CHAPTER 3 CASE STUDIES IN OFFSHORE WIND FARMS PILOT PROJECTS

Transcription

1 CHAPTER 3 CASE STUDIES IN OFFSHORE WIND FARMS PILOT PROJECTS 3.1 INTRODUCTION The first "offshore" wind turbines were built at Helgoland in Germany in 1989, Blekinge in Sweden in 1990 and Vindeby in Denmark in 1991 table 3.1. The wind turbines later, moved significantly from shore into deep waters. The first high capacity offshore wind turbine registered was 4.95 MW at Vindeby, off the Danish island of Lolland. The total capacity of offshore wind power installed in the world stands at 4,620 MW, which is about 2% of the total installed wind power capacity. More than 90% of the wind farms are installed off northern Europe [1] (North Baltic and Irish Seas) and the English Channel. The rest are located off China s east coast. Countries like Japan, Korea, the United States, Canada, Taiwan and even India have shown enthusiasm for developing offshore wind energy. The worldwide offshore energy is expected to grow to an estimated 80 GW by 2020 [2]. Early conceptual design of wind turbines for offshore was principally to ensure that the structures were adequately protected against corrosion and the entry of salt laden air to sensitive equipments. The most important concept for offshore use was the higher wind speeds [3]. This meant that high power ratings could be used to deliver increased energy yield.

2 Location Date Turbines / rating kw Output MW Water depth,(meters) / Distance from shore (meters) Foundation Helgoland Denmark Blekinge Sweden Vindeby Denmark Lely Netherlands Tuno Denmark Dronten Netherlands Bockstigen Sweden / /10 Gravity / /250 Tripod / /1500 Box caisson / /800 Monopile / /6000 Box caisson / Shallow /50 Monopile / /4000 Monopile Table 3.1 First few experimental offshore pilot projects details worldwide.

3 In contrast, the first offshore wind farms used modified versions of commercial machines. The specification for the machines at Vindeby required the following: Airtight towers and nacelle, A de-humidification system, Surface finishes to guard against corrosion, A permanent crane in the nacelle for small components up to 300 kg and provision for a temporary crane to deal with the larger components Transformers and switchgear to be located inside the turbine towers. These requirements led has led to modifications of the system, including the provision of a heat exchanger for the cooling air, a platform for the transformer in the base of the tower, corrosion protection and a higher access door to prevent icing in the winter. The turbine manufacturer supplied machines with a rotational speed 10% higher than normal. This increased the energy output, as peak aerodynamic efficiency was reached at a higher wind speed than normal. A number of manufacturers are now promoting machines designed specifically for offshore use, or "particularly suited to offshore installations", due to anticipation growth in offshore wind farms [4] The major challenge is to bring down the capital project cost in order to lower the cost per kw. Selection of sites in deeper waters far away from shore, with more difficult soil conditions and higher waves has contributed to drive the costs higher. The higher construction cost is to protect wind turbine machinery, external surfaces from salt spray, to lay underwater electrical cable and offshore/onshore grid connection. The need for engaging appropriate expensive vessels for operation and maintenance will increase the capital cost of the project[5]. Wind power is the world s leading source of renewable electricity status as of 2012 shows that 4,600 MW of offshore energy installed, from the total 238,000 MW of wind energy. The United Kingdom contribution is the highest offshore wind generation of 2500 MW, almost half of the world total installed wind power and has the largest offshore wind

4 farm capacity 630 MW is under construction. The global annual installed wind capacity figure 3.1 shows the percentage of growth overall in wind energy.[6] China and Japan have operational offshore wind farms from 2010 as the first project for observation. China ranks fourth in terms of wind farm capacity and is behind the United Kingdom, while Denmark and Belgium lead with 260 MW. China has plans to generate 30,000 megawatts from offshore wind energy by Japan with a capacity of 25 megawatts from offshore wind forms and is developing a pilot project of 16 MW floating wind farm, off the coast of Fukushima. The countries in East Asia, South Korea too have plans for 2,500 MW offshore winds to be operated by [6] A proposed 470 MW offshore cape wind offshore project off the coast of Massachusetts has been obtaining permits and facing legal challenges from opposed groups. Two other proposed projects off the U.S. East Coast planned to begin construction in 2013 are will become the country s first offshore wind farm. A proposed three 1,000 MW offshore wind for New England and Mid-Atlantic regions needs are in the planning stages[7]. One mega project would be the development far from shore is the Atlantic Wind Connection, a proposed offshore wind form with highly efficient underwater high voltage direct current cables. It is about 300 miles from New York to Virginia, this could connect some 7,000 MW of offshore wind and will take 10 years for completion.[8] India is exploring the potential for offshore wind power generation. The Ministry of New and Renewable Energy (MNRE) is conducting the feasibility of setting up wind farms in India s offshore areas. India may take one more year to study and gather data on the potential for offshore wind energy. Preliminary studies indicate that coastal areas off Tamil Nadu, Kerala and Gujarat states may have potential. The results from the studies need to be validated by setting up offshore

5 Figure 3.1 Global annual installed wind capacity

6 masts to measure one to two years of wind speed data and by analyzing the seabed to see if it can provide an adequate foundation for offshore wind projects.[9] It is expected that MNRE have plans to set up a few demonstration projects and a small target for offshore wind. The draft policy for Indian offshore projects introduced this year by the Indian government will attract the industry for setting new projects. The reason for demand in offshore wind farms is higher velocity and more consistent winds compared over land. This will assist in generating more power generation. 3.2 GLOBAL OFFSHORE PROJECTS The purpose is to review global offshore wind farms figure global cumulative installed wind capacity is to gather and evaluate experiences. The cumulative installed wind capacity figure 3.2 shows the demand for offshore wind. The main objective is to derive information and recommendations for future wind farm projects and assist global experts towards advancing offshore technology. The planning and construction of offshore wind farms is quite different from the development procedure for onshore wind farms. The combination of electrical power generation and offshore technology is quite new and challenging. For the purpose of the study, a total of eight farms are reviewed worldwide in countries like Belgium, Denmark, Germany, Great Britain and the Netherlands. These projects were selected since they cover a wide range of conditions offshore deep water wind, near shore in shallow waters and the global frameworks.[10] Egmond aan Zee (Netherlands) Project description Egmond aan Zee (OWEZ)[20] was the first offshore wind farm built in the Dutch North Sea as a pilot project in the territorial waters near Egmond aan Zee. The Dutch government decided to start an offshore wind pilot project in the year The Environmental Impact Assessment of the area off the coast of Egmond aan Zee was determined as the best suitable compared to any other in the selected list. The wind farm site decision was finalized in April 2002 and the final investment decisions were finalized in May 2005.

