Durham Research Online Deposited in DRO: 11 August 2015 Version of attached le: Published Version Peer-review status of attached le: Peer-reviewed Citation for published item: Crabtree, C. J. and Zappal¡a,D. and Hogg, S. I. (2015) 'Wind energy : UK experiences and oshore operational challenges.', Proceedings of the Institution of Mechanical Engineers, Part A : journal of power and energy., 229 (7). pp. 727-746. Further information on publisher's website: http://dx.doi.org/10.1177/0957650915597560 Publisher's copyright statement: This article is distributed under the terms of the Creative Commons Attribution 3.0 License (http://www.creativecommons.org/licenses/by/3.0/) which permits any use, reproduction and distribution of the work without further permission provided the original work is attributed as specied on the SAGE and Open Access page (https://us.sagepub.com/en-us/nam/open-access-at-sage). Additional information: Use policy The full-text may be used and/or reproduced, and given to third parties in any format or medium, without prior permission or charge, for personal research or study, educational, or not-for-prot purposes provided that: • a full bibliographic reference is made to the original source • a link is made to the metadata record in DRO • the full-text is not changed in any way The full-text must not be sold in any format or medium without the formal permission of the copyright holders. Please consult the full DRO policy for further details. Durham University Library, Stockton Road, Durham DH1 3LY, United Kingdom Tel : +44 (0)191 334 3042 | Fax : +44 (0)191 334 2971 https://dro.dur.ac.uk Special Issue on Renewables Proc IMechE Part A: J Power and Energy 0(0) 1–20 Wind energy: UK experiences and ! IMechE 2015 Reprints and permissions: offshore operational challenges sagepub.co.uk/journalsPermissions.nav DOI: 10.1177/0957650915597560 pia.sagepub.com Christopher J Crabtree, Donatella Zappala´ and Simon I Hogg Abstract This paper presents a discussion of the development of wind energy generation in the United Kingdom and the chal- lenges faced by the wind industry including reliability, performance and condition monitoring, particularly in the offshore environment. The worldwide installed capacity of offshore wind has now risen to over 7 GW, with an ever increasing deployment rate of new assets. About 90% of the global currently installed capacity is in Northern Europe, with the United Kingdom having the world’s largest share at 4 GW. Capacity factor data from UK offshore wind farms is pre- sented, providing an insight into the current performance of large Round 2 offshore wind farms compared to the earlier Round 1 farms and to onshore farms. The data reveal that the United Kingdom’s Round 2 offshore farms are achieving an average monthly capacity factor of 38.3% with a peak value of 75.8%. The older Round 1 farms have a lower average capacity factor of 33.6% while large onshore farms with capacities above 100 MW have achieved 25.6%. Offshore wind turbine performance has improved over time, and the industry is applying the learning from early experiences to achieve better performances at the more recently installed farms. Despite these improvements in turbine availability, the cost of energy from wind, particularly offshore, remains too high for it to be a commercially viable form of generation without subsidies. Reducing the cost of energy from wind to economically sustainable levels is the most important challenge facing the industry today. Operation and maintenance costs constitute up to 30 % of the total cost of energy from wind in large farms. The industry must overcome the challenges associated with improving component reliability and the devel- opment and adoption by operators of appropriate condition monitoring systems and maintenance strategies, in order to reduce costs to sustainable levels. Research and development work carried out with these goals in mind is also reviewed in the paper. Keywords Wind, offshore wind, reliability, performance, condition monitoring Date received: 9 December 2014; accepted: 15 June 2015 Introduction by 2030 with the aim of decarbonising the economy The challenges of climate change, energy security and by between 80% and 95% by 2050.2 cost of energy are becoming ever more present for gov- Wind energy has become the strongest and fastest ernments across the world. As a result, governments growing renewable energy technology worldwide are changing their approaches to electricity generation over the last 30 years, thanks largely to recent techno- and countries are seeing significant diversification in logical advances and commercial growth. It now plays their energy generation mixes, moving towards renew- a central role in the immediate and longer-term energy able sources, nuclear and clean conventional