Vee is for vertical - and it may take off in the UK

A consortium of British companies has received R&D funding from a government-backed agency to support the development of a well known but little tried design of wind turbine, a variation from a whole cluster of designs that come under the general heading of vertical axis. Known as Project Nova, it is on of four innovative projects aimed at supporting achievement of the UK’s targets for the reduction in greenhouse gas emissions that were given the go ahead in January with funding from a new source that ultimately could provide support of up to £1.1 billion in total to deserving projects.

Resulting from a joint plan of the Energy Technologies Institute (ETI) and the Carbon Trust, which joined forces in December 2007 for this purpose, an initiative was announced to create one of the ETI’s first technology programmes. This is an ambitious £40 million scheme known as The Offshore Wind Programme aimed at cutting the costs of offshore wind power and accelerating its deployment around the UK.

The UK has the makings of the largest offshore wind resource in the world, with relatively shallow waters and a favourable wind pattern extending far into the North Sea. It has been estimated to have over 33% of the total European potential offshore wind resource – enough to power the country nearly three times over. But as has been made apparent over the last ten years or so it is a long step from creating a viable technology for harnessing the wind to creating the means to do it on any worthwhile scale. However, the potential to reduce carbon emissions, create economic prosperity and increase security of energy supply cannot be ignored. Of course many barriers still exist before it can make a significant contribution to the UK’s energy demands. Cost, variability of output in relation to wind strength, how wind enegy is to be connected to and transmit power via the national grid, as well as the supply chain for deployment of wind energy are all areas on which developers need to focus their efforts.

The funding for all projects comes from the six current private sector partners – BP, Caterpillar, EDF Energy, E.On, Rolls-Royce and Shell. The ETI’s public funds are received from the Department for Innovation, Universities and Skills (DIUS) through the Technology Strategy Board (TSB) and the Engineering and Physical Sciences Research Council (EPSRC) with additional funding from the Department for Transport.

Competition

Expressions of Interest were invited from organisations from across the spectrum of offshore wind technology and project development, plus other organisations with relevant expertise, to create a range of projects involving research, development and demonstration activities. Over 130 EoIs were received. The Carbon Trust and the recently-formed ETI, a unique partnership between global industries and the UK government, together managed the EoI process to select project participants.

The ETI has now revealed the first four projects to receive funding, totalling approximately £20 million, all with the ultimate aim of producing more affordable, low carbon electricity. Three of them will focus on designing cutting edge offshore wind turbine technology, while the fourth will demonstrate a new commercial scale tidal turbine. Of the three wind projects two will concentration on the development of offshore wind farms based on conventional horizontal axis turbines but one of them, Project NOVA (Novel Offshore Vertical Axis) is for the development of wind turbines of a new vertical axis design, Aerogenerator, the brainchild of inventor David Sharpe and developed by Wind Power Ltd. The design can be likened to a pair of giant vertical wings arranged in a Vee shape and is said to have the benefit of ruggedness, stability and simpler maintenance access compared to the horizontal axis concept of conventional turbines. It is said to be capable of sizing up in this design to 9 MW, but at a size roughly equivalent to a present day 3 MW conventional turbine.

The creation of more powerful but smaller unit generators has another attractive feature that probably influenced heavily the decision to include it. In January 2008 the UK government's business secretary, John Hutton, made a commitment to create enough offshore wind turbines to supply 25 million homes with electricity by 2020. This would require in the order of 5000 large turbines around the coastline. With the Aerogenerator this could be achieved with far fewer units.

NOVA

The ultimate aim of NOVA is to provide no less than 1 GW of power from offshore vertical axis turbines by 2020. Offshore VAWTs are thought to offer the potential for a breakthrough in offshore wind energy availability and reduced life-cycle costs owing to their inherent design characteristics of fewer moving parts, insensitivity to wind direction, and the siting of the generator at base level potentially allowing large-scale direct drive. Their relatively low centre of gravity and overturning moments (in the case at least of NOVA’s Aerogenerator) make the turbines highly suitable for offshore installation. In addition, they are potentially ‘radar friendly’ compared to existing horizontal axis wind turbine technology.