7 Figure 3.2 Global cumalative installed wind capacity

8 The permission regarding offshore installations had to be obtained from the Public Works Act (PWA) and the Environmental Management Act (EMA). The Onshore construction works were started in the year 2005 and the offshore installation started in March and commissioned at the end of The seabed and depths favoured the use of monopole type of foundation. The monopiles are cost effective and decided to use at the initial planning stage itself. The wind farm layout consists of four rows at a distance of a kilometre and with distance between the turbines is approximately 600 metres. A 116-metre meteorological mast has been installed, to measure the wind speeds, temperature, rainfall and humidity. The project comprises an area of approximately 30 km² table 3.2, surrounding with cables and pipelines determine the boundaries of the site. The area was closed for shipping (recreational shipping and fishing included). A 500-metre safety zone has been incorporated all around. The total investment for the entire project was 200 million. The Contractor was awarded with three types of financial support by the government. A 27 million subsidy has been awarded based on a Carbon-dioxide reduction scheme, in return to the contractor is obliged to execute the Monitoring and Evaluation Programme. The feed-in tariffs was agreed upon for the first 10 years of operation at 9,7 cents per produced kwh plus the actual electricity tariff. The 36 turbines of the project will be divided into three sections of 12 each. Each section of 12 turbines will be interconnected as one group by means of a 34 kv sub-sea cable, buried at a depth of three metres. The cables will follow a direct line to the shore, approximately 50 metres apart. The cables will be brought together at a point approximately 3 kilometres offshore. The total length of the cables will be approximately 43kilometres. Given the relatively short distance to shore, the contractor has decided not to build an offshore transformation station, instead 34 kv cables are used and conversion to 150 kv will occur onshore [11]. From this substation, it is connected to the national high voltage grid located at a distance of 7 kilometres.

9 project name Distance from shore Area covered Water depth Total capacity Eagmond ann Zee (Netherlands) kilometres off the Dutch coast 30 km² metres 108 MW Number of turbines 36 Turbine rating Hub height Rotor diameter SUM 27 million CONDITIIONS Monitoring and Evaluation Programme (nature compensation programme, information and communication activities, to be decided upon) 3 MW 70meters above Mean Sea Level(MSL) 90 meters 9.7 cents per kwh + actual electricity tariff. (Maximum 44% of investment costs deducted from taxable profits.. One time contract for 10 years based on the Marine environmental pollution regulation of the Ministry of Economic affairs (still some investment and taxable are unknown) Table 3.2 Technical details of Eagmond ann Zee (Netherlands) project Corrective action

10 The project lacks a full-fledged knowledge base for assessing the impact of offshore wind farms. Environmental impact has increased the cost of the project. The future applications and benefits from offshore potential have to be improved and expanded, thereby utilizing the current project knowledge on both environmental consequences and the management of offshore wind farms. The review has shown that offshore wind energy in The Netherlands is a young, not-yet-mature industry to which both government and market have adapted. It has also shown how several decisions have had a lasting impact on the project s progress. The review has also shown that strong involvement by the government can contribute significantly to the realization of an offshore wind farm. Offshore Wind Farm Egmond aan Zee has taken advantage of the attitudes and policies of the involved Dutch ministries. Likewise, the Dutch government has benefited from the project. The benefits of a tender system used in this project too may be utilized in the future projects. [11] Thornton Bank (Belgium) Thornton Bank[20] is the first offshore wind farm project table 3.3 in Belgium. The site selection and project proposal was done by a private company and not by the government. The proposal was accepted by the government and was promoted to demonstrate offshore wind energy in Belgium at a designate area specifically for offshore wind farms at sea. The project lies within this area and the increased distance to shore had a severe impact on the economic viability of the project[12]. Thus the government agreed to improve the situation by subsidizing the grid connection by 30% and rendering guarantees for the energy sales price. A pilot phase was accepted in order to analyze the impact of the wind farm on the environment. The contractor was selected from the eight companies which submitted project proposals for the development of a large-scale offshore wind farm in the North Sea. A big advantage for the approval process in Belgium is the one-stop office approach. The approval for the sea cable route had to be granted by the Federal Minister for Energy. Two studies were performed to analyze the available

11 capacity and technical issues of the grid connection and as per the results, an agreement with the network operator was signed for grid connection and started installation in April An intensive soil investigation was carried out in 2004, for adjustments concerning the design and budgeting. The soil investigation was the basic investigation for selecting the foundation type and design. A detailed soil investigation was performed for the entire cable route starting from the wind farm up to the shore. A measurement metrology mast was setup, to determine the wind conditions at the project site in 2004[13]. A tunnel will be drilled offshore from a jack-up platform towards the inland onshore landing point. The sea cable will be drawn though the tunnel from land. The project permit into the deep sea had a negative impact on the project economics. This has resulted in increased costs for foundations and for grid connection drastically. The transmission technology for the project was a high voltage AC on a 150 kv voltage level. The grid connection consisting of three partitions such as internal cabling, sea to shore and onshore cable with the following data: The internal cabling between the single turbines and the offshore transformer station will be realised by 36 kv submarine cables with a total length of 50,75 km. The connection between the offshore transformer station and the onshore landing point will be done by 3-phase 150kV submarine cables with a length of 35,95 km each. The further connection from the landing point to the 150 kv high-voltage grid at Slijkens in Bredene will be realised by six mono-phase underground land cables with a length of 3,3 km each.

