Onshore wind turbines

Wind onshore Wind turbines that are installed on land, instead of being installed offshore (in the sea). The term onshore is not limited to coastal areas. 

The onshore wind turbine blades and the hubs are currently supported on a steel column, although there are examples where reinforced concrete material has been used (see Chapter 20, Section 20.5.6). The production area of the turbines is generally referred to as a wind farm, which is a group of wind turbines in the same location. A large wind farm may consist of several hundred individual wind turbines, which could cover an area of hundreds of square kilometres, but generally an onshore wind farm of 20... 

Offshore wind turbines endure higher stresses than onshore wind turbines such as environmental and power utilizations ones, due to being located in the marine environment. Thus, they experience higher failure rates (Karyotakis Bucknall 2010) and for this reason onshore failure distributions are not adequate for modelling the behaviour and performance of an offshore wind turbine. However, there is a lack of available reliability data of offshore wind turbines (Karyotakis Bucknall 2010), in fact only a few field data exists in the public domain (Tavner 2012). Consequently, power rating and environmental stress factors for mechanical systems (Davidson 1994) are considered in the present study as an empirical approach to derive failure distributions for the offshore wind turbine components from the typical onshore failure models (Ding Tian 2012) of Table 7. 

Failures rates of components of onshore wind turbines were used by Karyotakis Bucknall (2010) in a reliability model based on stress factors for mechanical systems (Davidson 1994) to estimate a range of failure rates for offshore wind turbines. To do so, one has to assume that both onshore and offshore wind turbines are of the same type and also account for the higher environmental and power utilization stresses that offshore wind turbines are subject to (Karyotakis Bucknall 2010). 

A technical availability of 98% for an onshore wind turbine can be considered as reference for a comparison with the values in Table 11. Compared to this reference value, the analysed availability of the offshore turbine is considerably lower. That means the higher energy yield of an offshore turbine should at least compensate the lower operation time. It should be mentioned here that the analysed availability of the variants is purely depending on the modelled scenario. Different specification parameters may lead to a different availability or variant ranking. 

Wind energy Wind turbines capture the energy from the wind to produce electricity. They have been developed for various purposes, from large groups of grid-connected wind turbines, wind farms, both onshore and offshore, to very small autonomous turbines used for battery charging or in combined wind-diesel projects for off-grid application. 

For wind turbines most of the GHG emissions arise at the turbine production (rotor, tower, nacelle) and plant construction (foundation). The emissions related to the construction of the foundation of the power plant can vary widely, as offshore wind turbines require significantly higher amounts of steel and cement than an onshore counterpart. Typically, larger turbines have lower life-cycle GHG emissions than smaller ones. GHG emissions generally lie between 9 and 19 g C02-eq/kWhg for offshore wind turbines, and between 8 and 30 g C02-eq/kWhe for onshore units, with outliers up to 100 g C02-eq/kWhg (Pehnt, 2006 Weisser, 2007 Evans et ah, 2009 Martinez et ah, 2009). 

Whether located onshore or offshore, wind turbines are characterized as machines or devices that convert wind energy into electricity. They consist of similar components, including a tower that rests on a substructure (or foundation), a nacelle that sits on top of the tower, and a rotor assembly that connects to the nacelle and includes a hub to which... 

The marine environment differentiates offshore work from that done onshore. Work is done on the water, in or with a boat under the water in diving operations or above the water, in or on a wind turbine. Weather is a factor for land-based work, but in the offshore environment, the weather and sea state (wind speed, wave height, visibility, etc.) are deciding factors. A typical offshore wind project will plan for significant downtime due to bad weather conditions. Unlike workers onshore, offshore technicians do not drive themselves to the work site but are transported by a vessel, which has its own crew. Offshore technicians are dependent on a complex logistical arrangement that includes transfer to and from a vessel or helicopter, coordination with other marine vessels, and extra marine rescue equipment (for example, an immersion suit). Training,... 

Floating offshore wind turbines have great potential as they are not limited by the same conflicts of interest as the onshore and the near-shore offshore turbines. Furthermore, wind farm developers have greater... 

Analyses of field failure data collected from various databases like Elforsk in Sweden (Elforsk.se) show that the availability of onshore wind power plants is typically between 95% to 99%, while it is evaluated to be in the range of 60% to 70% for offshore plants. Moreover, offshore wind turbines suffer from a higher failure rate compared to the wind turbines located onshore (Tavner 2012). The main reason might be that offshore wind power generation systems are typically subject to a wider range of operational risks, hazards, or damages. 

Shafiee, M. and Dinmohammadi, F., 2014. An FMEA-based risk assessment approach for wind turbine systems a comparative study of onshore and offshore. Energies 7(2) 619-642. 

Four degraded components of the wind turbine are considered. The failure models are based on onshore ones and derived using an empirical approach based on stress factors for mechanical systems. Generalized Stochastic Petri Nets (GSPN)... 

The power rating stress factor represents the possible effect of different operation power ranges on the reliability of a wind turbine. Given that an offshore turbine is subjected to higher winds than an equivalent onshore one the percentage of power available relatively to the turbine s nominal rating is higher. Therefore, can be considered... 

An age-based imperfect PM combined with CM replacements was modelled for an offshore wind turbine using GSPN with predicates coupled with MCS and considering the logistics, times and costs, and weather constraints. The PM repairs were modelled to be performed after a repair threshold age, p X MTTF, of the components. The failure models of the components were obtained from onshore ones using an empirical approach based on stress factors for mechanical systems. 

Both the inherent aspects of the offshore wind industry and the reliability problems it is facing contribute to the high Operation and Maintenance (O M) costs and eventually hinder its competitiveness compared to other sources of energy. It is commonly assumed that up to 25% of the cost of energy produced by offshore wind turbines is due to O M activities, which is twice as expensive as onshore installations (Sonderkar 2013). 

The global WT failure rate was assumed to be 3.8 failures/turbine/year, based on an initial onshore value of 1.5 and conversion coefficients K1 = 1.75 and K2 = 1.447 for environmental stress and near shore location respectively (Karyotakis 2011). The components contribution to total wind turbine failure rate was then obtained from (Rehawind 2010), where exponential distribution is assumed. 

Specialized cable installation vessels and underwater cable installation equipment are also used to bury cable from the ESP to the onshore connection point. Once the installation process is complete and before normal operations of the wind farm can begin, the turbine must be commissioned. For financial reasons, on larger wind farms the turbines are... 

Gas turbines are used extensively in onshore and ofifehore environments for power generation, but their use introduces a munber of potential hazards. To reduce the risks caused by fire and high noise levels, enclosures, with intake and exhaust silencers, are fitted aroimd the turbines. These enclosures and silencers must be capable of withstanding large static loads produced by equipment sited on top of them and large djmamic loads due to wind. 

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