The NOVA team is a UK-based consortium led by Guildford energy specialists OTM Consulting and including representatives from three universities – Cranfield, Strathclyde and Sheffield – the Centre for Environment, Fisheries and Aquaculture (CEFAS) and SME Wind Power. Key sub-contractors include James Ingram Associates and QinetiQ. The project aims to assess the feasibility of the Aerogenerator design, and of its declared features of ruggedness, stability and simple maintenance access.

QinetiQ’s role in modelling the aerodynamics will be a key part of the project as it will provide the main profile data on which the rest of the solution will be based, and during later development additional expertise in a variety of technological areas including specialist materials and turbine performance optimisation.

The project will follow a well-structured three-phase approach over a six-year period, starting with concept selection and feasibility (15 months), followed by subsystem development, testing and detailed design (24 months), and finally offshore demonstrator construction, installation and test (36 months). The project will in the first phase develop relationships with other organisations with a view to their participation in future phases. This will include a potential systems integrator, component manufacturers and suppliers.

Project NOVA starts with the unique Aerogenerator wind turbine design based on a pair of giant composite wings, in a vee vormation that will utimately be scaled up to 120 metres high, that rotate around its central axis to create power. The aim is for a large scale demonstrator to be installed offshore within six years.

Aerogenerator design

The basic idea for VAWTs has been around for decades, but has to date attracted little interest other than academic interest. The design is an adaptation of the egg whisk-shaped Darrieus wind turbine but it improves on it, solving a number of problems originally posed by the technology.

Not least is the ability it confers to build giant turbines, says Neven Sidor of architectural firm Grimshaws – Windpower's collaborator and the company behind the giant geodesic domes of the UK’s Eden Project.

A Darrieus turbine becomes unstable above a certain height. For different reasons, very large horizontal axis turbines also present problems as they get larger because the engineering has to counter the increasing top heaviness of the design. Moreover as the larger and heavier blades turn, they undergo great stresses because gravity compresses them as they rise and stretches them as they fall. The larger you make these structures, the more robust they must be in order to withstand these forces, and so do the towers that support them.

Theoretically at least the the Aerogenerator gets round these problems, mainly because its centre of gravity is at the base, making the structure much more stable. And this feature remains true whatever size of structure is built.

Sharpe’s variation on the well known egg whisk shape with blades that bow outwards and meet at the top – like a typical Darrieus – has two arms projecting from its base, with rigid ‘sails’ mounted along their length at intervals. As the wind passes over these they act like aerofoils, generating lift which turns the structure as a whole at roughly 3 rpm.

Back in 2007 Wind Power carried out wind tunnel tests on a 6 kW scaled version of the Aerogenerator at the New and Renewable Energy Centre in Blyth. These suggested that the predicted power outputs could be achieved.

ETI’s goals

The ETI has a list of primary aims for offshore wind to be achieved by 2020.

• To reduce the cost of energy to at least the prevailing lowest-cost wholesale price of electricity.

• To increase the yield as measured by annual windfarm availability to 97- 98% or better, equivalent to onshore wind today.

• To reduce investment risks by reducing technical uncertainties, allowing offshore farms to be financed in a manner, and at costs, equivalent to onshore wind today.

Its programme is not limited to design. It will focus on the technical enablement of large-scale deployment, focusing on the design and demonstration of novel offshore systems, including technologies that are fundamentally different to those currently being deployed – including of course offshore-specific wind turbine designs, possibly integrated within alternative overall wind farm configurations (eg using centralised power conversion), and systems for deep-water installation – as well as improvements to existing technologies, to enable large-scale deployment and improved wind farm design, construction (eg foundation structures) and operation (eg access methods) including reliability. While these latter are less radical such developments are vitally needed in the short-to-medium term for incorporation in wind farms to be built in the next 5 years. And in addition, to support studies on other issues critical to deployment, for instance, mapping offshore wind resources, improved environmental impact assessment methods and construction health and safety.