12 Total MW Number of Turbines Turbine manufacture and rating Hub height Rotor diameter Pilot phase 21, 6 MW First expansion phase 120 MW Final phase 300 MW 6 in demonstration phase in 2006/2007, 24 in first expansion phase 2009 and 60 in final phase ,6 MW to 5 MW 80 or 85 m above sea level meters Submission of application August 2002 Approvals All permits received by 2005 Installation start of the pilot phase, 6 WTGs, 1 st wind measurement mast and 1 st 150 kv sea cable 2006/2007 Start of operation of the pilot phase 2007 Installation of second phase construction of 18 turbines and the offshore transformer station Installation of final phase construction of 36Turbines, 2 nd wind measuring mast, 2 nd electricitycable : 150kV (40 kilometer) Investment costs Specific investment costs pilot phase final phase pilot phase final phase 100 million 500 million 4630 per kw 1667 per kw Subsidies for grid connection Specific investment costs considering subsidies pilot phase final phase 33 % of cost Maximum 25 million 3472 per kw 1583 per kw Feed-in tariff 10.7 cents per kwh + actual feed in tarrif Table 3.3 Technical details of Thornton Bank (Belgium) project

13 The government decided both to increase the value of green certificates and to support the grid connection financially due to the bad economic situation. The government requirement to install a first pilot phase with a limited number of turbines had also a caused negative effect on the grid connection cost. The cable, which is laid in the first phase, has the capacity to transport the energy from 30 wind turbines. The costs of the cable connection amount to 20% of the total project cost and more than 35% of the total cost of the pilot phase. There is a large difference in specific costs ( /kw) between the pilot phase and the final phase, which results from the high grid connection cost and low installed wind farm capacity for the pilot phase high. The board of ministers decided to co-finance 1/3 of the cable costs with a maximum of 25 million, to be distributed over five years. A value of 107 EUR/MWh was set by the government for the entire project lifetime of 20 years. The green certificate reimbursement is paid on top of the feed-in tariff for energy production. As the wind farm has to participate in the electricity market, the price will vary severely. Therefore the costs per installed MW for wind power will decrease rapidly with a growing project size Corrective action Three issues had a large impact on the viability of the Thornton Bank offshore wind farm project. The decision of the government to shift the wind farm area further out to sea led to increased costs for the grid connection and the decision for a pilot phase with a small number of turbines[14]. The third impeding issue was the lack of information on the soil conditions at the project site. Earlier site investigations could have revealed the need to use more expensive foundations at the initial stage. The higher expenses could not have been avoided if the governmental decision to locate the wind farm at the initial stage. This un-favourable situation was the result of a lack of experience with offshore wind farms and could not be foreseen. The financial adjustments by the government helped to rectify this situation. Thus the major lesson learnt is to conduct the site investigation at an early stage and to follow a complete investigation program, to obtain maximum soil data.

14 3.2.3 Borkum West (Germany) Borkum West[20] was the first offshore wind farm project began in Germany. The project was located in an environmental protected area, between two main traffic routes in the German Bight. The project was designed as a pilot phase with 12 turbines table 3.4 of 5MW each. The offshore wind farm installation was stalled by grid connection sea cables and financing issues. The government s interest was to buy the planning, approval and utilization rights of the pilot phase of the wind farm from the contractor and offer the wind farm to a different developer or manufacturer. Thus the rights of the pilot phase were transferred to a newly established foundation with the task of managing the installation of the first German offshore wind farm. The first application hearing was held in Hamburg, together with all interested stakeholders and public agencies on 16 th May The approval process for the offshore wind farm includes all relevant public agencies and stakeholders. A pre-investigation by Germanischer Lloyd carried out the risk analysis concerning ship safety. The offshore permit for the wind farm was granted on 9 November 2001[4]. The approval process for the sea cable through the 12 nautical miles zone, turned out to be complicated as the offshore cable should be laid along with other polar high voltage direct current. The environmental impact assessment paid particular attention to the electric and magnetic fields, as well as the heat development in the seabed around the cable[15]. The main topics considered for the approval procedure from experts were: Environmental Impact Assessment (EIA): at least two years of investigations Ship collision risk analysis Development of temperature profiles in the seabed around sea cables Scan of sea floor to investigate the suitability of the sea bottom for wind farm installations. The investigation area was the entire wind farm plus, a reference area of the same size for comparison with the same marine conditions.

15 Total Pilot phase 60 MW Extension phase 1000 MW Number of turbines Pilot phase 12 Extension phase 208 Turbine manufacturer Expected annual output Hub height Rotor diameter Water depth Distance to shore Originally planned multigrid 5 MW Now probably 3 different types of 5 MW turbines Pilot phase 260 GWh/annum Extension phase 4300 GWh/annum Approx 90 meters Minimum 116 meters 30 meters 45 kilometer Start of pre-planning 1998 Start of planning phase 1999 Erection of foundation and wind turbine of the pilot phase Planned start of established of the extension phase May October / 2009 Offshore wind farm is finalized 2011 / 2012 Cable laying in the traffic routes in the wadden sea Cable laying in the tideways Cable laying in the wadden sea 3.0 meters 2.0 meters 3.0 meters Wind turbine ready installed 9 million Total wind turbine costs 108 million Grid connection 30 million Total wind farm cost 138 million Specific price per kw 2.3 / kw Table 3.4 Technical details of BORKUM WEST (GERMANY)

