the success of any windfarm operation.

The MVAWT offers a significant access advantage for helicopters in providing an unrestricted helideck access and uniform flight path in the windfarm at all altitudes for approach to helidecks located within it. This feature allows instrumented landing

approaches to be possible in weather states where helicopter access to HAWT wind farms is not possible.

4 The Way Forward

In the UK with imminent energy deficiency and ever increasing costs of carbon emissions the case for far offshore deepwater wind power developments has never been more compelling. However the industry appears to be in a state of limbo waiting on the next big event to happen in wind power development. It is our view that the industry is in a rut and constrained with development models incorporating the conventional three bladed HAWT scaled up to the point where it becomes impracticable. Alternatively there are a number of ill conceived vertical axis wind turbine concepts that have been conceived with a lack of knowledge of the harshness of the offshore operating model or basic understanding of reliability concepts, not to mention the ability to realistically scale these up. These words may seem harsh however the industry needs to react to the challenge and this has to be delivered by a technically robust alternative.

We obviously as the concept developer of the MVAWT unit believe it to be the best prospect as an alternative model for large scale offshore wind power developments using ever larger HAWT technology. We cannot guarantee at this stage that this concept is the ultimate solution however we firmly believe it to be worthy of development on the following compelling grounds:

i. The blades will utilise existing technology within the maximum size range already deployed in HAWT technology

ii.Multiple generators on a single offshore structure will offer improved overall online uptime

iii.The weather dictated access issues related to HAWT designs do not apply to MVAWT

iv.For a given offshore location utilising the same number of support structures the power output will be higher

v.A number of HAWT key components can be eliminated, principally yaw drive and pitch control, thus availability and reliability can be increased

At Microgen Technologies ltd we believe that there is a compelling case to develop the MVAWT technology and prove the concept on an industrial scale for a number of commercial reasons in addition to the technical issues cited above and these commercial advantages are:

i. Development time can be swift due to readily available component technology in the market place

ii. This is a suitable product for a new entrant to renewable energy systems

iii. For an offshore location the project NPV would be expected to be favourable on the basis of higher power output and uptime for little extra capital cost for a given structure size and load out tonnage.

The concept development through to commercial scale is depicted in the attached plan.

Activity Detail Timeline Enablers

Concept Engineering

University Research Project

Mid 2015-2016 Funding from appropriate body to allow University selection

Small Scale Prototype Build

Early 2016 Prototype funded from same grant as University research funding.

Onshore Prototype (250-500 kW)

Site selection and test body selection

Early-Mid 2017 Requires significant funding, up to 10 million Euros

Selection of turbine builder

Mid 2017-Early 2018

Turbine builder may contribute partly to funding for intellectual property rights transfer

Design, build and construct

Mid-late 2018

Test and evaluation

Late 2018-end 2019

Full season of data, preferably compared to similar size HAWT unit in same location.

Offshore Prototype (2-5 MW)

Design, build and construct

Late 2019 through to beginning 2020

Significant funding required to allow this project to be commenced. Initial estimate 50 million Euros

Activity Detail Timeline Enablers

Offshore Prototype (2-5 MW)

Installation engineering and execution

Engineering 2020Execution early summer 2021

Funded from same monies to design build and construct

Test and evaluation

summer 2021 to Summer 2022

Gain a full offshore season of test data to allow economic evaluation of full scale unit and incorporate lessons learned on reliability and design in to final design.An operational budget of 2 million Euros will be required to support test and evaluation phase.

Type approval (5-10 MW)

Incorporation of lessons learned from offshore prototype to final design

2023 Requires manufacturer to accept the concept and assume all intellectual property rights and to self fund full scale product development.