... Offshore Wind Energy ... • Definition • Economics and benefits • Challenges & difficulties • Technical details ... • Design environment ............................................................................................................
Definition: Offshore wind power refers to the construction of wind farms in bodies of water to generate electricity from wind . Unlike the typical usage of the term "offshore" in the marine industry offshore wind power includes inshore water areas such as lakes.
Economics and benefits: 1. Offshore wind power can help to reduce energy imports. 2. reduce air pollution and greenhouse gases. 3. meet renewable electricity standards . 4. create jobs and local business opportunities.
The advantage is that the wind is much stronger off the coasts, and unlike wind over the continent . • offshore breezes can be strong in the afternoon, matching the time when people are using the most electricity. • Offshore turbines can also be "located close to the power-hungry populations along the coasts, eliminating the need for new overland transmission lines".
Challenges & difficulties : • The current state of offshore wind power presents economic challenges significantly greater than onshore systems - prices can be in the range of 2.5-3.0 million Euro/MW. The turbine represents just one third to one half of costs in offshore projects today, the rest comes from infrastructure, maintenance, and oversight.
Larger turbines with increased energy capture make more economic sense due to the extra infrastructure in offshore systems. • Additionally, there are currently no rigorous simulation models of external effects on offshore wind farms, such as boundary layer stability effects and wake effects. • This causes difficulties in predicting performance accurately, a critical shortcoming in financing billion-dollar offshore facilities.
A report from a coalition of researchers from universities, industry, and government, lays out several things needed in order to bring the costs down and make offshore wind more economically viable: • Improving wind performance models, including how design conditions and the wind resource are influenced by the presence of other wind farms. • Reducing the weight of turbine materials • Eliminating problematic gearboxes • Turbine load-mitigation controls and strategies • Turbine and rotor designs to minimize hurricane and typhoon damage • Economic modeling and optimization of costs of the overall wind farm system, including installation, operations, and maintenance • Service methodologies, remote monitoring, and diagnostics.
Technical details ... In 2009, the average nameplate capacity of an offshore wind turbine in Europe was about 3 MW, and the capacity of future turbines is expected to increase to 5 MW. Offshore turbines require different types of bases for stability, according to the depth of water. To date a number of different solutions exist: • A monopile (single column) base, six meters in diameter, is used in waters up to 30 meters deep. • Gravity Base Structures, for use at exposed sites in water 20– 80 m deep.
Tripod piled structures, in water 20–80 metres deep. • Tripod suction caisson structures, in water 20-80m deep. • Conventional steel jacket structures, as used in the oil and gas industry, in water 20-80m deep. • Floating wind turbines are being developed for deeper water .
The planning and permitting phase can cost more than $10 million, take 5–7 years and have an uncertain outcome. The industry puts pressure on the governments to improve the processes. In Denmark, many of these phases have been deliberately streamlined by authorities in order to minimize hurdles, and this policy has been extended for coastal wind farms with a concept called ’one-stop-shop’. USA introduced a similar model called "Smart from the Start"in 2012.
Design environment : Offshore wind resource characteristics span a range of spatial and temporal scales and field data on external conditions. Necessary data includes : water depth, currents, seabed, migration, and wave action, all of which drive mechanical and structural loading on potential turbine configurations. Other factors include marine growth, salinity, icing, and the geotechnical characteristics of the sea or lake bed. Existing hardware for these measurements includes Light Detection and Ranging (LIDAR), Sonic Detection and Ranging (SODAR), radar, autonomous underwater vehicles (AUV), and remote satellite sensing .
Because of the previous factors, one of the biggest difficulties with offshore wind farms is the ability to predict loads. Analysis must account for the dynamic coupling between translational (surge, sway, and heave) and rotational (roll, pitch, and yaw) platform motions and turbine motions, as well as the dynamic characterization of mooring lines for floating systems. Foundations and substructures make up a large fraction of offshore wind systems, and must take into account every single one of these factors. • Corrosion is also a serious problem and requires detailed design considerations. The aspect of remote monitoring of corrosion looks very promising using expertise utilised by the offshore oil/gas industry and other large industrial plants.
Common environmental concerns associated with offshore wind developments include: • The risk of seabirds being struck by wind turbine blades or being displaced from critical habitats; • The underwater noise associated with the installation process of driving monopole turbines into the seabed; • The physical presence of offshore wind farms altering the behavior of marine mammals, fish, and seabirds with attraction or avoidance; • The potential disruption of the nearfield and farfield marine environment from large offshore wind projects
At the end of 2012, 1,662 turbines at 55 offshore wind farms across 10 European countries are generating electricity enough to power almost five million households. • At the end of June 2013 total European combined offshore wind energy capacity was 6,040 MW. • As of October 2010, 3.16 GW of offshore wind power capacity was operational, mainly in Northern Europe. According to BTM Consult, more than 16 GW of additional capacity will be installed before the end of 2014 and the United Kingdom and Germany will become the two leading markets. • Offshore wind power capacity is expected to reach a total of 75 GW worldwide by 2020, with significant contributions from China and the United States.
Conclusion : refers to the construction of wind farms in bodies of water to generate electricity from wind Better wind speeds are available offshore compared to on land so offshore wind power’s contribution in terms of electricity supplied is higher However, offshore wind farms are relatively expensive.. the most expensive energy generating technology being considered for large scale deployment