16 The following were drafted and assessed for the entire project: Basic assessment: two consecutive years of investigations without interruptions Installation phase: continuous monitoring Operation phase: after operations commence, the wind farm environment were monitored for three to five years. The financial figures for the project were calculated at the beginning of the planning phase and remained largely unchanged. The specific costs of the pilot phase amount to approximately 2300 /kw, more than twice the price of current onshore wind farm projects. The financing banks interest rates were increased to cover a higher risk level, economic viability may still be given, but at a level which is no longer interesting for investors. To overcome this situation, a state guarantee has covered the loans substantially. [15] The most suitable and economical foundation and undersea construction were investigated at the initial stage. The support structures were subject to static and dynamic load calculations with respect to turbine s fatigue effects. Finally the tripodtype support structure was found to be the most economical solution for the site. The transmission technologies for the pilot and extension phases were different. The substation for transforming medium voltage to high voltage will be at sea connected to this substation and transferred to the high voltage alternating current sea cable to shore Corrective action The project faced a lot of obstruction at the initial stage of planning due to utilization and nature preserve conflicts. The 12 nautical miles zone was excluded to avoid conflicts with tourism oriented, East Frisian North Sea islands such as Borkum, Juist and Norderney. The area between the shipping routes of the German

17 Bight was selected carefully providing maximum distance to both routes.[4] The later projects were carried out with less caution with a shorter distance to the shipping routes and / or within the 12 nautical miles zone. These two are the basic guidelines for the approval process of offshore wind farms in Germany in future: 1. The investigation and monitoring of the impact of offshore wind turbines on the marine environment 2. The definition of the minimum requirements for the foundation of offshore wind turbines and for the laying of the undersea electric cables The concept of the project initiators of building the wind farm in two separate phases as a pilot phase and an extension phase was soon became a basic requirement of Germany s future projects. There is still an ongoing discussion about the size of the wind farm as planned was too small to be an economically viable project or if it is the best economic solution for a pilot project Butendiek (Germany) The Butendiek project[20] was planned from the start as a co-operative wind farm by local private parties. The project was financed by private parties for the planning phase along with a large amount of equity capital from the public. The project was divided into two phases, such as planning and installation. In the first phase, the proposal was subjected to a project hearing in July 2001 and subsequent approval was given in December 2002 by the Federal Office for Shipping and Hydrography in Hamburg. The planning proposal was sanctioned in the end of the year The second phase was sanctioned in summer The finalization of equity and capital allocation was finalized in mid 2006 and the completion of the wind farm was commissioned in autumn [15] The approval for the project offshore and onshore cable route was sanctioned in spring The project experienced problems with economic viability due to major constraints in the financing plans. The private owners of the project are

18 already involved in public offshore management and consulting services. The banks awarded the contract to the initiators to work out the problems facing the financing scheme and this was successfully completed in the year Public hearings were held at different locations on various occasions to find the public acceptance in the offshore project. The project approval was associated with an Environmental Impact Assessment on birds, fish, common porpoises and benthos. During the three-year planning phase ( ), all relevant environmental impact parameters were investigated in the proposed wind farm area along with the additional reference area. The technical details of the project are given in table 3.5 It was decided the onshore cable will lead along the border to Denmark connecting the utility high voltage grid with a cable length of 50 km for offshore and 50 km for onshore. The length of the cables is lengthy and has to cross three districts and ten communities. Several public hearings were held with the affected communities and landowners and finally the contract was signed with a fixed land price as accepted by the landowners [15]. The following were the permits required for the offshore cable for the Butendiek project: Offshore permission for the pilot phase Permission for laying the cable in the seabed by the authorizing agency for river and navigation specific police approval Lease contract to use the 12 nautical miles zone for laying a sea cable Exemption from the prohibitions of the National Park Permission for laying the sea cable in the European Economical Zone Consent for grid connection

19 Area of the offshore wind farm Water depth Distance to shore 34 km² meters 34 km Total MW 240 Number of turbines 80 Turbine rating Hub height Rotor diameter 3 MW 80 meters 90 meters Planning phases, time schedule Autumn 2000 Installation start 2007 /2008 Start of operation 2008 Total equity capital 5000 shares 100,000,000 Equity share 24 % 100 million Outside financing 76% 320 million Total project financing 420 million Wind farm internal network Offshore cable connecting to the utility network 33 kv 155 kv Grid connection level 400 kv Table 3.5 Technical details of Butendiek (Germany) project

20 Butendiek project: The following were the permits required for the onshore cable for the Nature conservation approval by the state administration Permissions to cross federal, state, district and community roads Permissions to cross rivers Permission to cross train tracks Approval by the agency for protection of historic buildings and monuments. The financing of the complete project was supposed to be based widely on money from private parties from the region in Northwest Schleswig-Holstein. 20,000 shares were sold to private people and due to the delay in developing the project, an additional amount of 1million Euros was needed to finance the extension period and was paid solely by the nine project initiators Corrective action The major obstacles in realizing the Butendiek offshore wind farms in Germany lies in the poor ratio between project costs and reimbursement. The major investment in offshore wind farms are the wind turbines foundations. The offshore wind farm developers developed an alternate cheap foundation made out of concrete. There were expensive demands from the banks to cover project risks by expensive guarantees and high interest rates. Several strategies to improve the financial situation of German offshore wind farms were discussed such as: a) Lowering interest rates to the current standard values for industrial projects of 3% (instead of 6%) b) A dedicated subsidy programme paying 2 to 3 ct per kwh in addition to the England Energy Group granted reimbursement c) Adaptation of the tariffs defined in the England Energy Group to a costcovering amount.