plant. strategies of many countries. The exploitation of renewable energy resources is By the end of 2013, the global installed capacity of central to European Union (EU) environmental and wind turbines (WT) stood at 318.1 GW, of which energy policy goals. The EU has committed to a leg- 117.3 GW was installed in the EU.3 Projections by ally binding target of meeting 20% of its total energy the European Wind Energy Association (EWEA) in demand (heating, transport and electricity) from 2011 suggest that 230 GW of wind capacity will be renewable sources by 2020. If this target is to be rea- lised it means that 34% of electricity generated1 will need to come from renewable sources by this date. In School of Engineering and Computing Sciences, Durham University, UK a communication entitled ‘A policy framework for Corresponding author: climate and energy in the period from 2020 to 2030,’ Christopher J Crabtree, School of Engineering and Computing the EU proposes increasing the share of renewable Sciences, Durham University, Durham, DH1 3LE, UK. energy to at least 27% of EU energy consumption Email: [email protected] Downloaded from pia.sagepub.com at UNIV OF DURHAM LIBRARY on August 7, 2015 2 Proc IMechE Part A: J Power and Energy 0(0) installed in the EU by 2020, rising to 400 GW by 2030 in 2001 of the ‘Offshore Wind Capital Grants Scheme’ and 735 GW by 2050.4 In 2007, the European by the UK Department of Trade and Industry led to Commission reported5 a lower target installed capacity investment in five farms of 60–90 MW scale (North of 146 GW by 2030 of which 129 GW would be onshore Hoyle, Scroby Sands, Kentish Flats, Barrow and and 17 GW offshore. The EWEA 2014 European Burbo Bank). All of these have now been fully oper- Statistics report6 shows 128.8 GW of installed capacity ational for at least 7 years. The sites offered the poten- in the EU with approximately 120 GW onshore and tial for the United Kingdom to gain vital experience of 8 GW offshore. These current figures suggest that the offshore technology and operations. Under the Capital EU is on course to pass the European Commission Grants Scheme, a number of reports on the operating expectation for 2030; however, there is a long way to history of the wind farms were made publicly available. go before the EWEA projections are realised. The data, analysed in Feng et al.,8 found that the A significant proportion of this forecast installed farms were achieving an overall average availability capacity is expected to be offshore, with many new of 80.2% with an average capacity factor over 3 large-scale sites already identified for development in years of 29.5%.9 However, the capacity factor Europe due to the favourable wind resources and sub- remained below the estimate for EU offshore wind sea conditions. farms of 35%, based on Danish experience. This was Offshore wind has advantages over onshore both partly due to the low availability of 80.2%. technically and in terms of public perception. Offshore In the United Kingdom, The Crown Estate has average wind speeds are higher and turbulence is now held three rounds of bidding for the award of generally lower than in the onshore environment, wind farm site development rights in UK waters, which results in greater energy capture for a given resulting in the United Kingdom now having 22 oper- wind farm size. Politically and in terms of public per- ational offshore wind farms with capacities ranging ception, offshore wind has the advantage that visual from 60 MW to 630 MW. The UK offshore portfolio impact and noise concerns are largely mitigated by is summarised in Table 1. London Array and Greater distance, although challenges remain with respect to Gabbard are, respectively, the world’s largest and marine life. There is also significant potential for very second largest offshore wind farms by capacity. large-scale offshore sites to be developed. Onshore In addition to the farms listed in Table 1, the farms are generally much more limited in capacity United Kingdom has two test sites, each with two due to space constraints; however, large-scale sites turbines. The two 2 MW Vestas turbines at Blyth, have been developed in the USA where the large Northumberland, were the United Kingdom’s first plains can deliver favourable wind conditions. offshore turbines. These have been operating intermit- The worldwide installed capacity of offshore wind tently since the year 2000. The Beatrice wind farm, in current stands at approximately 7 GW3 and is increasing the Moray Firth, features two 5 MW REpower tur- on a daily basis. Around 90% of this capacity is in north- bines. These were constructed in order to assess the ern Europe. The United Kingdom is the world leader in feasibility of installation and operation in deeper offshore wind with an installed capacity of over 4 GW.