21 d) A shift of the common connection point of the utility grids to the outer side of the islands in the German Bight or directly into the offshore wind farm areas Greater Gabbard (United Kingdom) The Greater Gabbard table 3.6 is one of the world s largest offshore wind farms[20] in the United Kingdom and is located in the Outer Thames Estuary. The British government has identified this region, as one of the three strategic areas for the second round of offshore wind farm development in the UK. The wind farm is located 23 km off the Suffolk Coast. It is at the two shallow sandbanks known as the Inner Gabbard and the Galloper. The site lies both inside and outside the United Kingdom territorial waters. Wind farm planning foresees up to 140 turbines, with an installed capacity of 500 megawatts. The cables were planned to be brought ashore through a new adjacent onshore substation connecting the existing 400 kv line at Sizewell, near Leiston in Suffolk.[16] The project is a 50-year lease with the Crown Estate for the wind farm site and the construction of the wind farm lasted 36 months with onshore began in 2007 and offshore in The project commissioning completed in Greater Gabbard Offshore Winds safety zones had prohibiting entry for non project vessels. The zones had a 50 m radius around each wind turbine structure, sub- station for offshore and metrology mast platform. In addition, trawling, drift netting, aggregate extraction and dredging or anchoring (public vessels) within 500 m of any wind turbine, substation platform or met mast was prohibited. The wind farm was finally commissioned in 2009.[17]

22 Area Water depth Distance to shore Total installed capacity Energy generation per year Estimated average mean wind speed 147 km² 3.6 m to 8 m (Inner Gabbard) 2.4 m to 10 m (the Galloper) 20 m to 50 m (off the banks) 23 km (12 nautical miles0 500 MW 1,750 GWh per annum 8.5 to 9.5 m/s(predicted) at 80 meters above mean sea level Numbeer of turbine 140 Rating of turbine 3 7 MW TUBINES 3 MW with rotor diameter 90 meters 3.6 MW 4.5 MW 5 7 MW At 80 meters hub height At 90 meters hub height At 95 meters hub height At 105 meters hub height Project cost estimation million Table 3.6 Technical details of Greater Gabbard (United Kingdom) project

23 The selection of this project site was based on the following reasons: Good wind resources Distance from shore reduces likelihood of visual impact Low maritime recreation usage No significant bird concentrations in the immediate vicinity of the site Few sites designated for nature conservation near the wind farm location Onshore electrical infrastructure is strong Candidate ports for construction and operations nearby Seabed properties for support structures are good No known marine archaeological sensitivities in the immediate vicinity Relatively little fishing activity in the vicinity of the site No Ministry of Defence or Civil Aviation Authority objections The need for the onshore and offshore works The process of site and cable route selection The design, construction, operation and decommissioning of the wind farm Onshore and offshore cabling Onshore substation and connection to the onshore transmission grid and ancillary works Environmental impact assessment Assessment of alternative cable landfalls, on-land routes and substations Appropriate mitigation and monitoring measures. The environmental agency presented three options for foundations such as driven steel monopile, driven steel multi-pile and concrete gravity base. The installation of the driven monopile support structure option is expected to take

24 between 4 and 6 hours. For a multi-pile structure with 3 piles, the time is expected to be 2-3 hours for each pile. The pile will have a maximum wall thickness of 95 mm, a weight up to 775 t and ground penetration will be m below mud line [16]. The installation of the concrete gravity base was finally selected but the litigation with the sub-contractor ended in the year 2011on a mutual understanding. The wind farm was generating electricity for 87 per cent of the time till March 2013 and a forecast to increase to over 90 per cent during 2013/14. Greater Gabbard offshore wind is now confident about the long-term structural integrity of the disputed foundations. The wind farm has performed well since it was energized as safe and efficient. It is a significant contribution to the United Kingdom's targets for renewable energy. A ship called SWATH figure 3.3 was built and engaged to significantly increase the wave height limits for technician transfer to keep the down time low during bad weather days. The design of this ship s engine was very economical as the fuel consumption is 100 litres per hour at an impressive speed of 20 knots. The project grid connection location was selected as Sizewell (in Suffolk) due to sufficient spare capacity in the network and the shortest route to shore. Four offshore transformer platforms collected the cables and transform the turbine interconnection voltage to potentially 132kV for transmission ashore by four cables of length approximately 42 km. Two geophysical surveys were carried out for selecting the cable route. The total length of cables of 33 kv at the Greater Gabbard Offshore Wind Farm is around 200 km and buried at a depth of 1.0 m Corrective Action The 500 MW project started operation in the year 2009 with a strong political support in the United Kingdom. Public has shown support and acceptance for the project. The environmental and technical details of the wind farm have been published in the environmental statement. Communication was organized by a project briefing to local and regional consultants. Pre-application briefing for officers and members of relevant councils, a project brochure and a public exhibition[18]was carried out.

25 Figure 3.3 Swath ship built for offshore wind farms maintenance

26 The project team has a proven track record in wind farm projects. The distance from shore (23 km) reduces the likelihood of visual impact. The site has low maritime recreation usage and no significant bird concentrations in the immediate vicinity of the site. Greater Gabbard Offshore Winds has set to measure for possible environmental impacts and risk reduction for ship accidents. A report was published in an environmental statement in October 2005 with a detailed report from the start of the planning to commission of the project Horns Rev (Denmark) Horns Rev offshore wind farm table 3.7 is the first wind farm[20] built in the open waters of the North Sea. It is located on the Danish west coast close to Esbjerg harbour. This project was part of the Danish Offshore Action Plan established in 1997 selecting five offshore areas for wind farm installation. Based on the feasibility report, it was decided to install a demonstration project at each location to develop 4,000 MW of offshore wind power by The project was contracted to a production company, which was permitted to build only the offshore wind farm and the internal offshore network. The offshore platform and the transmission grid permit were given to another contractor experienced in transmission business. A tight time schedule was calculated for the entire Horns Rev project. However, the commissioning phase had to be prolonged due to problems after installation. Due to the extension of commissioning phase, the project was completed in mid 2003 instead in late 2002 as originally planned. The various installation works are performed largely in parallel, including production of the different components (towers, nacelle and rotor blades). These include production and installation of the internal wind farm cables. Moreover, the process of procuring and installing of the components for offshore / onshore high-voltage connection was also performed in parallel to the wind farm development. In spite of parallel processes, the individual site works had to be performed sequentially, due to limited capacity of the contracted transport and installation vessels.

27 Area Water Depth Distance to shore 20 km² 6-14 meters 14 km. Turbines are arranged in 10 rows Wind turbine rating 2 MW Number of turbines 80 Expected annual output 600 GWh per annum Wind farm capacity 160 MW Rotor diameter 80 meters Hub height 70 meters Blade weight 6.5 tonnes Tower weight 79 tonnes Foundation weight 160 tonnes Total weight per wind turbine tonnes Cut-in wind speed 4 m/s Full power output from 13 m/s Cut-out wind speed 25 m/s Mean wind speed at 62 meters height 9.7 m/s Depth of water 6-14 meters Distance from shore km Distance between wind turbines 560 meters Wind farm site 20 km² Project cost including grid connection 278 million Foundations,internal cales and turbines 238 million Cost per turbine 2.97 million Offshore cable and conversion system 40 million (interconnection to main Without grid / with grid connection 1488 /1738 /kw Feed-in tariff and contract period Selling price of 0.04 cents per kwh during a fixed number of full load hours (42,000 equivalnt to 11 years of Table 3.7 Technical details of Horns Rev (Denmark) project

28 following schedule: The plan was to install 80 turbines in 6 stages of 14 each and with the First foundation pile driven on 30 March Transition piece fitted on the last foundation on 3 August First turbine erected on 7 May Last turbine erected on 21 August The 1200-tonne transformer platform was placed on the piles on 16 April All the piles were in place by April The 150 kv sub-marine cable was pulled up on the platform on 9 May 2002, and subsequently terminated in the 150 kv sub-station. First cable laid in park on 19 May Last cable laid between the turbines on 23 August The connection onshore went on line on 27 June 2002, performed by Eltra. The connection work was performed until May The first turbine commenced operations 29 July All the turbines were in operation by 11December The wind farm was commissioned on 7 July Corrective action A public hearing was held by the Danish Energy Agency for approval process of offshore wind farm. The tourist organizations were against initially but later turned positive and include it in their tourism programmes. The early integration of stakeholders was supported more towards fact-oriented rather than emotional discussion with the involved parties. The planned schedule for commissioning of the project must have been in time but delayed by six months. The meteorological measurement was unproblematic and showed good availability. The wave measurements showed minor deficiency for possible collisions with fishing gear but the results of energy yield assessment were good[18]. The prediction system for wind energy production on a 48 hours basis was sufficient.

29 The determination of suppliers for the different project components had to be carried out by the project manager of the contracted engineering company. The tendering process for wind farm manufacturing and installation was more extensive, but it enables complete risk management by the investor itself. The selection of a multi-contractual project concept had a clear economic advantage over the (EPC) concept, where the complete turnkey project is delivered to the investor by one contractor or syndicate. From the investor s point of view, the clear advantage of the EPC is that it minimizes risks. The increase in project cost for risk coverage is estimated at around 20%. This was learnt from the first offshore wind farms in Denmark and possibility of moving from the EPC contracts to multi-contractual concepts in the UK in order to reduce the high project costs. In the multi-contractual concept, the risks are shared between the different contractors and the investor. The investor s task is to manage and negotiate the risk sharing between the different parties. Then investor can influence the project costs by taking self on more or less risk. The basis for reliable work is a good understanding of the risks inherent in the different components of the project. Each contractor understands the weather risk for its project component better than anyone else, so the most economic way is to demand that every contractor directly bears the majority of its own weather risk. The wind turbine type still in the prototype stage can turn out to be far too problematic for a project. In the case of Horns Rev, improvements had to be made to a considerable extent at a very late stage and even after installation. The determined time frame by the contractor and manufacturer were followed as per the agreed time schedule. As a matter of fact, the manufacturing and assembly of the new turbine type was accompanied by problems, which by all means delayed the installation. The job of finalizing the assembly offshore is far more expensive than doing this work onshore and this may also lead to lower the assembly quality. The major lesson learnt is that the assembly and final check of each turbine should be

30 performed onshore, even though the installation is delayed. The technical benefits of a successful complete assembled turbine are greater compared with delayed commissioning. The main difficulties were foreseen in the offshore logistics during the planning process. The main problem that turned up during the installation phase was that harbor logistics were insufficiently planned and prepared. Thus the onshore planning caused many more problems than the offshore planning. This is due to the fact that the turbine suppliers were focused on the manufacturing and installation tasks. The underestimated onshore pre-installation and fitting works was the main reason for the delay. The strong efforts to adhere to the planned time schedule must have been considered as the main cause for the problems during the commissioning phase. The turbine assembly was incomplete due to time pressure and caused the delay Nysted (Denmark) A workgroup under the Danish Energy Authority pointed out four areas in Danish territorial waters suited for offshore wind farms[20] in the year This led to an agreement in 1997, between the Minister of Energy and the two major Danish utility companies. It was decided to establish five demonstration projects with a total capacity of 750 MW. The second to be completed was the Nysted Offshore Wind Farm. The Danish government and production companies reached an agreement in 1998 to establish a large scale demonstration programme for offshore wind. The objective of the programme was to investigate economic, technical and environmental issues to enable large-scale offshore development and to open up selected areas for future wind farms. The Danish Energy Authority approved the installation and the environmental impact assessment for the wind farm in 2001[18]. The technical details of the project are tabled in 3.8.

31 Area Water depth Distance to shore Total installed capacity 24 km² meters 9 km MW 480 GWh per year Number of turbine 72 Rating of each turbine Hub height Blade length Rotor diameter 2.3 MW 69 meters 41 meters 82.4 meters Turbines 120 million Foundations 45 million Internal grid 15 million SCADA 10 million Substation, offshore and onshore cable 30 million Others 30 million Total 250 million Investment cost per MW installed 1.51 million Table 3.8 Technical details of Nysted (Denmark) project

32 The offshore construction work for foundations commenced at the end of June 2002.The first turbine was installed on 9 May 2003 and operation started on 12 July The complete project was completed and commissioned in December The complete studies on various effects have been investigated. These include noise from constructing the wind farm, operation of the wind farm (under and above water), migratory birds, vibrations under water during operation and electromagnetic field near the underwater cables. Specific requirements in the tender documents covered availability, reliability and ease of servicing. The following three areas of the project were thoroughly investigated: Demonstration of ease of servicing with a fully equipped full-size model of the lower tower section (tests to replace equipment) Erection of a prototype turbine at Rødby Haven (onshore), an exact model of the 72 turbines at Nysted Practical tests (e.g. installation and removal of major components) and training programmes at the prototype turbine. The offshore windmill foundation design had to consider operational and environmental loads. It had to withstand the hydrographical and geotechnical conditions at the project site. The suitability of the foundation type was determined by turbine size, soil conditions, water depth, wave heights and formation of ice. The hydraulic model studies included probabilistic definition of extreme events, numerical modeling of wave disturbance, and calculation of wave, current and ice forces. The area for the wind turbine foundations has taken up an area of about 45,000 m², corresponding to a 0.2% of the total area of the wind farm. These turbines start at wind speed as low as 3 m/s and stop at a maximum wind speed of 25 m/s. The costs of grid connection were split between the grid operator and the wind turbine owner. Costs for the offshore grid junction point (transformer station, cable to shore, reinforcement of onshore cable) were paid by the grid operator, while the internal grid of the wind farm was paid by the owner of the turbines. The

33 substation at sea including the offshore and onshore cables was of the value of 12% of the project cost. The Danish Parliament decided in 2001, to convert the state subsidy schemes for renewable electricity production to a market-based system for tradable green certificates. The transmission system operator was responsible for the sale of the electricity production, from the date of its commissioning Corrective action The Nysted Offshore Wind Farm project had strong political support from the Danish Government. The objective of the wind farm was to investigate the economic, technical and environmental aspects of offshore development in Denmark. The wind farm was commissioned on 1 December The owner followed a multi-contracting approach. The technically detailed invitation to tender was prepared for selecting contractors based on experiences gained during the construction, engineering and operation of conventional power stations and from other existing offshore wind farms. The success of the project was that the developer had full access to the contractors design process and quality control [18]. The project developer had a very good working relationship with the manufacturer from design to commissioning. The developer kept everything as simple as possible to maintain operation costs as low as possible. The turbine manufacturer focused on supply chain management intensively from an early stage from the manufacturing and assembly of main components at company facilities. The critical component was the sea transport from the logistic centre to the site and back by the ship and the loading process was an important issue during optimization. The installation time amounted to less than 1 day per turbine and the work was completed one month ahead of schedule. A facility was built to test prototypes and blades picked at random from serial production were the reason for good quality control. The tests comprised dynamic testing corresponding to a 20 year lifetime and pulling blade to fracture. Practical tests such as installation and removal of major components and training programmes using prototype turbines were introduced. The project is accompanied by a sophisticated environmental monitoring

34 program for two years of studies (before construction of the wind farm) and two years of monitoring during operation Scroby Sands (United Kingdom) Scroby Sands table 3.9 is one of the first offshore wind farms[20] in the United Kingdom. It was commissioned in 2004 and a privately owned wind farm. The wind farm is located 2.5 km offshore Great Yarmouth on the east coast of Anglia. The project comprises 30 turbines with an installed capacity of 60 megawatts. The water depth is 5 10 m. The cables were brought ashore in Great Yarmouth, North Denes and connected to the local grid network system[16].the time schedule for planning, installation and commissioning of the of the Scroby Sans offshore wind farm: Site assessment carried out in the year Anemometry mast installed in the year 1995 First and second invitation to tender and evaluation of bids in June 2002 / Feb 2003 Project awarded in Feb 2003 Foundation installed in November 2003 / January 2004 Onshore cable installed in April 2004 Turbine installed in May 2004 Tested and commissioned in July 2004 / November 2004 The project was prepared through basic technical studies. The work started with site assessment in and in 1995 an anemometry mast was installed to provide data about wind resources. The site was chosen because of the good port facilities at Great Yarmouth and good grid connection facilities. Dynamic analyses were carried out to determine wall thickness and penetration depth of monopoles.

35 Area Water depth Distance to shore Total installed capacity Energy generation per year 10 km² 3-12 meters 2.5 km 60 MW 171 GWh per annum Number of turbines 30 Turbine rating Hub height Rotor diameter Piles: Diameter Length Weight Buried depth Height above mean sea level Tower: Diameter Length Weight Turbine: Nacelle weight Blade weight 2MW 68 meters above mean sea level 80 meters 4.2 meters 40 to 50 meters Upto 200 tonnes 30 meters 8 meters 4.2 meters 60 meters 110 tonnes 65 tonnes 6.5 tonnes Development 20,56,000 Construction 8,58,41,000 Operation 80,79,000 Total project cost 9,47,93,000 Table 3.9 Technical details of Scroby Sands (United Kingdom) project

36 The monopoles, with a diameter of 4.2 m, were pre-fitted with welded flanges on the top for connection to the tower. They were installed in a pure piledriving operation. The boat landing and access platform was installed immediately after pile-driving. Offshore operations are simplified. This cost-efficient design was used for the first time at Scroby Sands. A jack-up rig transported the piles (up to 200 tonnes per pile) and steel structures to the construction site. This simplified logistics and minimized the number of offshore operations. The total installation time for one foundation was around 24 hours Corrective action Scroby Sands main obstacles were lack of experience and underestimation of time required to plan the project. The scheduled time during planning could not be followed at the start of the project due to technical problems. The tendering period was given a short time of six weeks, such that the process was repeated due to less publicity. The sub-sea cabling proved to be time-consuming and diver intervention was limited by strong tidal currents leading to delay commissioning of the project. The insufficient time during construction of foundation tubes led to develop, scour holes at the time of installation [16]. The most important corrective action during the entire process of the project is summarized below: System designers / fabricators must be consulted prior material procurement during the planning process. Factory acceptance tests (FAT) should be comprehensive to enable fix problems to save time and reduce cost at the factory, which is estimated to be five times less than offshore. All data related geotechnical, possible tidal and wave rider, ordnance surveys and information on submerged objects are necessary during project planning.

37 Piling installation and turbine installation has delayed the project completion. The two contract companies manufacturing piles has allowed enough lead time and improved design. Different installation vessels were necessary to install turbines in shallow and deep water. Bad weather window period was too short and this has to be properly estimated between cabling and commissioning. Early and broad involvement of stakeholders, project charities and information centers led to high public acceptance in spite of its short distance off the coast. One person should be responsible for commissioning and testing as well as focal point of all aspects. The task should include producing documentation and providing personnel. Small boat access for commissioning should be given greater consideration due to inclement weather periods, even in summer. All test procedures should be planned in advance and agreed. A steady series of developments and increased demand is necessary for manufacturers to provide some level of continuity of work and sustained employment.

38 3.3 OFFSHORE WINDMILL FOUNDATION Introduction The foundation of the windmill ensures the stability of the wind turbine. This is done by transferring and spreading the loads acting on the foundation to the ground. The vertical force acting on the foundation is mainly dead load from the tower, the nacelle and the rotor blades. The winds also give rise to some vertical force and the most significant load on the foundation originates from the wind due to its height. A horizontal force from the wind acts as a large bending moment at the foundation. The tower usually is in the form of a hollow truncated cone and made of high quality steel. The wide tower base connects the prefabricated tower to the immovable foundation through an interface. One method is a giant steel pipe with a flange, which is embedded on a concrete foundation. The other method is to have a large round steel flange with many bolt holes to suit the long bolts embedded in the concrete. Each foundation is customized to the water depth at its particular location in the offshore wind farm. [19] The combination of water depth, increased wind tower heights and rotor blade diameters create loads that complicate the foundation design and hence costeffective foundations and structures are in demand. Moreover, offshore foundations are exposed to additional loads such as ocean currents, storm wave loading, ice loads and potential ship impact loads. All of these factors pose significant challenges to the design and construction of wind turbine support structures and foundations. The entire process of selecting suitable type of structure to withstand variable loads at the actual situation during its life span is challenging. There are numerous important parameters that should be taken into account in designing of offshore structures. The standard concepts on structural and geotechnical design were stability, material strength, functions of the structure. It also must resist fire, earthquake, flooding, frost, moisture, temperature differences and resist termites and insects. The higher quality wind, proximity to coasts, potential for reducing land use, aesthetic concerns, and ease of transportation and installation are a few of the compelling reasons for offshore development.

39 Figure 3.4 Offshore wind turbine foundation verses water depth cost

40 The offshore turbines[21] are made larger capacity to compensate the high costs of foundation figure 3.5 and transmission. The recent demand for large turbines for offshore wind farms has resulted in rotor diameters exceeding 150 meters and power ratings exceeding 10 MW. The increasing numbers of offshore wind farms at a distance of 15 to 50 km from shore in water depths of over 50 m are in great demand. The foundation consists of a transition piece and scour protection. The primary purpose of the foundation is to support the turbine. A transition piece is attached to the foundation to absorb tolerances on inclination and simplify tower attachment. Scour protection helps to ensure that ocean conditions do not degrade the mechanical integrity of the support system. Foundations are prefabricated onshore in one piece, transported offshore by barge or ship, launched at sea, and set on site by a crane or derrick barge. Five types of foundations have been used in offshore wind farms: monopoles, jackets, tripods, gravity foundation and floating structure. A total of 155 Monopoles, 39 concrete base and 6 jacket / tripod type foundations are used till the end A two-thirds probability of wind farms are supported by a monopole. At the end of 2012, 1,923 of the world s 2,688 offshore wind turbines used monopoles for support. The reasons for using monopoles by most wind farms are: Simplicity in design and production The shape allows for effective transportation to site The installation technique is well known and widely used by the construction industry. Foundation selection for offshore wind turbines are based on: Soil Conditions that facilitate installation and performance Drivability for driven piles and depth penetration for suction anchors Constructability and logistics of installation Availability of equipment / steel and Costs of fabrication Environmental impact considerations

41 Figure 3.5 Offshore wind turbine foundation cost with reference the water depth

42 The construction aspects and method of installation depends on the soil conditions figure 3.6 at a project site. Driven monopoles are most adaptable to a variety of soil conditions. They are currently the most commonly used foundation for offshore wind turbine projects. Their construction procedure can be modified to suit the site conditions. For example, drilling and driving to the design depth is carried out at a monopile foundation site, where boulders or very dense sands are found. In the presence of soft rock, drilled shafts or post-grouted closed end pipe are suitable. Gravity base foundations will be feasible in shallow waters and suction caissons will be geo-technically feasible in soft clay, pebbles and medium dense sands [2]. The final selection of the foundation may be driven by other factors such as environmental impact, costs of construction, availability of equipment and contractor preference. The various types of offshore foundation commonly used worldwide shown in figure Monopile These are large diameter, thick walled, steel tubular that are driven (hammered) or drilled and sometime both operations are simultaneously carried out into the seabed. Outer diameters usually range from 4 to 6 meters and typically 40 50% portion of the pile is inserted into the seabed figure 3.8. The thickness and the depth of the piling driven depend on the design load, soil conditions, water depth, environmental conditions and design codes. Pile driving is more efficient and less expensive than drilling. Monopoles are currently the most common foundation in shallow water due to its lower cost and simplicity. They are limited by depth and subsurface conditions and are likely to decline in popularity in deeper water. However for the near term future, monopoles are expected to be heavily employed.[4]

43 Figure 3.6 Wind turbine foundation showing soil reaction forces

44 Figure 3.7 Types of offshore wind mills foundations

45 Figure 3.8 View of an offshore wind mill foundation (monopile type)